Parallel combustor configuration for unmanned underwater vehicle propulsion turbine

A propulsion system for an unmanned underwater vehicle includes at least one fuel storage tank. A plurality of combustors is connected to the at least one fuel storage tank. Each of the combustors is connected to a turbine via a corresponding nozzle. An output shaft is connected to the turbine and configured to output rotational energy from the turbine.

TECHNICAL FIELD

The present disclosure relates generally to a torpedo propulsion turbine, and specifically toward a gas powered turbine having multiple combustors for utilization in a torpedo propulsion system.

BACKGROUND

Unmanned underwater vehicles, such as torpedoes, can be deployed from submarines, aircraft, ships, or any similar deployment platform. Once deployed, the unmanned underwater vehicle is propelled towards a target. Historically, unmanned underwater vehicles have been propelled by many different power sources included liquid fuel (such as Otto Fuel) engines, electric motors and batteries, electric motors and fuel cells, chemically heated steam engines, compressed gas engines, and solid rocket motors.

Maximizing an effective range, while also maintaining a sprint speed (maximum high speed) capability, is one goal of unmanned underwater vehicle design, and is impacted by the type of power source utilized to achieve propulsion. The longer the unmanned underwater vehicle's range, the further the deployment platform can be from the target of the unmanned underwater vehicle, protecting the safety of the deployment platform. In addition to the range, a high sprint speed allows the unmanned underwater vehicle to overtake a moving target once the moving target has been alerted to the unmanned underwater vehicle's presence. As is appreciated in the art, most engine configurations trade off effective range for a higher sprint speed, or sprint speed for a higher effective range.

SUMMARY OF THE INVENTION

In one exemplary embodiment a propulsion system for an unmanned underwater vehicle includes at least one fuel storage tank, a plurality of combustors connected to the at least one fuel storage tank, each of the combustors being connected to a turbine via a corresponding nozzle, and an output shaft connected to the turbine and configured to output rotational energy.

Another example of the above described propulsion system for an unmanned underwater vehicle further includes a propulsor connected to the output shaft via a geared connection.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle each combustor in the plurality of combustors is the same size as each other combustor in the plurality of combustors.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle at least one combustor in the plurality of combustors is larger than each other combustor in the plurality of combustors.

Another example of any of the above described propulsion systems for an unmanned under underwater vehicle further includes a controller controllably coupled to each combustor in the plurality of combustors and configured to control a flow of fuel from the at least one fuel storage tank to each combustor.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle the controller is a dedicated propulsion system controller.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle the controller is a general systems controller.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle the turbine is a partial admission axial flow turbine.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle the nozzles are distributed evenly about a circumference of a turbine inlet.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle each of the combustors is individually sized to a corresponding propulsion system operational mode.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle each of the combustors is sequentially sized to at least one corresponding propulsion system operational mode.

In another example of any of the above described propulsion systems for an unmanned under underwater vehicle the propulsion system is disposed in a torpedo. In one exemplary embodiment an unmanned underwater vehicle includes a body housing at least a first fuel storage tank, a general controller, and a propulsion system, and the propulsion system including a gas powered turbine engine mechanically connected to a propulsor, wherein the gas powered turbine engine includes a plurality of parallel combustors.

Another example of the above described unmanned underwater vehicle further includes a second fuel storage tank.

In another example of any of the above descried unmanned underwater vehicles the plurality of parallel combustors are sequentially sized.

In another example of any of the above descried unmanned underwater vehicles the plurality of parallel combustors are individually sized.

In another example of any of the above descried unmanned underwater vehicles each combustor in the plurality of parallel combustors is connected to a single turbine via one of a plurality of supersonic nozzles.

In another example of any of the above descried unmanned underwater vehicles the supersonic nozzles are distributed evenly about a first end of the turbine.

In another example of any of the above descried unmanned underwater vehicles a mechanical connection between the gas powered turbine engine and the propulsor includes an output stage and a geared connection.

An exemplary method of driving a propulsion system for an unmanned underwater vehicle, includes generating combustion products in a single combustor and expanding the combustion products across a turbine in a first propulsion mode, and generating combustion products in at least two combustors and simultaneously expanding the combustion products across the turbine in a second propulsion mode.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1schematically illustrates a cross sectional view of an exemplary unmanned underwater vehicle100. A forward end102of the unmanned underwater vehicle100includes a navigation system110, a payload120, such as a warhead, and control electronics130. A mid-section of the unmanned underwater vehicle100includes fuel storage tank150. Alternative example unmanned underwater vehicles utilizing multiple fuel types can include two or more distinct fuel storage tanks, each corresponding to its own fuel type. A rear end104of the unmanned underwater vehicle100includes a gas turbine engine160and a propulsor170.

With continued reference toFIG. 1, and with like numerals indicating like elements,FIG. 2schematically illustrates an exemplary gas turbine engine160, such as could be utilized in the unmanned underwater vehicle100ofFIG. 1. The gas turbine engine160includes a combustor162connected to a partial admission axial turbine164via a supersonic nozzle166. Rotational motion generated by the partial admission axial turbine164is output via an output shaft168. In some examples, the output shaft168is directly connected to the propulsor170(illustrated inFIG. 1), and directly drives rotation of the propulsor170. In alternative configurations, the output shaft168is connected to the propulsor170via a geared connection. In the alternative configuration, the geared connection allows a controller, such as the control electronics130, to adjust the speed at which the propulsor170is rotated, thereby controlling the speed of the unmanned underwater vehicle100. In yet further alternative examples, the output shaft168can be connected to alternative systems, such as electrical generators, in addition to or instead of directly to the propulsor170.

Once launched, the turbine engine160converts chemical energy from the fuel in the fuel storage tank150into mechanical energy by combusting the fuel in a combustor162to produce high temperature gas, referred to as a combustion product. The combustion product is expelled through the supersonic nozzle166into the partial admission axial turbine164. The turbine164converts the high speed, high temperature, gas into a rotational power which drives rotation of the output shaft168. The output shaft168is connected to the propulsor170. In the alternative examples utilizing two fuel types, fuel in the first fuel storage tank150and an oxidizer in a second tank is mixed in the combustor162and combusted. The control electronics130control the operations of the turbine engine160, as well as any directional controls, or other electronic systems onboard the unmanned underwater vehicle100. Further, alternative examples utilizing alternative turbine configurations from the described and illustrated partial admission axial turbine164can be utilized

FIG. 3illustrates an exemplary propulsion power vs. speed curve300of the exemplary unmanned underwater vehicle100. As can be seen, the curve300is non-linear, and the amount of propulsion power (axis310) required to increase the speed of the unmanned underwater vehicle (axis320) by a given amount increases exponentially as the current speed of the unmanned underwater vehicle100increases. The specific curve300illustrated inFIG. 3is purely exemplary in nature and does not include actual unmanned underwater vehicle propulsion power or speed values. During operation the propulsion power of an unmanned underwater vehicle is related to the unmanned underwater vehicle's forward speed. In order for an unmanned underwater vehicle to operate properly at a very high sprint speed (i.e. with a high maximum velocity), the gas turbine engine160has to be capable of providing a very large power level. In order to achieve the exponentially higher power output required for an unmanned underwater vehicle at sprint speed exponentially more fuel must be expended.

Due to the specific power requirements of the unmanned underwater vehicle100, operation of the unmanned underwater vehicle100at slower speeds can increase the range of the unmanned underwater vehicle100, by requiring less of the fuel to be expended to cover the same distance. Certain combustion engines powered by liquid fuels, such as Otto Fuel, are very efficient at their maximum power design point, allowing for high speed operation, however their efficiency degrades at lower power levels resulting in less fuel saved by operating at low speed than if the combustion engine could maintain a high efficiency while operating at low power. This phenomenon yields a reduction in underwater vehicle range.

With reference again toFIG. 2, the size of the supersonic nozzle166is optimized to provide an optimum turbine blade velocity to gas velocity (U/C) ratio while the gas powered turbine engine160is operating at the highest power setting. When the power setting is reduced, such as when the engine is operating to extend the range of the torpedo, the pressure in the combustor162is reduced by reducing the flow of fuel from the fuel storage tank150to the combustor162. In one example, this is achieved by reducing the pressure of a fuel pump connecting the fuel storage tank150to the combustor162. The reduced pressure in the combustor162lowers the velocity of the combustion products approaching the turbine blades. The mismatch in velocity between the turbine blades and the gas velocity causes increased entrance losses into the turbine, and reduces the efficiency of the turbine engine160.

With continued reference toFIGS. 1-3,FIG. 4illustrates an alternate gas powered turbine400including three parallel combustors410A,410B,410C. Each of the combustors410A,410B,410C is connected to the turbine section464via a corresponding nozzle466. Each of the combustors410A,410B,410C is approximately identical in size412, and receives fuel through a fuel inlet420.

In the example gas powered turbine engine400, each of the multiple combustors410A,410B,410C and the corresponding nozzles466are sized to provide an optimum U/C ratio for a low power mode of operations. In the example utilizing three parallel combustors410A,410B,410C, the low power mode of operations is approximately ⅓ the maximum power mode of operations. In the example, the propulsion system can operate in three modes of operation: a low power mode, a medium power mode, and a high power mode. At low power, fuel is provided to only one of the three combustors410A,410B,410C and the propulsion system operates at ⅓ of the maximum possible power.

As the engine power level is increased above ⅓ maximum power, the engine controller causes a fuel control valve to open, allowing fuel to enter a second combustor410A,410B,410C through the corresponding inlet420. The two combustor mode is referred to as a medium power level mode of operations and can provide up to ⅔ of the maximum power. As the engine power level is increased above ⅔ maximum power, the engine controller causes another fuel control valve to open, allowing fuel to enter a third combustor410A,410B,410C through the corresponding inlet420.

The operation of combustors410A,410B,410C in the above described manner to provide an additive power is referred to herein as sequential operation, and the combustors410A,410B,410C are sequentially sized. While described herein as identical combustors412, the sequential operation, and sequential sizing, of the combustors410A,410B,410C does not necessitate identical sizing of the combustors410A,410B,410C.

FIG. 5schematically illustrates an alternative configuration of a gas powered propulsion system500for unmanned underwater vehicles including three parallel combustors510A,510B,510C. Each of the combustors510A,510B,510C is connected to the turbine section564via a corresponding nozzle566. Each of the combustors510A,510B,510C has a distinct size512, and receives fuel through a fuel inlet520.

In the example gas powered turbine engine500, each of the multiple combustors510A,510B,510C and the corresponding nozzles566are sized to provide an optimum U/C ratio for a corresponding mode of operations. By way of example, the middle illustrated combustor510B is the smallest combustor510A,510B,510C and is sized for operating at a lowest power mode of operations. The bottom illustrated combustor510C is an intermediate size, and is sized for operating at an intermediate mode of operations, and the top illustrated combustor510A is the largest combustor510A,510B,510C and is sized to operate at a highest power mode of operations. In other words, each of the combustors510A,510B,510C is sized to provide the full amount of power required at the corresponding mode of operations. This configuration is referred to as each combustor510A,510B,510C being individually sized for a corresponding mode of operations.

In the example ofFIG. 5, the propulsion system500can operate in three modes of operation: a low power mode, a medium power mode, and a high power mode. At low power, fuel is provided to smallest combustor510B, through the fuel inlet520, and the turbine562operates at a corresponding speed. As the propulsion system500transitions to a speed that exceeds the available speed from the lowest power combustor510B, fuel to the smallest combustor510B is cut off, and provided to the intermediate sized combustor510C instead. Similarly, once the power requirements of the gas turbine engine exceed the power output of the intermediate sized combustor510C, fuel to the intermediate combustor510C is removed, and fuel is provided to the largest combustor510A.

The propulsion system500ofFIG. 5can be further adapted to provide an even higher operational speed by providing fuel to all the combustors510A,510B,510C and operating the combustors510A,510B,510C simultaneously.

With reference to bothFIG. 4andFIG. 5, the size dimension is indicated at a diameter412,512of the combustor410A,410B,410C,510A,510B,510C. However, one of skill in the art having the benefit of this disclosure, will understand that the size dimension can be any alternative dimension, or combination of dimensions, include length, volume, and circumference.

Further, in each of the examples400,500, the nozzles466,566can be distributed evenly circumferentially about an inlet to the turbine464,564. In alternative examples, an unevenly spaced distribution can be utilized to better balance flow inlet between unevenly sized combustors.

By utilizing parallel combustors, the low power efficiency of the propulsion system400,500can be increased without negatively impacting the efficiency of the turbine operations at higher powers. The increased efficiencies at low power, increase the range of the torpedo, while still maintaining the high sprint speed capability of the torpedo.

While illustrated herein as including three parallel combustors, it should be appreciated that two, four, or any other number of combustors can be utilized, depending on the number of operational modes the gas powered turbine will be operating in. Further, it should be appreciated that while illustrated inFIG. 4as including approximately identical combustors, the parallel combustors can be created having distinct sizes, with the size of any given combustor corresponding to an optimum U/C ratio for a corresponding mode of gas powered turbine operation.

Further, while described above within the specific context of a torpedo, one of skill in the art will understand that the propulsion system can be utilized in any similar unmanned underwater vehicle and is not limited to torpedo propulsion systems.

It is further understood that the operating pressure of each combustor in any of the above examples could be varied to provide variable power within each of the power settings (i.e. variable power output capability can be achieved by varying the combustor pressure while utilizing the low power combustor, variable power output capability by varying the combustor pressure while utilizing the medium power combustor, or variable power output capability by varying the combustor pressure while utilizing the high power combustor, etc.)