FR2776069A1 - METHOD AND DEVICE FOR MEASURING A GAS PASSAGE SECTION - Google Patents

Abstract

The invention relates to a method for determining the effective passage section of a constriction (7) in a gas flow passage (3), comprising the steps of providing a gas reservoir (1), placing the 'restriction in communication with a regulated flow of gas from the reservoir via flow regulating means (2, 9), and then actuating the means (9) to establish a transient flow of pressurized gas through throttling from the reservoir, sonic flow being temporarily maintained at the throttle by maintaining the ratio of the back pressure of the throttle to the gas pressure in the reservoir below a critical value. The invention also relates to a device for implementing this method.

Description

Method and device for measuring a gas passage section La

  The present invention relates generally to a method and a device for determining the effective passage cross section of a throttle in a gas flow passage. It relates in particular, although not exclusively, to a method and a device for measuring the surface of the guide vane (or nozzle) of a gas turbine engine, and for adapting the surface of the guide vane of a turbocharger and a power turbine. The size of the guide vane (also known as the nozzle) has a considerable impact on the performance of gas turboshaft engines because it changes the operating point on the compressor curve. Any variation in the surface of the turbine guide vane readjusts the engine to a gas generator speed, to a flow rate

  mass and at a different compressor pressure rate.

  For example, increasing the guide vane area of the turbocharger (CT), while the guide vane area of the power turbine (PT) remains constant, has the effect of decreasing the speed of the gas generator, the mass flow and the pressure rate of the compressor, at a constant output power. Conversely, increasing the area of the guide vane of PT, while the area of the vane guide of CT remains unchanged, has the effect of forcing the engine to increase the speed of the gas generator, the mass flow and the compressor pressure rate,

  at a constant output power.

  The adaptation of the guide vane according to the effective passage cross section constitutes a crucial procedure of the general overhaul of an engine to foresee optimal performances of this one and to obtain an output and an energy consumption optimum. Improper guide vanes result in lower than expected engine performance, which often results in engine failure under test, and increases fuel consumption

fuel.

  Traditionally, due to the excessively high cost and difficulties involved in establishing a stable gas flow at sonic speed, most engine overhaul installations use a flow device which measures the blade area directrix to subsonic flows. However, when the engine is actually running, the guide vane is in sonic regime (or almost) and the gas speed at the level of the neck

  the directing dawn is equal (or almost) to the speed of sound.

  Due to its inability to simulate real sonic flows, the subsonic flow apparatus provides less precise and less consistent measurements of the surface of the guide vane, which complicates the problem of refusals.

  engines due to unsuitability of the leading dawn.

  One of the aims of the present invention is to provide a method and a device which make it possible to attenuate or solve the problems posed by the lack of precision and consistency inherent in conventional techniques for measuring the flow of a gas at through a choke and

adaptation of a guide vane.

  To achieve this object and according to a first aspect of the present invention, there is provided a method for determining the effective passage cross section of a throttle in a gas flow passage, characterized in that it comprises the steps which consist providing a gas reservoir, placing the throttle in communication with a regulated flow of gas from the reservoir via flow control means, and then actuating the flow control means to establish a flow transient gas under pressure through the throttle from the reservoir, a sonic flow being temporarily maintained at the throttle by maintaining the ratio of the throttle back pressure to the pressure of the gas in the reservoir below a critical value. According to a second aspect of the present invention, there is provided a device for determining the effective passage section of a constriction in a gas flow passage, comprising a reservoir, means for making the constriction communicate with the reservoir, and flow control means for letting gas flow through the throat from the reservoir, characterized in that the flow control means are operable to control the flow of gas under pressure through the throttle from the reservoir in order to temporarily maintain a sonic flow at the throat, and characterized in that it also comprises pressure detection means for reacting or providing a signal relating to the pressure gas in the tank, and timing means capable of acting to provide a signal relating to the duration of gas flow at

through the strangulation.

  The method and the device of the invention may include timing means capable of acting to measure the time interval corresponding to a predetermined pressure drop in the tank during the flow of gas through the throttle. Alternatively, the timing means may provide a signal which controls the duration of the discharge flow, the pressures at the start and end of this flow (or the pressure variation) being measured by the pressure detection means. pressure. It is therefore proposed in the context of the present invention a sonic flow device capable of being implemented in accordance with the thermodynamic theory applicable to the transient discharge in the atmosphere of a compressed gas contained in a reservoir, a guide vane , a nozzle or similar throttle being located at the outlet of the tank to restrict gas flow. It is possible to create a sonic flow at the level of the neck of

  the guiding dawn maintaining the counter report

  guide vane pressure over the gas pressure in the tank below a critical value for the duration of the discharge process. The guide vane is considered in sonic regime when the gas speed at

  neck level reaches the speed of sound.

  Unlike a steady flow regime, the sonic flow proposed by the present invention is transient because the mass flow decreases with the drop in pressure and temperature of the tank during the course of the discharge process. The flow is nevertheless sonic and the costs are comparable to those of a

subsonic flow apparatus.

  The invention provides a duration of the transient sonic discharge flow of at least 5 (five) seconds, but less than 80 (eighty) seconds. Preferably, the sonic discharge flow has a duration between 8 (eight) seconds and 15 (fifteen) seconds. Due to the limited duration of the discharge flow, the volume of the reservoir intended to pass through a constriction having a cross-sectional area between 32.3 and 161 square centimeters (between 5 and 25 square inches) does not need '' be greater than 42,475,500 cubic centimeters (1,500 cubic feet) for a

  maximum tank pressure of 862 kPa (125 psi).

  It is within the scope of the method and the device of the invention to provide a flow through a throttle placed between the reservoir and the flow control means, or downstream of the flow control means. The invention teaches the use of a tank having a maximum operating pressure not exceeding 2758 Kpa (400 psi), and preferably not exceeding 862 kPa (125 psi). The invention can in particular be applied to a sonic discharge through a throttle having a cross section of at least 6.45 square centimeters (1 square inch) and typically at least 32.3 square centimeters (5 square inches). It is envisaged that the surface of the constriction may be in a range of up to 161 square centimeters (25 square inches) and

  even up to 645 square centimeters (100 square inches).

  It can therefore be appreciated that the invention is applicable to the measurement of the gas passage cross section of a throttle having a value characteristic of those

  found in gas turboshaft engines.

  In at least one of its aspects, the invention calls upon the theory according to which the mass flow rate of a gas through a converging nozzle reaches a maximum value when the speed of the gas at the level of the neck is equal to the speed of sound (Mach number equal to unity, or M = 1). Under these conditions, no change on the downstream side of the nozzle can propagate on the upstream side. An additional reduction

  downstream back pressure, will not affect the upstream flow.

  The mass flow will remain optimal and the nozzle is said

in sonic regime.

  When M = 1, the pressure at the nozzle throat is called the critical pressure and the critical pressure to stagnation pressure ratio is called the critical pressure rate. For an ideal gas, the critical pressure rate is a constant function of the specific heats of the gas. Sonic flow through a nozzle is generated when the ratio of back pressure to upstream stagnation pressure is less than or equal to the pressure rate

critical.

  In a tank discharge system in which a nozzle restricts the flow of gas, the nozzle

  is in sonic regime when the ratio of the counter

  pressure of the guide vane on the gas pressure in the tank is less than the critical pressure rate. Assuming an isentropic expansion of the gas, the thermodynamic formula governing the effective passage section of the guide vane is: -2Z [(Pf) l] AP in which: A represents the effective area of the guide vane (of the nozzle or another constriction), V represents the volume of the tank (of the tank), t represents the discharge time, pi represents the initial absolute pressure of the gas in the tank, pf represents the final absolute pressure of the gas in the tank , Ti represents the initial absolute temperature of the gas in the tank, R represents the specific constant of the gas,

  y represents the ratio of the specific heats of the gas.

  The area of the guide vane can be calculated directly from the above formula by substituting pressure, temperature and time data from the flow test. R and y are constants specific to the particular gas used. The volume of the tank must have been measured beforehand by the gravimetric method or

volumetric.

  As a variant, the surface of the guide vane can be obtained by calibration as opposed to a reference nozzle whose effective cross-section is already known. In accordance with this method, the reference nozzle and the guide vane to be tested are subjected in turn to flow in the sonic flow apparatus at an identical initial pressure and final pressure of the tank. As R, y, pi, pf and V remain constant between the two tests, the effective passage section of the guide vane to be tested can be calculated from the following formula: 35.g. in which: A represents the effective passage section of the nozzle to be tested, Am represents the effective passage section of the reference nozzle, tm represents the discharge time of the reference nozzle, Tim represents the initial temperature of the gas in the tank during the test of the reference nozzle, tt represents the discharge time of the nozzle to be tested, Tit represents the initial temperature of the gas in the

  tank during the test of the nozzle to be tested.

  The sonic flow apparatus of the invention is suitable for measuring the effective cross-section of the guide vane or of a similar throttling of gas turboshafts in sonic regime. It can consist of a tank (a tank) storing a large volume of compressed gas. The guide vane can be installed on a fastening element mounted in a discharge pipe, very close to the outlet of the tank. The discharge pipe can end with a silencer. The tank and the discharge pipe can be fitted with instruments, such as high-precision pressure transducers and temperature probes. A computer system may be provided to scan the output of the transducers / probes at a speed

very high sampling.

  After having pressurized it, the tank can be allowed to discharge its gaseous content under pressure by opening an on-off valve with quick opening in the discharge line. While collecting pressure and temperature data, the computer system can activate an integrated chronometer when the tank pressure reaches an initial setpoint value and deactivate it when the tank has discharged and reached a final setpoint pressure. Preferably, the preset initial and final pressures of the tank are maintained at values high enough to ensure that the critical pressure rate is not exceeded during the entire duration of the discharge process, thereby ensuring sonic flow. If the volume of the tank is known beforehand, the surface of the guide vane can be obtained using the appropriate thermodynamic formula, the initial temperature of the gas in the tank, the initial pressure of the gas in the tank, the pressure gas final in the tank and the discharge time given. The volume of the tank can be measured

  by gravimetric or volumetric methods.

  If the volume of the tank is not known, the surface of the guide vane is obtained by a flow comparison as opposed to a reference guide vane (or nozzle) whose surface is already known. When the two guide vanes are subjected to a flow at identical initial and final pressures of the tank, the surface and the discharge time of the guide vane to be tested, are directly proportional to the surface and the discharge time of the reference guide dawn. A temperature correction can be applied to compensate for the small difference in initial gas temperature between the test of the guide vane to be tested and the test of the vane

reference director.

  The foregoing, as well as other objects, advantages and features of the present invention, will become more apparent

  clearly from the following detailed description of a mode of

  embodiment given by way of nonlimiting example with reference to the appended drawings in which: FIG. 1 is a schematic perspective view of the device of the invention, and FIG. 2 is an exploded view of part of the

Figure 1 device.

  With reference to the drawings, a storage tank 1 is an ASME certified pressure vessel serving as a reservoir for the large volume of compressed gas necessary for carrying out the flow test. The tank is equipped in a known manner with an inlet valve, an outlet flange, a manhole, a pressure reducer, a purge valve and various threaded connections intended for pressure transducers and temperature probes. The inlet valve is connected by hose to a source of clean, dry compressed gas, i.e. an air system

  compressed gas or compressed gas tanks.

  A main tank closing valve 2 is used to isolate the storage tank 1 during the installation of a guide vane to be tested or of a reference nozzle 7. It avoids having to completely depressurize the tank during replacement of the guide vane to be tested or of the reference nozzle, which makes it possible to conserve the gas

  residual tablet remaining in the cell at the end of the test.

  Pipe fittings 3 serve as a discharge line to direct the flow of the large volume of gas into a silencer 10. They are structurally supported and provided with a withdrawal member which helps to move the discharge pipe axially to allow to access a mounting front plate 4 of the guide vane to be tested 7. Threaded connections are also provided for temperature probes T and pressure transducers P. A vent valve is used to relieve the pressure in the part of the guiding dawn to be tested. The ends of the pipe fittings serve as mounting flanges for the shut-off valve 2,

  the front plate 4 and an on / off valve 9.

  The front plate 4 defines the common mounting surface for different blade fastening elements

director 5.

  The guide vane fixing element 5 serves to secure the guide vane to be tested (or the reference nozzle) 7 to the center of the discharge pipe. Several fasteners are used in service. Each fastener is designed to match the dimensional configuration of the guide vane. The fasteners are provided with seals to prevent gas leakage through their mating surfaces and those of

the item to test.

  Blanking plates 6 provided with seals and having appropriate configurations are used to seal any orifice of the element to be tested, which

  is not on the gas flow path.

  Clamps 8 are used to fix the blade

  test guide 7 to the fixing element 5.

  The quick opening on / off valve 9 controls the discharge operation of the storage tank 1. It is actuated by a pneumatic actuator which

  facilitates quick opening and closing of the valve.

  The silencer 10 suppresses the noise produced by the sonic flow. Since it is the final point of discharge into the atmosphere, the silencer should be installed in a safe place, preferably outside the building. The pressure transducers P and the temperature probes T measure the pressure and the temperature of the gas in the tank 1 and in the discharge pipe 3. The output signals supplied by the transducers are transmitted to a computer system 11 via shielded cables. The computer system 11 controls the main operation of the sonic flow apparatus. It includes the hardware and software necessary for signal conditioning and rapid acquisition, reduction, storage and output to data printer. It also sends output signals which actuate the shut-off valve 2 and the valve

on / off 9.

  When the device described above is in service, the sequence of operations begins with the installation of the guide vane to be tested on the device. This operation is carried out by installing the closing plates 6 on the guide vane to be tested 7, by subjecting the latter to the fixing element 5 using collars 8, it by mounting the fixing element 5 on the front plate 4, removing the hose connector 3 to its closed position and securing the flange connector to

using nuts and bolts.

  The tank is then pressurized by the opening of its intake valve. The computer system 11 controls the pressure and temperature prevailing in the tank and the pipe during the charging process. Once the required pressure in the tank is reached, the inlet valve of the tank is closed and the shut-off valve 2 located at the

tank outlet is open.

  The discharge process begins with the opening of the on / off valve 9 via a start switch of the computer system 11. The computer system 11 records the temperature and pressure data during the discharge. It also starts its built-in stopwatch once the preprogrammed initial pressure of the tank is reached and stops the stopwatch when the preprogrammed final pressure of the tank is reached, to signal the end of the discharge process. The computer system then closes the valve

on / off 9.

  From the acquired data, the computer system 11 calculates the effective passage section of the guide vane and provides a printed output of the test result. The guide vane to be tested 7 is removed from the device by closing the valve 2, depressurizing the test part by opening the vent valve of the discharge pipe 3, disconnecting the flange at the test part, opening of the discharge pipe 3 to allow access to the guide vane 7, and separation of this

  last opposite the front plate 4.

  The above sequence of operations is repeated twice during a comparison as opposed to a reference nozzle. It emerges from the above that the present invention makes it possible to measure the effective cross-section, in the sonic flow regime, of a throttle like that formed by the nozzle or the guide vane of a gas turbine engine, and this , with a degree of precision and reliability which until now has only been possible using expensive equipment ensuring continuous sonic flow. The invention also makes it possible to quickly carry out comparisons in order, for example, to adapt the surface of the guide vane of the stages of turbocharger and of power turbine of a turbine engine.

  Although the previous description focused on a mode

  particular embodiment of the present invention, it is of course not limited to the specific example described and illustrated here, and those skilled in the art will readily understand that it is possible to make numerous variants and modifications without departing from the scope of the invention.

Claims (29)

  1. Method for determining the effective passage cross section of a throttle (7) in a gas flow passage (3), characterized in that it comprises the steps which consist in providing a gas tank (1), placing the throttle in communication with a regulated flow of gas from the reservoir (1) via flow control means (2, 9), and then actuating the flow control means (9) to establish a transient flow of pressurized gas through the throttle (7) from the reservoir, a sonic flow being temporarily maintained at the throttle by maintaining the ratio of the back pressure   the throttle on the gas pressure in the tank below a critical value.   2. Method according to claim 1, characterized in that timing means (11) are provided for measuring the time necessary for the pressure prevailing in the tank (1) to fall from an initial pressure preset at a pre-set final pressure.   3. Method according to claim 2, characterized in that the initial and final pressures are chosen to ensure that the critical pressure rate is not exceeded during the flow of gas through the throttle from The reservoir.   4. Method according to claim 1, characterized in that the timing means (11) serve to control the period during which the gas flows through the throttle (7).   5. Method according to claim 4, characterized in that the pressure prevailing in the tank is measured at   start and end of the gas flow period.   6. Method according to claim 1, characterized in that the reservoir (1) has a known volume, and in that the effective passage section of the throttle (7) is obtained mathematically using measurements made in relation with the change in gas pressure in the tank over a measured period of time, and a gas temperature measurement.   7. Method according to any one of claims 1   to 5, characterized in that the effective passage cross section of the throttle (7) is obtained by comparison of the flow characteristics of the gas through the throttle and through a comparison throttle having a cross section of known effective passage.   8. Method according to claim 7, characterized in that a throttle to be measured and a comparison throttle are successively subjected to a gas flow, the same initial and final pressures being measured for each flow and used to establish the section   effective passage of the measured constriction.   9. Method according to any one of the claims   previous, characterized in that the transient flow   less than 80 (eighty) seconds.   10. Method according to claim 9, characterized in that the transient flow has a duration of less than 15 (fifteen) seconds.   11. Method according to any one of the claims   previous, characterized in that the initial pressure in the tank (1) before the discharge flow is less than 2758 kPa.   12. Method according to claim 11, characterized in that   that the pressure is less than 862 kPa.   13. Method according to any one of the claims   above, characterized in that it is applied to the measurement of a constriction of a gas flow passage, having an effective passage section characteristic of those that   found in gas turboshaft engines.   14. Method according to any one of the claims   previous, characterized in that the throttle has a   cross section between 6.45 and 645 square centimeters.   15. The method of claim 14, characterized in that the constriction has a cross section greater than 32.3 square centimeters.   16. Method according to any one of the claims   previous, characterized in that it calls for the use of a flow regulation means (9)   arranged downstream of the throttle.   17. Method according to any one of claims 1   to 15, characterized in that it calls for the use of a flow regulation means disposed upstream of the throttle.   18. Method according to any one of the claims   above, characterized in that it is applied to the measurement of the surface of a guide vane or of a nozzle of a gas turbine engine.   19. Method according to any one of the claims   above, characterized in that it is applied to the adaptation of the guide vane surface of a   turbocharger to that of a power turbine.   20. Device for determining the effective passage cross section of a constriction (7) in a gas flow passage (3), comprising a reservoir (1), means (2) for communicating the constriction with the reservoir , and flow control means (9) for letting gas flow through the throat from the reservoir, characterized in that the flow control means (9) are adapted to act to control the flow of a pressurized gas through the constriction (7) from the reservoir (1) in order to temporarily maintain a sonic flow at the constriction, and characterized in that it also comprises means for pressure detection to react or provide a signal relating to the pressure of the gas in the tank, and timing means (11) capable of acting to provide a signal relating to the duration of flow gas through the throttle.   21. Device according to claim 20, characterized in that the timing means (11) are capable of acting to measure a time interval corresponding to a predetermined pressure drop in the tank during   the flow of gas through the throttle (7).   22. Device according to claim 20, characterized in that the timing means (11) are capable of acting to control the period during which the gas flows through the strangulation.   23. Device according to claim 22, characterized in that the pressure detection means are capable of acting to measure the pressure in the tank (1) at the start and at the end of the flow of timed transient gas at through the strangulation.   24. Device according to any one of claims   to 23, characterized in that the throttle (7) has a   cross section of at least 6.45 square centimeters.   25. Device according to claim 24, characterized in that the constriction (7) has a cross section between   32.3 square centimeters and 161 square centimeters.   26. Device according to any one of claims   to 25, characterized in that the throttle (7) of the gas flow passage has an effective passage cross section characteristic of those found in gas turboshaft engines.   27. Device according to any one of the claims   to 26, characterized in that the reservoir (1) has a known volume.   28. Device according to any one of claims   22 to 27, characterized in that it comprises means (T) intended to supply a signal relating to the temperature of the gas in the tank.   29. Device according to claim 28, characterized in that it comprises processing means (11) programmed to obtain a measurement relating to the effective passage section of the throttle by processing information from   pressure, temperature and time.