CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. provisional patent application serial number 63/421 ,210 filed on November 1 , 2022, incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

NOTICE OF MATERIAL SUBJECT TO COPYRIGHT PROTECTION

[0003] A portion of the material in this patent document may be subject to copyright protection under the copyright laws of the United States and of other countries. The owner of the copyright rights has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the United States Patent and Trademark Office publicly available file or records, but otherwise reserves all copyright rights whatsoever. The copyright owner does not hereby waive any of its rights to have this patent document maintained in secrecy, including without limitation its rights pursuant to 37 C. F. R. § 1 .14.

BACKGROUND

[0004] 1. Technical Field

[0005] The technology of this disclosure pertains generally to propellers, and more particularly to a noise-reducing and efficiency increasing propeller blade configuration.

[0006] 2. Background Discussion

[0007] Drones were initially developed for military use, however, in recent years, their use has extended to urban applications. In urban areas, drones are used for leisure, commercial, medical, public safety, and scientific activities, among others. Currently in the United States, there are 1.32 million drones used for leisure and 0.385 million drones for professional purposes. By 2024, these numbers are expected to grow by 12% and 115%, respectively. However, the increase in noise pollution associated with these drones may be detrimental to the environment. Studies have shown that drone noise is significantly more annoying than other vehicle noises, even at the equivalent sound levels. Additional studies have shown that the presence of drones, even in environments with significant traffic noise, resulted in increased noise annoyance. Drone-associated noise pollution and disturbance may limit the adoption of drones in different applications. One possible solution is to reduce noise from the propeller through new propeller designs.

[0008] Previous research has shown that passive noise control, through modifying the aerodynamic geometry to optimize the interaction pressure profile, is an efficient and low-cost solution for noise reduction. For example, leading edge serrated airfoils tend to facilitate a span-wise turbulence distortion, which keeps the far-field , high-speed airstream attached to the surface of an airfoil. This interaction reduces flow separation and the corresponding energy dissipation that would otherwise be caused by increased noise generation. Many leading and trailing edge serration configurations inspired by wings of owls have been explored to reduce turbulence-associated broadband noise of propellers. Despite the effectiveness of current owl-inspired serration designs, such designs mainly consist of two-dimensional configurations. These propellers are designed with modifications to the leading or trailing edge without altering the shape of the propeller along the rest of the chord.

BRIEF SUMMARY

[0001] The transformation of two-dimensional (2D) serrations into a three- dimensional (3D) configuration enhances the integrity of coherent vortex structures on a propeller surface and provides more powerful control over the tonal and broadband flow noise emanations from a rotating propeller. Accordingly, this disclosure describes a three-dimensional serrated cicada surface (3D-SC) design created by lofting two-dimensional airfoils with spatial splines. These splines are created by superimposing a sinusoidal wave function to the propeller’s leading and trailing edge. By setting these splines as reference lines for lofting, the serration feature extends across the entire surface of the propeller. In one embodiment, these serrations comprise three- dimensional sinusoidal-shaped features applied to the surface topology of the propeller’s blades, which alters the airflow characteristics and ameliorates both aeroacoustic and aerodynamic performance metrics. Extensive empirical results have shown that this propeller configuration is able to improve the power efficiency and reduce the associated noise emissions when compared to conventional propeller designs.

[0002] Further aspects of the technology described herein will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the technology without placing limitations thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The technology described herein will be more fully understood by reference to the following drawings which are for illustrative purposes only:

[0004] FIG. 1 A is an orthographic perspective view of a serrated propeller blade.

[0005] FIG. 1 B is an enlarged section of the serrated propeller blade of FIG. 1A on the trailing edge, which shows that a sinusoidal pattern extends across the propeller with a sinusoidal amplitude (A) and a wavelength (X).

[0006] FIG. 1 C is a planform view of a cicada wing that extends from wing root to wing tip.

[0007] FIG. 1 D is a graph of the digitization measurements of the cicada wing of FIG. 1 C, where the upper edge of the cicada wing appears on the upper curve of the graph as a polynomial fit of the leading edge, and similarly, the trailing edge appears as the lower curve on the graph as a polynomial fit of the trailing edge.

[0008] FIG. 1 E is a side view of the propeller of FIG. 1 A.

[0009] FIG. 1 F is a top view of the propeller blade of FIG. 1 A.

[0010] FIG. 1 G is an enlarged portion of the leading edge of the propeller blade of FIG. 1 F.

[0011] FIG. 1 H is a side view of the propeller blade of FIG. 1 F.

[0012] FIG. 2A is a graph of a planform shape using a polynomial fit of a leading edge and a trailing edge for a wingspan length of b, which is a more detailed representation of the cicada wing digitization previously seen and described in FIG. 1 D.

[0013] FIG. 2B is a graph that shows the planform shape curves of FIG. 2A with additional sinusoidal serrated edges incorporated, which can be used to model a drone propeller that utilizes both three-dimensional surface serrations and a planform with sinusoidal serrated edges.

[0014] FIG. 3A is a planform view of a prior art propeller most analogous to the 3D-SC propeller disclosed herein.

[0015] FIG. 3B is a planform view of the 3D-SC serrated propeller prototype that was manufactured using a Polyjet 3D printing on a Stratasys Objet 260 platform.

[0016] FIG. 4A is a graph of the observed Overall Sound Pressure Level (OASPL) in dB compared between a conventional propeller curve and the 3D- SC curve at a rotational rate of 2000 rotations per minute (RPM), showing the 3D-SC to be significantly quieter.

[0017] FIG. 4B is a graph comparing the sound power level (SPL) in dB for the conventional propeller and the 3D-SC propeller, showing that that the 3D- SC propeller is quieter over a broad frequency range of 0-20 kHz at a 2000 RPM test speed.

[0018] FIG. 4C is a graph comparing the sound power level (SPL) in dB for the conventional propeller and the 3D-SC propeller, showing that that the 3D- SC propeller is quieter over a broad frequency range of 0-20 kHz at a 5000 RPM test speed.

[0019] FIG. 5A is a graph of the 3D-SC surface serration propeller sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leadingedge serration propeller with an amplitude of 2.5 mm and a wavelength of 5 mm.

[0020] FIG. 5B is a graph of the 3D-SC surface serration propeller sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leading- edge serration propeller with an amplitude of 8.0 mm and a wavelength of 5 mm.

[0021] FIG. 5C is a graph of the 3D-SC surface serration propeller sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leadingedge serration propeller with an amplitude of 2.5 mm and a wavelength of 10 mm.

[0022] FIG. 5D is a graph of the 3D-SC surface serration propeller sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leadingedge serration propeller with an amplitude of 6.5 mm and a wavelength of 10 mm.

[0023] FIG. 5E is a graph of the 3D-SC surface serration propeller sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leadingedge serration propeller with an amplitude of 2.0 mm and a wavelength of 15 mm.

[0024] FIG. 5F is a graph of the 3D-SC surface serration propeller sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leadingedge serration propeller with an amplitude of 2.5 mm and a wavelength of 15 mm.

[0025] FIG. 6A is a graph displaying the very similar aerodynamic thrust performance of a conventionally designed propeller and the 3D-SC propeller.

[0026] FIG. 6B is a graph of propulsive efficiency versus rotational speed in RPM of the conventional propeller and the 3D-SC propeller.

[0027] FIG. 7A and 7B are streamline plot visualizations of the 3D-SC design in FIG. 7A, and the smooth cicada design in FIG. 7B, both of which are modeled as operating at 2000 RPM.

[0028] FIG. 7C and FIG. 7D are visualizations that show helicity isosurface contours of the propellers of FIG. 7A and 7B, respectively.

[0029] FIG. 7E and FIG. 7F are visualizations that show the dipole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 7A and 7B, respectively.

[0030] FIG. 7G and FIG. 7H are visualizations that show the quadrupole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 7A and 7B, respectively. [0031] FIG. 8A and 8B are streamline plot visualizations of the 3D-SC design in FIG. 8A, and the smooth cicada design in FIG. 8B, both of which are modeled as operating at 5000 RPM.

[0032] FIG. 8C and FIG. 8D are visualizations that show helicity isosurface contours of the propellers of FIG. 8A and 8B, respectively.

[0033] FIG. 8E and FIG. 8F are visualizations that show the dipole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 8A and 8B, respectively.

[0034] FIG. 8G and FIG. 8H are visualizations that show the quadrupole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 8A and 8B, respectively.

DETAILED DESCRIPTION

[0035] A three-dimensional (3D) surface serration design has been created by lofting two-dimensional airfoils with spatial splines. These splines are created by adding a sinusoidal wave function to the propeller’s leading and trailing edge.

[0036] Refer now to FIG. 1A and FIG 1 B. FIG. 1 A is an orthographic perspective view 100 of a propeller blade 102. Here the propeller blade 102 rotates about an axis of rotation 104 in the counter-clockwise rotational direction indicated 106, with a leading edge 108 and a trailing edge 110.

[0037] FIG. 1 B is an enlarged section 112 of the propeller 102 on the trailing edge 110, which shows that a sinusoidal pattern that extends across the propeller 102 with an amplitude of A (giving rise to a peak to valley depth of 2A) and a wavelength of X.

[0038] Refer now to FIG. 1 C, which is a planform view 114 of a cicada wing 116 that extends from a wing root 118 to wing tip 120. A horizontal reference line 122 connects the wing root 118 to the wing tip 120. By measuring the vertical extent of the cicada wing 116, the wing may be digitized into y versus x measurements.

[0039] Refer now to FIG. 1 C and FIG. 1 D. FIG. 1 D is a graph 124 of the y versus x measurements of the cicada wing of FIG. 1 C, where the upper edge of the cicada wing 116 appears as a polynomial fit of the leading edge 126. Similarly, the lower, trailing edge 128 appears below. The measured cicada wing 116 points are indicated by small circles on the FIG. 1 D graph 124.

[0040] By setting the leading edge 126 and trailing edge 128 curve fits as reference lines for lofting, the serration feature detailed in FIG. 1 B may be made to extend across the entire surface of the propeller blade 102. In this implementation, the serrations are substantially perpendicular to the horizontal reference line 122.

[0041] Refer now to FIG. 1A and FIG. 1 C. In the propeller blade 102, the horizontal reference line 122 of FIG. 1 C would be observed to be parallel to a radial line extending from the propeller blade 102 axis 104 of rotation.

[0042] The three-dimensional surface serration design may be created by lofting two-dimensional airfoils with spatial splines. These splines are created by adding a sinusoidal wave function to the propeller blade 102 on the leading edge 108 and the trailing edge 110. As previously shown in FIG. 1A, these splines may be used as reference lines for lofting, thereby causing the serration feature to extend across to the entire surface of the propeller blade 102.

[0043] The term “splines” is used loosely here, meaning that the spline may be a Gaussian spline fit, or a fit to the 5 ^th degree polynomial described herein.

[0044] The geometry of the serrations is driven by a fundamental sinusoidal function. This sinusoid is applied to the guide curves used to generate the propeller in a lofting process, which results in a regular pattern of depressed grooves and raised features along the span of the propeller blade 102. The wavelength (X) of the sinusoid dictates the distance between two adjacent sinusoidal grooves on the propeller, while the amplitude (A) dictates the depth and height of each individual waveform (giving rise to an overall top to bottom depth of 2A).

[0045] The sharpness of the tips of the projections on the edge of the propeller are quantified by the ratio of amplitude to wavelength (A/X). When the amplitude is large relative to the wavelength (A/X large), the edge serration features are more “sharp” and “thin”. On the contrary, when the amplitude is small relative to the wavelength (A/X small), the edge serration features are more “blunted” and “rounded.” [0046] To design a propeller with better overall performance, the aim is to mitigate the aerodynamic performance reduction typically coupled with noise reduction by using an innovative propeller profile. The overall propeller profile is modeled with an emphasis on placement of the maximum chord length at an outward location relative to the span of the propeller blade. This leads to an unconventional planform geometry that is narrow and tapered at the root of the propeller (near the axis of rotation), while widening in chord length closer to the propeller's outer tip. The resultant leading edge follows a relatively uniform convex curve with consistent curvature; the trailing edge is characterized by a greater range of curvatures, specifically a concave segment with multiple points of inflection near the root of the propeller blade.

[0047] Three-dimensional (3D) serrations are added across the entire surface of the propeller with the geometry as described above. These serrations are applied along the spanwise dimension of the propeller and follow a fundamental sinusoidal pattern with a consistent waveform throughout. The resultant geometry comprises a uniform pattern of parallel raised features and grooves along the primary surface of the propeller. At the leading and trailing edges of the propeller, these features terminate to create three-dimensional pointed protrusions-effectively adding an advanced edge serration. These projections represent the local extrema points of the fundamental sinusoidal used, and are of uniform sharpness and angle throughout as dictated by the ratio A/X.

[0048] The planform is defined by first obtaining discretized points for the leading and trailing edge obtained from point-tracking of a reference cicada wing image as previously described in FIG. 1 C and FIG. 1 D. These points are subsequently interpolated into two fifth-order polynomial functions, yielding an analytical description of the bio-inspired geometry.

[0049] Refer now to FIG. 1 E, which is a side view of the propeller blade 102 of FIG. 1A. Here, it is seen that the rake angle of the propeller blade 102 is 20°.

[0050] Refer now to FIG. 1 F, which is a top view 130 of the propeller blade 102 of FIG. 1A, with a length 132 of 76.2 mm, and a width 134 of 22.4 mm. Here, the diameter of the rotor 136 is 20 mm. This makes the overall tip-to-tip width of the entire propeller blade 102 to be: 2*76.2 mm + 20mm = 172.4 mm

[0051] Refer now to FIG. 1G, which is an enlarged portion of the propeller blade 102 of FIG. 1 F. The actual serrations used here have a wavelength X of 2 mm, and an amplitude A of 1 mm.

[0052] Refer now to FIG. 1 H, which is a corresponding side view of the propeller blade 102 of FIG. 1 F. Here, the rotor 136 is seen to have a thickness 138 of 5 mm.

[0053] Refer now to FIG. 2A and FIG. 2B. FIG. 2A shows a graph 200 of the planform shape using a polynomial fit of a leading edge 202 and a trailing edge 204 for a wingspan length of b, which is a more detailed representation of the previously seen and described in FIG. 1 D.

[0054] Refer now back to FIG. 1 C. The resulting 5 ^th -degree polynomial curve fits for both the leading edge 202 and trailing edge 204 (of FIG. 2A) of the planform view 114 of the cicada wing 116 of FIG. 1 C in a 2D plane are given as:

Equation 1. Polynomial Equations for Planform where: x is the wingspan coordinate along the span line (where the reference line begins with x=0); fieading(x) is the polynomial curve describing the leading edge of the propeller; ftraning(x) is the polynomial curve describing the trailing edge of the propeller; and b is the radial wing span of the propeller blade.

[0055] Equation 1 may suitably be increased or decreased in size based on the desired span of the propeller. The sinusoidal serrations are then added by superimposing a sinusoidal function onto the polynomial function for the leading edge 202 and trailing edge 204, as seen in the equations below.

[0056] Refer now to FIG. 2B, which shows the results in the curves of FIG. 2A with sinusoidal serrated edges superimposed, which can be used to model a drone propeller that utilizes both three-dimensional surface serrations and a planform with sinusoidal serrated edges.

Equation 2. Sinusoidal Serrations where: x is the wingspan coordinate along the span line (where the reference line begins with x=0); fieadingedge(x) is the polynomial curve describing the leading edge of the serrated propeller; ftramngedge(x) is the polynomial curve describing the trailing edge of the serrated propeller; fieading(x) is the polynomial curve describing the leading edge of the non-serrated propeller; ftraning(x) is the polynomial curve describing the trailing edge of the non-serrated propeller; fsinusoidai(x) is the curve describing the sinusoidal serrations lofted onto the propeller surface;

A is the amplitude of the sinusoidal serrations; and

2 is the wavelength of the sinusoidal serrations.

[0057] Refer now to FIG. 3A and FIG. 3B. In FIG. 3A, a planform view of a propeller 300 (Prior Art), is shown. This propeller 300 utilizes a cambered airfoil, the NACA8412, and a constant attack angle of 20 degrees. Limited by the strength of the digital ABS material used for fabrication, the chosen propeller span length (b) (i.e. , rotor radius) was 7.62 centimeters to avoid fracture under designed loading conditions.

[0058] Refer now to FIG. 3B, which is a planform view of the 3D-SC serrated propeller prototype 302 that was manufactured using a Polyjet 3D printing on a Stratasys Objet 260 platform. Experimental testing results were collected to further validate the design. This 3D-SC propeller prototype 302 was compared to the prior art propeller 300 with a more conventional design previously seen in FIG. 3A.

[0059] Refer now to FIG. 4A, FIG. 4B, and FIG. 40, where comparisons between the experimental outcomes of a 3D-SC propeller and a conventional propeller are depicted. In FIG. 4A, where a graph 400 of the observed Overall Sound Pressure Level (OASPL) (in dB) compares a conventional propeller 402 curve to the 3D-SC 404 curve at a rotational rate of 2000 rotations per minute (RPM). This comparison finds the 3D-SC 404 performance to be significantly quieter that the conventional propeller 402.

[0060] In FIG. 4B, a graph 406 is presented comparing the sound power level (SPL) in dB for the conventional propeller 408 and the 3D-SC 410 propeller. From this graph, it is clear that the 3D-SC propeller is quieter over a broad frequency range of 0-20 kHz at the 2000 RPM test speed.

[0061] In FIG. 4C, a graph 412 is presented comparing the sound power level (SPL) in dB for the conventional propeller 414 and the 3D-SC 416 propeller. From this graph, it is clear that the 3D-SC is again quieter over a broad frequency range of 0-20 kHz at the increased 5000 RPM speed.

[0062] Refer again to FIG. 4B and FIG. 4C. Specifically, Overall Sound Pressure Level (OASPL) reductions of 6.76 dB and 10.25dB are documented at 2000RPM and 5000 RPM, respectively. It was discovered that the magnitude of noise reduction improves as the rotational speed increases.

[0063] The detailed spectrum plots presented above in FIG. 4B and FIG. 4C underscore the 3D-SC topology's proficiency in suppressing both tonal and broadband noises at rotational speeds of 2000 RPM and 5000 RPM, respectively.

[0064] Refer now to FIG. 5A, FIG. 5B, FIG. 5C, FIG. 5D, FIG. 5E, and FIG. 5F.

[0065] Establishing a comparative analysis between 3D serrations and leading-edge serrations is essential for understanding their respective performance attributes in propeller designs. In the disclosed experiment, six propellers of conventional planform were each modified using six distinct types of serrations. For consistency, and to eliminate potential biases from sinusoidal waveform variances, the 3D-SC serrated prototype was uniformly set with an amplitude and wavelength of 2.5 mm and 10 mm, respectively.

[0066] FIG. 5A is a graph 500 of the 3D-SC surface serration propeller 502 sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leading-edge serration propeller 504 with an amplitude of 2.5 mm and a wavelength of 5 mm.

[0067] FIG. 5B is a graph 506 of the 3D-SC surface serration propeller 502 sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leading-edge serration propeller 508 with an amplitude of 8.0 mm and a wavelength of 5 mm.

[0068] FIG. 5C is a graph 510 of the 3D-SC surface serration propeller 502 sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leading-edge serration propeller 504 with an amplitude of 2.5 mm and a wavelength of 10 mm.

[0069] FIG. 5D is a graph 514 of the 3D-SC surface serration propeller 502 sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leading-edge serration propeller 516 with an amplitude of 6.5 mm and a wavelength of 10 mm.

[0070] FIG. 5E is a graph 518 of the 3D-SC surface serration propeller 502 sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leading-edge serration propeller 520 with an amplitude of 2.0 mm and a wavelength of 15 mm.

[0071] FIG. 5F is a graph 522 of the 3D-SC surface serration propeller 502 sound power level (SPL) in dB over a range of 0-20 kHz, compared to a leading edge serration propeller 524 with an amplitude of 2.5 mm and a wavelength of 15 mm.

[0072] The FIG. 5A, FIG. 5B, FIG. 50, FIG. 5D, FIG. 5E, and FIG. 5F study set described above of leading-edge serrated prototypes were developed with varied amplitudes and wavelengths, encompassing the baseline prototype of 2.5mmx10mm (found in FIG. 50), to facilitate a comprehensive comparison between the leading-edge serration and the overall lofted 3D-SC serrations (in all plots, depicted as curve 502). Experimental results indicated that the OASPL of a 3D-serrated propeller was reduced by 3.63 dB (4.2%) relative to its leading-edge serrated counterpart under identical amplitude and wavelength conditions. Further, the 3D-SC serrated prototype consistently demonstrated superior noise reduction capabilities compared to all other leading-edge serrated prototypes.

[0073] Refer now to FIG.6A and FIG. 6B. In FIG. 6A, a graph 600 is presented regarding the aerodynamic thrust performance of a conventionally designed (prior art) propeller 602 and the 3D-SC propeller 604. Here, it is seen that the relative thrusts in grams versus rotor rotational speed in revolutions per minute (RPM) are nearly identical.

[0074] FIG. 6B shows a graphical comparison of thrust and propulsive efficiency of the same propellers previously shown in FIG. 6A. Propulsive efficiency is defined as a ratio between a rotor system’s net power output and input:

Equation 3. Propulsive Efficiency of a Rotor System where: q is the efficiency;

T is the thrust; u ₀ is the freestream airspeed; and P is the electrical power input.

[0075] This q efficiency is indicative of the energy consumption rate under a fixed thrust. In comparison to the conventional design, the 3D-SC model 604 may generate a very slightly lower thrust compared to the conventional design 602 under the same rotational speed, as indicated by the thrust curve shown in FIG. 6A.

[0076] In FIG. 6B, which is a graph 606 of propulsive efficiency versus rotational speed in RPM, it is readily apparent that the propulsive efficiency of the conventional propeller 608 is significantly lower than the propulsive efficiency 3D-SC propeller 610. This increased efficiency is apparent across a variety of thrust conditions. In one embodiment, when subjected to a thrust equivalent of 50 grams (0.49 N) 612, the 3D-SC design demonstrates an efficiency enhancement of approximately 48.14% in comparison to traditional configurations. Such a marked increase in propulsive efficiency implies that the 3D-SC configuration requires a significantly reduced energy input to achieve a thrust output commensurate with that of conventional designs.

[0077] Computational Fluid Dynamics (CFD) simulations aids in elucidating the mechanisms for noise and drag reduction. The FIG. 7 and FIG. 8 figure sets below depict a range of salient flow characteristics associated with the 3D-SC topology.

[0078] Refer now to FIG. 7A and 7B, which are streamline plot visualizations of the 3D-SC design in FIG. 7A, and the smooth cicada design in FIG. 7B, both of which are operating at 2000 RPM.

[0079] Refer now to FIG. 7C and FIG. 7D, which are visualizations that show helicity isosurface contours of the propellers of FIG. 7A and 7B, respectively. Here, the vorticity of the smooth cicada design in FIG. 7D is greatly improved as viewed in the 3D-SC design of FIG. 7C.

[0080] Refer now to FIG. 7E and FIG. 7F, which are visualizations that show the dipole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 7A and 7B, respectively. Such coherent vortex structures emerging from the transition from smooth propeller to serrated propeller are instrumental in diminishing harmonic sound pressure fluctuations and curtailing the magnitude of dipole pressure sources, as shown by the comparison of FIG. 7E and FIG. 7F. Furthermore, the accentuated streamwise vorticity (shown in FIG. 7C and FIG. 7D) preserves the flow's momentum, thereby postponing its fragmentation into diminutive eddies, a process governed by the energy cascade principle.

[0081] Refer now to FIG. 7G and FIG. 7H, which are visualizations that show the quadrupole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 7A and 7B, respectively. Owing to the sustenance of expansive vortex configurations, the 3D-SC surface topology effectively curbs broadband noises, by reduction of the extent of high-pressure quadrupole source.

[0082] Refer now to FIG. 8A and 8B, which are streamline plot visualizations of the 3D-SC design in FIG. 8A, and the smooth cicada design in FIG. 8B, both of which are operating at 5000 RPM.

[0083] Refer now to FIG. 8C and FIG. 8D, which are visualizations that show helicity isosurface contours of the propellers of FIG. 8A and 8B, respectively. Here, the vorticity of the smooth cicada design in FIG. 8D is greatly improved as viewed in the 3D-SC design of FIG. 8C. Such visual comparisons underscore that the three-dimensional surface serrations play a pivotal role in boosting surface vorticity and stimulating spanwise flow motion.

[0084] Refer now to FIG. 8E and FIG. 8F, which are visualizations that show the dipole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 8A and 8B, respectively. Such coherent vortex structures emerging from the transition from smooth propeller to serrated propeller are instrumental in diminishing harmonic sound pressure fluctuations and curtailing the magnitude of dipole pressure sources, as shown by the comparison of FIG. 8E and FIG. 8F. Furthermore, the accentuated streamwise vorticity (shown in FIG. 8C and FIG. 8D) preserves the flow's momentum, thereby postponing its fragmentation into diminutive eddies, a process governed by the energy cascade principle.

[0085] Refer now to FIG. 8G and FIG. 8H, which are visualizations that show the quadrupole pressures in Pascals (Pa) arising from the operation of the propellers of FIG. 8A and 8B, respectively. Owing to the sustenance of expansive vortex configurations, the 3D-SC surface topology effectively curbs broadband noises, by reduction of the extent of high-pressure quadrupole source.

[0086] These simulation and experimental testing results show that the 3D-SC propeller design can improve aeroacoustic and aerodynamic performance when compared to both current conventional propeller and smooth cicada propeller designs. The 3D-SC propeller design serves as a strong baseline geometry, with extensive iterations and variations possible. Consideration of other unique geometries for the planform may be of interest as well. [0087] Further optimization of the serration geometry, such as an implementation of variable wavelength and amplitude along the span of the blade, is also of significance to explore. In a related field, adding composite structures to the design of the propeller blades, such that the leading or trailing edges are flexible and compliant, has also been explored with promising preliminary results.

[0088] It will be appreciated, therefore, that the 3D-SC propeller design presents a novel three-dimensional serration topology with geometric characteristics dominating the entire propeller surface. Distinctive from leading-edge or trailing-edge serration, the new design incorporates high design flexibility that facilitates both spanwise and chordwise optimization without diminishing the integrity of the cross-sectional airfoil. Owing to the extra design freedom, the new design is not only quieter than traditional serrations but also more advanced in aerodynamic performance in the sense that it consumes less power to produce equivalent thrust when compared to conventional designs.

[0089] Furthermore, based on the CFD results and the testing data analysis, the innovative 3D-SC propeller configuration is conducive to producing a structured vortex field over the blade surface. Reiterating, this unique vortex architecture serves to suppress the dipole and quadrupole sound pressure sources while mitigating the high energy dissipation rate caused by energy cascade, ultimately serving to improve the propulsive efficiency of a propeller.

[0090] Additionally, the three-dimensional serration embraces a high potential for parametric improvement. Thanks to the additional degree of freedom for design, parametric optimization is promising for extra enhancement. In practice, machine-learning-based modification successfully improved the performance of an optimized propeller compared to its baseline counterparts in terms of propulsive efficiency and Overall Sound Pressure Level (OASPL).

[0091] Because the propeller design disclosed herein is both aeroacousticly and aerodynamically advanced, the potential application scenario is comprehensive. First and foremost, flight quietness will be a significant interest of Urban Air Mobility (UAM), where the Federal Aviation Administration (FAA) noise regulations strictly limit drone usage for transportation and cargo. For instance, reductions in noise emission can enable drones to become more successful in markets such as urban delivery, where current efforts have been substantially encumbered by noise-related problems. Additionally, drones are widely used in daily life for entertainment, such as in aerial cinematography. This trend has been dramatically increasing in recent years. Therefore, the quiet propeller design helps reduce noise pollution and keeps a healthy residential environment. However, the applications of this aeroacoustic innovation extend even beyond the drone industry. Reductions in noise emission and fluid dynamic improvements can potentially be found in the fields of green energy and hydrodynamics, with applications in wind turbine design and quiet Unmanned Underwater Vehicle (UUV) operation.

[0092] Additional 3D-SC applications could include: an airplane propeller, a drone propeller, a gaseous pump component, a liquid pump component, a helicopter, a propeller designed for water operation, a wind turbine, and a tidal water turbine. Furthermore, the propeller could be based upon curve fitting of owl wings to form an owl-equivalent 3D-SC propeller blade, otherwise termed a three-dimensional serrated owl (3D-SO) propeller.

[0093] From the description herein, it will be appreciated that the present disclosure encompasses multiple implementations of the technology which include, but are not limited to, the following:

[0094] A noise-reducing propeller blade apparatus, comprising: a propeller blade having a surface, a leading edge, and a trailing edge; a sinusoidal pattern of depressed grooves and raised ribs spanning the surface of the propeller blade; and edge serration features along the leading edge and the trailing edge.

[0095] The apparatus of any preceding or following implementation: wherein distance between adjacent grooves is defined by sinusoidal wavelength (X); wherein depth of each individual groove is defined by sinusoidal amplitude (A); and wherein said serration features along the edges of the blade have a sharpness defined by the ratio of amplitude to wavelength (A/X).

[0096] The apparatus of any preceding or following implementation: wherein said sinusoidal pattern of depressed grooves and raised ribs spanning the surface of the propeller blade comprise three-dimensional serrations.

[0097] The apparatus of any preceding or following implementation: wherein said three-dimensional serrations span the entire surface of the propeller blade.

[0098] The apparatus of any preceding or following implementation: wherein said three-dimensional serrations follow a sinusoidal pattern with a consistent waveform.

[0099] The apparatus of any preceding or following implementation: wherein said three-dimensional serrations terminate at the leading and trailing edges of the propeller blade to form said edge serration features.

[0100] A noise-reducing propeller blade apparatus, comprising: a propeller blade having a surface, a leading edge, and a trailing edge; a sinusoidal pattern of depressed grooves and raised ribs spanning the surface of the propeller blade; and edge serration features along the leading edge and the trailing edge.

[0101] The apparatus of any preceding or following implementation: wherein a depth of each individual groove is defined by sinusoidal amplitude (A); wherein distance between adjacent grooves is defined by sinusoidal wavelength (X); and wherein said serration features along the edges of the blade have a sharpness defined by the ratio of amplitude to wavelength (A/X).

[0102] The apparatus of any preceding or following implementation: wherein when the amplitude is large relative to the wavelength (A/X large), the edge serration features are more “sharp” and “thin” than with a smaller amplitude; and wherein when the amplitude is small relative to the wavelength (A/X small), the edge serration features are more “blunt” and “rounded” than with a larger amplitude.

[0103] The apparatus of any preceding or following implementation, wherein said sinusoidal pattern of depressed grooves and raised ribs spanning the surface of the propeller blade comprise three-dimensional serrations.

[0104] The apparatus of any preceding or following implementation, wherein said three-dimensional serrations span the entire surface of the propeller blade.

[0105] The apparatus of any preceding or following implementation, wherein said three-dimensional serrations follow a sinusoidal pattern with a consistent waveform.

[0106] The apparatus of any preceding or following implementation, wherein said three-dimensional serrations terminate at the leading and trailing edges of the propeller blade to form said edge serration features.

[0107] A noise-reducing propeller blade apparatus, comprising: a propeller blade having a surface, a leading edge, and a trailing edge; wherein the blade comprises a horizontal reference line that rotates about an axis of rotation of the blade; a pattern of serrations spanning at least a portion of the surface of the propeller blade; and a pattern of edge serration features disposed along at least a portion of the leading edge and at least a portion of the trailing edge of the propeller blade.

[0108] The apparatus of any preceding or following implementation, wherein the pattern of serrations is substantially perpendicular to the horizontal reference line when viewed along the axis of rotation of the blade.

[0109] The apparatus of any preceding or following implementation, wherein the pattern of serrations on the blade surface are within an angle a of perpendicular to the horizontal reference line when viewed along the axis of rotation of the blade; wherein the angle a is selected from a group ranges of of angles consisting of: 0-0.5°, 0.5-1.0°, 1.0-3.0°, 3.0-5.0 ⁰ , 5-10°, 10-15°, 15- 20°, and 20-30°.

[0110] The apparatus of any preceding or following implementation, wherein the pattern of serrations that span the surface of the propeller blade are substantially spatially continuous with the pattern of edge serration features disposed along the leading edge and the trailing edge.

[0111] The apparatus of any preceding or following implementation: wherein a depth of each individual groove in the pattern of serrations is defined by sinusoidal amplitude (A); and wherein a distance between adjacent serrations in the pattern of serrations is defined by sinusoidal wavelength (X).

[0112] The apparatus of any preceding or following implementation, wherein said pattern of serrations spanning the surface of the propeller blade comprise a ratio (R) of wavelength to amplitude (X/A) selected from a group of ratios within a range consisting of: 0-1 , 1 -2, 2-3, 3-4, 4-5, 5-6, 6-10, 10-20, 20-50, and 50-100.

[0113] The apparatus of any preceding or following implementation, wherein said sinusoidal pattern of serrations comprises: depressed grooves and raised ribs spanning at least a portion of the surface of the propeller blade.

[0114] The apparatus of any preceding or following implementation, wherein the sinusoidal pattern of serrations comprise three-dimensional serrations.

[0115] The apparatus of any preceding or following implementation, wherein said pattern of serrations spanning at least a portion of the surface of the propeller blade span a percentage of the surface of the propeller blade.

[0116] The apparatus of any preceding or following implementation, wherein said percentage is selected from a group of percentages consisting of: 0-10%, 10-20%, 20-30%, 30-40%, 40-50%, 50-60%, 60-70%, 70-80%, 80-90%, and 90-100%.

[0117] The apparatus of any preceding or following implementation, wherein said pattern of serrations terminate at the leading and trailing edges of the propeller blade to form the pattern of edge serration features disposed along the leading edge and the trailing edge of the propeller blade.

[0118] The apparatus of any preceding or following implementation, wherein said propeller blade is used in an application selected from a group of applications consisting of: an airplane propeller, a drone propeller, a helicopter, a propeller designed for water operation, a wind turbine, and a tidal water turbine.

[0119] A noise-reducing and efficiency increasing propeller blade apparatus, comprising: a propeller blade having a surface, a leading edge, and a trailing edge; wherein the blade comprises a horizontal reference line that rotates about an axis of rotation of the blade; a pattern of serrations spanning the surface of the propeller blade; and a pattern of edge serration features disposed the leading edge and the trailing edge of the propeller blade; wherein the pattern of serrations on the blade surface are within an angle a of perpendicular to the horizontal reference line when viewed along the axis of rotation of the blade; wherein the angle a is within a range of: 0-5.0°; wherein the pattern of serrations that span the surface of the propeller blade are substantially spatially continuous with the pattern of edge serration features disposed along the leading edge and the trailing edge of the propeller blade; wherein a depth of each individual serration in the pattern of serrations is defined by sinusoidal amplitude (A); and wherein a distance between adjacent serrations in the pattern of serrations is defined by sinusoidal wavelength (X); and wherein said pattern of serrations spanning the surface of the propeller blade comprise a ratio (R) of wavelength to amplitude (X/A) selected from a group of ratios within a range consisting of: 0-1 , 1-2, 2-3, 3-4, 4-5, 5-6, 6-10, 10-20, 20-50, and 50-100.

[0120] As used herein, the term "implementation" is intended to include, without limitation, embodiments, examples, or other forms of practicing the technology described herein.

[0121] As used herein, the singular terms "a," "an," and "the" may include plural referents unless the context clearly dictates otherwise. Reference to an object in the singular is not intended to mean "one and only one" unless explicitly so stated, but rather "one or more."

[0122] Phrasing constructs, such as “A, B and/or C”, within the present disclosure describe where either A, B, or C can be present, or any combination of items A, B and C. Phrasing constructs indicating, such as “at least one of” followed by listing a group of elements, indicates that at least one of these groups of elements is present, which includes any possible combination of the listed elements as applicable.

[0123] References in this disclosure referring to “an embodiment”, “at least one embodiment” or similar embodiment wording indicates that a particular feature, structure, or characteristic described in connection with a described embodiment is included in at least one embodiment of the present disclosure. Thus, these various embodiment phrases are not necessarily all referring to the same embodiment, or to a specific embodiment which differs from all the other embodiments being described. The embodiment phrasing should be construed to mean that the particular features, structures, or characteristics of a given embodiment may be combined in any suitable manner in one or more embodiments of the disclosed apparatus, system, or method.

[0124] As used herein, the term "set" refers to a collection of one or more objects. Thus, for example, a set of objects can include a single object or multiple objects.

[0125] Relational terms such as first and second, top and bottom, upper and lower, left and right, and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.

[0126] The terms "comprises," "comprising," "has", "having," "includes", "including," "contains", "containing" or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, apparatus, or system, that comprises, has, includes, or contains a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, apparatus, or system. An element proceeded by "comprises . . . a", "has . . . a", "includes . . . a", "contains . . . a" does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, apparatus, or system, that comprises, has, includes, contains the element.

[0127] As used herein, the terms "approximately", "approximate", "substantially", "essentially", and "about", or any other version thereof, are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. When used in conjunction with a numerical value, the terms can refer to a range of variation of less than or equal to ± 10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1 %, less than or equal to ±0.5%, less than or equal to ±0.1 %, or less than or equal to ±0.05%. For example, "substantially" aligned can refer to a range of angular variation of less than or equal to ±10°, such as less than or equal to ±5°, less than or equal to ±4°, less than or equal to ±3°, less than or equal to ±2°, less than or equal to ±1 °, less than or equal to ±0.5°, less than or equal to ±0.1 °, or less than or equal to ±0.05°.

[0128] Additionally, amounts, ratios, and other numerical values may sometimes be presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. For example, a ratio in the range of about 1 to about 200 should be understood to include the explicitly recited limits of about 1 and about 200, but also to include individual ratios such as about 2, about 3, and about 4, and sub-ranges such as about 10 to about 50, about 20 to about 100, and so forth.

[0129] The term "coupled" as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is "configured" in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

[0130] Benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or element of the technology described herein or any or all the claims.

[0131] In addition, in the foregoing disclosure various features may be grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Inventive subject matter can lie in less than all features of a single disclosed embodiment.

[0132] The abstract of the disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

[0133] It will be appreciated that the practice of some jurisdictions may require deletion of one or more portions of the disclosure after the application is filed. Accordingly, the reader should consult the application as filed for the original content of the disclosure. Any deletion of content of the disclosure should not be construed as a disclaimer, forfeiture, or dedication to the public of any subject matter of the application as originally filed.

[0134] The following claims are hereby incorporated into the disclosure, with each claim standing on its own as a separately claimed subject matter.

[0135] Although the description herein contains many details, these should not be construed as limiting the scope of the disclosure, but as merely providing illustrations of some of the presently preferred embodiments. Therefore, it will be appreciated that the scope of the disclosure fully encompasses other embodiments which may become obvious to those skilled in the art.

[0136] All structural and functional equivalents to the elements of the disclosed embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed as a "means plus function" element unless the element is expressly recited using the phrase "means for". No claim element herein is to be construed as a "step plus function" element unless the element is expressly recited using the phrase "step for".