RU2603234C1 - Subsonic wind tunnel with flow rate pulsing component - Google Patents

Abstract

FIELD: test equipment.

SUBSTANCE: invention relates to closed type wind tunnels and can be used for carrying out of various tests of aircraft models, ground transport, buildings, structures, bridges. Device includes antechamber, collector, open working part, diffuser with length L with through damping holes with total area of 0.4-0.5 of collector outlet section area S with arrangement of holes rows at a distance from 0.6-0.9 of collector diameter D to L/3 of diffuser length from its inlet section, circular funnel above diffuser, rotary sections with rotary blades, return channel, blade fan, arranged behind diffuser. At that, diffuser has built-in damping holes shutter mechanism.

EFFECT: technical result consists in simplification of control by set of pulsating flow parameters in wind tunnel.

3 cl, 10 dwg

Description

The invention relates to wind tunnels of a closed type and can be used for various tests of models of aircraft, ground vehicles, buildings, structures, bridges. The invention can be used to upgrade existing wind tunnels.

Information on and parameters of subsonic wind tunnels is widely presented in the literature [1, 2].

Subsonic wind tunnels can be divided into three main classes: flow type, closed type and with the Eiffel chamber.

Wind tunnels have become widespread in Russia, see [1, 2], of a closed type with an open working part, containing a prechamber, a collector, an open working part, a diffuser, an annular bell above the diffuser, rotary sections with rotary blades, one return channel located directly behind the diffuser is a fan blade. In such wind tunnels tend to get a uniform uniform flow in the open working part.

At the same time, there is a need to conduct aerodynamic studies in the presence of a pulsating component of the flow velocity that is significant in amplitude in the working part of the wind tunnel.

A wind tunnel is known, see [3], which provides an operating mode for the aggregate pulsating flow parameters of the working part:

- pulsation rate of flow rate;

- the amplitude of the pulsations of the flow velocity;

- a constant component of the flow rate.

This wind tunnel is made with an Eiffel chamber, contains an inlet path with a valve and a throttle for introducing compressed air, a prechamber, a pulsator, a collector, a working part, an exhaust tract, a working chamber, two throttles in a prechamber, one of which acts as a pulsator, and the other is designed to control the stationary component of the flow rate. The disadvantage of this pipe is the complexity of the technical solution for managing the operating parameters of the flow in the working part.

Investigations of the flow pulsations in wind tunnels with an open working part to ensure the operating mode in terms of the set of specified parameters of the working part — the frequency and amplitude of the pulsations of the flow velocity, the constant component of the (average) flow velocity — were practically not carried out. Here it can be noted as the most significant work [4]. But even in this work, studies were aimed at damping pulsations, and the question of controlling pulsations was practically not discussed.

Closest to the claimed invention according to the technical result and the technical solution of the problem and adopted as a prototype is a wind tunnel of the closed type T-103 TsAGI, [4]. The T-103 wind tunnel includes a prechamber (1), a collector (2), an open working part (3), a diffuser (4) of length L with through damping holes (5) with a total area of 4 to 0.5 of the output section S the collector (2) with the arrangement of rows of holes (5) at a distance from 0.6-0.9 of the diameter D of the collector (2) to L / 3 of the length of the diffuser (4) from its inlet section, an annular socket (6) above the diffuser (4 ), rotary sections (7) with rotary blades (8), a return channel (9), a fan blade (10) located behind the diffuser (4).

The listed features of the prototype (T-103 pipe) are common with the claimed device of the wind tunnel.

A disadvantage of the known device (T-103 wind tunnel) is the limitation of the technical solution for controlling the set of pulsating flow parameters in the open working part at medium speeds up to 40 m / s.

The claimed invention is free from this drawback.

The technical result of the proposed device is to solve the problem of controlling the set of pulsating flow parameters in the open working part at medium speeds up to 40 m / s.

The specified technical result is achieved by the fact that in a wind tunnel of a closed type with an open working part in accordance with the claimed invention

1) a mechanism (11) for locking the damping holes (5) is integrated in the diffuser (4);

2) through holes (12) are made in the annular socket (5);

3) the annular bell (6) above the diffuser (4) is made with a mechanism (13) for the longitudinal movement of the bell (6) parallel to the axis of the wind tunnel.

The essence of the claimed invention is illustrated in FIG. 1, which shows a diagram (circuit) of a closed-type wind tunnel device with an open working part.

A closed type wind tunnel with an open working part, as can be seen from FIG. 1 of the circuit, contains a prechamber (1), a collector (2), an open working part (3), a diffuser (4) of length L with through damping holes (5) with a total area of 0.4 to 0.5 of the area S of the outlet cross section of the collector ( 2) with the arrangement of rows of holes (5) at a distance from 0.6-0.9 of the diameter D of the collector (2) to L / 3 of the length of the diffuser (4) from its inlet section, an annular socket (6) above the diffuser (4), rotary sections (7) with rotary blades (8), one return duct (9), a fan blade (10) located behind the diffuser (4), a damper hole shutter mechanism (11) (5), triplets in the diffuser (4), through holes (12) in the annular bell (6), the mechanism (13) for longitudinal movement of the annular socket (6).

The work of the proposed wind tunnel closed type with an open working part is as follows. When the driven motor of the blade fan is turned on, the air flow is sucked into the diffuser of the wind tunnel. The pressure developed by the fan is enough to overcome the resistance of the entire contour of the wind tunnel. The air flow in its movement passes the diffuser, the channel after the fan, four rotary sections, the return channel and is turned 360 °. Then the air stream enters the prechamber and flows through the collector into the open working part and is then sucked into the diffuser. The change in the flow rate in the open working part is achieved by adjusting the speed of the electric motor.

When the proposed wind tunnel of the closed type with an open working part, intense pulsations of the infrasonic range flow take place. The amplitudes of flow pulsations, respectively pressure pulsations and velocity pulsations, can be controlled

- a mechanism (11) for the shutter of the damping holes (5) integrated in the diffuser (4);

- through holes (12) in the annular socket (6);

- a mechanism (13) for the longitudinal movement of the annular socket (6).

An example of a specific implementation of a subsonic wind tunnel with pulsating flow parameters in the open working part is based on the AT-11 subsonic industrial wind tunnel of St. Petersburg State University. The outline of an AT-11 wind tunnel can be represented in FIG. 2, which shows practically the main geometric dimensions of the pipe.

Technical parameters of the AT-11 pipe:

Collector diameter 2250 mm The width (thickness) of the collector wall at the outlet 180 mm Working length ~ 4000 mm Diffuser diameter 2450 mm The diameter of the annular socket 3500 mm

The AT-11 wind tunnel includes a prechamber (1), a collector (2), an open working part (3), a diffuser (4) of length L with through damping holes (5) with a total area of 0.4 to 0.5 of area S the outlet cross section of the collector (2) with the arrangement of rows of holes (5) at a distance from 0.6-0.9 of the diameter D of the collector (2) to L / 3 of the length of the diffuser (4) from its inlet section, an annular socket (6) above the diffuser (4), rotary sections (7) with rotary blades (8), one return duct (9), a blade fan (10) located behind the diffuser (4).

The setting of the experiment. The AT-11 wind tunnel model can be represented as shown in FIG. 3. Here the model of the wind tunnel is elongated along the longitudinal axis. The given length for it is given taking into account the length of the open working part.

In wind tunnels with an open working part, self-oscillating and resonant oscillatory processes can be observed. Self-oscillating processes can exist in the diffuser of a wind tunnel, and resonant processes can appear in the prechamber when the frequencies of these processes coincide. For the existence of a self-oscillating process in the diffuser, it is necessary to create heterogeneity in the flowing stream. Here the heterogeneity in the flowing stream is created by a rotating fan.

Damping holes in the diffuser, made in accordance with the characteristics of the prototype, significantly damped infrasonic flow pulsations in the wind tunnel. The solution to the problem of controlling a set of pulsating flow parameters in an open working part, at average speeds of up to 40 m / s, is possible by using infrasonic pulsations of a flow in a wind tunnel using various structural mechanisms.

The determined parameters of the oscillatory process in the wind tunnel: the amplitude and frequency of pressure pulsations. It is desirable to measure these parameters in the diffuser and in the chamber of the wind tunnel. In this case, it is possible to determine at least at what flow rates (Mach numbers M of the flow) this or that resonator “sounds” in the open working part.

Defining parameters: process similarity parameters - Mach number M, Strouhal number St, Reynolds number Re and geometrical parameters of the wind tunnel at the inlet to the diffuser.

From here the goal of experimental research is formulated:

- determine the main resonator in the wind tunnel;

- find constructive mechanisms that contribute to the control of pressure pulsations of the infrasonic range in the wind tunnel.

In FIG. Figure 4 shows the arrangement of the differential small-sized inductive pressure sensors DMI 0.1 used to register pressure pulsations in the wind tunnel AT-11. The sensors are installed at the following points: D1 - on the wall of the prechamber; D2 - on the wall of the diffuser; D3 - on the flow axis (the pitot tube is placed on the flow axis and the pressure is transferred to the D3 sensor from the pitot tube with silicone hoses); D4 - in the near field of the flow. The first two sensors record the pulsating pressure in the stream near the walls of the channel of the wind tunnel.

A block diagram of a pressure pulsation measurement system is shown in FIG. 5. Pressure sensors are connected to inductive high-frequency converters IVP-2. The outputs of the measuring channels IVP-2 are connected

- with the PULSE measuring and computing complex through the LAN-XI data acquisition system (Bruhl and Kjерr equipment) and

- with a digital oscilloscope (4-beam oscilloscope LECROY WaveSurfer 24Xs-A).

A digital oscilloscope allows recording temporary implementations of sensor signals at the open or closed inputs of Y-amplifiers, as well as working in the registration mode of X-Y signals. In the X-Y signal registration mode, it is possible to obtain signal responses to pressure pulsations at the points of installation of the sensors as a function of the pressure head recorded by the D3 sensor.

Pressure pulsations are observed in the pitot tube and in the connecting hose from the tube to the D3 sensor, caused by the vibration of the pitot tube in the flow and the pulsations of the flow itself. For satisfactory damping of pulsations, it is enough to firmly fix the Pitot tube to the design of the wind tunnel and make a long connecting hose from the Pitot tube to the D3 sensor.

Additional difficulties in registering pressure pulsations with DMI 0.1 sensors are manifested in the fact that the membrane of a sensitive differential DMI 0.1 sensor in an experimental study of flow pulsations in a wind tunnel can be subject to proportional pressure on both sides. To increase the accuracy of measuring the working pressure and eliminate phase-frequency distortions of the sensor signal from the non-working side, connect a silicone hose up to 100 mm long to the nozzle-receiver of the sensor, plug it and shield it.

Difficulties arise with the dynamic calibration of inductive sensors DMI 0.1. Here you can use the results of static calibration of sensors on a pneumohydraulic press [5] and carry out dynamic calibration of sensors using a model 4228 pistonphone from Bruhl and Kjерr. The 4228 Pistonphone is an accurate reference reference source for calibrating sound measurement equipment in laboratory and field conditions (the sound pressure level of the reference signal is 124 dB, the frequency of the reference signal is 250 Hz).

раза выше чувствительности по СКЗ. Таким образом, при отсутствии эталонных генератора давления и преобразователя давления появляется реальная возможность измерить амплитуды пульсаций давления в канале аэродинамической трубы.The sensitivity determined by the RMS and introduced into the programs of the Bruhl and Kjерr measuring and computing complex as a parameter of the DMI 0.1 sensor leads to a pressure level of 124 dB when processing the reference signal. A comparison of the sensitivity values of the sensors determined by the RMS and the results of the static calibration of the sensors shows that the sensitivity during static calibration in

times higher sensitivity for VHF. Thus, in the absence of a reference pressure generator and pressure transducer, there is a real opportunity to measure the amplitude of the pressure pulsations in the channel of the wind tunnel.

When measuring pressure pulsations in an AT-11 wind tunnel, it is necessary to verify that the sensors are installed correctly. The check consists in whether the points where the sensors were located in the diffuser and in the prechamber in the node or in the antinode of the acoustic wave in the closed channel of the wind tunnel were found.

The verification of the correct placement of the sensors in the diffuser and in the prechamber is illustrated by the following drawing, see Fig. 6.

In FIG. 6 axis X - velocity head in the stream at the outlet of the collector. Y axis - dynamic pulsations of static pressure at the points of installation of the sensors. As can be seen from the presented oscillograms, an oscillatory process develops in the diffuser (sensor D2) and in the prechamber (sensor D1), starting from low flow rates at the outlet of the collector, in the closed channel of the wind tunnel. It is not necessary to speak about any characteristic points or zones (modes) in the oscillatory process according to these results. The process lives in the entire speed range. In the near field of the jet stream (sensor D3) outside the open working part of the wind tunnel there are no intense pressure pulsations.

Example 1

The tests were carried out on model 1. (The through holes in the diffuser are closed. The annular bell is made with a longitudinal movement mechanism.)

- 0.315. В работе [5] дана только качественная оценка влияния раструба на пульсации потока в аэродинамической трубе: раструб сужает области существования пульсационных режимов в аэродинамической трубе по скорости потока.On the wind tunnel T-103 TsAGI (prototype) the annular bell is fixed motionless with respect to the diffuser. The distance from the nozzle to the annular bell is 4000 mm with a working part length of 4740 mm. Consequently, the extension of the bell l with respect to the diffuser is equal to 740 mm or, with one of the dimensions of the ellipsoidal nozzle 2350 mm,

- 0.315. In [5], only a qualitative assessment of the effect of the bell on the flow pulsations in the wind tunnel was given: the bell narrows the regions of existence of the pulsation regimes in the wind tunnel by the flow velocity.

- от 0,1 до 0,3. Влияние положения раструба на пульсации потока в трубе AT-11 показано на приведенных осциллограммах пульсаций давления в форкамере и диффузоре в функции скоростного напора потока на выходе сопла, см. Фиг. 7.On the AT-11 wind tunnel, the annular bell is mounted on the trolley, and it can be moved towards the nozzle at a distance

- from 0.1 to 0.3. The influence of the position of the socket on the flow pulsations in the AT-11 pipe is shown in the waveforms of pressure pulsations in the prechamber and diffuser as a function of the flow velocity head at the nozzle exit, see FIG. 7.

The influence of the position of the annular bell is obvious. The position of the annular bell can change the amplitude of the pressure pulsations in the channel of the wind tunnel and the magnitude of the pulsation velocity in the open working part.

= 0,1, приведены результаты измерений амплитуд (СКЗ) и частот пульсаций давления в форкамере и в диффузоре аэродинамической трубы АТ-11 в зависимости от скорости вращения вала вентилятора и средней скорости потока (числа Маха М потока) в открытой рабочей части. Фиг. 9: а - пульсации давления в форкамере; б - пульсации давления в диффузоре; с - частоты пульсаций давления и вращения вала вентилятора (черная линия).In FIG. 8, for the departure of the bell

= 0.1, the results of measurements of amplitudes (RMS) and frequencies of pressure pulsations in the chamber and in the diffuser of the AT-11 wind tunnel are presented, depending on the speed of rotation of the fan shaft and the average flow rate (Mach number M of the flow) in the open working part. FIG. 9: a — pressure pulsation in the prechamber; b - pressure pulsations in the diffuser; c - frequency of pressure pulsations and fan shaft rotation (black line).

The experimental results — with the damping holes in the diffuser completely closed — show that an intense oscillatory process in the diffuser and in the prechamber is observed in the range of the average flow velocity from 15 m / s to 34 m / s. In this case, a resonance process may develop in the chamber of the wind tunnel, since the amplitudes of the pressure fluctuations in the chamber exceed the amplitudes of the pressure pulsations in the diffuser.

The experimental results show that the rms amplitude of the pressure pulsations in the prechamber is up to 25% of the average dynamic pressure measured by the Pitot tube. Thus, the RMS of the amplitudes of the velocity pulsations in the open working part is a significant value.

By adjusting the size of the damping holes, up to complete closure, it is possible to change the amplitude of pressure pulsations in the chamber of the wind tunnel and the value of the pulsation velocity in the open working part.

Example 2

The tests were carried out on model 2. (Annular bell with through holes). (The damping holes in the diffuser are open; the holes in the annular bell are ~ 10% of the collector area S.)

= 0,1, приведены результаты измерений амплитуд (СКЗ) и частот пульсаций давления в форкамере и в диффузоре аэродинамической трубы АТ-11в зависимости от скорости вращения вала вентилятора и средней скорости потока (числа Маха М потока) в открытой рабочей части.In FIG. 8, for the departure of the bell

= 0.1, the results of measurements of the amplitudes (RMS) and frequencies of pressure pulsations in the chamber and in the diffuser of the AT-11 wind tunnel are presented, depending on the speed of rotation of the fan shaft and the average flow rate (Mach number M of the flow) in the open working part.

The results of the experiment for model 2 show that the rms amplitudes of the pressure pulsations in the prechamber are smaller than the corresponding values for model 1, but remain acceptable for controlling the amplitudes of the velocity pulsations in the open working part.

In FIG. Figure 9 shows the spectra of signals and the temporal implementation of the signals of the pressure sensors installed in the diffuser and in the chamber of the AT-11 wind tunnel.

The experimental results are illustrated in FIG. 10 spectrograms of the amplitudes of pressure pulsations in the chamber and in the diffuser of the AT-11 wind tunnel. In the spectrograms: the X axis is the frequency axis, the Y axis is the rms values of the pressure pulsation amplitudes, the Z axis is the step-by-step spectral estimates as functions of the AT-11 fan shaft speed.

As the results of the tests show, the claimed invention allows you to control a set of pulsating flow parameters in the open working part of the wind tunnel at average flow velocities up to 40 m / s and take into account the most complex flows in designs of this type in contrast to devices with a closed working part [6].

Information Sources Used

1. Wind tunnels of eastern hemisphere / a report prepared by the federal research division, library of congress, for the aeronautics research mission directorate, national aeronautics and space administration. 2008 .-- 245 p.

2. Wind tunnels of western hemisphere / a report prepared by the federal research division, library of congress, for the aeronautics research mission directorate, national aeronautics and space administration. 2008 .-- 646 p.

3. RF patent No. 2526515 C1 (IPC: G01M 9/02); "Aerodynamic tube"; authors N.I. Batura, G.S. Vereisky, V.A. Golovkin, M.A. Golovkin et al.

4.S.P. Strelkov, G.A. Bendrikov, N.A. Smirnov. Pulsations in wind tunnels and methods for damping them. - Proceedings of TsAGI, 1946, c. 593, 56 p.

5. RF patent No. 2504747 (IPC: G01L 27/00); Patent holder - St. Petersburg State University; authors G.A. Leonov, A.I. Tsvetkov, B.A. Schepanyuk. "Device for calibration of measuring instruments for differential pressure"; Registered in the Register of Inventions of the Russian Federation on January 20, 2014

6. Application DE 0010049533 A1, CL G01H 0001/00.

Claims (3)

1. A subsonic wind tunnel of a closed type containing a prechamber, a collector, an open working part, a diffuser of length L with through damping holes with a total area of 0.4 to 0.5 of the area S of the outlet cross section of the collector with the arrangement of rows of holes at a distance of 0.6- 0.9 of the diameter D of the collector up to L / 3 of the diffuser length from its inlet section, an annular socket above the diffuser, rotary sections with rotary blades, a return duct, a fan blade located behind the diffuser, characterized in that the diffuser is integrated damping hole shutter mechanism. 2. The subsonic wind tunnel of the closed type according to claim 1, characterized in that through holes are made in the annular bell. 3. The closed-type subsonic wind tunnel according to claim 1 or 2, characterized in that the annular bell above the diffuser is made with a longitudinal movement of the bell parallel to the axis of the wind tunnel.

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