CN108955981B - Applicable to the method and device for measuring the shear stress on the wall of the rotating boundary layer - Google Patents

Abstract

The invention discloses a method for measuring the shear stress of a rotating boundary layer wall surface. The probes are preset; the preset probes are used to measure the velocities at multiple different preset distances on the rotating boundary layer wall, and the obtained multiple measurement results are transmitted; select a linearly distributed velocity function in the area closest to the wall of the rotating boundary layer, and linearly fit the velocity function; the velocity gradient obtained by the linear fitting operation is obtained by translation, assumption estimation and dimensionless operation to complete the measurement. The method does not require any treatment on the wall surface, does not affect the flow near the wall surface, and can realize the measurement of the wall shear stress, which is simple and convenient; the determination of the wall shear stress τw and the wall distance _y can be realized at the same time; the miniaturization test adopted The system can realize the measurement of wall shear stress under rotating conditions, and has high application efficiency and ease of use. The invention also discloses a device for measuring the shear stress of the wall of the rotating boundary layer.

Description

Applicable to the method and device for measuring the shear stress on the wall of the rotating boundary layer

technical field

The invention relates to the technical field of testing and measurement, in particular to a method and a device for measuring the shear stress of a rotating boundary layer wall.

Background technique

In the study of rotating machinery, the wall shear stress is a very important quantity. Under normal static conditions, due to the large installation space, a variety of methods can be used to measure shear stress. However, under rotating conditions, the measurement of wall shear stress has always been a difficult problem due to the limited space.

The conventional method of measuring the wall shear stress generally uses a thin film sensor to measure the shear stress of the wall surface. However, in order to prevent the influence of the thin film sensor on the flow of the wall surface, a groove is generally opened on the wall surface, and the thin film sensor is embedded in the groove and ensured. The outer surface of the thin film sensor is flush with the wall, thereby eliminating the influence on the flow near the wall. However, this method requires special grooving treatment on the channel wall surface, which is relatively complicated; especially when the wall surface is heated, this method is more difficult to implement due to the need to arrange a heating device.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a method and device suitable for measuring the shear stress of the wall of the rotating boundary layer in view of the problems existing in the traditional technology. Specifically, in the present disclosure, in order to solve the problem of wall shear stress measurement in rotating machinery, the present disclosure proposes a method for measuring wall shear stress of a rotating boundary layer, specifically, a rotating boundary layer wall surface based on the assumption of a linear bottom layer. Shear stress measurement method. The method uses boundary layer hot wire probe, displacement mechanism, small CTA module, small digital-to-analog conversion module, slip ring inducer and computer to measure the boundary layer velocity under rotating conditions, and finally calculate the wall shear through the linear underlying assumption. stress. Through the proposal of this method, the measurement of the wall shear stress can be realized without any treatment on the wall and without affecting the flow near the wall, which is simple and convenient; at the same time, the determination of the wall shear stress τw and the wall distance _y can be realized. ; Further, the adopted miniaturized test system can realize the measurement of wall shear stress under rotating conditions.

In a first aspect, an embodiment of the present invention provides a method for measuring shear stress on a wall of a rotating boundary layer, the method comprising: presetting a probe; Measure the velocities at different preset distances, and transmit the obtained multiple measurement results; select a linearly distributed velocity function in the area closest to the wall of the rotating boundary layer, and perform a linear fitting operation on the velocity function ; The velocity gradient obtained by the linear fitting operation is measured through translation, assumption estimation and dimensionless operation in turn.

In one embodiment, the presetting of the probe includes: fixing the boundary layer hot wire probe above the displacement mechanism through a support rod, and fixing the boundary layer hot wire probe on the rotating boundary layer wall surface pre-setting Set distance.

In one embodiment, the measuring the velocities at multiple different preset distances from the rotating boundary layer wall by using the preset probes includes: measuring the distances from the rotating boundary layer wall through the preset boundary layer hot wire probe. The speed of the nearest point is measured, and the speed of the point farthest from the wall of the rotating boundary layer is measured by a pre-set boundary layer hot-line probe.

In one of the embodiments, the method further comprises: measuring the velocities of multiple points between the closest point and the farthest point on the wall of the rotating boundary layer by using the preset boundary layer hot wire probe.

In one embodiment, the transmitting the multiple acquired measurement results includes: sequentially transmitting the multiple acquired measurement results to the computer through the CTA module, the digital-to-analog conversion module, and the slip ring diverter.

In one embodiment, the method further includes: checking whether the coordinate points on the velocity function selected for performing the linear fitting operation all coincide with all coordinate points within a preset range; The coordinate points on the velocity function selected by the linear fitting operation coincide with all the coordinate points within the preset range, and the velocity gradients obtained by the linear fitting operation are sequentially obtained by translation and assumption estimation. The rotating boundary layer wall shear stress is the true rotating boundary layer wall shear stress.

In one embodiment, the method further includes: if the coordinate points on the velocity function selected for performing the linear fitting operation do not all coincide with all coordinate points within a preset range, selecting the preset The velocity function of the coordinate points within the set range is sequentially operated through translation, assumption estimation and dimensionlessization until the real wall shear stress of the rotating boundary layer and the corresponding ordinate are obtained.

In a second aspect, an embodiment of the present invention provides a computer-readable storage medium, where a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, implements the rotation boundary applicable to the first aspect above Method for measuring the shear stress of the layer wall.

In a third aspect, an embodiment of the present invention provides a computer program product including instructions, which when the computer program product runs on a computer, causes the computer to execute the method described in the first aspect.

In a fourth aspect, an embodiment of the present invention also provides a device for measuring shear stress on a rotating boundary layer wall, the device includes: a setting module for pre-setting the probe; a measurement and transmission module for passing through The preset probe measures the velocities at multiple different preset distances on the wall of the rotating boundary layer, and transmits the obtained multiple measurement results; the fitting processing module is used for the closest distance to the wall of the rotating boundary layer. A linearly distributed velocity function is selected in the region, and a linear fitting operation is performed on the velocity function; a measurement module is used to measure the velocity gradient obtained by the linear fitting operation through translation, assumption estimation and dimensionless operations in sequence.

The invention provides a method and a device for measuring shear stress on the wall of the rotating boundary layer, wherein the probe is preset; and transmit the obtained multiple measurement results; select a linearly distributed velocity function in the area closest to the wall of the rotating boundary layer, and perform a linear fitting operation on the velocity function; the velocity gradient obtained by the linear fitting operation is sequentially translated through translation , hypothesis estimation, and dimensionless operations complete the measurement. The method uses boundary layer hot wire probe, displacement mechanism, small CTA module, small digital-to-analog conversion module, slip ring inducer and computer to measure the boundary layer velocity under rotating conditions, and finally calculate the wall shear through the linear underlying assumption. stress. Through the proposal of this method, the measurement of the wall shear stress can be realized without any treatment on the wall and without affecting the flow near the wall, which is simple and convenient; at the same time, the determination of the wall shear stress τw and the wall distance _y can be realized. ; Further, the adopted miniaturized test system can realize the measurement of wall shear stress under rotating conditions, and has high application efficiency and ease of use.

Description of drawings

1 is a schematic flowchart of steps of a method for measuring the shear stress of a rotating boundary layer wall in an embodiment of the present invention;

FIG. 2 is a schematic structural diagram of a device for measuring the shear stress of a rotating boundary layer wall according to an embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the following examples and the accompanying drawings will further describe the specific embodiments of the present invention applicable to the method and device for measuring the wall shear stress of the rotating boundary layer. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

As shown in FIG. 1 , it is a schematic flowchart of a method for measuring the wall shear stress of a rotating boundary layer in one embodiment. Specifically include the following steps:

Step 102, preset the probe. It should be noted that the pre-setting of the probe includes: fixing the boundary layer hot wire probe above the displacement mechanism through a support rod, and fixing the boundary layer hot wire probe at a preset distance from the rotating boundary layer wall.

Step 104: Measure the velocities of the rotating boundary layer wall at multiple different preset distances by using a preset probe, and transmit the multiple obtained measurement results.

In one embodiment, measuring the velocities at multiple different preset distances from the wall of the rotating boundary layer by using a preset probe includes: measuring the speed of a point closest to the wall of the rotating boundary layer by using a preset hot-line probe of the boundary layer Measurements are made and the velocity of the point farthest from the rotating boundary layer wall is measured by a pre-set boundary layer hot wire probe.

Further, a method for measuring the shear stress of a rotating boundary layer wall surface related to the present disclosure further includes: measuring a plurality of points between the nearest point and the farthest point from the rotating boundary layer wall surface through a preset boundary layer hot wire probe. The speed of the point is measured.

In addition, it should also be noted that the transmission of multiple acquired measurement results includes: multiple measurements to be acquired through the CTA (Constant Temperature Anemometer) module, the digital-to-analog conversion module, and the slip ring inducer in sequence The results are transferred to the computer. As a result, the efficiency and ease of use for the computer to acquire the measurement results in real time are improved.

Step 106: Select a linearly distributed velocity function in a region closest to the wall of the rotating boundary layer, and perform a linear fitting operation on the velocity function.

Step 108: Complete the measurement of the velocity gradient obtained by the linear fitting operation through translation, hypothesis estimation, and dimensionless operations in sequence.

In one embodiment, the method for measuring the wall shear stress of the rotating boundary layer involved in the present disclosure further includes: checking whether the coordinate points on the velocity function selected for performing the linear fitting operation are consistent with all pre-set coordinates The coordinate points within the range are all coincident; if the coordinate points on the velocity function selected for the linear fitting operation are coincident with all the coordinate points within the preset range, the velocity gradients obtained by the linear fitting operation are sequentially The wall shear stress of the rotating boundary layer obtained by translation and assumption estimation is the real wall shear stress of the rotating boundary layer.

In addition, it should be noted that the method for measuring the shear stress on the wall of the rotating boundary layer involved in the present disclosure further includes: if the coordinate points on the velocity function selected for the linear fitting operation are the same as all the pre-set coordinates The coordinate points within the range are not all coincident, and the velocity function of the coordinate points within the preset range is selected in turn through translation, assumption estimation and dimensionless circular operations until the real rotating boundary layer wall shear stress and its corresponding ordinate are obtained.

In order to further understand and apply a method for measuring the wall shear stress of the rotating boundary layer proposed by the present disclosure, the following example is carried out. It should be noted that the scope of protection of the present disclosure is not limited to the following examples.

Specifically, the present disclosure relates to the field of boundary layer velocity measurement of rotating turbomachinery, and in particular, to a method for measuring the wall shear stress of a rotating boundary layer based on a linear underlying assumption. The method for measuring the wall shear stress of the rotating boundary layer based on the assumption of a linear bottom layer includes the following steps:

First, the boundary layer probe is fixed on the displacement mechanism through the strut, and the probe is placed close to the wall, assuming that the distance from the wall is y ₀ ; The (ConstantTemperature Anemometer, constant temperature hot wire anemometer) module, small digital-to-analog conversion module and slip ring inducer are transferred to a stationary computer to measure the velocity (v ₀ ) of the first point near the wall, assuming the first point The distance between the probe and the wall is y ₀ .

Further, under the control of the displacement mechanism, move the hot wire probe away from the wall by a distance of Δy (y ₁ ), and measure the velocity v ₁ again; further, repeat the above process until enough principle wall is measured. The speed of the distance y _n , v _n .

It should be noted that, according to the speed (v ₀ , v ₁ ··· v _n ) and distance (y ₀ , y ₁ ··· y _n ) obtained above, a speed close to a linear distribution is selected in the region close to the wall surface (v _m ~ v _t ), perform linear fitting on it to obtain the velocity gradient; translate the y coordinate system (δy) so that the fitted straight line can pass through the origin (y' ₀ , y' ₁ ··· y' _n , where y ' ₀ =δy+y ₀ ).

v_m<v<v_t,y’_m<y’<y’_t)。需要说明的是，τ_w是壁面剪切应力，其中右上角标记符号代表的是第一次迭代的结果，且其中μ是流体的粘性系数。根据初步估计的壁面剪切应力对平移后的y坐标(y’₀,y’₁···y’_n)以及速度v(v₀,v₁···v_n)进行无量纲化，即获得无量纲的

需要说明的是，在获得无量纲的第一个结果中，其中y+代表的是无量纲的测点距离壁面距离，ρ代表密度，此处分母的v代表流体动力粘度；在获得无量纲的第二个结果中，U+代表无量纲的速度，其中，公式中的分子v代表速度。It is understandable that this velocity gradient is assumed to be the linear underlying velocity gradient, and the wall shear stress is preliminarily estimated based on this velocity gradient (

v _m <v<v _t ,y' _m <y'<y' _t ). It should be noted that τ _w is the wall shear stress, where the upper right corner symbol represents the result of the first iteration, and where μ is the viscosity coefficient of the fluid. According to the preliminarily estimated wall shear stress, the translated y-coordinates (y' ₀ , y' ₁ ··· y' _n ) and the velocity v (v ₀ , v ₁ ··· v _n ) are dimensionless, namely get dimensionless

It should be noted that, in obtaining the first dimensionless result, y+ represents the distance between the dimensionless measuring point and the wall, ρ represents the density, and v in the denominator here represents the hydrodynamic viscosity; In the two results, U+ represents the dimensionless velocity, where the numerator v in the formula represents the velocity.

Finally, check whether the coordinate points (v _m <v<v _t , y' _m <y'<y' _t ) on the velocity selected for fitting the straight line are within the range of 3.5<y ⁺ <5 The coordinate points are all coincident. If so, the previously obtained wall shear stress is the true wall shear stress, and the translated y-coordinate is the true y-coordinate. If not, select the velocity of all coordinate points in the range of 3.5 < y ⁺ < 5 and repeat the steps of translation, hypothesis estimation and calculation to obtain dimensionless until the true wall shear stress and y coordinate are obtained.

The invention provides a method for measuring the shear stress of a rotating boundary layer wall surface, wherein the probes are preset; The obtained multiple measurement results are transmitted; a linearly distributed velocity function is selected in the area closest to the wall of the rotating boundary layer, and a linear fitting operation is performed on the velocity function; the velocity gradient obtained by the linear fitting operation is sequentially translated, assuming Estimation and dimensionless operations complete the measurement. The method uses boundary layer hot wire probe, displacement mechanism, small CTA module, small digital-to-analog conversion module, slip ring inducer and computer to measure the boundary layer velocity under rotating conditions, and finally calculate the wall shear through the linear underlying assumption. stress. The method does not require any treatment on the wall surface and does not affect the flow near the wall surface, and can realize the measurement of the wall surface shear stress, which is simple and convenient; at the same time, it can realize the determination of the wall surface shear stress τw and the wall surface distance _y ; further, The adopted miniaturized test system can realize the measurement of wall shear stress under rotating conditions, and has high application efficiency and ease of use.

Based on the same inventive concept, a device for measuring the shear stress of the wall surface of the rotating boundary layer is also provided. Since the principle of the device to solve the problem is similar to the aforementioned method for measuring the shear stress of the wall of the rotating boundary layer, the implementation of the device can be implemented according to the specific steps of the aforementioned method, and the repetition will not be repeated.

As shown in FIG. 2 , it is a schematic structural diagram of a device for measuring the shear stress of a rotating boundary layer wall in one embodiment. The device 10 for measuring wall shear stress of a rotating boundary layer includes: a setting module 100 , a measurement and transmission module 200 , a fitting processing module 300 and a measurement module 400 .

Wherein, the setting module 100 is used to preset the probes; the measurement and transmission module 200 is used to measure the velocities at multiple different preset distances on the wall of the rotating boundary layer through the preset probes, and use the obtained multiple The measurement results are transmitted; the fitting processing module 300 is used to select a linearly distributed velocity function in the area closest to the wall of the rotating boundary layer, and perform a linear fitting operation on the velocity function; the measurement module 400 is used to obtain the linear fitting operation. The velocity gradient of is measured through translation, hypothesis estimation, and dimensionless operations in turn.

The invention provides a device for measuring the shear stress of the rotating boundary layer wall surface. First, the probe is preset through a setting module; Set the velocity at the distance to measure, and transmit the obtained multiple measurement results; again, through the fitting processing module, select a linearly distributed velocity function in the area closest to the wall of the rotating boundary layer, and perform linear fitting on the velocity function operation; finally, the velocity gradient obtained by the linear fitting operation is measured by the measurement module through translation, assumption estimation and dimensionless operation in sequence. The device uses the boundary layer hot wire probe, displacement mechanism, small CTA module, small digital-to-analog conversion module, slip ring inducer and computer to measure the boundary layer velocity under rotating conditions, and finally calculate the wall shear through the linear underlying assumption. stress. The method does not require any treatment on the wall surface and does not affect the flow near the wall surface, and can realize the measurement of the wall surface shear stress, which is simple and convenient; at the same time, it can realize the determination of the wall surface shear stress τw and the wall surface distance _y ; further, The adopted miniaturized test system can realize the measurement of wall shear stress under rotating conditions, and has high application efficiency and ease of use.

Embodiments of the present invention also provide a computer-readable storage medium. A computer program is stored on the computer-readable storage medium, and the program is executed by the processor in FIG. 1 .

Embodiments of the present invention also provide a computer program product including instructions. When the computer program product is run on a computer, the computer is caused to perform the method of FIG. 1 described above.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented by instructing relevant hardware through a computer program, and the program can be stored in a computer-readable storage medium. During execution, the processes of the embodiments of the above-mentioned methods may be included. The storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM), or a random access memory (Random Access Memory, RAM) or the like.

The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described. However, as long as there is no contradiction between the combinations of these technical features, All should be regarded as the scope described in this specification.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that, for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (3)

1. A method for measuring shear stress of a wall surface of a rotating boundary layer is characterized by comprising the following steps:

presetting a probe;

wherein the presetting of the probe comprises: fixedly arranging a boundary layer hot wire probe above the displacement mechanism through a support rod, and fixedly arranging the boundary layer hot wire probe at a preset distance on the wall surface of a rotating boundary layer;

measuring the speeds of a plurality of different preset distances on the wall surface of the rotating boundary layer through a preset probe, and transmitting a plurality of obtained measuring results;

wherein, the measuring the speed of a plurality of different preset distances of the rotating boundary layer wall surface through the preset probe comprises: measuring the speed of a point closest to the rotating boundary layer wall surface by a preset boundary layer heat ray probe, and measuring the speed of a point farthest from the rotating boundary layer wall surface by a preset boundary layer heat ray probe;

wherein the transmitting the obtained plurality of measurement results comprises: the obtained measurement results are transmitted to a computer sequentially through a constant-temperature hot-wire anemometer module, a digital-analog conversion module and a slip ring current-leading device;

selecting a section of linearly distributed speed function in a region closest to the wall surface of the rotating boundary layer, and performing linear fitting operation on the speed function;

the velocity gradient obtained by linear fitting operation is subjected to translation, hypothesis estimation and dimensionless operation in sequence to complete measurement;

further comprising: measuring the speed of a plurality of points in the middle of the nearest point and the farthest point of the rotating boundary layer wall surface by the preset boundary layer hot-wire probe;

further comprising: checking whether the coordinate points on the speed function selected for performing the linear fitting operation are all coincided with all coordinate points within a preset range; if the coordinate points on the speed function selected for the linear fitting operation are all overlapped with all coordinate points in a preset range, sequentially translating the speed gradient obtained by the linear fitting operation, and assuming that the obtained wall shear stress of the rotating boundary layer is estimated as real wall shear stress of the rotating boundary layer;

further comprising: if the coordinate points on the speed function selected for the linear fitting operation are not completely overlapped with all the coordinate points in the preset range, the speed function of the coordinate points in the preset range is selected to sequentially pass through translation, hypothesis estimation and dimensionless circulating operation until the real wall shear stress of the rotating boundary layer and the vertical coordinate corresponding to the wall shear stress are obtained;

wherein, the boundary layer probe is fixed on the displacement mechanism through the support rod, and the probe is arranged at a position close to the wall surface, and the assumed distance from the wall surface is y₀(ii) a Near the wall for probe measurementsThe speed is transmitted to a stationary computer through a small constant-temperature hot-wire anemometer module, a small digital-to-analog conversion module and a slip ring current-leading device, so that the speed v of a first point near the wall surface is realized₀Assuming that the first point probe is close to the wall surface by a distance y₀；

Under the control of the displacement mechanism, the hot wire probe is moved to a position far away from the wall surface by a distance of delta y to obtain y₁Measuring the velocity v again₁；

The above process is repeated until a velocity v is measured which is sufficiently far from the wall surface_n；

Selecting a section of speed close to linear distribution in the area close to the wall surface according to the obtained speed and distance, and performing linear fitting on the speed to obtain a speed gradient;

translating the y-coordinate system so that the fitted straight line can pass through the origin;

assuming that the velocity gradient is a linear bottom velocity gradient, and preliminarily estimating the wall shear stress according to the velocity gradient

τ_wIs the wall shear stress, where the top right hand corner symbol represents the result of the first iteration, and where μ is the viscosity coefficient of the fluid;

dimensionless is carried out on the translated y coordinate and the velocity v according to the preliminarily estimated wall shear stress, namely dimensionless is obtained

In the first result of obtaining dimensionless, where y + represents the distance of the dimensionless measuring point from the wall, ρ represents the density, and v in the denominator represents the hydrodynamic viscosity; in obtaining a second result that is dimensionless, U + represents a dimensionless velocity, wherein the numerator v in the formula represents the velocity;

checking if the coordinate points at the speed chosen for fitting the line lie with all points at 3.5 < y⁺All coordinate points within the range of less than 5 coincide; if so, itThe wall surface shear stress obtained in the previous step is the real wall surface shear stress, and the y coordinate after translation is the real y coordinate; if not, all are selected to be 3.5 < y⁺And repeating the steps of translating, supposing estimation and calculating to obtain dimensionless coordinates at the speed of the coordinate point within the range of less than 5 until the real wall shear stress and the y coordinate are obtained.

2. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method as claimed in claim 1.

3. A computer device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, wherein the steps of the method of claim 1 are implemented when the program is executed by the processor.

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