3 air density variable wind tunnel technology description

wind tunnel service air density wind tunnel with a closed loop design variables and the circulation reflux. Wind tunnel in the low turbulent level ( < 0. 5%) Under the special uniform flow characteristics. Wind tunnel is mainly used to study the different total air pressure and air temperature of the anemometer. Environmental conditions limit by IEC 61400 - 12 - 1 [ 1] Is given. On this basis, established the following design criteria:

test section of part of the flow velocity:

now to 16 m/s

planned to extend to 25 m/s

air temperature range: - 20 C + 40 C

air density range: 0. 9 kg/m 1. 35 kg/m³

air pressure: 600 hPa 1100 hPa

based on these standards and constraint conditions, the right wind tunnel design is a closed loop with closed beta period of channels. Test section design of 0. 8 meters long cross-sectional area 0. 5 m x 0. 5 meters. For the expectations of the anemometer under different air density test provides acceptable blocking ratio. Channel shrinkage ratio of 3. 3-1.

figure 5 and figure 6 shows the headquarters of the variable air density pictures of wind tunnel.

figure 5: air density variable wind tunnel of the installation process. Figure 6:

wind tunnel service company air density variable wind tunnel.

wind tunnel itself is composed of sheet metal structure, test segment is sealed, so can change the internal pressure. In addition, the wind tunnel is placed in a separate control room.

in order to obtain high quality flow, sediment consisting of five screen and a honeycomb special honeycomb/screen layout. In order to determine the size of the individual wind tunnel parts, channels to different parts of the pressure change and flow velocity, were calculated. These calculations based on fully verified expansion Angle, shrinkage rate and pressure drop coefficients. Fan and set up the device to compensate for the pressure loss, and in the test section of the part to produce the required wind speed.

3。 1 measurement system

schematically in figure 7 shows the measurement system. Two pitot static reference velocity is given. In addition, the wind tunnel and the indoor climate and monitoring air temperature and humidity. Figure 7:

measurement set sketch

4 calibration process

in order to reduce the uncertainty of measurement, first anemometer must under the condition of normal environmental wind tunnel service company approved by the calibration in wind tunnel. Then, in during the first measurement in air density variable wind tunnel measurement need in almost the same temperature and pressure. Anemometer itself as a standard source device. In the completion of two calibration, the measurement of air density variable wind tunnel can be determined transfer factor.

this process has the advantage of the blocking effect can be neglected. Only need to consider to have repeatability ( Type A) And basic calibration uncertainty.

for the purposes of this report, use the following calibration procedure. However, this is not a standardized procedure.

in air density variable wind tunnel during calibration, measurement of anemometer output velocity in 4 m/s and 15. Between 5 m/s. For each measurement point, allow enough time to produce steady flow conditions. After the stabilization time, maintain a constant speed and sampling interval of at least 30 s. Sampling frequency for at least 4 Hz. In order to cover the velocity rising and falling, select the following order: 4,8,12,15. 5，14，10，6m / s。

4。 Variable air temperature calibration process of 1

is determined as the anemometer transfer factor, the air temperature dropped to - 20° C and complete the calibration. And then the air temperature to 5 & deg; Step up to 40 & deg C; C, the highest air temperature, air pressure at the same time remain the same. At each temperature, calibration according to the above description is complete. In order to reduce the & # 39; 一个“ Model uncertainty, sampling interval, the minimum duration of 30 s. Calibration for each run, all want to linear regression analysis, to produce a specific air temperature slope and intercept of calibration function.

4。 2 adjustable air pressure calibration process

used in variable air pressure calibration process similar to the process temperature is variable. After measuring the transfer factor, air pressure is increased to 1100 from 700 hpa hpa, step length 50 hpa. In order to cover about 0. 8 kg/m 3 to 1. 4 kg/m 3 air density, different pressure measurement in fixed air temperature under 10 ℃. For each calibration operation with variable environment pressure, perform a linear regression analysis, with each specific environmental air pressure of the slope and intercept of calibration function.

as mentioned in chapter 3, also can be in the parameter study on combination of pressure and temperature range.

5 measurement uncertainty

the process described in chapter 4 of the uncertainty of measurement is the equipment under test ( DUT) The uncertainty of measurement