Fluidic device

A fluidic device for providing analogue output control includes a main channel, a first control channel, a second control channel, a comparator which receives respective input fluid flows from the main, the first and the second control channels. The first control channel is configured such that the input fluid flow therefrom carries an oscillating pressure wave signal, the second control channel includes a flow regulator controllable to vary the mass flow rate of the input fluid flow from the second control channel, and the main channel is configured such that the input fluid flow therefrom is at a reference mass flow rate. The comparator is configured such that the input fluid flows from the first control and the second control channels act in combination on the input fluid flow from the main channel to produce an output fluid flow from the comparator having a PWM mass flow rate characteristic.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from British Patent Application No. GB 1711950.4, filed on 25 Jul. 2017, the entire contents of which are herein incorporated by reference.

BACKGROUND

Technical Field

The present disclosure relates to a fluidic device for providing analogue output control.

Description of Related Art

Fluidic components were used in the 1950s for building fluidic-based computers. However with invention of the transistor these had gone obsolete by the 1960s. Since then the use of fluidic components has been limited to niche applications such as the control of variable stator vanes on aero gas turbine engines (see for example U.S. Pat. No. 4,252,498).

Many fluidic devices are known, but common ones are based on the Coanda effect, which describes the tendency of a jet flow near a wall to attach to that wall through an entrainment process. A component that operates on this principle is a fluidic diverter, shown schematically inFIG. 1. The diverter has a main channel1, a first control channel2and a second control channel3. The diverter further has a first output channel4and a second output channel5. Flows from the first and second control channels arrive in the diverter transversely to a flow from the main channel. By suitable control of the transverse control flows, which may be less than 20% of the mass flow rate of the main flow, an output flow can be switched between the first and the second output channels. Such a diverter can be thought as an amplifier with a typical gain>=5.

An advantage of such a component is the lack of moving parts, making it suitable for use in harsh environments, such as jet engines and nuclear reactors. A disadvantage, however, is that it is a digital component, which is unable to vary the output flow in a continuous manner.

FIG. 2shows schematically at left another known fluidic device, in this case a vortex amplifier6, and at right a plot of amplifier output against time. The amplifier has a primary flow source, a primary flow sink and a control valve7which allows servo fluid into the amplifier when opened. In the absence of servo fluid through the control valve, the fluid from the primary flow passes in a radial direction of the amplifier to the sink at a relatively high flow rate. Opening the control valve introduce the servo fluid, which generates a vortex in the amplifier. The resulting vortex produces an increased resistance to radial flow, and thus throttles the primary flow out of the sink to a leakage level. Thus the output from the amplifier is again essentially binary.

SUMMARY

In general terms, the present disclosure provides a fluidic device that extends the operation of known devices so as to provide an output which is suitable for use in analogue control, and thus enables greater levels of control and performance.

Accordingly, in a first aspect, the present disclosure provides a fluidic device for providing analogue output control, the device including:

a main channel, a first control channel and a second control channel, and

a comparator which receives respective input fluid flows from the main, the first control and the second control channels;

wherein the first control channel is configured such that the input fluid flow therefrom carries an oscillating pressure wave signal, the second control channel includes a flow regulator which is controllable to vary the mass flow rate of the input fluid flow from the second control channel, and the main channel is configured such that the input fluid flow therefrom is at a reference mass flow rate; and

wherein the comparator is configured such that the input fluid flows from the first control and the second control channels act in combination on the input fluid flow from the main channel to produce an output fluid flow from the comparator having a pulse width modulation mass flow rate characteristic.

Such a characteristic can be usable as an analogue control signal. The fluidic device may be adapted for controlling a gas turbine engine component(s). For example, the controlled gas turbine engine component(s) can be a bleed valve, variable guide vanes, variable stator vanes, or an air system providing turbine tip clearance control.

Accordingly, in a second aspect, the present disclosure provides a gas turbine engine having one or more fluidic devices according to the first aspect for controlling respective components of the engine.

Optional features of the present disclosure will now be set out. These are applicable singly or in any combination with any aspect of the present disclosure.

Conveniently, the first control channel may be configured such that the input fluid flow therefrom carries a saw tooth pressure wave signal.

In the context of a gas turbine engine, the reference mass flow rate may vary with engine cycle. However, conveniently, the main channel may be configured such that the input fluid flow therefrom is at a constant reference mass flow rate.

Typically, the first and second control channels are configured such that the input fluid flows therefrom are transverse to the input fluid from the main channel. Typically, the first and second control channels are configured such that the input fluid flows therefrom impinge at the same point on the input fluid from the main channel. Typically, the first and second control channels are configured such that the input fluid flows therefrom are opposed to each other.

The first control channel may extend in flow series through a fluidic oscillator and a fluidic capacitor to produce the oscillating pressure wave signal.

The flow regulator may be controllable to continuously and smoothly vary the mass flow rate of the input fluid flow from the second control channel. For example, the flow regulator can be a modulating valve.

The fluidic device may be configured such that input mass flow rates to the main, first control and second control channels are identical.

The comparator may be a fluidic diverter having first and second output channels and the output fluid flow may be a first output fluid flow taken from the first output channel, the input fluid flows from the first control and the second control channels acting in combination on the input fluid flow from the main channel to provide the first output fluid flow with the pulse width modulation mass flow rate characteristic. In such an arrangement, a second output fluid flow from the second output channel generally has an opposite pulse width modulation mass flow rate characteristic to the first output fluid flow. Typically, the output channels are configured such that the output fluid flows which flow therethrough are taken from the same point on the input fluid from the main channel. Typically, the output channels are configured such that the output fluid flows diverge at angles from the direction of the input fluid from the main channel. The angles are typically equal and opposite angles.

According to one option when the comparator is a fluidic diverter, a second output fluid flow may be taken from the second output channel, the device may further include a feedback loop from the second output channel to the second control channel, and the flow regulator is controllable to vary a proportion of the mass flow rate of a second output fluid flow entering the second control channel from the second output channel via the feedback loop. Such a feedback loop may typically be configured to take from 5% to 20% of the second output fluid flow from the second output channel.

Additionally or alternatively when the comparator is a fluidic diverter, the fluidic device may further include an actuator comprising a piston which is movable in a piston chamber, the piston chamber to one side of the piston receiving the first output fluid flow, and the piston to the other side of the piston receiving a second output fluid flow taken from the second output channel, whereby the position of the piston in the chamber is controllable by varying pulse widths in the pulse width modulation mass flow rate characteristic. The fluidic device may then further have a feedback control loop which controls the flow regulator to vary the mass flow rate of the input fluid flow from the second control channel on the basis of the piston position.

According to another option, a fluidic device in which the comparator is a fluidic diverter may further include a vortex amplifier having a source for receiving a flow of a primary fluid into the vortex amplifier, a sink through which the primary fluid leaves the vortex amplifier, and a control port for introducing a control fluid flow into the vortex amplifier, wherein the vortex amplifier is configured such that a relatively high mass flow rate of the control fluid forms a vortex from the primary fluid between the source and the sink to set a flow of the primary fluid from the sink to a relatively low level, and a relatively low or zero mass flow rate of the control fluid reduces or eliminates the vortex to set the flow of the primary fluid from the sink to a relatively high level; wherein the first output fluid flow from the fluidic diverter forms the control fluid flow into the vortex amplifier. When the comparator is a fluidic diverter and the first output fluid flow has a pulse width modulation mass flow rate characteristic, this option enables fast switching on and off of the vortex amplifier, which in turn enables it to effectively operate as an analogue device with a range of flows of the primary fluid from the sink rather than binary flows.

The fluidic device may be a pneumatic device.

DETAILED DESCRIPTION

With reference toFIG. 3, a ducted fan gas turbine engine is generally indicated at10and has a principal and rotational axis X-X. The engine comprises, in axial flow series, an air intake11, a propulsive fan12, an intermediate pressure compressor13, a high-pressure compressor14, combustion equipment15, a high-pressure turbine16, an intermediate pressure turbine17, a low-pressure turbine18and a core engine exhaust nozzle19. A nacelle21generally surrounds the engine10and defines the intake11, a bypass duct22and a bypass exhaust nozzle23.

During operation, air entering the intake11is accelerated by the fan12to produce two air flows: a first air flow A into the intermediate-pressure compressor13and a second air flow B which passes through the bypass duct22to provide propulsive thrust. The intermediate-pressure compressor13compresses the air flow A directed into it before delivering that air to the high-pressure compressor14where further compression takes place.

The engine10has components such as bleed valves, variable guide vanes, variable stator vanes, and air systems for providing turbine tip clearance control. Such components may be controlled using an analogue control signal derived from the output fluid of a fluidic device. Advantageously, such a device can operate reliably in the harsh environment of the engine.

FIG. 4shows schematically the fluidic device30. A fluid diverter31of the type shown inFIG. 1functions as a comparator, receiving respective input fluid flows from a main channel32, a first control channel33and a second control channel34, and producing an output fluid flow with a pulse width modulation (PWM) mass flow rate characteristic from a first one of its two output channels.

Conveniently, the main channel32, first control channel33and second control channel34can receive fluid at an identical input mass flow rate.

The first control channel33has, in flow series, a fluidic oscillator35and a fluidic capacitor36. The fluidic oscillator generates stable, constant frequency mass flow rate pulses. See for example, V. Tesař,High-frequency fluidic oscillator, Sensors and Actuators A: Physical, volume 234, 1 Oct. 2015, pages 158-167. The fluidic capacitor then filters the oscillator output to create an oscillating pressure wave signal, such as a saw tooth pressure wave signal. The capacitor can be implemented as an appropriately sized pressure chamber with an orifice. See for example, K. Xu et al.,Fluidic capacitor-based, self-contained and self-powered microfluidic chip,15th International Conference on Miniaturized Systems for Chemistry and Life Sciences, Oct. 2-6, 2011, Seattle, Wash., USA, pages 233-235. The fluidic oscillator and the fluidic capacitor preferably have no moving parts. Another option for producing the oscillating wave signal is to use a Hartmann or Galton whistle device.

The second control channel34has a flow regulator37, e.g. in the form of a pneumatic, modulating valve, which is used to controllably vary the mass flow rate of the input fluid flow to the fluid diverter31from the second control channel. In particular, the mass flow rate from the second control channel determines the widths of the PWM mass flow rate pulses from the first output channel.

Thus a first output fluid flow from the fluid diverter31is the flow from the first output channel, which flow is set ON (corresponding to initiation of a PWM pulse) when the diverter receives a pressure spike from the first control channel33. The first output fluid flow is kept switched ON (corresponding to the width of a PWM pulse) for a duration that is determined by the mass flow rate of the input fluid flow from the second control channel34. Conversely, when the first output fluid flow is OFF (i.e. between its PWM pulses), the second output fluid flow from the second output channel is ON, producing an opposite (inverse) PWM mass flow rate characteristic to the first output fluid flow.

The PWM mass flow rate pulses can be modulated to produce an average mass flow rate value that is smoothly and continuously variable, and suitable for providing analogue control. Thus narrow pulses produce a low average mass flow rate and wide pulses a high average mass flow rate. The pulse frequency (i.e. ON-OFF switching speed) is determined depending on the size of the load (i.e. the load volume) such that during the OFF state the load pressure does not drop significantly (e.g. <1%).

Thus the longer the switch is ON compared to the OFF periods, the higher the total flow supplied to the load. Applied to the control input of a vortex amplifier, this allows a full modulation of the output flow from the amplifier rather than just the binary full and leakage flows.FIG. 5shows schematically at left a vortex amplifier38having the fluidic device30in place of a conventional control valve, and at right a graph of amplifier output against time with the hatched area showing how the output from the primary flow sink can be set to any value within a range at any given moment.

There are, however, other control possibilities. ThusFIG. 6shows schematically the fluid diverter31of the fluidic device30connected to an actuator in the form of a pneumatic piston arrangement39in which, by connecting one of the output channels40of the diverter to the chamber on one side of the piston and connecting the other output channel41of the diverter to the chamber on opposite side of the piston, the direction of travel of the piston can be controlled by the duration of the ON periods relative to the OFF periods. In addition, feedback of piston position to the flow regulator37of the second control channel34can be used to provide closed loop control of piston movement. In this way, by adjusting a control setting of the flow regulator (i.e. effectively setting its “gain”), the piston position can be correspondingly adjusted.

As another option, shown schematically inFIG. 7, the flow control of the second control channel34may be via a direct feedback loop42from the second output channel41. The flow regulator37can be set such that the feedback loop typically takes from 5% to 20% of the second output fluid flow from the second output channel41. As the first output fluid flow from the first output channel40goes to a high mass flow rate (i.e. a PWM pulse), the input fluid flow from the main channel32is pushed towards the second output channel41, upon which the feedback tries to push the input fluid flow from the main channel back to the first output channel. Depending on the strength of the feedback, the input fluid flow from the main channel stays directed to the second output channel until the first input channel pressure spike reduces below a given value, as determined by the feedback from the second input channel moderated by the flow regulator setting.

Although described above in relation to a gas turbine engine, the fluidic device is advantageously applicable to other situations—particularly harsh environments where electronic control may not be suitable. Thus possible uses can be found in fields diverse as marine, automotive, industrial, processing industry, nuclear etc.