**2.3 Part-depth simulation of the atmospheric boundary layer**

Two Irwin-type generators separated 1.5 m were used to simulate the part-depth boundary layer by means of the Standen method [10]. The windward plate of the

#### **Figure 6.**

*Boundary Layer Flows - Theory, Applications and Numerical Methods*

Three spectra obtained at positions *z* = 0.23, 0.58, and 0.97 m are presented in **Figure 6**. An important characteristic of the spectra is the presence of a clear region of the Kolmogorov's inertial subrange. The comparison of the results obtained through the simulations with the atmospheric boundary layer is made by means of dimensionless variables of the auto-spectral density and of the frequency using the von Kármán spectrum (Eq. (3)). A good agreement is observed at *z* = 0.23 m, but this agreement diminishes at positions *z* = 0.58 and 0.97 m, and this behavior is

*Vertical mean velocity and turbulence intensity profiles measured for the full-depth boundary layer simulation.*

*Counihan vortex generators, barrier, and roughness elements of the full-depth boundary layer simulation.*

These measurements were realized at velocity *Uref* ≈ 27 m/s, being *Uref* measured at gradient height *zg* = 1.16 and the corresponding Reynolds number value of

[5], using the roughness length *z*0 and the integral scale *Lu* as key parameters. The

. A scale factor of 250 was calculated through the Cook's procedure

coincident with the behavior observed for the turbulence intensities.

**130**

Re ≈ 2.10 × 106

**Figure 5.**

**Figure 4.**

*Dimensionless spectra obtained at different heights for the full-depth boundary layer simulation and the von Kármán spectrum.*

simulator has a trapezoidal shape of 1.50 m height, 0.53 and 0.32 m sides. The roughness elements distributed on the test section floor is the same that was used for the Counihan method (**Figure 7**).

Measurements of mean velocity and longitudinal velocity fluctuations were made along a vertical line on the center of rotating table and along lines 0.60 m to the right and left of this line. Vertical velocity distribution and the corresponding log-graph representation to verify the extension of the logarithmic behavior are shown in **Figure 8**. The three measured velocity profiles are quite similar, and the fit to Eq. (2) determines a value of the exponent *α* of 0.23.

#### **Figure 8.**

*Vertical mean velocity and turbulence intensity profiles measured for the part-depth boundary layer simulation.*

#### **Figure 9.**

*Dimensionless spectra obtained at different heights for the part-depth boundary layer simulation and the von Kármán spectrum.*

**133**

**Figure 10.**

*Physical Models of Atmospheric Boundary Layer Flows: Some Developments and Recent…*

**Figure 8**, to the right, also shows turbulence intensity distribution at the same locations. The values are higher than those obtained by full-depth boundary layer, mainly in the positions located above, but lower than those obtained using Harris-Davenport formula if the condition of part-depth is considered. However, higher turbulence levels in these positions indicate a coherent behavior when a part-depth ABL is simulated. **Figure 9** has shown spectra obtained at positions z = 0.23, 0.58, and 0.97 m. Dimensionless spectral comparison indicates a shift of the experimental peak toward low frequencies with respect to the von Kármán spectrum. Higher differences of energy contents are also observed between the spectrum obtained at

The reference velocity for these tests was *Uref* ≈ 25.5 m/s and the gradient height

Next, tests made at the wind tunnel of the UFRGS (**Figure 10**) are analyzed. The Prof. Joaquim Blessmann boundary layer wind tunnel at the Laboratório de Aerodinâmica das Construções of UFRGS, Brazil, is a closed-return circuit, and it has a cross-section of 1.30 m × 0.90 m at downstream end of the main working section that is 9.32 m long (**Figure 10**). A detailed description of the characteristics

Four perforated spires, a barrier, and surface roughness elements were used to simulate a full-depth boundary layer. The arrangement of the simulation hardware is shown/illustrated in **Figure 11**. Velocity and longitudinal velocity fluctuations were measured by means of a TSI hot-wire anemometer along a vertical line on the

. Finally,

*zg* = 1.21 m. The corresponding Reynolds number value of Re ≈ 2.01 × 106

the Cook's procedure [5] was applied, and a scale factor of 150 was calculated.

**3.1 Simulation of atmospheric boundary layers with different velocities**

center of rotating table located downstream of the working section.

*The Prof. Joaquim Blessmann boundary layer wind tunnel of the UFRGS.*

*DOI: http://dx.doi.org/10.5772/intechopen.86483*

z = 0.23 m and spectra measured at upper positions.

**3. Boundary layer flows at the UFRGS wind tunnel**

of the tunnel is indicated in Blessmann's previous work [11].

*Physical Models of Atmospheric Boundary Layer Flows: Some Developments and Recent… DOI: http://dx.doi.org/10.5772/intechopen.86483*

**Figure 8**, to the right, also shows turbulence intensity distribution at the same locations. The values are higher than those obtained by full-depth boundary layer, mainly in the positions located above, but lower than those obtained using Harris-Davenport formula if the condition of part-depth is considered. However, higher turbulence levels in these positions indicate a coherent behavior when a part-depth ABL is simulated.

**Figure 9** has shown spectra obtained at positions z = 0.23, 0.58, and 0.97 m. Dimensionless spectral comparison indicates a shift of the experimental peak toward low frequencies with respect to the von Kármán spectrum. Higher differences of energy contents are also observed between the spectrum obtained at z = 0.23 m and spectra measured at upper positions.

The reference velocity for these tests was *Uref* ≈ 25.5 m/s and the gradient height *zg* = 1.21 m. The corresponding Reynolds number value of Re ≈ 2.01 × 106 . Finally, the Cook's procedure [5] was applied, and a scale factor of 150 was calculated.
