Patent Description:
Evacuation slides for aircraft and other structures are inflated using gas, for example from a high pressure source such as a pressurised gas vessel. Such systems are fitted with a pressure regulator to ensure that a sufficient inflation pressure is maintained during inflation, given that the pressure of inflating gas will fall during inflation as the pressurising gas empties from the pressurised vessel. Such regulators are typically mechanical valves, for example spool or slide valves comprising a spring loaded control element, the spring force reacting aerodynamic forces during operation to provide the necessary regulation.

While effective, such regulators may be complicated in construction, require careful calibration and therefore expensive in terms of manufacture and maintenance.

Non mechanical arrangements for increasing the volume of gas that is used to inflate an inflatable structure have been proposed. For example <CIT> describes an augmentation amplifier for aspirating gas flow from a surrounding medium, for example the atmosphere. The amplifier connects at an inlet to a pressurized gas source and at an outlet to a gas receiver such as an inflatable boat. Ambient gas from the atmosphere supplements a source of compressed gas, for example a self contained underwater breathing apparatus (SCUBA) tank. The amplifier includes a Venturi conduit which includes a convergent section, a throat, and a diffusion chamber, and a cavity downstream of the Venturi conduit. The conduit receives and flows pressurized gas from the inlet through the throat and into the diffusion chamber. The cavity receives gas from the atmosphere. The diffusion chamber expands and accelerates the pressurized gas from the throat to entrain the ambient gas via aspiration in the cavity. The accelerated and ambient gases combine into an exhaust gas which passes into the inflatable structure. <CIT> discloses an ejector.

From a first aspect, the invention provides a pressure regulator comprising a primary fluid inlet for connection to a source of high pressure fluid and a fluid outlet for connection to a space to receive the high pressure fluid. The regulator further comprises a convergent-divergent nozzle having an upstream convergent section, a throat and a downstream divergent section, the primary fluid inlet being in fluid communication with the convergent section of the nozzle. The regulator further comprises an outlet pipe having an upstream end arranged around but radially spaced from the outlet of the divergent section of the nozzle. The outlet pipe is arranged to receive fluid flow from the outlet of the divergent section of the nozzle and conduct the fluid flowing from the nozzle to the fluid outlet. The radial spacing between the upstream end of the outlet pipe and the outlet of the divergent section of the nozzle forms a secondary fluid inlet for introduction of a fluid into the outlet pipe from outside the nozzle at a location adjacent the outlet of the divergent section of the nozzle. The outlet pipe comprises a radially expanding section at its upstream end adjacent the nozzle, and the radially expanding section expands from smaller to larger dimension in a downstream direction, and a flow recirculation conduit connected at a first end to the secondary fluid inlet and configured to be connected at a second end to the space.

In any embodiment of pressure regulator in accordance with the invention, the outlet pipe may be a diffuser.

The outlet pipe may have a constant diameter section downstream of the radially expanding section.

The connection of the flow recirculation conduit to the secondary fluid inlet may be upstream of the outlet of the nozzle.

In any embodiment of pressure regulator in accordance with the invention, the secondary fluid inlet may be an annular space.

In any embodiment of pressure regulator in accordance with the invention, the nozzle and outlet pipe may have the same cross-sectional shape, for example circular.

The invention also provides an inflation system comprising a source of high pressure fluid, a body for inflation and a pressure regulator in accordance with the invention, wherein the primary fluid inlet of the pressure regulator is connected to the source of high pressure fluid and the fluid outlet of the pressure regulator is connected to the body and the pressure of the source of the high pressure fluid. The configuration of the nozzle is such that when the high pressure fluid is supplied to the nozzle from the source, the nozzle will operate as an underexpanded nozzle, so as to produce supersonic flow in the outlet pipe.

Any embodiment of inflation system in accordance with the invention may further comprise an aspirator fluidly connected to the outlet pipe for inducing a supplementary flow of inflation fluid into the body.

In any embodiment of inflation system in accordance with the invention, the source of high pressure fluid is a pressurised vessel, for example a bottle or canister.

In any embodiment of inflation system in accordance with the invention, the body is an inflatable evacuation slide, for example for an aircraft.

The invention also provides a method of regulating the pressure of a fluid supplied to a space from a high pressure fluid source. The method comprises supplying fluid from the high pressure fluid source to an inlet of a convergent-divergent nozzle, the pressure of the fluid source and configuration of the nozzle being such that the nozzle operates in an underexpanded condition, thereby producing a supersonic flow at an outlet of the nozzle, supplying the underexpanded flow from the outlet of the nozzle to an outlet pipe having an upstream end arranged around but radially spaced from the outlet of the nozzle, expanding the fluid flow in the outlet pipe, conducting the fluid flow from the nozzle to the fluid outlet along the outlet pipe, a flow recirculation conduit connected at a first end to the secondary fluid inlet and configured to be connected at a second end to the space, and introducing a secondary fluid into the outlet pipe at a location adjacent the outlet of the nozzle. The outlet pipe comprises a radially expanding section at its upstream end adjacent the nozzle, and the radially expanding section expands from smaller to larger dimension in a downstream direction.

The secondary fluid may be supplied from the space.

In any embodiment, <NUM>%-<NUM>% of the mass of fluid entering the space is recirculated to the outlet pipe.

Some embodiments of the invention will now be described by way of example only with reference to the accompanying drawings in which:.

With reference to <FIG>, inflation system <NUM> comprises a body <NUM> to be inflated, a vessel <NUM> holding a high pressure fluid, a pressure regulator <NUM> for regulating the pressure of the fluid flowing from the vessel <NUM> to the body <NUM>, a conduit <NUM> connecting the pressure regulator <NUM> to the body <NUM> and a fluid recirculation conduit <NUM> connecting the body <NUM> to the pressure regulator <NUM>.

The vessel <NUM> holding a high pressure fluid may be provided with a release valve for releasing the high pressure fluid from the vessel in response to an actuating signal. Such relief valve mechanisms are well known in the art and need not, therefore, be described in further detail here.

The inflatable body <NUM> may be, for example, an inflatable evacuation slide for an aircraft, an inflatable vessel or some other inflatable device.

The conduit <NUM> may be provided with an aspirator <NUM> (illustrated schematically) for inducing an additional flow of air into the conduit <NUM> to assist in inflating the body <NUM>. Such aspirators <NUM> are well known in the art and need not, therefore, be described in further detail here.

It is necessary to regulate the flow of high pressure fluid from the fluid source <NUM> to the inflatable body <NUM> so as to achieve inflation of the body <NUM> within an acceptable time period. The inflation pressure should be maintained at a sufficiently high level for as long as possible to ensure inflation of the body <NUM>. For example, in the case of an evacuation slide the slide should be fully inflated in a period of <NUM> to <NUM> seconds.

A pressure regulator <NUM> in accordance with the invention is illustrated in greater detail in <FIG>.

The pressure regulator <NUM> comprises a primary fluid inlet <NUM> for connection to the vessel <NUM>. A convergent-divergent nozzle <NUM> is fluidly connected to the primary fluid inlet <NUM> for receiving pressurised fluid from the vessel <NUM>. The nozzle <NUM> comprises an upstream convergent section <NUM>, a throat <NUM> and a downstream divergent section <NUM> (see <FIG>).

The pressure regulator <NUM> further comprises an outlet pipe <NUM>. The outlet pipe <NUM> has an upstream end <NUM> arranged around but radially spaced from the outlet <NUM> of the divergent section <NUM> of the nozzle <NUM>. The outlet pipe <NUM> is therefore arranged to receive fluid flow from the outlet <NUM> of the divergent section <NUM> of the nozzle <NUM> and conduct the fluid flowing from the nozzle <NUM> to a fluid outlet <NUM>. The fluid outlet <NUM> may connect directly with the inflatable body <NUM> or, as shown to the conduit <NUM> which connects to the inflatable body <NUM>.

A radial spacing <NUM> exists between the upstream end <NUM> of the outlet pipe <NUM> and the outlet <NUM> of the divergent section <NUM> of the nozzle <NUM>. This forms an annular space <NUM> between the upstream end <NUM> of the outlet pipe <NUM> and the outlet <NUM> of the divergent section <NUM> of the nozzle <NUM>. As will be described further below, this annular space <NUM> acts as a secondary fluid inlet <NUM> for introduction of a further fluid into the outlet pipe <NUM> from outside the nozzle <NUM> at a location adjacent the outlet <NUM> of the divergent section <NUM> of the nozzle <NUM> in order to influence the flow in the outlet pipe <NUM> downstream of the nozzle <NUM> and thereby influence the pressure of the fluid at the regulator fluid outlet <NUM>. The outlet <NUM> is formed with a sharp edge, as shown.

The annular space <NUM> may, as illustrated schematically in <FIG> be open to ambient, for example having an open end <NUM>. In other embodiments, however, the open end <NUM> may be closed, for example by a plate <NUM> illustrated schematically in <FIG>.

The outlet pipe <NUM> has an upstream radially expanding section <NUM> at its upstream end adjacent the nozzle <NUM> and a constant diameter section <NUM> downstream of the radially expanding section <NUM>. The outlet pipe <NUM> therefore acts as a diffuser. The shape of the outlet pipe <NUM> should be consistent with that of the nozzle <NUM>. Thus, in the illustrated embodiment where the nozzle <NUM> has a circular cross section, the outlet pipe <NUM> is also circular in cross section. It should also be designed so that the radially expanding section smoothly increases in diameter to the constant diameter section so as to avoid sharp or rapid changes in flow which might lead, for example, to flow separation which is undesirable. The radius of the outlet pipe <NUM> may also be important as influences the maximum value of Mach number in the outlet flow.

The flow of fluid through a converging/diverging nozzle is well known. The flow regime is determined by the shape and dimensions of the nozzle and also the pressure ratio which exists across the nozzle. As the pressure ratio across the nozzle increases, the velocity of the fluid flow through the divergent section of the nozzle may increase to supersonic. At relatively high pressure ratios across the nozzle, the flow emanating from the outlet of the divergent section of the nozzle may be "underexpanded".

Such a condition is illustrated in <FIG> which illustrates a typical flow velocity distribution in a flow regulator <NUM> in accordance with the invention.

As can be seen in <FIG>, in an underexpanded operating condition expansion waves <NUM> emanate from the outlet <NUM> of the divergent section <NUM> of the nozzle <NUM>. Shocks <NUM> form in the flow further along the outlet pipe <NUM>, further away from the outlet <NUM> of the convergent section <NUM> of the nozzle <NUM>. The effect of the shocks <NUM> is to reduce the total pressure of the flow through the regulator to a pressure which is compatible with the pressure required for inflation of the inflatable body <NUM>. The particular arrangement of the shocks <NUM> will depend upon the shape and configuration of the nozzle <NUM> and also the shape and configuration of the outlet pipe <NUM>.

In the embodiment illustrated, the nozzle <NUM> has an inlet radius Li of <NUM> an outlet radius R0n also <NUM> and a throat radius Rt of <NUM>, an overall length LN of <NUM> and an inlet to throat distance Lt of <NUM>. The outlet pipe has an inlet radius R2i of <NUM> and a constant section radius R<NUM> of <NUM>. The radial spacing <NUM> is <NUM>. However, the dimensions of the nozzle <NUM> and outlet pipe <NUM> can be chosen to suit the particular pressure and flow rates required.

During dispensing the fluid from the high pressure vessel <NUM>, the pressure at the fluid inlet will fall. As it does so, so will the pressure of fluid being supplied to the inflatable body <NUM>. As discussed above, it is desirable in some embodiments to maintain the inflation pressure as high as possible for as long as possible to ensure rapid inflation of the inflatable body <NUM>. Maintaining the outlet pressure of the regulator <NUM> relatively high is potentially of particular significance in systems using aspirators <NUM> as a certain minimum pressure is required to allow these to operate successfully.

It has been recognised that by feeding back fluid from the inflating body <NUM> to the secondary inlet <NUM> of the pressure regulator <NUM> that the reduction in outlet pressure can be reduced. The pressure of the secondary fluid will increase (as the inflatable body inflates) as the pressure of the supply decreases. The addition of higher pressure fluid at the secondary inlet <NUM> affects the strength of the shocks <NUM> such that the drop in pressure across the shocks <NUM> decreases, leading to higher outlet pressure being maintained. According to the invention, a fluid recirculation conduit <NUM> is provided between the inflatable body <NUM> and the secondary inlet <NUM>. The outlet <NUM> of the fluid recirculation conduit <NUM> in the secondary inlet <NUM> is arranged upstream of the downstream end <NUM> of the nozzle <NUM> such that supersonic fluid exiting the nozzle <NUM> cannot enter the conduit outlet <NUM> as it would have to turn through <NUM>° to do so.

Some CFD modelled Mach number distributions and total pressure distributions for a system in accordance with the invention are shown in <FIG>.

<FIG> show the flow Mach number and total pressure of the fluid in a regulator as illustrated in <FIG>, with the conduit <NUM> at the start of inflation. The fluid pressure at the nozzle inlet <NUM> is <NUM> psi (<NUM>. 8MPa) and atmospheric pressure (<NUM> psi (101kPa) at the inflatable body <NUM> and at the secondary inlet <NUM>. In this condition, the average total pressure over the outlet <NUM> is <NUM> psi (<NUM> MPa).

<FIG> show the flow Mach number and total pressure of the fluid at a later stage in inflation where the inlet pressure has fallen to <NUM> psi (<NUM>. 3MPa) but the pressure within the inflatable body <NUM> and thus at the secondary inlet <NUM> has risen to <NUM> psi (<NUM> kPa) conduit <NUM>. In this condition, the average total pressure over the outlet <NUM> has fallen to <NUM> psi (<NUM> MPa).

In a comparative example, with no flow recirculation conduit <NUM> and same initial pressure conditions, by the time the inlet pressure had fallen to <NUM> psi (<NUM>. 3MPa), the average total pressure over the outlet <NUM> had fallen to 540psi psi (<NUM> MPa). The use of a recirculation conduit therefore maintains outlet pressure at a higher value than otherwise.

Although flow is recirculated from the inflatable body <NUM> through the recirculation conduit <NUM>, only a small percentage of the fluid mass is recirculated, meaning that the pressure within the inflatable body will still increase.

In a typical embodiment, between <NUM>% and <NUM>%, for example <NUM>% of the mass flow into the inflatable body <NUM> may be recirculated. However, in other embodiments the percentage may be different, for example between <NUM>% and <NUM>%.

While the embodiments above have been described in relation to inflation systems, the pressure regulator may be used in other applications where a relatively constant output pressure is required.

The pressure regulator of the invention is advantageous, inter alia, in that it has no moving parts and as such does not need maintenance to the same degree as a traditional mechanical regulator.

Claim 1:
A pressure regulator (<NUM>) comprising:
a primary fluid inlet (<NUM>) for connection to a source (<NUM>) of high pressure fluid
a fluid outlet (<NUM>) for connection to a space (<NUM>) to receive the high pressure fluid;
a convergent-divergent nozzle (<NUM>) having an upstream convergent section (<NUM>), a throat (<NUM>) and a downstream divergent section (<NUM>), the primary fluid inlet (<NUM>) being in fluid communication with the convergent section (<NUM>) of the convergent-divergent nozzle (<NUM>); and
an outlet pipe (<NUM>) having an upstream end (<NUM>) arranged around but radially spaced from the outlet (<NUM>) of the divergent section (<NUM>) of the convergent-divergent nozzle (<NUM>), the outlet pipe (<NUM>) arranged to receive fluid flow from the outlet (<NUM>) of the divergent section (<NUM>) of the convergent-divergent nozzle (<NUM>) and conduct the fluid flowing from the convergent-divergent nozzle (<NUM>) to the fluid outlet (<NUM>);
the radial spacing (<NUM>) between the upstream end (<NUM>) of the outlet pipe (<NUM>) and the outlet (<NUM>) of the divergent section (<NUM>) of the convergent-divergent nozzle (<NUM>) forming a secondary fluid inlet (<NUM>) for introduction of a fluid into the outlet pipe (<NUM>) from outside the convergent-divergent nozzle (<NUM>) at a location adjacent the outlet (<NUM>) of the divergent section (<NUM>) of the convergent-divergent nozzle (<NUM>);
the outlet pipe (<NUM>) comprising a radially expanding section (<NUM>) at its upstream end adjacent the convergent-divergent nozzle (<NUM>), and the radially expanding section (<NUM>) expanding from smaller to larger dimension in a downstream direction; and characterized in that
a flow recirculation conduit (<NUM>) is connected at a first end to the secondary fluid inlet (<NUM>) and configured to be connected at a second end to the space (<NUM>).