A transient flow field uniformity evaluation method

Abstract

The present invention discloses a method for evaluating the uniformity of a transient flow field, and belongs to the field of fluid mechanics. The method records the flow velocity at two time points before and after each monitoring point in the flow field, divides the flow velocity difference by the time interval to obtain the velocity change rate, and uses the flow velocity change rate of each monitoring point as a sample to solve the standard deviation. The evaluation method can reflect the degree of deviation of the fluid flow velocity change rate at each position in the transient flow field from its average value, and can measure the uniformity of the flow velocity change rate of the flow field at a certain moment. The transient flow field uniformity measuring device includes a fluid flow velocity information recorder, a flow velocity signal processor, an external power supply, a test flow channel, and the like. When the fluid flows through the flow velocity information recorder, the fluid impact causes the rotor on the flow velocity information recorder to rotate, and the magnetic sensors around the rotor capture the rotation speed information of the magnet on the rotor. The information recorded by the flow velocity information recorder is transmitted to the flow velocity signal processor via a data line to obtain the flow velocity, providing a data source for calculating the uniformity of the transient flow field.

Description

Technical Field

[0001] The invention belongs to the field of fluid mechanics, and in particular relates to an evaluation method capable of measuring the uniformity of flow velocity change rate at a certain moment. Background Art

[0002] Flow field uniformity is of great significance in valves, cooling systems, denitrification systems, engines, wind tunnels, agricultural irrigation systems, and other fields. If the flow field in the cooling system is highly non-uniform, this will lead to inconsistent operating conditions in various parts of the cooling system, resulting in reduced cooling system efficiency. The uniformity of flue gas concentration in the catalyst layer of the denitrification system will also affect denitrification efficiency. To address this issue, a transient flow field uniformity evaluation method and measurement device are needed to comprehensively reflect the distribution characteristics and discreteness of the dynamic velocity change rate of the entire transient flow channel, providing a basis for mitigating or eliminating flow field non-uniformity.

[0003] In transient, unsteady flow fields, the velocity and rate of change of the fluid at each location within the flow field vary but conform to the laws of fluid mechanics. Therefore, the distribution of the rate of change of the fluid velocity at different locations within the flow field is an important evaluation criterion for flow field uniformity. Traditional flow field uniformity evaluation methods, however, primarily focus on the distribution of fluid velocity at each location at a given moment, or the discreteness of the velocity relative to the average velocity of the flow field, but lack an examination of velocity variations within the flow field.

[0004] The transient flow field uniformity measurement device sets up several monitoring points in the flow field, measures and records the velocity values at two time points before and after each monitoring point, divides the velocity difference by the time interval to obtain the velocity change rate, and uses the velocity change rate of each monitoring point as a sample to solve the standard deviation. Through subsequent mathematical conversion, an evaluation method for transient flow field uniformity is obtained. Summary of the Invention

[0005] The main focus of traditional flow field uniformity evaluation methods is on the distribution of fluid velocity at each position in the flow field at a certain moment, or the discreteness between the flow velocity and the average flow velocity of the flow field, and there is a lack of examination of the change in flow field velocity. The purpose of the present invention is to overcome the defects in the prior art and provide a transient flow field uniformity evaluation method. The evaluation method can record the flow velocity at two time points before and after each monitoring point in the flow field, divide the flow velocity difference by the time interval to obtain the velocity change rate, and use the flow velocity change rate of each monitoring point as a sample to solve the standard deviation. The standard deviation is a measure of the degree of dispersion of the average value of a set of data. A larger standard deviation means that there is a large difference between most values and their average value; a smaller standard deviation means that these values are closer to the average value. Therefore, the present invention can achieve the evaluation of the uniformity of the flow velocity change rate at a certain moment through the standard deviation.

[0006] The specific technical solutions adopted in the present invention are as follows:

[0007] The present invention provides a method for evaluating transient flow field uniformity, which is as follows:

[0008] S1: Set n measurement points at the same section of the target flow channel, and each measurement point is numbered M i , where i∈[1,n], n>1; a fluid flow rate information recorder is set at each measurement point;

[0009] S2: Based on the following formula, the speed information N measured by each fluid flow rate information recorder is obtained through numerical simulation method. i and the flow velocity V i The relationship between

[0010] V i =c i *N i

[0011] Where c i is the coefficient;

[0012] S3: Use the fluid flow rate information recorder to measure and record the first flow rate information V of each measurement point i1 After a time interval t, the second flow velocity information V of each measuring point is measured and recorded using the fluid flow velocity information recorder i2 , use the following formula to calculate the fluid velocity change rate A at each measuring point i ;

[0013] A i =(V i2 -V i1 ) / t

[0014] S4: Calculate the average flow velocity of the fluid at the same section of the target flow channel before and after the time interval t according to the following formula:

[0015] V m1 =(V 11 +V 21 +V 31 +…+V n1 ) / n

[0016] V m2 =(V 12 +V 22 +V 32 +…+V n2 ) / n

[0017] Where V m1 is the average velocity of the fluid at the section before time interval t, V m2 is the average flow velocity of the fluid at the section after time interval t;

[0018] S5: According to the following formula, the average flow rate change rate A of the fluid in the time interval t is obtained m ,

[0019] A m =(V m1 -V m2 ) / t

[0020] S6: The standard deviation S of the flow rate change rate at each measuring point is obtained according to the following formula:

[0021]

[0022] S7: The transient flow field uniformity TFU of the target flow channel is obtained according to the following formula:

[0023] TFU=S / A m .

[0024] Preferably, the fluid flow rate information recorder includes a pipeline, a rotor, a rotor magnet and a magnetic sensor; the pipeline has a structure with a gradually narrowing inlet, a cylindrical middle part and a gradually widening outlet, and a three-section continuous measuring flow channel is formed inside; a groove is opened at the top of the middle cylindrical section, and a rotor is installed in the groove, and a number of blades are provided on the outer periphery of the rotor, and the blades do not interfere with the inner wall of the groove; some of the blades located at the bottom extend out of the groove and are located in the measuring flow channel, and can be driven by the fluid to drive the blades to rotate the rotor; a magnetic sensor is also installed in the groove, and a rotor magnet is provided at the outer end of a blade, which can generate a periodic signal when the rotor magnet passes through the magnetic sensor.

[0025] Furthermore, the lengths of the inlet gradually converging section and the outlet gradually expanding section of the pipeline are equal.

[0026] Furthermore, the blades on the outer periphery of the rotor are evenly distributed.

[0027] Furthermore, the step S2 is specifically as follows:

[0028] S21: using 3D modeling software to establish a 3D model of the fluid flow rate information recorder and obtain a flow channel model;

[0029] S22: importing the flow channel model into meshing software to perform meshing;

[0030] S23: importing the meshed flow channel model into computational fluid dynamics software, and using the computational fluid dynamics software to simulate and obtain the rotor speed at different inlet flow rates;

[0031] S24: Divide the inlet flow rate by the corresponding rotor speed to obtain the coefficient c i .

[0032] Preferably, each of the fluid flow rate information recorders is connected to a flow rate signal processor and is powered by an external power supply.

[0033] Preferably, the measuring points are evenly distributed on the same section.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) The present evaluation method targets transient, unsteady flow fields. By recording the flow velocity at two time points before and after each monitoring point in the flow field, the velocity change rate is calculated by dividing the velocity difference by the time interval. The standard deviation of the velocity change rate at each monitoring point is then calculated to obtain the transient flow field uniformity (TFU). This method comprehensively reflects the distribution and dispersion of the dynamic velocity change rate of the entire transient flow channel. The present calculation process is simple and easy to understand.

[0036] 2) The measuring device of the present invention has strong pertinence, compact structure, simple manufacturing and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the measuring device.

[0038] Figure 2 Schematic diagram of the flow rate information recorder.

[0039] Figure 3 Schematic diagram of the evaluation method flow chart.

[0040] In the figure: 1 target flow channel; 2 fluid flow rate information recorder; 3 flow rate signal processor; 4 external power supply; 5 pipeline; 6 rotor; 7 rotor magnet; 8 magnetic sensor. DETAILED DESCRIPTION

[0041] The present invention will be further described and illustrated below with reference to the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention may be combined accordingly, provided that there is no conflict between them.

[0042] The present invention provides a transient flow field uniformity evaluation method, which can record the flow velocity at two time points before and after each monitoring point in the flow field, divide the flow velocity difference by the time interval to obtain the velocity change rate, and use the flow velocity change rate of each monitoring point as a sample to solve the standard deviation.

[0043] In order to facilitate the implementation of the above evaluation method, the present invention first designs a transient flow field uniformity measurement device. Figure 1As shown, the measuring device mainly includes a target flow channel 1, a fluid flow rate information recorder 2, a flow rate signal processor 3 and an external power supply 4. In actual application, the target flow channel 1 has different structures, boundary conditions and fluid media depending on the research object, and then different measurement point arrays are set for target flow channels 1 with different shapes. The measurement point array contains multiple measurement points, all of which should be located at the same section of the target flow channel 1, and a fluid flow rate information recorder 2 is set at each measurement point. The flow rate signal processor 3 is placed outside the target flow channel 1 and is connected to each fluid flow rate information recorder 2 through a data line for data transmission. The external power supply 4 is placed outside the target flow channel 1 and supplies power to the flow rate signal processor 3 and each fluid flow rate information recorder 2 through a power line.

[0044] In this embodiment, the fluid flow rate information recorder 2 adopts the following method: Figure 2 The structure shown mainly includes a pipe 5, a rotor 6, a rotor magnet 7 and a magnetic sensor 8. The pipe 5 is a structure with a gradually narrowing inlet, a cylindrical middle part and a gradually widening outlet, and a three-section continuous measuring flow channel is formed inside. A groove is provided at the top of the middle cylindrical section, and the rotor 6 is fixed in the groove by a rotating shaft. A number of blades are provided on the outer periphery of the rotor 6, and the blades do not interfere with the inner wall of the groove. Some of the blades located at the lower part of the rotor 6 extend out of the groove and are located in the measuring flow channel. Each blade is tilted to one side so that when the fluid flows through the pipe 5, the blades can be driven by the action of the fluid to drive the rotor 6 to rotate. A magnetic sensor 8 is also installed in the groove, and a rotor magnet 7 is provided at the outer end of a blade on the rotor 6. The magnetic sensor is fixed around the rotor to facilitate receiving the magnet periodic signal generated by the rotation of the rotor.

[0045] In this embodiment, the target flow channel is a sideways standard cylinder with an inner diameter of 1000 mm and an outer diameter of 1050 mm. The left side of the cylinder is the inlet, and the right side is the outlet. The fluid is liquid water. The inlet boundary condition is a pressure of 0.8 MPa, and the outlet boundary condition is a pressure of 0 MPa. The number of measurement points and fluid flow rate information recorders is 8, and the number of rotor blades is 8. The target flow channel is surrounded by openings, through which a data cable is inserted to connect the fluid flow rate information recorder to the flow rate signal processor. The target flow channel opening is sealed with packing, and the fluid flow rate information recorder is fixed in the fluid by a slender cylindrical support.

[0046] like Figure 3 As shown, the present invention provides a method for evaluating the uniformity of a transient flow field using the above-mentioned measuring device, which is specifically as follows:

[0047] S1: Set n measurement points at the same section of the target flow channel 1, and each measurement point is numbered M i , where i∈[1,n], n>1.

[0048] In this embodiment, the number of measurement points n is 8, and each measurement point is numbered M1, M2, M3...M8. Then, a fluid flow rate information recorder is installed at each measurement point, such as Figure 1 The flow rate information recorders 2 installed at the measuring points M1, M2, M3…M8 are connected to the signal processor 3 and powered by the external power supply 4.

[0049] S2: Through numerical simulation method, the speed information N measured by each fluid flow rate information recorder 2 is obtained i and the flow velocity V i The relationship between:

[0050] V i =c i *N i

[0051] Where c i is the coefficient.

[0052] In this embodiment, the steps are as follows:

[0053] S21: Using three-dimensional modeling software to build a three-dimensional model of the fluid flow rate information recorder 2 and obtain a flow channel model.

[0054] S22: Import the flow channel model into the meshing software and perform meshing.

[0055] S23: Importing the meshed flow channel model into computational fluid dynamics software, and using the computational fluid dynamics software to simulate and obtain the rotational speed of the rotor 6 at different inlet flow rates.

[0056] S24: Divide the inlet flow rate by the corresponding rotor 6 speed to obtain the coefficient c i Then, the speed N of the flow rate information recorder is calculated by the following formula: i and coefficient c i Calculate the flow velocity V at this location i :

[0057] V i =c i *N i .

[0058] S3: Then, actual measurement is performed. First, the fluid flow rate information recorder 2 is used to measure the first flow rate information V of each measurement point. i1 The signal is transmitted to the signal processor 3 and recorded by the computer. Then after a time interval t (t value is determined by yourself), the second flow velocity information V of each measuring point is measured by the fluid flow velocity information recorder 2. i2 , the signal is passed to the signal processor 3 and recorded by a computer.

[0059] In this embodiment, the first flow rate information is V 11 、V 21 、V 31 …V 81 , the second flow rate information is V 12 、V 22 、V 32 …V 82 .

[0060] Then the fluid velocity change rate A at each measuring point is calculated using the following formula: i :

[0061] A i =(V i2 -V i1 ) / t.

[0062] S4: Calculate the average flow velocity of the fluid at the same section of the target flow channel 1 before and after the time interval t according to the following formula:

[0063] V m1 =(V 11 +V 21 +V 31 +…+V n1 ) / n

[0064] V m2 =(V 12 +V 22 +V 32 +…+V n2 ) / n

[0065] Where V m1 is the average velocity of the fluid at the section before time interval t, V m2 is the average flow velocity of the fluid at the section after time interval t.

[0066] S5: According to the following formula, the average flow rate change rate A of the fluid in the time interval t is obtained m :

[0067] A m =(V m1 -V m2 ) / t.

[0068] S6: The standard deviation S of the flow rate change rate at each measuring point is obtained according to the following formula:

[0069]

[0070] S7: Obtain the transient flow field uniformity TFU of the target flow channel 1 according to the following formula:

[0071] TFU=S / A m .

[0072] The method of the present invention records the flow velocity at two time points before and after each monitoring point in the flow field, divides the flow velocity difference by the time interval to obtain the velocity change rate, and uses the flow velocity change rate of each monitoring point as a sample to solve the standard deviation. This evaluation method can reflect the degree of deviation of the fluid flow velocity change rate at each position in the transient flow field from its average value, and can measure the uniformity of the flow velocity change rate of the flow field at a certain moment. The transient flow field uniformity measurement device includes a fluid flow velocity information recorder, a flow velocity signal processor, an external power supply, a test flow channel, and the like. When the fluid flows through the flow velocity information recorder, the fluid impact causes the rotor on the flow velocity information recorder to rotate, and the magnetic sensors around the rotor capture the rotation speed information of the magnet on the rotor. The information recorded by the flow velocity information recorder is transmitted to the flow velocity signal processor via a data line to obtain the flow velocity, providing a data source for calculating the transient flow field uniformity.

[0073] The embodiment described above is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Persons skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of protection of the present invention.

Claims

1. A transient flow field uniformity evaluation method, characterized in that: The details are as follows: S1: Set n measurement points at the same section of the target flow channel (1), and each measurement point is numbered M i , where i∈[1,n], n>1; a fluid flow rate information recorder (2) is set at each measuring point; S2: Through numerical simulation method, the speed information N measured by each fluid flow rate information recorder (2) is obtained i The flow velocity V i The relationship between: V i =c i *N i Where c i is the coefficient; S3: Use the fluid flow rate information recorder (2) to measure and record the first flow rate information V of each measurement point i1 After a time interval t, the second flow velocity information V of each measuring point is measured and recorded using the fluid flow velocity information recorder (2). i2 , use the following formula to calculate the fluid velocity change rate A at each measuring point i ; A i =(V i2 -V i1 ) / t S4: Calculate the average flow velocity of the fluid at the same section of the target flow channel (1) before and after the time interval t according to the following formula: V m1 =(V 11 +V 21 +V 31 +…+V n1 ) / n V m2 =(V 12 +V 22 +V 32 +…+V n2 ) / n Where V m1 is the average velocity of the fluid at the section before time interval t, V m2 is the average flow velocity of the fluid at the section after time interval t; S5: According to the following formula, the average flow rate change rate A of the fluid in the time interval t is obtained m , A m =(V m1 -V m2 ) / t S6: The standard deviation S of the flow rate change rate at each measuring point is obtained according to the following formula: S7: Obtain the transient flow field uniformity TFU of the target flow channel (1) according to the following formula: TFU=S / A m 。 2. A transient flow field uniformity evaluation method according to claim 1, characterized in that: The fluid flow rate information recorder (2) comprises a pipe (5), a rotor (6), a rotor magnet (7) and a magnetic sensor (8); the pipe (5) is a structure with a gradually converging inlet, a cylindrical middle section and a gradually expanding outlet, and a three-section continuous measuring flow channel is formed inside; a groove is provided at the top of the middle cylindrical section, a rotor (6) is installed in the groove, and a plurality of blades are provided on the outer periphery of the rotor (6), and the blades do not interfere with the inner wall of the groove; some of the blades located at the bottom extend out of the groove and are located in the measuring flow channel, and can drive the blades to drive the rotor (6) to rotate under the action of the fluid; a magnetic sensor (8) is also installed in the groove, and a rotor magnet (7) is provided at the outer end of a blade, and a periodic signal can be generated when the rotor magnet (7) passes through the magnetic sensor (8).

3. A transient flow field uniformity evaluation method according to claim 2, characterized in that: The inlet gradually contracting section and the outlet gradually expanding section of the pipeline (5) are equal in length.

4. The method for evaluating transient flow field uniformity according to claim 2, wherein: The blades on the outer periphery of the rotor (6) are evenly distributed.

5. The method for evaluating transient flow field uniformity according to claim 1, wherein: Each of the fluid flow rate information recorders (2) is connected to a flow rate signal processor (3) and is powered by an external power supply (4).

6. The method for evaluating transient flow field uniformity according to claim 2, wherein: The step S2 is specifically as follows: S21: using three-dimensional modeling software to establish a three-dimensional model of the fluid flow rate information recorder (2) and obtain a flow channel model; S22: importing the flow channel model into meshing software to perform meshing; S23: importing the meshed flow channel model into computational fluid dynamics software, and using the computational fluid dynamics software to simulate and obtain the rotational speed of the rotor (6) at different inlet flow rates; S24: Divide the inlet flow rate by the corresponding rotor (6) speed to obtain the coefficient c i .

7. The method for evaluating transient flow field uniformity according to claim 1, wherein: The measuring points are evenly distributed on the same section.

Images