Side-Intake Piston Water Jet Propulsor

FIELD OF THE INVENTION

Propellers, impeller-driven water jet propulsor and piston or reciprocating water jet propulsors for marine vehicles, Water pumps.

BACKGROUND OF THE INVENTION

For marine vehicle propulsion, propellers or impeller-driven water jets are mostly being used. The principle to generate thrust in water is to use some mechanism to build up the water kinetic energy from the water velocity in line with the thrust axis. Marine propellers or marine impeller- driven water jets all depend on the spin of blades in water to build up the water kinetic energy. Because of the spin of blades in water, the kinetic energy built up in water is contributed not only from the water velocity in the thrust-producing axis but also from the water rotational velocity about the spin axis. The kinetic energy from the rotational velocity of water doesn't contribute to the generation of thrust and therefore it is an energy waste. This principally-embedded energy waste leads to the fact that such propulsors could hardly reach close to the ideal efficiency of propulsor. The highly rotational water kinetic energy not only brings down the efficiency of the propulsor but also the sources of blade surface cavitations and the helical vortices in the propulsor flow wake that generate water noises. Further more, the increase of water velocity in the thrust-producing axis through the spinning of the blades works on the principle of a lifting foil. A foil requires an optimal angle of attack for maximum lift, likewise an optimal pitch angle of the blade is required to have a maximum increase of the thrust-producing water kinetic energy. For a given design of propeller or impeller-driven water jet, it could hardly operate in optimal pitch angle at all vehicle speeds, and that is why a propeller or an impeller-driven water jet can only reach its highest efficiency at the design point. As the vehicle operates at off-deign points, the efficiency of such propulsors degrades greatly. In other words, such propulsors could hardly offer the thrust power that is proportional to the input power. In real life, that fact reflects a poor acceleration of a marine vehicle equipped with such propulsors.

Our forefathers had long before understood that to most effectively propel and offer almost linear propulsion power to his boat one should do what oarsman does commonly seen in boat racings. In one propulsion cycle, oarsman gives a powerful stroke of his oar to expel or discharge the water, which generates a reaction force, i.e., the thrust on the oar surface to push the boat, and then follows an effortless oar recovering stroke through the air. The reason of such a propulsion cycle being highly efficient is that the mechanical work done on the oar to expel the water only accelerates the water velocity in line with the thrust and the oar recovering through the air introduces negligible resistive energy loss. There also exists piston or reciprocating water jet propulsors to propel marine vehicles. From the way of expelling or discharging water, such propulsors work in the same principle of oars. Similarly, the biggest advantage of a piston water jet propulsor is that the mechanical motion of the piston is in line with the thrust-producing axis and therefore such a motion builds up the water kinetic energy only from the water velocity in the thrust-producing axis. Because of this reason, such a propulsor has a nearly constant efficiency at any working condition or vehicle speed. This characteristic of a piston water jet is consistent with the common knowledge that the efficiency of a positive displacement pump is nearly constant and higher than an impeller-driven pump of same power.

Unlike the oar recovering through air, an issue relating to the efficiency of a piston water jet propulsor is the energy cost in the water intake process during the piston's recovering or back stroke. Prior arts of piston water jet propulsor all employ the water intake from the axial direction of the cylinder as the piston takes a back stroke, for example, through the openings on the piston. With this axial intake, the piston during its back stroke moves in a direct headwind of the intake flow, resulting in a large resistance to the piston's motion. The piston's mechanical work to overcome this resistance during the back stroke is an energy waste, which negatively affects the efficiency of the propulsor.

OBJECTIVES OF INVENTION

The primary objective of the invention is to achieve that the piston moves in atmospheric air condition during its back stroke for water intake, and therefore leads to a negligible energy loss for water intake for a piston water jet propulsor. Another objective is to invent an open-close valve for the Side-Intake of water that makes the piston's back stroke through air achievable. A further objective is to achieve an actual design of the Side- Intake Piston Water Jet Propulsor that embodies the principle of the Side- Intake concept. All these achieved objectives results in the invention of a high-efficiency piston water jet propulsor for marine vehicles. VI SUMMARY OF THE INVENTION

The current Side-Intake Piston Water Jet Propulsor is characterized by the principle feature of the Side-Intake of water. The principle feature of Side- Intake of water in a piston water jet propulsor is that the piston separates the cylinder into a dry and a wet compartment at any time it moves for water intake and discharge. The dry compartment is always at atmospheric condition, which allows the piston encounters only air resistance that consumes a negligible amount of energy during its back stroke and water intake.

An efficient, simple and reliable inner-ring rotational valve is invented to achieve the Side-Intake of water for the current propulsion system.

Further more, the principle of the Side-Intake of water together with the inner-ring rotational valve leads to the invention of the current Side- Intake Piston Water Jet Propulsor. Not limited to its advantages in acoustics, simplicity and reliability, the primary advantages of the Side- Intake Piston Water Jet Propulsor particularly include that the propulsor is able to attain unlimitedly to the ideal efficiency of propulsor and offer a linear thrust power because of its feature of a nearly constant efficiency.

VII DESCRIPTON OF THE FIGURES

The working principle of the Side-Intake concept and the design of the

Side-Intake Piston Water Jet Propulsor and their advantages will be well appreciated with the accompanying figures.

FIG. 1 -(a) is a schematic diagram for a Side-Intake process.

FIG. 1 -(b) is a schematic diagram for a discharge process.

FIG. 2 is a schematic diagram for first principle analysis for a two-cylinder

Side-Intake Piston Water Jet Propulsor.

FIG. 3 is a side, break-away view of the Side-Intake Piston Water Jet Propulsor.

FIG. 4 is a front, break-away view of the Side-Intake Piston Water Jet Propulsor.

VIII DESCRIPTON OF THE INVENTION 1. The Principle of Side-Intake

The concept of Side-Intake of water for a piston water jet propulsor can be shown in a schematic diagram in FIG. 1 . First, it requires a tube for a piston to do reciprocating motion inside. The tube could be, but not limited to, a cylinder; however the inventor will refer such a tube to as a cylinder for convenience throughout. The concept of the Side-Intake opens intake holes on the side and near the discharging end of the cylinder wall. An open-close valve must be installed to open and close the Side-Intake holes during the piston's strokes for intake and discharge respectively. The discharge end is completed with a jet nozzle. With a piston installed inside the cylinder, the system becomes a one-cylinder Side-Intake Piston Water Jet Propulsor. FIG. (1 )-(a) shows the water intake process. In this process, the valve is in fully open position and the piston takes the back stroke, namely the piston moves toward left as shown in the picture. FIG. (1 )-(b) shows the process of water discharge through the jet nozzle for thrust generation. In this process, the valve is in fully closed position and the piston takes the forward stroke, namely the piston moves toward the right as shown in the picture.

The principle feature for the Side-Intake concept is the separation of the inside of the cylinder to be a dry and a wet compartment by the piston at any moment during piston's motion. This feature can be explained with FIG. 1 -(a) and -(b). As shown in FIG. 1 -(a) and -(b), whether during intake or discharge, the left compartment of the cylinder separated by the piston is always dry and opens to the inside of a vehicle, which is in an atmospheric pressure condition, and on the other hand the compartment to the right of the piston is always wet containing the water. Because the left compartment of the cylinder is always opens to the atmospheric air condition, the piston only confronts atmospheric air during the back-stroke for water intake, which requires a negligible energy. From hydrodynamic point of view, this characteristic of piston's back stroke through air for water intake achieves the same function as an oarsman returns his oar in the air. However, the current Side-Intake for piston water jet propulsor achieves that under the water line.

Following the description of the above, such a piston water jet propulsor, if with just one-cylinder, will have no water intake during the discharge and also no water discharge during the water intake. To keep a continuous water intake and discharge, a Side-Intake Piston Water Jet Propulsor will take at least a pair of cylinders in an actual design.

2. First Principle Analysis

To facilitate an analysis with first principles for a Side-Intake Piston Water Jet Propulsor, a schematic diagram for such a system with two cylinders that could maintain a continuous inflow and jet exit flow is shown in FIG. 2. First principles used in the analysis are the mass, momentum and energy conservation laws in a control volume. The control volume is taken to be the water region enclosed in the dash-dotted line, which is a constant at any moment of the pistons' motion. Neglecting the elevation difference between the intake and discharge as well as water viscous effect, applying the first principles to this control volume leads to,

Q = p A _p - V _p (1 )

(2)

U _a is the ambient water velocity, which is the same as the vehicle's speed but in the opposite direction when considering the vehicle is fixed. Equations (1 )-(3) govern the mass flow rate, the thrust generation and the piston's net mechanical work added into water. Note that V _j and V, are in the thrust axis. As it can be seen, the piston's mechanical work of such a system is the work done on the boundary of the control volume and during the piston's back stroke for water intake, i.e., the piston moves to the left as shown by the up-piston in FIG. 2, that piston does a negligible amount of work because the left compartment of the piston is always at atmospheric condition. The useful work is the product of vehicle's speed and the thrust and therefore the efficiency of the propulsor is,

_ ^YV useful _ ^{Δ U} a j i

1 propulsor ~ ^~ y ₊ y ^' y2 _ TJ2 (4)

P j i j a

The first factor in the right side of Equation (4) is the well-known ideal efficiency of propeller or water jet. The second factor is considered to be the inflow effect on the propulsor efficiency. Because the area of the intake opening of the valve, A ₀ , will be made larger than the piston area, from the law of mass conservation, V,, will be very close to or even a bit less than U _a if considering the boundary layer effect. Thus, the factor of the intake effect of a Side-Intake Piston Water Jet Propulsor could be greater than one and therefore gives a boost to the propulsor efficiency.

The energy equation, Equation (3), for the current Side-Intake Piston Water Jet Propulsor, revealed the fundamental difference from those for the propeller, or the impeller-driven water jet or the axial-intake water jet. For propeller or impeller-driven water jet, the right side of Equation (3) will have an additional term for the water kinetic energy due to water rotational velocities and for the axial-intake piston water jet, the right side of Equation (3) will also have an additional term for the water resistant work on the piston during the intake. These additional and non- trivial energy costs increase the denominator in the efficiency equation, Equation (4) and answered why the prior arts could hardly reach close to the ideal efficiency even though assuming that the prior and current arts could have the same inflow effect.

The first principle analysis showed that the current Side-Intake Piston Water Jet Propulsor is able to achieve the ideal efficiency of propulsor in theory. However, it should be acknowledged that the analysis neglects the energy cost in the open and close of the open-close valve for the intake and discharge. For the current art to beat the efficiency of prior arts, a nontrivial question is to design an open-close valve that costs least energy, or at least less than the energy waste in prior arts, during opening and closing in water. An inner-ring rotational valve is invented and discussed in VIII, which is expected to cost a negligible amount of energy to open and close in water.

The above analysis is based on a steady water jet. In reality, the piston motion is unsteady. Recent studies have proven that the water jet generated from an unsteady piston motion is able to form a vortex ring in the jet exit flow, which engulfs the ambient flow, and results in an additional increase of the axial water momentum. Because of this reason, the vortex ring generated from the water jet of unsteady piston motion will contribute to an additional thrust and therefore a further boost to the propulsor's efficiency.

DESCRIPTION OF THE PREFERRED EMBODIMENT

There are many ways to design open-close valves to accomplish the current Side-Intake principle. A primary principle for the design of an open- close valve for the current application is the simplicity and the minimum energy loss during the valve open and close process.

The current design of the Side-Intake Piston Water Jet Propulsor employs an inventive inner-ring rotational valve for open-close actuated by an electric-magnetic actuator. The propulsion system is a Side-Intake Piston Water Jet Propulsor with 4 cylinders.

In FIG. 3 and FIG. 4,

(1 ) is the jet nozzle;

(2) is the 4 cylinders;

(3) is the 4 inner ring rotational valves;

(4) is the ball bearings;

(5) is the permanent magnets installed on the inner ring rotational valves;

(6) is the 4 electrical coil winding pats in the electric-magnetic actuator;

(7) is the 4 pistons;

(8) is the 4 energy absorbing springs, one for each piston;

(9) is the baffle cap.

For this 4-cylinder Side-Intake Piston Water Jet Propulsor, each two piston-cylinder set is synchronized to move together. For example, one pair of the pistons takes the forward stroke to discharge water from the jet nozzle while the other pair is to take the back stroke to intake water from the Side-Intake openings. This can be seen in both FIG. 3 and FIG. 4. Each inner ring rotational valve has rows of ball bearings for easy rotation and two or four permanent magnet pads embedded in at 90 degree apart along its circumference. The electric-magnetic actuator will make the inner-ring rotational valve to turn 90 degree to open the valve before the intake stroke takes place and turn back or another 90 degree to close the valve before the discharge stroke takes place. The rotational motion to open and close the valve cuts across the flow, which introduces resistive energy loss. However, because the inner-ring is made thin and the cross area for flow cutting is small, the cutting motion of the ring into the flow will, therefore, excite only a little local secondary flow, comparing to a gross secondary flow generation due to the entire blades spin in propeller or impeller-driven water jet. In addition, with the use of ball bearings for easy rotation, the energy cost to open and close the valve is expected to be very small.

As indicated in FIG. 4, at this particular moment, the up- and down- cylinders have the inner-ring rotational valves in fully open position and the two pistons just to start the back stroke for water intake, while the cylinders shown in the left and right have the inner-ring rotational valves in fully closed position and the two pistons just to start the forward stroke for water discharging. Associated with FIG. 4, the pistons' positions can be seen in FIG. 3 at this same moment.

Each spring installed in the dry compartment and attached to the piston is to absorb the potential energy from the water during the intake. Because the air behind the cylinder is at atmospheric condition and the cylinder is submerged in water at certain depth of water depending on the waterline level of the vehicle, during the water intake the water hydrostatic pressure will do the work on the piston that adds energy into the system and the spring is designed such that to absorb and store that energy. That same amount of energy stored in the spring will then add back into water during piston's discharging stroke. That spring is particularly necessary when the current propulsor is applied to powering deeply- submerged vehicles.

The current propulsor can be applied to powering either surface or underwater vehicles. Prime mover to drive the piston's motion can either come from combustion engines or linear motors. If linear motors are used, then the rods connecting the pistons are not necessary.