WO2014036701A1

WO2014036701A1 - Tool for measuring pressure and speed of rotational flow field

Info

Publication number: WO2014036701A1
Application number: PCT/CN2012/081031
Authority: WO
Inventors: 路明
Original assignee: Lu Ming
Priority date: 2012-09-06
Filing date: 2012-09-06
Publication date: 2014-03-13

Abstract

The present invention relates to the field of fluid measuring, in particular to a device for measuring pressure and three-dimensional flow speed of rotational flow field by a seven-hole pressure probe and a one-dimensional hot-wire probe in a rotational flow field. The device comprises: a seven-hole pressure probe (1), a one-dimensional hot wire wind velocity probe (2), a support system with two rotary degrees of freedom (3), a translation mechanism with three degrees of freedom (4), seven pressure sensors (5), a pressure pipe (6), a normal bridge (7), a lead wire (8), a data acquisition management system (9) and a control computer (10) etc.

Description

Tool for measuring the pressure and velocity of a swirl field

Technical field

The invention relates to the field of measurement of fluids. Specifically, a device for measuring the pressure and three-dimensional flow velocity of a swirl field using a seven-hole pressure probe and a one-dimensional hot wire probe in a swirling flow field. Background technique

The cyclone field is a common phenomenon in engineering, and the distribution of large-scale vortices in the flow field is the main feature. For example, the flow field at the downwind position of the building, the wing tip vortex field of the wing, the flow field around the rotor of the turbine engine, etc., and are usually turbulent fields. Research on such physical phenomena must accurately measure the pressure of the fluid flow and the three-dimensional transient velocity. From the measurement point of view, during the measurement of the swirl field, the velocity change rate of the two adjacent measurement points is large, which is a measurement of the large flow angle.

With the advancement of electronic and optical technologies, fluid measurement methods such as laser Doppler velocimetry (LDA) and particle imaging velocimetry (PIV) have been widely used. However, the above fluid measuring instruments often require large manufacturing and use costs, and are applied in a small measuring area, and the measurement results must be obtained by post-processing techniques on the signals. Both Doppler velocity measurement and tracer particle imaging velocity require tracer particles to trace the follow-up of the particle relative to the fluid flow, ie, whether the tracer particle can truly reflect the flow state of the fluid. Due to the difference in density of the tracer particles and the density of the fluid, the moment of inertia of the two is different. In the cyclone field, the tracer particles do not truly reflect the trajectory of the local fluid. The reliability of this type of measurement technique is not guaranteed in the measurement of the cyclone field.

Hot-wire anemometer is another commonly used flow velocity measurement tool. The principle is to use the fluid to flow through the hot wire to cause heat loss in the hot wire, resulting in a change in resistance. In particular, it has the characteristics of fast response and high accuracy, so it is often used for transient measurement of flow field, which is very suitable for analysis of turbulence characteristics of flow field. The measurement of three-dimensional flow velocity requires a three-dimensional hot wire, that is, a probe made of three hot wires. In order to reduce the disturbance of the flow field of the thin rod-shaped hot wire probe, it is necessary to reduce the spatial scale as much as possible, which is not only high in manufacturing cost but also difficult. Moreover, in the actual application process, the hot wire is easily broken, resulting in measurement failure. When measuring the large flow angle with a three-dimensional hot wire anemometer, it is necessary to calibrate the state of the hot wire at all measurement angles. For example, it takes about 8 hours to calibrate a three-dimensional hotline with a flow field angle of -50° to +50°' and an interval of 5°. This can cause the electronic instrument to drift and distort the calibration results. Despite this, the hot wire anemometer is still the most effective flow measurement tool, especially the one-dimensional hot wire, which is widely used due to its simple structure and low production cost.

In many occasions, especially for the measurement of the average flow velocity of a fluid, a porous pressure probe has a wide range of applications due to its low cost and simple manufacturing. Porous Pressure Probes (including three, four, five, seven holes) The basic principle for the measurement of three-dimensional velocity vectors is that the pressure difference measured from the different holes can determine the magnitude and direction of the fluid velocity. In the swirl field, the fluid flow direction is a large flow angle with respect to the pressure probe fixed in the direction of placement. At this point, the fluid is exploring Flow separation occurs on the head, causing the fluid to not completely adhere to the probe surface. The pressure hole does not accurately obtain the local pressure value, and the measurement fails. This is often the case with three- and five-hole probes. In contrast, the seven-hole pressure probe has a high application value and is more reliable when measuring large flow angles.

In summary, the measurement of the pressure and velocity of the cyclone field requires the development of an accurate, reliable, and low-cost measurement tool. Summary of the invention

The invention utilizes the respective advantages of the seven-hole pressure probe and the one-dimensional hot wire anemometer to design a measuring tool for the fluid flow of the swirl field, which combines the seven-hole pressure probe and the one-dimensional hot wire to measure the three-dimensional flow of the swirl field fluid. Transient flow, the device and operating process involved in pressure, velocity (including average velocity, instantaneous velocity) at high flow angles.

The tool for measuring the pressure and velocity of a swirl field proposed by the present invention comprises a seven-hole pressure probe (1), a one-dimensional hot wire anemometer probe (2), a bracket system (2) having two rotational degrees of freedom, and a Three-degree-of-freedom translation mechanism (4), seven pressure sensors (5), pressure tube (6), room temperature bridge (7), wire (8), data acquisition management system (9), and control computer (10) component. Figure 1 is a layout diagram of a tool for measuring the pressure and velocity of a swirl field, showing the connection relationship of the above components. The figure indicates:

The seven-hole pressure probe (1) and the hot wire anemometer probe (2) are positioned on a two-rotation degree support system (3); the two-degree-of-freedom support system (3) is fixed in a three-degree-of-freedom flat On the moving mechanism (4);

The seven-hole pressure probe (1) is connected to seven pressure sensors (5) through a pressure tube (6), and then connected to the data acquisition system (9) and the control computer (10);

The one-dimensional hot wire anemometer probe (2) is connected to the room temperature bridge (7) via the wire (8), and then connected to the data acquisition system (9) and the control computer (10). The seven-hole pressure probe (1) has a long cylindrical shape and has a truncated cone shape at its measuring end. Figure 2 is an external view and a top view of the measuring end of a seven-hole pressure probe. The top view is a view of the measuring end along the cylindrical axis of the seven-hole pressure probe. The seven-hole pressure probe has a central hole (11) with six additional peripheral holes (12) spaced 120° apart along its circumference. The center hole is also called a dynamic pressure hole; the six peripheral holes are also called static pressure holes, and the center hole (dynamic pressure hole) and the peripheral hole (static pressure hole) are pressure holes.

The top view of Figure 2 illustrates the seven-hole unique partitioning strategy for a seven-hole pressure probe, as shown in Figure 3. The number on the center hole is 7 and the number of the peripheral holes is from 1 to 6. The seven wells are divided into six zones, each zone having four holes: holes 7-4-3-5; holes 7-3-2-4; holes 7-2-1-3; holes 7-1-2 - 6; Hole 7- 6- 1-5; Hole 7- 5- 4- 6. The above six areas are represented by area codes using 1 to 6. The measurement is effective as long as there is fluid adhesion in either zone. For the flow characteristics of the swirl field, the angle between the flow direction and the direction of the fixedly placed seven-hole pressure probe (1) is large, even if the fluid is likely to be at the end of (1) The flow separation phenomenon occurs, the fluid does not completely adhere to the end surface, but there must be fluid attached to any of the six zones. The pressure values of the four pressure holes in the zone can obtain the three-dimensional velocity of the local fluid. And stress. Thus, the seven-hole pressure probe (1) can measure large angle flows. The seven-hole pressure probe α) requires calibration before measurement.

The one-dimensional hot wire anemometer probe (2) has the shape of an elongated cylinder. Figure 4 is an external view of the measuring end of the one-dimensional hot wire anemometer probe. A hot wire (13) is welded to the top of the hot wire holder (14), the hot wire holder is an electrical conductor, and the root is connected to the wire (8). The wire (8) is placed in a wire sleeve (15) that is in the form of a slender cylinder. The other end of the wire is connected to a normal temperature bridge (7). The fluid flows through the superheated wire (13), causing it to have a certain heat dissipation, resulting in a change in its resistance, and the output voltage value of the normal temperature bridge (7) changes. The relationship between the speed of the fluid and the output of the room temperature bridge (7) requires calibration.

Figure 5 is a definition of two rotational degrees of freedom produced by a two-rotation degree support system (3), which means that the swing angles "° ( 16 ) and pitch angles ( 17 ) are generated in a Cartesian coordinate system. Turn. The angle of rotation of the two rotational degrees of freedom should cover the flow angle in the flow field. In the figure, y, z are the three-dimensional directions of the Cartesian coordinate system.

Figure 6 is a schematic view of the structure of a stent system having two rotational degrees of freedom. The figure shows the principle of the two degrees of freedom of the swing angles "° (16) and pitch angle (17). The system includes a probe positioning clip (18), a worm gear (19), a worm

(20), stepper motor No. 1 (21), bracket (22), drive shaft (23), thrust bearing (24), stepper motor No. 2 (25) and other components. The connection relationship of each component is as shown in the figure.

Figure 6 also shows that the two-degree-of-freedom bracket system (3) is attached to a three-degree-of-freedom translation mechanism (4). The three-degree-of-freedom translation mechanism refers to the motion in the three-dimensional plane direction in the Cartesian coordinate system, which is controlled by three stepping motors. The above two rotational degrees of freedom and three translational degrees of freedom constitute a total of five spatial degrees of freedom. Figure 7 shows the formation of a relationship between five spatial degrees of freedom. The figure shows: the translation (26) along the X-direction, the translation (27) in the y_ direction, and the translation (28) in the z_ direction, which can be used with two rotational degrees of freedom (3) Moving to any spatial point on the x_y, y_z, x_z plane, the swing angle "° (16) and pitch angle (17) shown in Figure 5 can be generated locally by a bracket system (3) with two degrees of rotational freedom. ) The rotation. The flow of the tool for measuring the pressure and velocity of the swirl field proposed by the present invention consists in: obtaining the flow direction of the measuring point with a seven-hole pressure probe, and then measuring the transient velocity in the flow direction at the same measuring point with a one-dimensional hot wire probe. Figure 8 is a flow chart of the process of using the tool. The figure shows that the tool usage process is divided into four steps. Specifically - the first step is the calibration of a seven-hole pressure probe;

The second step is the calibration of the one-dimensional hot wire anemometer;

The third step is to obtain the flow angle of the measuring point with a seven-hole pressure probe;

The fourth step is to replace the seven-hole pressure probe with a one-dimensional hot wire probe for transient velocity measurements along known flow angles. DRAWINGS

Figure 1 is a layout of a tool for measuring the pressure and velocity of a swirl field. In the figure, 1 seven-hole pressure probe, 2-dimensional hot wire anemometer probe, 3 bracket system with two rotational degrees of freedom, 4 three-degree-of-freedom translation mechanism, 57 pressure sensors, 6 pressure tubes, 7 room temperature bridge , 8 wires, 9 data acquisition management system, 10 control computer.

Figure 2 is an external view and a top view of the measuring end of the seven-hole pressure probe. In the figure, 11 center holes, 12 peripheral holes.

Figure 3 shows the partitioning strategy for seven holes in a seven-hole pressure probe.

Figure 4 is an external view of the measuring end of the one-dimensional hot wire anemometer probe. In the figure, 13 hot wire, 14 hot wire support, 15 wire sleeve. Figure 5 is a definition of two rotational degrees of freedom. In the figure, 16 swing angles, 17 pitch angle, 1 seven-hole pressure probe, 2 one-dimensional hot wire anemometer probe.

Figure 6 is a schematic view of the structure of a stent system having two rotational degrees of freedom. In the figure, 16 swing angles "°, 21 stepping motor No. 1, 24 thrust bearing, 22 bracket, 17 pitch angle, 1 seven-hole pressure probe, 2-wei hot wire anemometer probe,

19 worm gear, 18 positioning clamp, 20 worm, 23 drive shaft, 25 stepping motor 2, 4 three degrees of freedom translation mechanism. Figure 7 is the formation of the relationship between the five spatial degrees of freedom. In the figure, a seven-hole pressure probe, 2-dimensional hot wire anemometer probe,

17 pitch angle, 16 swing angle "°, 27 y_ direction translation, 28 z_ direction translation 26 χ-direction translation, 4 three-degree-of-freedom translation mechanism, 3 with two rotational degrees of freedom Bracket system.

Figure 8 is a flow chart of the process of using the tool to measure the pressure and velocity of the swirl field.

Figure 9 (a) and Figure 9 (b) are measurement schemes of the flow field of the three-dimensional wing wake. In the figure, 30 wind tunnel air flow direction, 31 three-dimensional wing, 29 wind tunnel, one seven-hole pressure probe, 2-dimensional hot wire anemometer probe, three bracket system with two rotational degrees of freedom, 4 three degrees of freedom translation Mechanism, 6 pressure tubes, 8 wires, 32 holes on the wall of the wind tunnel, 5 seven pressure sensors, 7 room temperature bridges, 33 signal amplifiers, 9 data acquisition management system, 10 control computers, 34 control lines.

detailed description

The structure and principle of the present invention will be further described below in conjunction with specific embodiments. This embodiment is based on the tool for measuring the pressure and velocity of a swirl field proposed by the present invention to measure a three-dimensional transient flow field of a three-dimensional wing wake in a subsonic wind tunnel. It is well known that the flow field of a three-dimensional wing wake is characterized by a wing tip vortex structure. The wing tip vortex structure appears as a spiral shape of the flow and propagates downstream, which is a highly rotating flow field. Figure 9 (a), (b) is a measurement scheme of the flow field of the three-dimensional wing wake, showing the connection relationship between the seven-hole pressure probe (1) and the one-dimensional hot wire probe (2), and other components. The component composition, layout, and connection relationship of the tool for measuring the pressure and velocity of the swirl field used in this embodiment are the same as those shown in Fig. 1, and will not be described here. As shown in (a) and (b), the measuring device proposed by the present invention is placed in the wind tunnel (29) as a whole, and is placed in the three-dimensional wing (31) along the flow direction (30) of the airflow generated in the wind tunnel. Downstream. The static pressure ρ of the wind tunnel can be obtained from the static pressure hole on the wall surface, and the total pressure is determined by the state of the wind tunnel entrance. The wind tunnel produces a horizontal one-dimensional flow, and the flow velocity can be adjusted from subsonic to supersonic. Under different wind speeds, the static pressure of the wind tunnel changes, and the total pressure p _{toi of the} wind tunnel does not change. The outline of the end of the seven-hole pressure probe in the shape of a slender cylindrical rod is the same as that of Fig. 2. The cone has a cone of thirty degrees and the cone volume is smaller than a sphere with a diameter of 3.5 mm. Each pressure hole has a diameter of 1.3 mm. The elongated cylinder has an outer diameter of 5 mm. The material is made of stainless steel. The partitioning strategy for the seven holes of the seven-hole pressure probe (1) is shown in Figure 3.

Figure 9 (a) shows the pressure tube (6) attached to the tail of the seven-hole pressure probe (1), here seven flexible thin tubes, protruding from the small hole (32) of the wall surface of the wind tunnel and seven pressure sensors ( 5) Connect, then connect the signal amplifier (33) and the data acquisition system (9).

Figure 9(b) shows the appearance of the one-dimensional hot wire probe as in Figure 4. The hot wire (13) is made of Nickel chromium and has a diameter of 5 μm. Hot wire bracket (14) Extends the long cylinder 3 wire (8) extends from the small hole (32) of the wind tunnel wall to the room temperature bridge (7), signal amplifier (33) and data acquisition system (9

The data acquisition system (9) is connected to the control computer (10) and the two-rotation degree support system (3) and the three-degree-of-freedom translation mechanism (4) are adjusted via the control line (34).

According to the flow chart of the use of the tool given in Figure 8, the first step is the calibration of the seven-hole pressure probe. Adjusting the three-degree-degree translation mechanism and the two-degree-of-freedom bracket system in the wind tunnel, positioning the seven-hole pressure probe in the center of the wind tunnel, and making the axial direction of the cylindrical shape of the seven-hole pressure probe The directions are the same, that is, the swing angle "° and the pitch angle are equal to zero. The calibrated flow angle is from -50° to 50° with an interval of 5° and a total of approximately 400 angles to be calibrated. For each angle that needs to be calibrated with a different representation, the seven pressure values obtained from the seven pressure sensors connected to the seven-hole pressure probe are calculated to obtain fourteen pressure coefficients. They are that the radial pressure coefficient C and the tangential pressure coefficient are expressed as

Cpr, ^ ; (1)

P

Cpti = ^Pj " ^Pj2 , (2) '· 2

The subscript of the variable in the formula indicates the label of the hole, which is also the area code of the partitioning strategy shown in Fig. 3, i=l, 2, ... 6. If =7, then J7=^J2= If J7=^J2=7, when equal to the other, jl=i+l;j2=il. For small angle flow directions (flow angle less than 30°), the fluid is completely attached to the probe, and the radial pressure coefficient and tangential pressure coefficient of the center hole (hole 7) can be obtained by the following formula.

Cptb - Cptc

Cpr ₇ = Cpta + - ( 3 )

2

Cpt ₇ = + Cptb), ( 4)

among them

Cpta

It can be seen from this process that there is no total pressure _Ptot and static pressure value of the wind tunnel associated with the _incoming flow velocity in the formula for determining the pressure coefficient. Therefore, the calibration of the flow angle is independent of the incoming flow rate, and no other speed conditions are considered. If it takes 20 seconds for each calibration angle, a total of 400 angle calibrations are required for a total of 2.2 hours. After the calibration is completed, a calibration data list is formed, in which each calibration angle forms a one-to-one correspondence with 14 pressure coefficients. The second step of the measurement is to calibrate the one-dimensional hot wire probe in the wind tunnel. This process is a speed calibration and the calibration method is well known. At the time of calibration, the probe with a thin rod shape is placed in the direction of flow. This process is quick and easy. According to the calibration of 20 speed conditions, each working condition takes 20 seconds, and it takes about 7 minutes in total. The calibration process, which measures the first and second steps, does not exceed 3 hours in total.

The third step of the measurement is to obtain the flow direction of the measuring point with a seven-hole pressure probe. Hold the seven-hole pressure probe at the nominal position, ie = 0, yT = 0. By adjusting the translation mechanism (4) of three degrees of freedom, the measuring end of the seven-hole pressure probe can be reached at each measurement point in space. The pressure values of the seven pressure holes were obtained at each measurement point. Calculate the pressure coefficient of the measuring point according to the formula (1) - (4), and use the measured pressure coefficient and the calibrated pressure coefficient data list to perform angular interpolation to obtain the flow direction of the measuring point, that is, the measuring point obtained by interpolation (" ^Fl , yT). The spatial position, flow angle and pressure coefficient of the measuring points are recorded as files by the data analysis and processing unit in the control computer of Fig. 1.

The fourth step in the measurement is to measure the transient velocity with a one-dimensional hot wire probe. Replace the seven-hole pressure probe (1) and replace it with a hot wire anemometer probe (2). Through the control computer (10), at each measurement point, follow the recorded data about the spatial position and flow angle of the measurement point. Adjust the two-degree-of-freedom bracket system (3) and the three-degree-of-freedom translation mechanism (4) to reposition the one-dimensional hot wire probe (2) until it flows along the measurement point, known (" ^fl ,yT". In this way, the three-dimensional flow measurement of the flow field is processed into a local one-dimensional flow measurement. The local transient flow velocity obtained, it is easy to find the three-dimensional component of transient velocity u - V co " cos β°; v = V ύη α° τν =— cos«. sin (6)

Through such a measurement process, specifically, each measurement point of the flow field is measured twice, the flow direction of the flow field is obtained by the first pressure probe for the first time, and the transient speed of the flow field is obtained by the second time using the one-dimensional hot line probe. . The above measuring device and flow are suitable for the swirl field, that is, the measurement of the flow field at a large flow angle, replacing the three-dimensional hot wire anemometer which is usually required in this situation. According to the device proposed by the present invention, the total measurement time is not significantly increased because the measurement of the seven-hole pressure probe and the one-dimensional hot wire is much less than that of the three-dimensional hot wire. If this embodiment uses a three-dimensional hot wire anemometer, the calibration range of the same angle, the calibration time of each angle, and the calibration range of the speed conditions, that is, according to 400 calibration angles, each calibration angle takes 20 seconds, 20 speed conditions. To calculate, only the calibration time is required: 20 seconds x 20 x 400 = 44 hours. The use of the invention makes the measurement process simple and fast. As mentioned above, the calibration time is less than 3 hours, saving 90% of the time, greatly shortening and simplifying the hot line calibration time and process, and reducing the length of the measuring instrument. The error caused by overheating makes the measurement result more reliable. The production cost of a seven-hole pressure probe is about 10% of that of a one-dimensional hot-wire probe, while the cost of a one-dimensional hot-wire probe is about 1% of that of a three-dimensional hot-wire probe. Thus, a three-dimensional transient measurement using a seven-hole pressure probe and a one-dimensional hot wire anemometer typically uses a three-dimensional hot wire anemometer method that reduces manufacturing costs by more than 95%.

List of reference signs

1 seven-hole pressure probe

2 one-dimensional hot wire anemometer probe

3 bracket system with two rotational degrees of freedom

4 three degrees of freedom translation mechanism

5 seven pressure sensors

6 pressure tube

7 normal temperature bridge

8 wire

9 data collection management system

10 control computer

11 center hole

12 peripheral holes

13 hot wire Hot wire bracket wire sleeve swing angle "° pitch angle positioning clip worm wheel

Worm

Stepper motor No. 1 bracket

Drive shaft

Thrust bearing Stepper motor No. 2 X-direction translation y_direction translation Z-direction translation Wind tunnel

Wind tunnel airflow direction 3D wing Small hole signal amplifier on the wall surface Control line

Claims

WO 2014/036701 Claim PCT/CN2012/081031

A tool for measuring the pressure and velocity of a swirl field, comprising a seven-hole pressure probe (1), a one-dimensional hot wire anemometer probe (2), and a bracket system having two rotational degrees of freedom (3), a three-degree-of-freedom translation mechanism

(4), seven pressure sensors (5), pressure tube (6), room temperature bridge (7), wire (8), data acquisition management system

(9) and control computer (10) and other components, the connection relationship of the above components:

The seven-hole pressure probe (1) is connected to seven pressure sensors (5) via a pressure tube (6) and then connected to the data acquisition system

(9), control computer (10);

The one-dimensional hot wire anemometer probe (2) is connected to the normal temperature bridge (7) through the wire (8), and then connected to the data acquisition system (9) and the control computer (10).

2. A tool for measuring the pressure and velocity of a swirl field according to claim 1, wherein the seven-hole pressure probe (1) has a long cylindrical shape at its measuring end. The part is in the shape of a truncated cone.

3. A tool for measuring the pressure and velocity of a swirl field according to claim 1, wherein said one-dimensional hot wire anemometer probe (2) has the shape of an elongated cylinder.

4. A tool for measuring the pressure and velocity of a swirl field according to claim 1, wherein the use process is specifically divided into four steps, specifically - the first step is a seven-hole pressure probe (1) Calibration

The second step is the calibration of the one-dimensional hot wire anemometer probe (2);

The third step is to obtain the flow angle of the measuring point with a seven-hole pressure probe (1);

The fourth step is to replace the seven-hole pressure probe (1) with a one-dimensional hot wire anemometer probe (2), along a known flow angle.