JP2001116763A - Flow velocity-measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem where it is necessary to secure a measurement window in a different direction for measuring three-dimensional internal flow and further a complex processing for compositing three-dimensionally is required. SOLUTION: The measuring device is provided with a first operation- processing means for calculating a spatial speed gradient according to speed information obtained at a plurality of measurement positions and a second operation-processing means for calculating a three-dimensional speed component according to the speed gradient and continuous conditions as compared with a conventional two-dimensional flow velocity measurement means, thus obtaining the three-dimensional components (ui, vi, wi) of flow velocity by relatively simple processing while a measurement window is in one direction only.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow velocity measuring device for measuring a flow velocity and a direction of a flow of a fluid to be measured. The present invention relates to a flow velocity measuring device devised so as to obtain a flow velocity.

[0002]

2. Description of the Related Art Currently used flow rate measuring means is:
It is classified into two types: a method that directly inserts measuring means into the fluid, such as a hot wire or a pitot tube, to obtain the flow velocity, and a method that estimates the flow velocity by calculating the moving velocity of particles mixed in the fluid by image processing or other methods. Is done. In particular, the latter has been rapidly commercialized in recent years with the advance of data processing technology such as images because of the advantage that the behavior of the fluid can be measured without disturbing the flow field.
LDV (Laser Doppler Velocimetry), PIV (Partic
le Image Velocimetry) is a typical optical method.

The principle of LDV is to irradiate two laser beams into a fluid so that they intersect at a measurement position to form interference fringes, and measure the frequency of scattered light emitted when particles in the fluid cross the interference fringes. In this way, the flow velocity of the component perpendicular to the interference fringes is obtained. Also,
The principle of PIV is to photograph the behavior of particles in a fluid by one or a plurality of photographing devices, and to calculate the flow velocity from image information such as a trajectory. In both cases, if a transparent window for measurement is provided, it is possible to measure the internal flow such as the flow in a closed pipeline.

A patent relating to LDV is disclosed in Japanese Unexamined Patent Publication No.
No. 8-54408 "and a patent on PIV as disclosed in
No. 8-201413 ".

[0005]

The above-described LDV and PIV have the following problems when measuring a three-dimensional flow, particularly a three-dimensional internal flow. Taking an LDV as an example, the interference fringes used in the LDV are generated in parallel to the intersection plane of the two laser beams. Normally, laser light is handled as a pair as shown in Japanese Patent Application Laid-Open No. 8-54408, and is irradiated into the fluid from a measurement window. As described above, since a set of velocity components perpendicular to the interference fringes can be obtained, it is necessary to use three sets (six) of laser beams in order to obtain the flow rates of the three-dimensional components x, y, and z. is there.

In the measurement of the internal flow, for example, the velocity of two components in the x direction and the y direction can be measured with one window, but in order to measure the component in the z direction, the windows must be opened in different directions. It needs to be added. This problem also appears when measuring the flow by PIV. Since only a two-dimensional component of speed can be obtained from a two-dimensional image taken by one camera, at least two components are required to perform three-dimensional measurement.
Shooting from a direction is required.

As described above, in order to measure a three-dimensional internal flow, it is necessary to secure measurement windows in different directions, and to perform three-dimensional synthesis, complicated processing is required.

[0008]

In order to solve the above-mentioned problems, a three-dimensional flow velocity measuring apparatus according to the present invention measures a flow velocity for measuring a one-dimensional or two-dimensional flow velocity at one or a plurality of measurement positions in a measurement target space. A measuring unit, a measuring position changing unit for changing the measuring position, a storing unit for storing a measurement result obtained by the flow measuring unit, and controlling the flow measuring unit, the measuring position changing unit, and the storing unit. In a flow velocity measuring device provided with arithmetic processing means, the arithmetic processing means calculates a spatial velocity gradient from velocity information obtained at a plurality of measurement positions; A second arithmetic processing means for calculating a three-dimensional velocity component from continuous conditions is provided.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a flow velocity measuring device (LDV) according to the present invention. In FIG. 1, reference numeral 1 denotes a pipe to be measured. A fluid to be measured flows inside the pipe 1 to be measured, and in this embodiment, a three-dimensional velocity distribution of the fluid is measured. Reference numeral 2 denotes a measurement window, which is a transparent window made of, for example, glass attached to the wall surface of the pipe 1 to be measured.
3 is a laser probe. One direction component can be measured using the interference fringes of one set (two) of laser beams. In this embodiment, two sets (four) of laser beams are irradiated into the fluid through the measurement window 2 to determine the flow velocity. X-direction component u and Y-direction component v of flow velocity
Are measured simultaneously.

Reference numeral 4 denotes a drive unit for moving and fixing the laser probe 3 to an arbitrary position (x, y, z) in the space. Reference numeral 5 denotes a signal processing device, which is composed of, for example, an optical filter and a frequency analysis device, and obtains a frequency of scattered light emitted by particles crossing the interference fringes, and calculates a moving speed. Numeral 6 denotes an arithmetic processing unit, which calculates the three-dimensional component of the speed based on the control of the drive unit 4 and the processing results of the arithmetic processing unit 6. Reference numeral 7 denotes a storage device that records the program of the arithmetic processing device 6 and measurement results.

FIG. 2 is a flowchart showing the processing procedure of the arithmetic processing unit 6. The flow velocity measuring device of the present invention uses the velocity gradient in the x direction and the y direction obtained by the LDV.

[0012]

１u / ∂x, ∂v / ∂y Continuous condition

[0013]

２u / ∂x + ∂v / ∂y + ∂w / ∂z = 0 A three-dimensional component of the flow velocity is obtained from the wall boundary condition w = 0. The processing procedure will be described below with reference to FIG.

Step 8 is initialization of a counter variable i.
Step 9 is the initialization of the _0th z-direction velocity w ₀ , where w ₀ = 0 is set as the wall surface boundary condition. Procedure 10 shows a procedure for measuring the velocity gradient in the X direction ∂u / ∂x. The laser probe 3 is operated to set the measurement position to Z = Z (i) and Y = Y.
Go to (i). Further, at this position, the measurement position is defined as X (i) + δ
It moves to two places of x, X (i) -δx, and measures the respective speeds u _i +, u _i-in the x direction. U _i +, u _i -velocity gradient in x direction from measured velocity in x direction

[0015]

Equation 3] _{∂u i / ∂x = (u i} + -u i -) / 2δx x -direction flow velocity

[0016]

## EQU4 ## u _i = (u _i + u _i- ) / 2 is obtained. Similarly, in step 11, the velocity gradient in the y direction

[0017]

Equation 5] _{∂v i / ∂y = (v i} + -v i -) / 2δy y -direction velocity

[0018]

[6] _{v i = (v i ++ v} i -) / by 2 steps 12 determines the z-direction velocity gradient from a continuous condition, calculates the z-direction flow velocity. That is, the velocity gradient in the z direction

[0019]

[Equation 7] _{∂w i / ∂z = -∂u i /} ∂x-∂v i / ∂y z direction speed

[0020]

[Equation 8] _{w i = w i-1 +} (Z (i) -Z (i-1)) is a * ∂w _i / ∂z, by the procedure 10 to 12 of more, i-th of the flow velocity u
_i, v _i, w _i can be obtained.

In step 13, the counter variable i is incremented by 1, and it is determined in step 14 whether or not it has been repeated n times. Steps 10 to 13 are repeated while i ≦ n.

FIG. 3 illustrates the above procedure, and is a view in which a measurement location is observed from inside the pipe 1 to be measured. The position of Z = Z (0) is the wall surface of the measurement window (the inside of the pipe), and u ₀ = 0, v ₀ = 0, w ₀ = 0. In steps 10 and 11 of FIG. 2, the flow velocity u at Z = Z (1)
_{From 1} +, u _1- , v ₁ +, v _1- , the velocity gradient in the x direction and the y direction is obtained, and the flow velocity u at Z = Z (1) is obtained from the above equation.
₁ , v ₁ and w ₁ are obtained. In the figure, the flow velocity is measured at a point indicated by a circle, and the flow velocity is measured at the point indicated by a black circle from the result. By sequentially performed in this order from the wall surface of the above processing operations, Z = Z (0), Z (1), Z (2) ... Z velocity u _i in _{(n), v i, w} i (i = 1~ n) can be obtained.

FIG. 4 shows a flow velocity measuring device (LD) according to the present invention.
It is a schematic diagram of V). Reference numeral 15 denotes a measured space. Reference numeral 16 denotes a photographing device, for example, a video camera. Reference numeral 17 denotes an image processing device for obtaining a two-dimensional flow velocity distribution in the x and y directions from a trajectory image of particles in a fluid captured by the imaging device 16. Reference numeral 18 denotes a light source, for example, a laser light source suitable for image processing. Reference numeral 19 denotes a probe for creating a sheet light, which expands the laser light in the x direction by, for example, a cylindrical lens. A traverse device 20 traverses the probe 19 in the z direction. Reference numeral 21 denotes a sheet light emitted from the probe 19 into the non-measurement space.

When the PIV is used as shown in FIG.
X from a single image, y direction of velocity u _i, v _i and the flow velocity distribution _{∂u i / ∂x, ∂v i /} ∂y are obtained simultaneously, the first embodiment similarly by the procedure of FIG. 2 The flow speeds u _i , v _i , w _i (i =
1 to n) can be obtained.

[0025]

According to the present invention, three-dimensional flow measurement can be performed without irradiating a laser beam from a plurality of places and photographing a flow field from a plurality of places, which are indispensable in conventional three-dimensional measurement. . There is also an advantage that three-dimensional measurement can be performed with almost the same hardware configuration as the conventional two-dimensional LDV and PIV.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a flow velocity measuring device (LDV) according to the present invention.

FIG. 2 is a flowchart showing a processing procedure of a processing unit 6;

FIG. 3 is a diagram showing a processing procedure of an arithmetic processing unit 6.

FIG. 4 is a schematic diagram of a flow velocity measuring device (PIV) according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Pipe to be measured, 2 ... Measurement window, 3 ... Laser probe, 4
... Drive device, 5 ... Signal processing device, 6 ... Calculation processing device, 7
... Storage device, 15 ... Measured space, 16 ... Imaging device, 17
... image processing device, 18 ... light source, 19 ... probe, 20 ...
Traverse device, 21 ... sheet light.

Claims (1)

[Claims] 1. A flow velocity measuring means for measuring a one-dimensional or two-dimensional flow velocity at one or a plurality of measuring positions in a measurement target space; a measuring position changing means for changing the measuring position; Storage means for storing the measurement result obtained by the means, and the flow velocity measuring means, the measurement position changing means, a flow processing device comprising an arithmetic processing means for controlling the storage means, the arithmetic processing means, a plurality of locations A first arithmetic processing unit for calculating a spatial velocity gradient from the velocity information obtained at the measurement position; and a second arithmetic processing unit for calculating a three-dimensional velocity component from the velocity gradient and a continuous condition. A flow velocity measuring device characterized by the following.