CN111537135A - Dynamic pressure field test method based on wall heat exchange characteristics - Google Patents
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Abstract
The invention provides a dynamic pressure field test method based on wall heat exchange characteristics, which comprises the steps of firstly, actually measuring and obtaining the heat flow density Q and the wall surface temperature t of a wall bodywAnd the temperature t of the air near the walla(ii) a Obtaining a heat exchange coefficient h according to the conversion relation; secondly, the heat exchange coefficient h and the wind speed u under different flowing states are utilizedzAccording to data obtained by field test and a heat transfer chemical formula, acquiring the comprehensive wind speed u of the wall surfacez(ii) a Finally, acquiring comprehensive dynamic pressure P according to the relation between the dynamic pressure and the wind speedd. The invention covers the comprehensive effect of wind speeds in different directions on the wall body, and the obtained test result is closer to the actual value of the dynamic pressure borne by the wall body through the heat exchange characteristic of the wall body to be tested. The invention is especially suitable for occasions where the wind speed field is not easy to be damaged by a test instrument and practical working conditions that nearby airflow is disordered and the airflow direction cannot be accurately obtained, and can provide dynamic pressure law analysis for the wall bodyAnd (4) data support.
Description
Technical Field
The invention belongs to the technical field of comprehensive dynamic pressure testing of walls, and particularly relates to a dynamic pressure field testing method based on the heat exchange characteristic of a wall.
Background
With the concern of people on the safety of the wall body in the operation process of the underground space, namely the attention of the regular change of the dynamic pressure born by the wall body and the attention of the upper limit value, the attention of how to accurately obtain the dynamic pressure born by the surface of the wall body is also increased. In the current research, a hot wire anemometer is mainly adopted to measure the wind speed vertical to a wall body, and then a dynamic pressure calculation formula is used
The dynamic pressure perpendicular to the wall is calculated, but the dynamic pressure only reflects the pressure action of the wind speed in the perpendicular direction on the wall, and cannot comprehensively represent the total dynamic pressure of the wind speed from different directions acting on the wall. On one hand, the wind speed is difficult to directly test under the working condition that the airflow is relatively disordered; on the other hand, the hot wire anemometer can also damage the flow field in the test process. Therefore, the problem of low testing precision of dynamic pressure bearing on the surface of the wall body exists in the prior art.
Disclosure of Invention
The invention aims to provide a dynamic pressure field test method based on wall heat exchange characteristics, which reflects the comprehensive wind speed from each direction of a wall through the measured wall heat exchange characteristics, so that the comprehensive dynamic pressure is calculated, and the test precision of the comprehensive dynamic pressure is higher. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a dynamic pressure field test method based on wall heat exchange characteristics comprises the following steps:
step S1, actually measuring and obtaining the heat flow density Q and the wall surface temperature t of the wall bodywAnd the temperature t of the air near the walla；
Step S2, obtaining a heat exchange coefficient h according to the conversion relation;
step S3, utilizing heat exchange coefficient h and wind speed u under different flow stateszAccording to data obtained by field test and a heat transfer chemical formula, acquiring the comprehensive wind speed u of the wall surfacez；
Step S4, acquiring comprehensive dynamic pressure P according to the relational expression of the dynamic pressure and the wind speedd。
Preferably, in step S2, the conversion equation is Q ═ h (t)w-ta)。
Preferably, in step S3, the heat exchange coefficient h and the wind speed u are determined in laminar flowzThe relation of (A) is as follows:
the formula of the heat transfer science is as follows: t is tm＝(tw+ta)/2。
Preferably, in step S3, Re < 5 × 105。
Preferably, in step S3, the heat exchange coefficient h and the wind speed u are determined in a turbulent statezThe relation of (A) is as follows:
the formula of the heat transfer science is as follows: t is tm＝(tw+ta)/2。
Preferably, in step S3, 5 × 105＜＜Re＜＜108。
Preferably, in step S4, the dynamic pressure and the wind speed uzHas the relation of
Preferably, the heat flow density Q and the wall surface temperature t arewAnd the temperature t of the air near the wallaRespectively tested by a heat flux density plate, a wall thermometer and an air thermometerAnd (5) obtaining the product.
Preferably, the accuracy of the heat flow density plate is 0.00001W/m2The precision of the wall thermometer is +/-0.1 ℃ and +/-0.1% RH; the precision of the air thermometer is +/-0.1 ℃ and +/-0.1% RH.
Preferably, the flow conditions include a wind speed steady state and a fluctuating state.
Compared with the prior art, the invention has the advantages that: the invention mainly provides a testing method for testing comprehensive dynamic pressure by utilizing the heat exchange characteristic of a wall body, which is particularly suitable for occasions where a wind speed field is not easy to be damaged by a testing instrument and practical working conditions that nearby airflow is disordered and the airflow direction cannot be accurately obtained, is very accurate and convenient to test the dynamic pressure borne by the wall body, and can also provide data support for the analysis of the dynamic pressure borne by the wall body. The method has important engineering value for the expansion of the wall dynamic pressure measuring method.
Drawings
Fig. 1 is a flowchart of a dynamic pressure field test method based on wall heat exchange characteristics according to an embodiment of the present invention;
FIG. 2 is a front view of the station arrangement involved in step 1 of FIG. 1;
FIG. 3 is a test view of the site placement involved in step 1 of FIG. 1.
Wherein, the heat flow density plate is 1, the wall surface thermometer is 2, and the air thermometer is 3.
Detailed Description
The dynamic pressure field test method based on the wall heat exchange characteristic of the present invention will be described in more detail with reference to the schematic drawings, in which preferred embodiments of the present invention are shown, it being understood that those skilled in the art can modify the present invention described herein while still achieving the advantageous effects of the present invention. Accordingly, the following description should be construed as broadly as possible to those skilled in the art and not as limiting the invention.
As shown in fig. 1, a dynamic pressure field test method based on wall heat exchange characteristics includes the following steps S1-S4, specifically:
step S1 is that for convective heat transfer between the wall and the air caused by the wind acting on the side wall,it can be regarded as 'heat exchange problem of sweepforward flat plate', heat flow density Q (W/m)2) Satisfies the following relation:
Q＝h(tw-ta) (1)
therefore, the heat flux density Q and the wall surface temperature t of the wall body are obtained through actual measurementwAnd the temperature t of the air near the wallaObtaining a heat exchange coefficient h;
step S3, the air flow passes through the flat plate to transfer heat under different flow states, and the convection heat transfer coefficient h and Reynolds number R of the air floweThe corresponding associations are different. By utilizing heat exchange coefficient h and wind speed u under different flowing stateszAccording to data obtained by field test and a heat transfer chemical formula, acquiring the comprehensive wind speed u of the wall surfacez(ii) a Specifically, for the convective heat transfer coefficient h, h and the wind speed u can be established according to the difference of corresponding Reynolds numberszSee formula (2) and formula (3), wherein ReSee formula (4):
in the laminar flow state, the flow velocity of the air is controlled,
when the air is in a turbulent flow state,
wherein the content of the first and second substances,
in the above formula, l (m) is the height of the wall body, which can be obtained by actual measurement on site; thermal conductivity of air lambda (W/m.K), kinematic viscosity of air v (m)2The number of Pr and/or the number of Pr are physical parameters of the fluid, and can be determined by the average temperature tmThe calculation of the mean temperature is found in the following formula:
tm＝(tw+ta)/2 (5)
wherein Re < 5 × 10 in laminar flow state5In the turbulent flow state, 5 × 105＜＜Re＜＜108。
According to the formula (2), the formula (3), the formula (4) and the formula (5), the comprehensive wind speed u is obtainedz(m/s)。
Step S4, acquiring comprehensive dynamic pressure P according to the relational expression of the dynamic pressure and the wind speedd. The relationship between dynamic pressure and wind speed is
In the formula, PdIs dynamic pressure (Pa) of wall, and rho is density kg/m of air3,uzIs the integrated wind speed (m/s).
In this embodiment, the heat flux Q and the wall surface temperature t arewAnd the temperature t of the air near the wallaObtained by testing the heat flux density plate 1, the wall thermometer 2 and the air thermometer 3 respectively. The instruments were calibrated in the laboratory before the test began. To ensure the credibility of the test data. The recommended value of the instrument precision is as follows: the accuracy of the heat flow density plate 1 is 0.00001W/m2The precision of the wall thermometer 2 is +/-0.1 ℃ and +/-0.1% RH; the accuracy of the air thermometer 3 is + -0.1 deg.C and + -0.1% RH.
In the present embodiment, the flow state includes a wind speed steady state and a fluctuating state. In the case that nearby airflow is disordered, a wall body in which the airflow direction cannot be accurately obtained and a nearby airflow field is not easily damaged by a test instrument, the direct test of the wind speed and the dynamic pressure calculation are extremely inaccurate. The problem can be effectively solved by the comprehensive dynamic pressure obtained by converting the heat exchange characteristics of the wall body, so that the test result is closer to the actual value. The method is also suitable for the working conditions of stable and fluctuating wind speed.
In this embodiment, a process of performing test analysis on the "one station to one station" middle air shaft brick wall of the shanghai subway 17 number line is specifically provided, which is as follows:
because the brick wall of the middle air shaft is influenced by internal resistance components such as an air valve, a barrier in the wall body, a room turning and the like, piston air flow generated during the running of a train inevitably generates directional deflection, forms phenomena such as vortex and the like and impacts the brick wall, so that the brick wall near the middle air shaft is impacted by air flows from different directions to generate dynamic pressure. Under the working condition, airflow at the brick wall is disordered, and the dynamic pressure is not accurately calculated by directly testing the wind speed. The engineering method is in accordance with the engineering method of reflecting the comprehensive wind speed from all directions on the wall by using the heat exchange characteristic of the measured wall so as to calculate the comprehensive dynamic pressure.
Firstly, various parameters of a middle air shaft underground layer facing a brick wall of a piston air valve are measured, and measuring points are arranged as shown in figures 2 and 3. Fig. 2 and 3 show the measuring point arrangement elevation diagrams of wall heat flux density, wall temperature and wall surface air temperature. Arranging a heat flow density plate 1 which is automatically recorded in the center of the wall to obtain the convection heat exchange quantity of the wall; the heat flow density board 1 is respectively provided with a button type wall surface temperature and humidity meter 2 for automatically recording, the two wall surface temperature and humidity meters 2 are positioned on the central line of the horizontal direction of the wall body, and the wall body is divided into three parts in the vertical direction, so that the wall surface temperature change of the wall body is obtained. The specific data analysis results are as follows:
1) measured data of a group of trains passing through a tunnel below the middle wind shaft, namely the heat flow density Q is 1.002W/square meter and the wall surface temperature tw28.8 ℃, air temperature ta26.5 ℃. According to Q ═ h (t)w-ta) The absolute value of the heat transfer coefficient h is determined to be 0.45W/(m)2·℃)。
2) Coefficient of heat transfer by convection h and average temperature tmCalculating and searching the relevant parameters, and the results are shown in Table 1
TABLE 1 convective heat transfer coefficient and physical property parameter data sheet
3) Based on the physical parameters, the thermal conductivity of air is lambda (W/m.K) and the motion viscosity of air is v (m)2The Pr number and the measured wall height l (m) are converted by using a formula (2), a formula (3) and a formula (4) to obtain the comprehensive wind speed uz＝0.78m/s。
4) According to the formula
The comprehensive dynamic pressure was calculated to be 0.36 Pa.
In summary, the dynamic pressure field test method based on the wall heat exchange characteristics provided by the embodiment of the invention covers the comprehensive effect of wind speeds in different directions on the wall, and the test result is closer to the actual value of the dynamic pressure borne by the wall. The invention is particularly suitable for occasions where a wind speed field is not easy to be damaged by a test instrument and practical working conditions that nearby airflow is disordered and the airflow direction cannot be accurately obtained, and can provide data support for the wall body to bear dynamic pressure law analysis. Therefore, the method has important engineering value for expanding the wall dynamic pressure measuring method.
The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any way. It will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A dynamic pressure field test method based on wall heat exchange characteristics is characterized by comprising the following steps:
step S1, actually measuring and obtaining the heat flow density Q and the wall surface temperature t of the wall bodywAnd the temperature t of the air near the walla；
Step S2, obtaining a heat exchange coefficient h according to the conversion relation;
step S3, utilizing heat exchange coefficient h and wind speed u under different flow stateszAccording to data obtained by field test and a heat transfer chemical formula, acquiring the comprehensive wind speed u of the wall surfacez；
Step S4, acquiring comprehensive dynamic pressure P according to the relational expression of the dynamic pressure and the wind speedd。
2. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 1, wherein in step S2, the conversion relation is Q ═ h (t)w-ta)。
3. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 1, wherein in step S3, the heat exchange coefficient h and the wind speed u are determined in laminar flow statezThe relation of (A) is as follows:
the formula of the heat transfer science is as follows: t is tm＝(tw+ta)/2。
4. The dynamic pressure on-site testing method based on wall heat exchange characteristics as claimed in claim 3, wherein in step S3, Re < 5 × 105。
5. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 1, wherein in step S3, the heat exchange coefficient h and the wind speed u are determined in a turbulent statezThe relation of (A) is as follows:
the formula of the heat transfer science is as follows: t is tm＝(tw+ta)/2。
6. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 5, wherein in step S3, 5 × 105＜＜Re＜＜108。
7. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 1, wherein in step S4, the dynamic pressure and the wind speed u are measuredzHas the relation of
8. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 1, wherein the heat flow density Q and the wall temperature t arewAnd the temperature t of the air near the wallaObtained by testing a heat flux density plate, a wall thermometer and an air thermometer respectively.
9. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 8, wherein the precision of the heat flow density plate is 0.00001W/m2The precision of the wall thermometer is +/-0.1 ℃ and +/-0.1% RH; the precision of the air thermometer is +/-0.1 ℃ and +/-0.1% RH.
10. The dynamic pressure field test method based on the wall heat exchange characteristic as claimed in claim 1, wherein the flow state comprises a wind speed steady state and a fluctuation state.
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