CN108955981A - Suitable for rotation boundary layer wall surface shear stress measurement method and device - Google Patents

Abstract

The invention discloses one kind to be suitable for rotation boundary layer wall surface shear stress measurement method, presets to probe；The speed at the rotation multiple and different pre-determined distances of boundary layer wall surface is measured by pre-set probe, the multiple measurement results that will acquire are transmitted；The velocity function that one section of linear distribution is selected in the nearest region of distance rotation boundary layer wall surface, to velocity function linear fit；Measurement is completed by translation, hypothesis estimation and nondimensionalization operation to the velocity gradient that linear fit operation obtains.This method do not need to carry out any processing to wall surface, does not influence near wall flowing, it can be achieved that cut off the measurement of stress to wall surface, simple and convenient；It can be realized simultaneously wall surface and cut off stress τ_wAnd the determination of wall surface distance y；The miniaturization test macro of use may be implemented the measurement of rotating condition lower wall surface shear stress, and have the high efficiency and ease for use of application.The invention also discloses be suitable for rotation boundary layer wall surface shear stress measuring device.

Description

Method and device for measuring wall shear stress of rotating boundary layer

technical field

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

Background technique

In the study of rotating machinery, wall shear stress is a very important quantity. Under normal static conditions, due to the large installation space, various methods can be used to measure the 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 wall shear stress generally uses a thin film sensor to measure the shear stress on the wall, but in order to prevent the influence of the thin film sensor on the flow of the wall, a groove is generally opened on the wall, and the thin film sensor is buried in the groove, and ensure The outer surface of the thin film sensor is flush with the wall surface, thereby eliminating the influence on the flow near the wall surface. However, this method requires special groove treatment on the wall surface of the channel, which is relatively complicated; especially when the wall surface is heated, because a heating device needs to be arranged, this method is more difficult to implement.

Contents of the invention

Based on this, it is necessary to provide a method and device suitable for measuring the wall shear stress of the rotating boundary layer for the problems existing in the traditional technology. Specifically, in this disclosure, in order to solve the problem of wall shear stress measurement in rotating machinery, this disclosure proposes a method for measuring wall shear stress applicable to rotating boundary layers, specifically, the rotating boundary layer wall surface based on the assumption of a linear bottom layer Shear stress measurement method. This method uses a boundary layer hot wire probe, a displacement mechanism, a small CTA module, a small digital-to-analog conversion module, a slip ring lead, and a computer to measure the boundary layer velocity under rotating conditions, and finally calculates the wall shear through the assumption of a linear bottom layer. 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 τ _w and the wall distance y can be realized ; Furthermore, the miniaturized test system adopted can realize the measurement of the wall shear stress under the rotating condition.

In the first aspect, the embodiment of the present invention provides a method suitable for measuring the shear stress of the wall surface of the rotating boundary layer. The method includes: pre-setting the probe; measure the velocity 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 sequentially measured through translation, hypothesis estimation and non-dimensionalization operations.

In one of the embodiments, the preset 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 on the rotating boundary layer wall preset Set the distance.

In one of the embodiments, the measuring the velocity at multiple preset distances from the wall of the rotating boundary layer through the preset probe includes: measuring the distance from the wall of the rotating boundary layer through the preset hot wire probe Velocity is measured at the nearest point and at the point furthest from the rotating boundary layer wall by a pre-set boundary layer hot wire probe.

In one of the embodiments, the method further includes: measuring the velocity of multiple points between the closest point and the farthest point from the wall surface of the rotating boundary layer by using the pre-set 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 lead.

In one of the embodiments, it also includes: checking whether the coordinate points on the velocity function selected for the linear fitting operation coincide with all the coordinate points within the 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 then the velocity gradient obtained by the linear fitting operation is sequentially acquired through translation and hypothetical estimation The wall shear stress of the rotating boundary layer is the real wall shear stress of the rotating boundary layer.

In one of the embodiments, it also includes: if the coordinate points on the speed function selected for the linear fitting operation do not coincide with all the coordinate points within the preset range, selecting the preset The velocity function of the coordinate points within the set range is sequentially operated through translation, hypothesis estimation and non-dimensionalization until the real wall shear stress of the rotating boundary layer and its corresponding ordinate are obtained.

In the second aspect, an embodiment of the present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the above-mentioned first aspect applicable to the rotation boundary can be realized. Method for measuring shear stress on layer wall.

In a third aspect, an embodiment of the present invention provides a computer program product including instructions, and when the computer program product is run on a computer, it causes the computer to execute the method described in the first aspect above.

In the fourth aspect, the embodiment of the present invention also provides a device suitable for measuring the shear stress of the wall surface of the rotating boundary layer, the device includes: a setting module, used to pre-set the probe; a measurement and transmission module, used to pass The preset probe measures the velocity at multiple preset distances from the wall of the rotating boundary layer, and transmits the obtained multiple measurement results; the fitting processing module is used for Select a section of linearly distributed velocity function in the region, and perform a linear fitting operation on the velocity function; the measurement module is used to measure the velocity gradient obtained by the linear fitting operation through translation, hypothesis estimation, and dimensionless operation in sequence.

The present invention provides a method and device suitable for measuring the shear stress of the wall surface of the rotating boundary layer. The probe is preset; the velocity at multiple preset distances on the wall surface of the rotating boundary layer is measured by the preset probe, And transmit the multiple measurement results obtained; 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 passed through translation , hypothetical estimation, and dimensionless operations to complete the measurement. This method uses a boundary layer hot wire probe, a displacement mechanism, a small CTA module, a small digital-to-analog conversion module, a slip ring lead, and a computer to measure the boundary layer velocity under rotating conditions, and finally calculates the wall shear through the assumption of a linear bottom layer. 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 τ _w and the wall distance y can be realized ; Further, the adopted miniaturized test system can realize the measurement of the wall shear stress under the rotating condition, and has high efficiency and ease of use.

Description of drawings

Fig. 1 is a schematic flow chart of a method for measuring wall shear stress of a rotating boundary layer in one embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a device suitable for measuring wall shear stress of a rotating boundary layer in an embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the specific implementation of the present invention, which is applicable to the method and device for measuring the wall shear stress of the rotating boundary layer, will be further described in detail through the following examples and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

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

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

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

In one embodiment, using a preset probe to measure the velocity at multiple preset distances from the wall of the rotating boundary layer includes: measuring the velocity of a point closest to the wall of the rotating boundary layer using a preset hot wire probe of the boundary layer Measurements are taken, as well as the velocity at the point farthest from the rotating boundary layer wall by a pre-set boundary layer hot wire probe.

Further, the method for measuring the shear stress of the wall surface of the rotating boundary layer according to the present disclosure further includes: using a pre-set boundary layer hot wire probe to pair a plurality of The velocity of the point is measured.

In addition, it should also be noted that the transmission of multiple measurement results obtained includes: multiple measurements that will be obtained through the CTA (Constant Temperature Anemometer, constant temperature hot wire anemometer) module, digital-to-analog conversion module, and slip ring lead-in device in turn. The results are transferred to a computer. As a result, the efficiency and ease of use of the computer for real-time acquisition of measurement results are improved.

Step 106, select a section of 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.

In step 108, the velocity gradient acquired by the linear fitting operation is sequentially measured through translation, hypothesis estimation, and dimensionless operations.

In one embodiment, the method for measuring the wall shear stress of the rotating boundary layer according to the present disclosure further includes: checking whether the coordinate points on the velocity function selected for the linear fitting operation are consistent with all the preset The coordinate points within the range are all coincident; if the coordinate points on the velocity function selected for the linear fitting operation coincide with all the coordinate points within the preset range, then the velocity gradient obtained by the linear fitting operation is 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 a method for measuring the wall shear stress of the rotating boundary layer involved in the present disclosure also includes: if the coordinate points on the velocity function selected for the linear fitting operation are all in the preset The coordinate points in the range are not all coincident, and the velocity function of the coordinate points in the preset range is selected through translation, assumption estimation and non-dimensionalization cycle operation until the real wall shear stress of the rotating boundary layer and its corresponding ordinate are obtained.

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

Specifically, the present disclosure relates to the field of velocity measurement of the boundary layer of a rotating turbomachinery, and in particular to a method for measuring wall shear stress of a rotating boundary layer based on a linear bottom layer 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 support rod, and the probe is placed close to the wall, assuming that the distance from the wall is y ₀ ; secondly, the velocity near the wall measured by the probe is measured by a small CTA (ConstantTemperature Anemometer, constant temperature hot-wire anemometer) module, small digital-to-analog conversion module and slip ring leads are transmitted to the static computer to realize the measurement of 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 △y (y ₁ ), and measure the velocity v ₁ again; furthermore, repeat the above process until a sufficient wall surface is measured. The speed y _n ,v _n of the distance.

It should be noted that, through the velocity (v ₀ , v ₁ ···v _n ) and distance (y ₀ , y ₁ ···y _n ) obtained above, select a section of velocity close to the linear distribution in the area close to the wall (v _m ～v _t ), linearly fit it to obtain the velocity gradient; translate the y coordinate system (δy), so that the fitted line can pass through the origin (y' ₀ ,y' ₁ ···y' _n , where y ' ₀ =δy+y ₀ ).

It is understandable that the velocity gradient is assumed to be a linear bottom 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 symbol in the upper right corner represents the result of the first iteration, and where μ is the viscosity coefficient of the fluid. According to the preliminary estimated wall shear stress, the translated y-coordinate (y' ₀ ,y' ₁ ···y' _n ) and velocity v(v ₀ ,v ₁ ···v _n ) are dimensionless, namely get dimensionless It should be noted that, in the first dimensionless result, y+ represents the dimensionless distance from the measuring point to 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, and the numerator v in the formula represents the velocity.

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

The present invention provides a method suitable for measuring the shear stress of the wall surface of the rotating boundary layer. The probe is preset; the velocity at multiple preset distances on the wall surface of the rotating boundary layer is measured through the preset probe, and the The multiple measurement results obtained are transmitted; a velocity function with linear distribution 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 passed through translation, assumption Estimation as well as dimensionless operations are performed on measurements. This method uses a boundary layer hot wire probe, a displacement mechanism, a small CTA module, a small digital-to-analog conversion module, a slip ring lead, and a computer to measure the boundary layer velocity under rotating conditions, and finally calculates the wall shear through the assumption of a linear bottom layer. stress. This 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 shear stress, which is simple and convenient; at the same time, it can realize the determination of the wall shear stress τ _w and the wall distance y; further, The miniaturized test system adopted can realize the measurement of wall shear stress under rotating conditions, and has high efficiency and ease of use.

Based on the same inventive concept, a device suitable for measuring wall shear stress of a rotating boundary layer is also provided. Since the problem-solving principle of this device is similar to the aforementioned method for measuring the wall shear stress of the rotating boundary layer, the implementation of the device can be realized 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 suitable for measuring wall shear stress of a rotating boundary layer in an embodiment. The device 10 suitable 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 .

Among them, the setting module 100 is used to pre-set the probe; the measurement and transmission module 200 is used to measure the velocity at multiple preset distances on the wall surface of the rotating boundary layer through the preset probe, and the obtained multiple The measurement results are transmitted; the fitting processing module 300 is used to select a section of linearly distributed velocity function in the area closest to the wall of the rotating boundary layer, and performs 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 sequentially through translation, assumption estimation, and dimensionless operations.

The present invention provides a device suitable for measuring the shear stress of the wall surface of the rotating boundary layer. Firstly, the probe is preset through the 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 finally measured by the measurement module through translation, hypothesis estimation and non-dimensionalization operations. The device uses a boundary layer hot wire probe, a displacement mechanism, a small CTA module, a small digital-to-analog conversion module, a slip ring lead, and a computer to measure the boundary layer velocity under rotating conditions, and finally calculates the wall shear through the assumption of a linear bottom layer. stress. This 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 shear stress, which is simple and convenient; at the same time, it can realize the determination of the wall shear stress τ _w and the wall distance y; further, The miniaturized test system adopted can realize the measurement of wall shear stress under rotating conditions, and has high efficiency and ease of use.

The embodiment of the present invention also provides 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 .

The embodiment of the present invention also provides a computer program product including instructions. When the computer program product is run on the computer, the computer is made to execute the above-mentioned method in FIG. 1 .

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 through computer programs to instruct related hardware, and the programs can be stored in a computer-readable storage medium. During execution, it may include the processes of the embodiments of the above-mentioned methods. Wherein, 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) and the like.

The technical features of the above-mentioned embodiments can be combined arbitrarily. To make the description concise, all possible combinations of the technical features in the above-mentioned embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, should be considered as within the scope of this specification.

The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (10)

1. A method for measuring wall shear stress applicable to rotating boundary layers, is characterized in that, the method comprises: Preset the probe; Using the preset probe to measure the velocity at multiple preset distances on the wall surface of the rotating boundary layer, and transmit the obtained multiple measurement results; Select a section of velocity function with linear distribution in the area nearest 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 measured through translation, hypothesis estimation, and dimensionless operation. 2. The method for measuring wall shear stress suitable for rotating boundary layers according to claim 1, wherein said presetting the probe comprises: fixing the boundary layer hot wire probe above the displacement mechanism through a support rod , and the boundary layer hot wire probe is fixedly arranged at a preset distance from the wall surface of the rotating boundary layer. 3. according to claim 1, be applicable to rotating boundary layer wall shear stress measuring method, it is characterized in that, described by the described probe that presets to the velocity at a plurality of different preset distances of rotating boundary layer wall Measurements include: measurement of the velocity at the point closest to the wall of the rotating boundary layer by a pre-set boundary layer hot-wire probe, and measurement of the velocity of a point farthest from the wall of the rotating boundary layer by a pre-set hot-wire probe of the boundary layer . 4. according to claim 3, be applicable to rotating boundary layer wall shear stress measurement method, it is characterized in that, also comprise: through described boundary layer hot-wire probe set in advance to distance the described nearest point of rotating boundary layer wall The velocities of multiple points intermediate to the furthest point are measured. 5. The method for measuring wall shear stress applicable to rotating boundary layers according to claim 1, wherein said transmitting a plurality of measurement results obtained comprises: The multiple measurement results obtained are transmitted to the computer through the CTA module, the digital-to-analog conversion module and the slip ring lead in sequence. 6. The method for measuring wall shear stress applicable to rotating boundary layers according to claim 1, further comprising: checking whether the coordinate point on the selected velocity function for carrying out the linear fitting operation is It coincides with all the coordinate points within the preset range; If the coordinate points on the velocity function selected for the linear fitting operation coincide with all the coordinate points within the preset range, the velocity gradient obtained by the linear fitting operation is sequentially translated , assuming that the estimated wall shear stress of the rotating boundary layer is the real wall shear stress of the rotating boundary layer. 7. the method for measuring wall shear stress applicable to rotating boundary layers according to claim 6, further comprising: if the coordinate point on the selected velocity function is used for carrying out the linear fitting operation and All the coordinate points within the preset range are not all coincident, and the velocity function for selecting the coordinate points within the preset range is sequentially operated through translation, hypothesis estimation, and dimensionless loop operations until the real rotation is obtained. Boundary layer wall shear stress and its corresponding ordinate. 8. A computer-readable storage medium, on which a computer program is stored, wherein when the program is executed by a processor, the steps of the method according to any one of claims 1-7 are implemented. 9. A computer device, comprising a memory, a processor, and a computer program stored on the memory and operable on the processor, characterized in that, when the processor executes the program, it implements claims 1-7 The steps of any one of the methods. 10. A device for measuring wall shear stress of a rotating boundary layer, characterized in that the device comprises: A setting module is used to pre-set the probe; The measurement and transmission module is used to measure the velocity at multiple preset distances on the wall surface of the rotating boundary layer through the preset probe, and transmit the obtained multiple measurement results; The fitting processing module is used to select a section of 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 is used to measure the velocity gradient obtained by the linear fitting operation through translation, assumption estimation and dimensionless operation in sequence.