RU2568962C1 - Device to measure flow parameters - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: device comprises pressure sensors. A pressure sensor comprises capacitance sensitive elements (CSE), coaxial with a strain gauge bridge (SGB). The CSE via a charge and voltage amplifier (VA) is connected to an indicator. The SGB at the outlet has low frequency equipment (LFE) and is connected to an indicator. The device comprises a cylindrical body, inside of which there is a three and/or five-tube receiver filled with soft sealant. Receiving parts of two receivers are cut at the angle of 45°. The device in the working section of the aerodynamic pipe moves with the help of an electromechanical scanner. The scanner is controlled by a control unit. Coaxial SGB and CSE of solid design are installed in three tubes aflush with the cutting surface of these receivers. Inner diameters of tubes are 3 mm and more, with length from 0 to 30 mm. Material of the body and tubes is stainless steel.

EFFECT: increased quality and accuracy of pressure measurement.

4 dwg

Description

The invention relates to measuring technique and can be used to measure the pressure of the full, static, sound pressure, determine the flow rate, etc.

Known devices for measuring pressure in the gas flow of a wind tunnel (ADT) when determining the pressure head q, flow velocity V, Mach number M, and also to obtain a picture of the pressure distribution over the surface of the tested models. At the top of the hemisphere of such devices, there is a receiving hole for the total pressure perceived through the nipple. Eight holes for receiving static pressure through another nipple are located around the circumference of the cylindrical part of the receiver. It is shown that when the static pressure receiving holes move downstream, the measured pressure will approach its value in the undisturbed flow. Receivers with a live head also have a small measurement error. Receivers can be used both at subsonic and at supersonic flow rates with a small measurement error. In subsonic speed ADT, it is recommended to use six-hole air pressure receivers (PVD-6). In the receiver, the central hole is used to measure the total pressure, two holes (along the vertical Y axis) are used to determine the pressure difference when determining the flow direction in the vertical plane, two holes on the horizontal plane to measure the pressure difference when determining the flow direction in the horizontal plane, and the sixth hole for measuring static pressure.

In the known system for measuring flow parameters, the device allows you to measure and determine the flow parameters in the ADT [1] Fig. 18, fig. 1-11, fig. 1-12, fig. 1-13 s. 47-48, p. 58-61. B.S. Oaks. Fundamentals of quality assurance tests in ADT).

The disadvantages of this device include: measuring the total and static pressure without emitting noise. And also the impossibility of measuring changes in pressure pulsations or sound pressure. These disadvantages are the reason for the decrease in the accuracy of measuring the total and static pressure and, consequently, in the decrease in the accuracy of the measurement of the flow rate.

The closest technical solution to the proposed invention are three and / or five tubular receivers for spatial flows. These receivers to determine the magnitude and direction of the velocity vector at any point in the flow must be rotated relative to the longitudinal axis, and then measure the pressure received by the receivers. Prior to use, receivers are graduated in a stream. The receiver is a combination of three and five tubes made of stainless steel with an outer diameter of 1.2 mm. In a three-tube receiver, the leading edges of the two side tubes (A, B) are cut at an angle of 45 ° relative to their central axes, and the third has a straight cut at an angle of 90 ° to the axis. Slices of laterally symmetrically installed tubes are directed in opposite directions from the axis of the receiver. All three tubes are welded together and placed in a cylindrical stainless steel case with an external diameter of 3 mm, located at a distance of 10 mm from a direct cut of the central receiving tube. The gaps between the tubes are filled with epoxy. Five-tube receivers are designed to measure the magnitude and direction of the velocity vector in spatial streams. The tubular receiver is made of five tubes 1.3 mm in diameter, welded together. The cylindrical body of the receiver has a diameter of 6.4 mm. The departure of the receiving tubes from the body to the flow has a length of 25 mm. The fifth tube with a straight cut is located in the center of the casing, and the remaining two tubes are located symmetrically with respect to the cylindrical casing in the horizontal and vertical planes passing through the central tube. The cutting angle of the four receiving tubes is 45 °.

Such receivers make it possible to measure flow parameters in spatial flows.

The device has the following disadvantages: it is difficult to isolate pressure pulsations from the static pressure, it is not possible to separately measure the total pressure and the pressure of the pressure head. (Receivers for determining the magnitude and direction of speed Department of Scientific and Technical Information TsAGI No. 612, 1982. - 100 S. p. 66-70, Fig. 100, 101, 103) [2]

The objective of the present invention is the expansion of the scope, increase the information content of the measurement, the quality and accuracy of the measurement. The technical result is achieved due to the use of compact pressure sensors in the pressure receivers (CHE) and due to the simultaneous measurement of the total pressure, static pressure, velocity head, pressure pulsation, velocity and direction of flow, with the allocation of external and internal noise and interference.

The objective and the technical result are achieved in that in a device for measuring flow parameters, containing a pressure receiver, consisting of three and / or five tubes symmetrically located inside the cylindrical body, the tubes are fastened together by glue based on epoxy resin, a cut of one tube is made at an angle 90 °, cross-sections of all other tubes at an angle of 45 °, the location of the device in the test object is normal and at different angles with free movement, pressure sensors and low-frequency equipment are additionally introduced into it astotics, power supply and polarization, charge amplifier, normalizing voltage amplifier, subtraction unit, protective capacitors, circuit board, indicator, coordinator and coordinator block, and sensors consisting of a symmetric coaxial strain gauge bridge, one sensor mounted flush with the surface of the pressure receiver tube at an angle of 90 °, the remaining sensors inside the tube are located at a cut angle of 45 °, and the sensors can be located at the same level on a horizontal plane along the x axis and can be offset from relative to each other along the vertical plane of the y axis, one shoulder of the strain gauge bridge and the input of the capacitive sensor are respectively connected to the power supply and polarization unit, the other shoulder of the strain gauge bridge through low-frequency equipment and the subtraction unit is connected to the indicator inputs, the output of the capacitive sensitive elements through protective capacitors, the charge amplifier, the normalizing voltage amplifier and the subtraction unit are connected to another indicator input, the charge amplifier and protective capacitors are mounted on the mounting plate, the coordinator is rigidly connected to the cylindrical body of the device, on the bottom plate, on the screen of the sensor and the mounting plate, support holes are made and connected with the atmosphere through an electromechanical scanner, the position of the device in the object under study is set using the control units, indicator and coordinator.

The proposed device is illustrated by drawings.

In FIG. 1a, b, c shows the design of the receiving part of the three-tube receiver and its position in space, in FIG. 2 shows the proposed device mounted inside the test object (IO), for example, in the gas stream of the working part of the ADT, and in FIG. 3 shows a simplified construction of a device for measuring flow parameters, FIG. 4 shows a flowchart for measuring flow parameters.

In FIG. 1 shows a three-tube air flow receiver comprising three tubes A, B, C made of stainless steel. All tubes are located in a cylindrical housing D with an outer diameter of 10 mm made of stainless steel and filled with a soft sealant of FIG. 1a, b, p.

In FIG. 2 shows a device 7 containing a three-tube receiver, a multi-stage coordinator 2. The coordinate allows you to move the device 1 along the angle of attack and the angle of slip using commands from the control unit of the coordinator 4 (Fig. 1). Device 1 is installed in the working part of the wind tunnel 3, respectively, along the x, y, z axes in the direction of distribution of the flow velocity vector V, where the axis of the receiver (device) is aligned with the z axis. The position of the device in the working part of the ADT 3 is regulated by the control unit of the coordinator 4.

In FIG. 3 shows the proposed device 1, in each tube A, B, C 1 mounted pressure sensor 5. Pressure sensor 5 consists of a strain gauge bridge (TM) 6 and capacitive sensing elements (ECE) of the tubes A, B, C (Fig. 3, 4 ) located on one axis (coaxial). Moreover, each ECHE contains an upper 7th capacitor lining, which is a sensor membrane, a lower 8th capacitor lining, a dielectric ring 9, a screen 10 with electrical insulation 11. ECHE and TM are separated by an insulating dielectric film 12. A cavity 13 ECHE behind the membrane 7 with the atmosphere are connected 10 th support holes 14 made in the mounting plate 15. The mounting plate 15, on which all the parts of the pressure sensor are assembled, also contains protective capacitors 16 and charge amplifiers 17, mounting wires 18. The pressure sensor 5 and mounting plate 15 inside the tubes A, B, C and the tubes are fastened together with epoxy adhesive. In FIG. 4, the flowchart for measuring the flow parameters contains three TM 6, AEC A, B, C, low-frequency equipment (ANF) 19, a power supply unit TM 6 and an EEC polarization A, B, C 20, protective capacitors 16, a subtraction unit 21, a charge amplifier 17, a normalizing voltage amplifier 22 and an indicator (by computer) 23.

In FIG. 3 three 5V pressure sensors can be mounted inside three tubes in the following 4 working surfaces:

1 - on one plane of a horizontal surface along the Y axis (section A-A). In this case, the pressure sensor 5 is located inside the tube C at a depth l, and the sensors 5 in the tubes (receivers) A, B are mounted flush with the wall of these tubes (Fig. 3, section A-A);

2 - pressure sensors can be mounted on the outer diameter d of the tubes A, B, C, (Fig. 1) while the outer diameter of the base of the sensor of the required shape is equal to the outer diameter of the tubes A, B, C;

3 - three pressure sensors are mounted flush with the walls in three tubes A, B, C (section B-B), while the two bases of the two pressure sensors in tubes A and B correspond to the cross-sectional shape of the tubes A, B at a cut angle of 45 °; (in the vertical plane along the Y axis);

4 - the pressure sensor in the pipe C is mounted flush with the pipe wall at points n (section B-B), and two sensors located in the pipes A, B are mounted flush with the initial edge (at point b) of the 45 ° cut of pipes A, B (sec. AA); in the X, Y planes, the tubes are offset relative to each other.

When the sensors are flush with the walls of the receivers (in the second case), the pressure is measured on the “passage” (practically without loss of time) simultaneously and without delay in the tubes A, B, C. In the first case, a delay in the measured pressure in tube C due to the deepening of the sensor inside the tube to a depth l (Fig. 3).

The pressure sensor 5, containing TM and ECE, is formed by vacuum cathodic deposition on the basis of a silicon-sapphire single-crystal structure with dielectric insulation 11, 12 from any dielectric, in particular artificial sapphire or Al ₂ O ₃ , with a thickness of about one μm and more. The dielectric ring 9 in the design of the ECE A, B, C can have a thickness of 2-40 μm with a hole diameter below the membrane of more than 3 mm. The thickness of the upper lining of the membrane 7 ECE from 2 microns to 20 microns or more, from any hard alloy, for example, from titanium alloy VT-9. The thickness of the lower lining 8 is 2-3 microns. The thickness of the screens 10 from 0.5 to 1.0 microns. The base of the ECE A, B, C, consisting of a screen 10, insulation 11 and a bottom plate 8 is perforated by support holes 14 with a diameter of not more than 0.35 mm, communicate with the cavity of the sensor 13, with atmospheric pressure p _a , through the support hole 14 on the mounting the circuit board 75 and the holder from the coordinator's metal pipe 2. Protective capacitors and charge amplifiers 17 are mounted on the surface of the circuit board 15. The location of the circuit board inside the cylindrical housing D allows you to protect the charge amplifier 17 (US) and the ECH from triboelectric effect, noise and interference. The cylindrical body D is bonded to the coordinator so that the device 1 can move in the vertical and horizontal planes along the angles of attack and slip. The mounting wires of device 1 with external units are connected by anti-vibration cables of the AVKT-6 brand with ⌀ 1 mm. The wiring harness is conducted along the surface of the pipe coordinator 2.

The flowchart for measuring flow parameters in FIG. 4 consists of three measuring channels containing TM 6 with the diagonals a , b (first shoulder), c, d (second shoulder) and resistance r ₁ , r ₂ , r ₃ , r ₄ . A multichannel ANF 19 was used. Diagonals a , b TM and plates 7 ECHE A, B, C are connected to a power source 20. The design of the ECHE A, B, C consisting of plates 7, a screen 10 and a dielectric film 11, 12 and TM 6 form pressure sensor 5. The outputs of the ECE sensor through protective capacitors 16 (overvoltage protection), UZ 17, voltage amplifiers (UN) 22 are connected to the inputs of the subtraction blocks 21 by an indicator 23. Other diagonals of TM v, d are connected through the ANF to the inputs of the subtraction 21. The input of the pressure sensor 5 are layers of metal 7, dielectric films 12 and T M 6, on which pressure is applied. Anti-vibration cable 18 of the AVKT-6 brand is used in operating conditions with increased radiation, vibration, and temperature. The shield 10 ECE together with the shield of the cable of the protective capacitor 16 are connected at the output of the ultrasonic amplifier 17 located on the circuit board 15 or at point B of the local ground (Fig. 4). All outputs of these blocks are connected to the inputs of the indicator block 23.

The indicator collects and processes the measurement results using a program based on a specialized algorithm. The indicator is connected with the scanner control unit 4 and the coordinator 2. Unit 4 allows the aerodynamic experiment to change the angular position of the device when it moves along the angle of attack α and along the angle of slip β. The indicator unit in its composition has a measuring and computing base that provides for the collection, processing and delivery of measurement results in the form of a protocol of the final measurement results with the necessary accuracy.

The proposed device for measuring flow parameters can be single-channel or more without limiting the number of channels. All elements used are unified and manufactured by the electronics industry.

The circuit board is made of a dielectric coated with copper, for example of fiberglass, 2-3 mm thick. Tracks on the surface of fiberglass are formed by photolithography. The cylindrical body is filled with a soft casting compound, grade ELK-12, (Fig. 1). Compound, grade ELK-12, operable at high vibrational shock loads in the temperature range from -60 to + 120 ° C. In the step of filling the cylindrical body compound should not disrupt communications receivers with atmospheric pressure P _a (FIG. 3). If necessary, connections to ELK-12 can be dismantled.

The used ANF is known in measurement technology in 4 and 8 channel versions at the carrier frequency. Four- and eight-channel ANFs are designed to amplify signals from the TM when measuring separately or simultaneously the total pressure, sound pressure, sound pressure and static pressure of the object under study. Coordination of the electrical signal from the output of the high-impedance EEC is carried out by ultrasound, then amplified, normalized to the UN and fed to the indicator. Coordination and amplification of the electrical signal from the output of the capacitive sensor can be carried out by the equipment of Bruhl & Kj фирмыr (Denmark), RION (Japan), RFT (Germany). Domestic ultrasound made on the integrated circuit 544UD1. The electrical capacitance of sensors from 3 pF and above (almost without restrictions) is consistent with the input of the ultrasound. The output voltage is 5 V, 10 V. The equipment output is designed to work with analog-to-digital converters, magnetic drives, etc. In the ANF, until the TM is matched with an external electric circuit, a direct current amplifier (DC) is used, then the output of the DC amplifier is coordinated with the input of the low-frequency amplifier. The input stage UPT is made according to the differential circuit. The reliability of the device is increased due to the protection of the ultrasound from the input of the polarization voltage to the input of the ultrasound by introducing protective capacitors between the ECH and UZ.

Four-arm TM with different resistances from r = 30-400 Ohm; r = 100-400 ohms; r = 200-400 ohms. The voltage at the output _OUT ANCh U = ± 5 V (resistance 160-170 ohm load). A TM developed on the basis of "silicon on sapphire" is supplied with a DC voltage of 36 V or 15-42 V. At the same time, these voltages can be an ECH polarization voltage. To increase the sensitivity of the EMF, the polarization voltage can increase <100 V from the other output of the polarization unit 20. Thus, it is assumed that the device allows at a given point of the object under study, at the same time, one sensor, consisting coaxially of TM and ECE, to simultaneously measure the pressure head pressure, full pressure, static pressure, pulsations and / or sound pressure without the influence of noise and interference.

Coordinate 2 consists of a swivel mechanism, angular sensors, amplifiers, coordinator, etc., and is controlled by an indicator unit and coordinate unit 4, consisting of an engine gearbox, control circuit, quantifies the values of these parameters in the coordinate system x, y, Z .

One of the main types of measurement at certain flow parameters is the measurement of total P ₀ , static P and pressure drop ΔP. Pressure measurement in ADT 3 is used to determine the pressure head q, flow velocity V, Mach number M, Reynolds number Re, and also to obtain the fields of pressure distribution modeled in ADT.

As a rule, the results of testing in ADT are determined in the form of functional dependences on the angular positions (α, β) at V = const, M = const or when measuring the flow velocity V at the angles of attack and at the slip angle β = const. The ADT test is carried out both at a fixed angle of attack of a device consisting of three tubular receivers 1 (Fig. 2) (α = const) with a change in the flow velocity V, and at a fixed flow velocity (M = const).

Shown in FIG. 1a, the oblique receivers A, B are sensitive to the bevels of the flow when the angle of attack is α = 0, compared with the direct receiver C. In addition, for the oblique receivers shown, their characteristics are weakly dependent on their length. Therefore, the obtained test results depending on L / d are valid for other values of L / d, where d is the outer diameter of the tube A, B, C

In the case of supersonic flow around it, it is also known that the location of the oblique receivers A, B, towards the flow, allows decreasing the static pressure gradient along the critical generatrix to zero, without causing the boundary layer to break. The induced bevelling of the initial portion of the receiver and the local additional increase in the slip angle usually lead to a weakening of the shock wave in the initial zone. With a decrease in the intensity of the shock wave of the receiver (tube) and with a shorter compression surface, distortion of the total pressure practically does not occur [2].

The device 1 (Fig. 3) operates as follows: placed in a normal position (Fig 1); IO 3 (Fig. 2) From the source 20 simultaneously with the same (or different) voltage they feed TM 6 and polarize the AEC A, B, C

- position for measuring the angle α (Fig. 1B);

- position for measuring the angle β (Fig. 1C).

.In a normal position, the pressure is not set on the device (the flow of speed in the EUT is zero). At the same time, from the output of ANF 19 (from each receiver A, B, C) and UN 22 (from each receiver A, B, C), the sum of the signals of the internal noise of the equipment and external noise are recorded on the indicator, i.e. measure zero signals. At the output of the ANF, an electrical signal U _{0 is} recorded, i.e. electrical signal proportional to the initial zero signal. At the output of the UN register - $${\tilde{U}}_0$$

.

не равное нулю. В этом случае с выхода АНЧ регистрируют сигнал U_ВЫХ и на выходе $$УН-{\tilde{U}}_{ВЫХ}$$

, т.е. измеряют основной сигнал. Оба сигнала регистрируют в индикаторе, затем определяют коэффициенты преобразования измерительных каналов, т.е. определяют значение последних сигналов с выхода АНЧ $$\Delta U_{ВЫХ}=\sqrt{U_{ВЫХ}^2-U_0^2}$$

; с выхода $$УН-\Delta U_{ВЫХ}=\sqrt{{\tilde{U}}_{ВЫХ}^2-{\tilde{U}}_0^2}$$

; при этом коэффициенты преобразования (в каждой трубке A, B, C) каналов определяют как: $$S_{\Delta U_{ВЫХ}}=\frac{\Delta U_{ВЫХ}}{{\tilde{P}}_{К}}$$

; $$S_{\Delta {\tilde{U}}_{ВЫХ}}=\frac{\Delta {\tilde{U}}_{ВЫХ}}{{\tilde{P}}_{К}}$$

. Затем задают статическое градировочное давление P_г в потоке. Не исключено, что градуировку устройства в потоке могут осуществлять специальной АДТ малой скорости потока 20 м/с [2]. Такой эксперимент позволяет приближаться к реальным экспериментам в АДТ. В этом случае с выхода АНЧ регистрируют сигнал $${\tilde{U}}_{ВЫХ}\equiv P_{Г}$$

и на выходе $$УН-{\tilde{U}}_0$$

(в каждой трубке A, B, C), т.е. измеряют основной сигнал в стадии градуировки датчиков статическим давлением. Оба сигнала регистрируют в индикаторе, затем определяют коэффициенты преобразования измерительных каналов, т.е. определяют значение последних сигналов с выхода АНЧ $$\Delta {\overline{U}}_{ВЫХ}={\overline{U}}_{ВЫХ}-U_0$$

; с выхода УН $$\Delta {\overline{U}}_{ВЫХ}=\sqrt{{\tilde{U}}_0^2-{\tilde{U}}_0^2}=0$$

; при этом коэффициенты преобразования каналов (в каждой трубке A, B, C) определяют как: для АНЧ $$S_{\Delta {\overline{U}}_{ВЫХ}}=\frac{\Delta {\overline{U}}_{ВЫХ}}{P_{Г}}$$

; для $$УН-S_{\Delta {\overline{U}}_{ВЫХ}}=\frac{0}{P_{Г}}$$

.The sensors are given a standard calibration sound pressure $${\tilde{P}}_{\mathrm{TO}}$$

not equal to zero. In this case, the output register ANCh U _OUT signal and the output $$\mathrm{At}N-{\tilde{U}}_{\mathrm{AT}SX}$$

, i.e. measure the main signal. Both signals are recorded in the indicator, then the conversion coefficients of the measuring channels are determined, i.e. determine the value of the last signals from the output of the ANF $$\Delta U_{\mathrm{AT}SX}=\sqrt{U_{\mathrm{AT}SX}^2-{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="00000040.png"\; state="\{\{state\}\}">U</figure-callout>}}_0^2}$$

; from exit $$\mathrm{At}N-\Delta U_{\mathrm{AT}SX}=\sqrt{{\tilde{U}}_{\mathrm{AT}SX}^2-{\tilde{U}}_0^2}$$

; the conversion coefficients (in each tube A, B, C) of the channels are determined as: $$S_{\Delta U_{\mathrm{AT}SX}}=\frac{\Delta U_{\mathrm{AT}SX}}{{\tilde{P}}_{\mathrm{TO}}}$$

; $$S_{\Delta {\tilde{U}}_{\mathrm{AT}SX}}=\frac{\Delta {\tilde{U}}_{\mathrm{AT}SX}}{{\tilde{P}}_{\mathrm{TO}}}$$

. Then set the static calibration pressure P _g in the stream. It is possible that graduation of the device in the flow can be carried out by a special ADT with a low flow velocity of 20 m / s [2]. Such an experiment allows one to approach real experiments in ADT. In this case, a signal is recorded from the output of the ANF $${\tilde{U}}_{\mathrm{AT}SX}\equiv P_G$$

and at the exit $$\mathrm{At}N-{\tilde{U}}_0$$

(in each tube A, B, C), i.e. measure the main signal in the stage of calibration of the sensors with static pressure. Both signals are recorded in the indicator, then the conversion coefficients of the measuring channels are determined, i.e. determine the value of the last signals from the output of the ANF $$\Delta {\overline{U}}_{\mathrm{AT}SX}={\overline{U}}_{\mathrm{AT}SX}-{\mathrm{<figure-callout\; id="0"\; label="U"\; filenames="00000040.png"\; state="\{\{state\}\}">U</figure-callout>}}_0$$

; from the output of the UN $$\Delta {\overline{U}}_{\mathrm{AT}SX}=\sqrt{{\tilde{U}}_0^2-{\tilde{U}}_0^2}=0$$

; wherein the channel conversion coefficients (in each tube A, B, C) are determined as: for ANF $$S_{\Delta {\overline{U}}_{\mathrm{AT}SX}}=\frac{\Delta {\overline{U}}_{\mathrm{AT}SX}}{P_G}$$

; for $$\mathrm{At}N-S_{\Delta {\overline{U}}_{\mathrm{AT}SX}}=\frac{0}{P_G}$$

.

The device is installed in the working normal position (Fig. 1a, Fig. 2) in the IO flow and the direction of the velocity vector at the measurement point is determined by finding two angles α and β [2], as follows:

преобразованное в электрический сигнал, через УЗ и УН подают на входы блока вычитания и индикаторный блок.- determine the angle α by turning the device 1 relative to the longitudinal axis until the pressure recorded by the TM and ECE in the receivers A and B (Fig. 1A, Fig. 2), become equal to each other. In this mode, the TM in the channels with tubes A, B, C (Fig. 3, Fig. 4) simultaneously convert the variable total (pulsation and / or sound) pressure in the form of an electric signal through the ANF and ECHE to the inputs of the subtraction unit 19 and indicator for registration and memorization. Moreover, from the outputs of the ECHE in the same channels of pressure pulsations (or / and sound pressure) $$\tilde{P}\equiv U$$

converted into an electrical signal, through the ultrasonic and universal signals are fed to the inputs of the subtraction unit and the indicator unit.

, поступающей с выхода УН, на вход блока вычитания. После вычитания $$P_0-\tilde{P}=P$$

на выходе блока вычитания имеем информацию о величине статического давления $$P\equiv U$$

в каждом канале (приемнике) в отдельности и регистрируем в индикаторе. Все операции выполняются в индикаторе и запоминаются. В этом случае (фиг. 1в) трубки A и B располагаются симметрично относительно плоскости (с помощью блока управления 4 и ЭМС 2), в которой располагается вектор скорости V [2].In the subtraction unit, after subtracting from the total pressure P ₀ (in each receiver A, B, C) the variable component of pressure $$\tilde{P}$$

coming from the output of the UN to the input of the subtraction unit. After subtraction $$P_0-\tilde{P}=P$$

at the output of the subtraction block we have information about the value of static pressure $$P\equiv U$$

in each channel (receiver) separately and register in the indicator. All operations are performed in the indicator and stored. In this case (Fig. 1c) the tubes A and B are located symmetrically relative to the plane (using the control unit 4 and EMC 2), in which the velocity vector V is located [2].

The angle α is counted directly by the control unit, which incorporates the principles and the scanning program of the device with three and five tubular receivers. The controls and software of the control unit are connected and provided by an indicator. Moreover, the angle α does not affect the calibration characteristics in the normal position of the device of FIG. 1a, to determine the angle β.

, преобразованного в электрический сигнал, регистрируют в индикаторе и запоминают. По результатами измеренного давления P_A, P_B, P_C определяют угол β, величину вектора скорости V, статическое P и полное P₀ давления, используя три взаимозависимых отношения давлений, полученных с помощью параметров градировки в потоке как [2]:At the command of the EMC control unit and the indicator unit, device 1 (Fig. 2) rotates 90 ° (Fig. 1c). According to [2], in this position, the velocity vector lies in the plane passing through the axis of the tube A, B. The pressure is recorded at the same time by all three tubes A, B, C. Similarly, in the case of the normal position of the device in the EUT using the conversion factors of each channel, the stream records pressure, P _A ≡ U _A , P _B ≡ U _B , P _C ≡ U _C , sound pressure $$\tilde{P}$$

converted into an electric signal, register in the indicator and remember. Using the measured pressure P _A , P _B , P _C , the angle β, the velocity vector V, the static P and the total pressure P ₀ are determined using three interdependent pressure ratios obtained using the gradation parameters in the flow as [2]:

f (β) = (P _A -P _C ) / (P _B -P _C ); g (β) = (P _A -P _C ) / (P ₀ -P); h (β) = (P ₀ -P _C ) / (P _B -P _C ).

, ρ - плотность потока 1,4; V - скорость потока. Когда угол β>0, значит P_A<P_B. При отрицательном угле β роль трубок A и B меняется, и в выражениях f(β), g(β) и h(β) можем найти угол β, величину вектора скорости V как:In these dependences, the values of total P ₀ and static pressure P in the flow are determined in the first experiment, i.e. normal position of the device according to FIG. 1a and FIG. 2 in operating mode. According to the block diagram of FIG. 4, the total pressure in the flow is recorded at the output of the ANF U _n ≡P ₀ , and the static pressure P≡U is recorded at the output of the subtraction unit, it is determined as follows: in the subtraction unit, the pressure head pressure P _q coming from the outputs of the ECHE is subtracted, t .e. $$P_0-P_q=P<figure-callout\; id="2"\; label="+\; \rho \; V"\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">+\; </figure-callout>\frac{\rho V^{}}{}\frac{{}^2}{2}-\frac{\mathrm{<figure-callout\; id="2"\; label="\rho \; V"\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">\rho \; </figure-callout>}{V}^{}{}^2}{2}=P$$

, ρ is the flux density of 1.4; V is the flow rate. When the angle β> 0, then P _A <P _B. For a negative angle β, the role of the tubes A and B changes, and in the expressions f (β), g (β) and h (β) we can find the angle β, the magnitude of the velocity vector V as:

f (β) = (P _B -P _C ) / (P _A -P _C ); q (β) = (P _B -P _C ) / (P ₀ -P); h (β) = (P ₀ -P _C ) / (P _A -P _C ).

. Полное давление на выходе АНЧ, $$P_0=\frac{U_{п}}{S_{\Delta {\overline{U}}_{ВЫХ}}}$$

. Пульсации и/или звуковое давление пропорционально давлению скоростного напора и определяют на выходе УН как: $$\tilde{P}=P_q=\frac{\tilde{U}}{S_{\Delta {\tilde{U}}_{ВЫХ}}}$$

. Где $$S_{\Delta {\stackrel{⃛}{U}}_{ВЫХ}}$$

, $$S_{\Delta {\tilde{U}}_{ВЫХ}}$$

- коэффициенты преобразования каналов (в каждой трубе A, B, C) содержащий АНЧ УН соответственно.Next, on the subtraction block, we obtain a signal carrying information on the excess static pressure in the flow P, i.e. we have $$P=\frac{U}{S_{\Delta U_{\mathrm{AT}SX}}}$$

. Full pressure at the exit of ANCh, $${\mathrm{<figure-callout\; id="0"\; label="P"\; filenames="00000040.png"\; state="\{\{state\}\}">P</figure-callout>}}_0=\frac{U_P}{S_{\Delta {\overline{U}}_{\mathrm{AT}SX}}}$$

. Ripples and / or sound pressure is proportional to the pressure of the pressure head and is determined at the output of the UN as: $$\tilde{P}=P_q=\frac{\tilde{U}}{S_{\Delta {\tilde{U}}_{\mathrm{AT}SX}}}$$

. Where $$S_{\Delta {\stackrel{⃛}{U}}_{\mathrm{AT}SX}}$$

, $$S_{\Delta {\tilde{U}}_{\mathrm{AT}SX}}$$

- channel conversion coefficients (in each pipe A, B, C) containing ANF AN, respectively.

ЕЧЭ и $$\frac{r}{r_0}$$

ТМ. Напряжение поляризации постоянного тока из выходов блока 20 подают к одной из диагоналей а, б ТМ 6. При этом напряжение на выходе ЕЧЭ (между обкладками 7 и 8), ТМ (между диагоналями в, г моста) пропорционально приращению $$\frac{\Delta c}{c}$$

, $$\frac{\Delta r}{r}$$

, напряжению поляризаций ЕЧЭ и питанию ТМ соответственно.The principle of operation of the device. When the pressure in the gas flow Ap changes, the layers of the metal 7 and dielectric 12 films are deformed. Due to the deformation of the membrane, the distance between the membrane 7 and the lower counter plate of the capacitor 8 simultaneously changes. Due to the deflection of the membrane 7, the deformation of TM 6 occurs. As a result of the deflection of the membrane, the initial capacitance c ₀ ECE A, B, C, resistance TM 6 r ₀ , increments Δc, Δr and relative change in capacitance $$\frac{\Delta \mathrm{<figure-callout\; id="0"\; label="c\; c"\; filenames="00000040.png"\; state="\{\{state\}\}">c\; </figure-callout>}}{c_{}}$$

ECE and $$\frac{\mathrm{<figure-callout\; id="0"\; label="r\; r"\; filenames="00000040.png"\; state="\{\{state\}\}">r\; </figure-callout>}}{r_{}}$$

TM The DC polarization voltage from the outputs of block 20 is supplied to one of the diagonals a , b TM 6. The voltage at the output of the ECE (between plates 7 and 8), TM (between the diagonals c, d of the bridge) is proportional to the increment $$\frac{\Delta c}{c}$$

, $$\frac{\Delta r}{r}$$

, the voltage of the polarizations of the ECE and the power of the TM, respectively.

и эти параметры преобразованное в электрический сигнал с помощью ТМ и ЕЧЭ, и новая конструкция предложенного устройства, выгодно отличается от выбранного прототипа и аналога.As a result of using known technical solutions i.e. the use of three and five tubular aerodynamic receivers to measure the magnitude and direction of velocity in spatial flows, total pressure P ₀ , static pressure P, high-speed flow pressure Pq, pulsation and / or sound pressure $$\tilde{P}$$

and these parameters are converted into an electrical signal using TM and ECE, and the new design of the proposed device compares favorably with the selected prototype and analogue.

. Также, с целью минимизации размеров мембраны был испытан датчик, разработанный на базе искусственных пъезо-пироэлектрических материалов, для измерения звукового давления. Размеры ЧЭ 2×2 мм, позволяет измерить звуковое давление 140 дБ.To this end, in TsAGI, a nine-element differential pressure module was manufactured on the basis of the ECE. The distance between the CE is 10 mm, the size of the rectangular plate is 4 × 6 mm, the ring between the capacitor plates is 20 μm thick, and the diameter of the cell (ring) is 3 mm. Capacitor plates were formed from copper foil on a 1.5 mm thick fiberglass surface by photolithography. Symmetrical through holes were drilled on the surface of the ECE and tubes were dressed. The pressure on the ECE is fed through tubes 12 mm long with an inner diameter of 1 mm. Tubes with the surface of the foil serving as an ECE shield are fastened with ordinary soldering and the places of soldering are filled with epoxy glue. The model of the differential pressure module was checked under the influence of overpressure of 10 kPa and 25 kPa. The accuracy of measuring pressure is 0.5%, the nonlinearity of the calibration characteristic is 2-3%. The pressure measurement was carried out by an R-589 type AC bridge. ECHEs were also manufactured and tested in laboratory conditions under the influence of sound pressure of 120 dB. ECE polarization voltage 100 V, measuring channel conversion coefficient $$1.26\frac{m\mathrm{AT}}{P\mathrm{but}}$$

. Also, in order to minimize the size of the membrane, a sensor was developed that was developed on the basis of artificial piezoelectric materials to measure sound pressure. The dimensions of the CE are 2 × 2 mm; it allows measuring the sound pressure of 140 dB.

. Напряжение питания ТМ 5 В.ТМ with resistance r ₀ = 800 Ohm was created on the basis of pressure sensitive elements with a thickness of 15 μm and a diameter of 3 mm made of silicon. With this sensor, it is possible to measure sound pressure (provided that the static pressure is zero), sound pressure and static pressure (provided that the sound pressure of the EUT is zero). Conversion factors of these sensors $$0.55-\mathrm{3,5}\frac{m\mathrm{to}\mathrm{AT}}{P\mathrm{but}}$$

. Supply voltage TM 5 V.

. При этом достигалось уменьшение разброса градировочных данных по сравнению с нормированными по истинному динамическому давлению. Рассматриваются следующие градировочные коэффициенты:According to [2], the receivers are made of five tubes 1.3 mm in diameter, welded together, a cylindrical body, the successor has a diameter of 6.4 mm. Departure of the receiving tubes at the casing is L≈25 mm. For stationary receivers, it is necessary to determine dimensionless pressure coefficients during calibration, which represent the relationships between the pressures measured by the receiving holes, the magnitude and direction of the velocity, as well as the total and static pressures in the flow. When determining the pressure coefficients, the quantity $$\overline{P}=\frac{{\mathrm{<figure-callout\; id="2"\; label="P"\; filenames="00000038.png,00000039.png"\; state="\{\{state\}\}">P</figure-callout>}}_2+{\mathrm{<figure-callout\; id="3"\; label="P"\; filenames="00000038.png"\; state="\{\{state\}\}">P</figure-callout>}}_3+P_{\mathrm{four}}+{\mathrm{<figure-callout\; id="5"\; label="P"\; filenames="00000039.png"\; state="\{\{state\}\}">P</figure-callout>}}_5}{\mathrm{four}}$$

. In this case, a decrease in the scatter of the calibration data was achieved in comparison with normalized values of the true dynamic pressure. The following grading factors are considered:

For the slip angle:

For angle of attack;

For full pressure

где P₁…P₅ - давление в пяти трубках преемника. Первая трубка расположена в центре цилиндрического корпуса, остальные четыре трубки расположены симметрично по осям x, y посредственной близости внутри поверхности цилиндрического корпуса.For static pressure

where P ₁ ... P ₅ is the pressure in the five tubes of the successor. The first tube is located in the center of the cylindrical body, the remaining four tubes are located symmetrically along the x, y axes of mediocre proximity inside the surface of the cylindrical body.

The results of tests in a three-dimensional flow [2] in ADT with the dimensions of the working part of 0.3 × 0.3 m at a flow velocity of less than 20 m / s. At these speeds, the effect of the Reynolds number on the calibration in the range of bevel angles from 45 ° to -45 ° was negligible. The installation angle of the device relative to the flow changed in increments of 2 °, 5. It was found that the values of the grading characteristics for negative bevel angles were 6% higher than those obtained at positive angles. The magnitude of the non-symmetry can be reduced through careful manufacture of the receiver head of the receiver. This allowed us to use the characteristic obtained for angles β = 0-45 ° at -45 ° <β <+ 45 °. From consideration of the characteristics, it follows that the successors have a fairly high sensitivity to the bevel angle β = 0 °, 5 °, 10 °, 15 °, 20 °, 30 °, 40 °, 45 ° (along the x axis). The value of the function f, g, h, (along the y axis) is equal to -0.6; -0.4; -0.2; 0; 0.2; 0.4; 0.6; 0.8; 1,0. It is assumed that three tubular receivers (Fig. 1) will provide greater accuracy of the results of velocity measurements in flows with significant velocity gradients. In practice, they allow you to measure the angle of the bevel of the flow with an error of ± 0 °, 25, the flow velocity with an error of less than ± 0.5 m / s.

In [2], the behavior of the total pressure receivers when they are installed in a uniform flow at an angle of 90 ° and 180 ° to the velocity vector is considered. It is shown that traditional receivers in the form of round pitot tubes with a straight cut and a ratio of about 0.6, used as full pressure receivers in laminar and turbulent flows, are not sensitive to the bevel of the flow within ± 10 ° relative to the axis of the successor. In studies of the behavior of Pitot successors at large bevel angles, the angle of 90 ° was chosen arbitrarily, and the angle of 180 ° was chosen to reduce the interference effect of the successor in the vortex flow. The study of the receiver was carried out in ADT, where the turbulence was 0.07%. It is established that, compared to a cylindrical receiver, the Pitot receiver is less sensitive to a change in the angle of the bevel at values of the angle of inclination close to zero. Using a Pitot tube, it is possible to record the value of static pressure up to angles of 60 °, while when using a cylindrical receiver, this angle is 35 °. The minimum pressure was detected by the Pitot receiver at 90 °, after which the pressure monotonically increased with increasing angle, reaching at 180 ° the static pressure in the unperturbed flow. When the receiver is installed at an angle equal to 0, 60 °, 90 °, and 180 ° to the velocity vector, it is considered characteristic when the full pressure successor flows around it with a direct cut, when its position in the stream changes relative to the velocity vector in the range of bevel angles from 0 to 180 °. The coefficients for receivers with a diameter ratio of 0.6 to 0.72 are determined, and in the other group 0.77-0.86. The test results of a series of receivers with a constant outer diameter equal to 6 mm are presented, it is concluded that with an increase in the inner diameter, the pressure indicated by the receiver increased. When the Pitot receiver is positioned upstream at an angle of 180 °, it measures a pressure that differs from the local static pressure by about 4-12%, depending on the ratio of receiver diameters and Reynolds number.

Claims (1)

A device for measuring flow parameters, comprising a pressure receiver, consisting of three and / or five tubes symmetrically located inside a cylindrical body, fastened together by glue based on epoxy resin, a slice of one of the tubes is made at an angle of 90 °, cuts of all other tubes are made at an angle 45 ° with respect to the central axes of the tubes, located in the studied flow normally with the possibility of angular movement, characterized in that in each of the tubes of the pressure receiver are installed coaxially capacitive, with a tensor pressure sensitive elements electrically connected respectively to low frequency equipment installed outside the wind tunnel, a power supply and polarization unit, a charge amplifier, a voltage regulating voltage amplifier, a subtraction unit, protective capacitors, a coordinator with a control unit, a circuit board, an indicator, and the sensors consist of symmetric coaxial strain gauge bridge and capacitive sensing element, the sensors are mounted inside the tubes of pressure receivers flush with surface, and the sensors can be located at the same level on the horizontal plane along the x axis and can be offset relative to each other along the vertical plane of the y axis, one arm of the strain gage bridge and the input of the capacitive sensing element are respectively connected to the power supply and polarization, the other arm of the strain gage bridge through low-frequency equipment and the subtraction unit is electrically connected to the indicator input, the outputs of capacitive sensitive elements through protective capacitors, a charge amplifier, n The framing voltage amplifier and the subtraction unit are connected to another indicator input, the charge amplifier and protective capacitors are mounted on the circuit board, the coordinator is rigidly connected to the device’s cylindrical body, the reference holes are made in the sensor screen and the circuit board through the coordinator, the device’s position in the studied the stream is set using control units, an indicator, and a coordinator.

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