**3. Mean flow evaluation of an atmospheric boundary layer simulation**

The above described Counihan simulation is used to illustrate the mean flow evaluation. In this case, mean velocity measurements were performed by means of a pitot-Prandtl tube connected to a Betz manometer. Velocity and longitudinal velocity fluctuations were meas‐ ured by a constant temperature hot wire anemometer, with a true-RMS voltmeter, using low and high-pass analogical filters. Data acquisition of hot wire signals was made by means of an A/D board connected to a personal computer. Uncertainty associated with the measured data depends of the hot wire resolution and the calibration system. In this case, an uncer‐ tainty order of ± 3 % was determined at high velocity measurements.

Previously to simulate ABL flows, an empty tunnel flow evaluation was realized. Mean ve‐ locity profiles were measured along a vertical line on the center of the rotating table 2. The boundary layer has a thickness of about 0.3 m and the velocity values have a maximal devia‐ tion of 3 %, by taking the velocity at the center of the channel as reference. Turbulence inten‐ sity distribution at the same locations shows values around 1% outside the boundary layer increasing, as expected, inside the boundary layer. Reference velocity at the center of the channel for empty tunnel tests was 27 m/s and the resulting Reynolds number 3.67×106 .

Once the empty tunnel evaluation was over, the mean flow of the full-depth boundary layer sim‐ ulation was analyzed. Measurement of the mean velocity distribution was made along a vertical line on the center of rotating table 2 and along lines 0.30 m to the right and left of this line. Fig. 4 shows the velocity distribution along the central line. Flow characteristics are presented in Table 1. There is a good similarity among the velocity profiles given by the values of the exponent α ob‐ tained. Turbulence intensity distribution at the same locations is shown in Fig. 5. The values are lower than those obtained by Cook [4] and by using Harris-Davenport formula for atmospheric boundary layer [3]. Values are reduced as the distance from the lower wall is increased.

**Figure 4.** Vertical mean velocity profile – experimental values and power law fit.

These mean velocity and turbulence intensity vertical profiles show a typical evaluation of the boundary layer mean flow applied to wind load studies. Similar analysis was made for other authors to different wind tunnel simulations. Some works include vertical profiles of longitudinal turbulence scales [12, 20]. When dispersion problems are analyzed and physic atmospheric research studies in wind tunnel are development the mean flow evaluation is usually realized utilizing the logarithmic expression, Eq. (1). A simple method to fit experi‐ mental values of mean velocity to the logarithmic law is presented by Liu et al. [22]. The characteristic parameters *u\** and *z0*, friction velocity and roughness height, respectively, are used to evaluate critical Reynolds number values on low velocity tests for wind tunnel dis‐ persion studies [23].


**Table 1.** Flow characteristics for full-depth boundary layer simulation.

**3. Mean flow evaluation of an atmospheric boundary layer simulation**

tainty order of ± 3 % was determined at high velocity measurements.

202 Wind Tunnel Designs and Their Diverse Engineering Applications

The above described Counihan simulation is used to illustrate the mean flow evaluation. In this case, mean velocity measurements were performed by means of a pitot-Prandtl tube connected to a Betz manometer. Velocity and longitudinal velocity fluctuations were meas‐ ured by a constant temperature hot wire anemometer, with a true-RMS voltmeter, using low and high-pass analogical filters. Data acquisition of hot wire signals was made by means of an A/D board connected to a personal computer. Uncertainty associated with the measured data depends of the hot wire resolution and the calibration system. In this case, an uncer‐

Previously to simulate ABL flows, an empty tunnel flow evaluation was realized. Mean ve‐ locity profiles were measured along a vertical line on the center of the rotating table 2. The boundary layer has a thickness of about 0.3 m and the velocity values have a maximal devia‐ tion of 3 %, by taking the velocity at the center of the channel as reference. Turbulence inten‐ sity distribution at the same locations shows values around 1% outside the boundary layer increasing, as expected, inside the boundary layer. Reference velocity at the center of the channel for empty tunnel tests was 27 m/s and the resulting Reynolds number 3.67×106

Once the empty tunnel evaluation was over, the mean flow of the full-depth boundary layer sim‐ ulation was analyzed. Measurement of the mean velocity distribution was made along a vertical line on the center of rotating table 2 and along lines 0.30 m to the right and left of this line. Fig. 4 shows the velocity distribution along the central line. Flow characteristics are presented in Table 1. There is a good similarity among the velocity profiles given by the values of the exponent α ob‐ tained. Turbulence intensity distribution at the same locations is shown in Fig. 5. The values are lower than those obtained by Cook [4] and by using Harris-Davenport formula for atmospheric

boundary layer [3]. Values are reduced as the distance from the lower wall is increased.

0.0

0.2 0.4 0.6 0.8 1.0

U/Ug (dimensionless velocity)

 measured power law

0.2

0.4

z/z (dimensionless height)

**Figure 4.** Vertical mean velocity profile – experimental values and power law fit.

g

0.6

0.8

1.0

.

**Figure 5.** Vertical turbulence intensities profiles.
