**4.4 Study of atmospheric dispersion by means of scale model**

The concentration fields in the proximities of a local gas emission source were experimentally analyzed in several combinations of wind incidences and source emissions. Concentration measurements were performed by an aspirating probe in a boundary layer wind tunnel. The analysis included the mean concentration values and the intensity of concentration fluctuations in a neutral atmospheric boundary layer flow [18–20].

To perform atmospheric diffusion studies, it is usual to consider full-scale wind speeds in the range of 5–20 m/s [21]. Thus, in order to fulfill the Froude number similarity, the wind tunnel modeling must be performed at low free-stream mean velocities. Atmospheric boundary layer developed with low mean velocities similar to the full-depth simulations described in Section 3.1 was used in the UFRGS wind tunnel.

The hot-wire anemometer, by incorporating the aspirating probe, becomes a density measurement system, and when binary gas mixtures are used, the system measures instantaneous concentrations. A gas mixer was used to provide known air-helium mixtures to calibrate the probe [22]. This type of probe produces a wide useful bandwidth of frequency response, and it allows the evaluation of the plume fluctuating concentration near the source in a turbulent wind. At each measurement point, a sample of 1 min was taken at a sampling frequency of 1024 Hz.

Different configurations were tested in the wind tunnel of Prof. Joaquim Blessmann of the UFRGS, but in this work only the case of an isolated stack in a homogeneous terrain is shown in partial form (**Figure 17**). The results obtained are presented as profiles of concentration coefficient *K* and intensity of the concentration fluctuations *Ic*, being *K = CUHH2 /Q0* and *Ic* = *σc/C*, where *C* and *σc* are the mean concentration and the standard deviation (rms) of the concentration fluctuations, respectively, *Q0* is the total exhaust volume flow rate (m3 /s), *UH* is the wind velocity at the emission source height (stack height), and *z* is the vertical coordinate measured from the wind tunnel floor.

**Figure 18** presents vertical profiles of concentration coefficient *K* and *Ic* for a specific condition of emission where plume velocity ratio is 0.66, plume momentum is 0.060, and the buoyancy parameter is −0.031. The experimental mean concentration values are contrasted with Gaussian profiles. It was possible to highlight the observation of the plume vertical asymmetry in the case of an isolated emission source and different probabilistic behavior of the concentration fluctuation data in a cross-sectional measurement plane inside the plume.

**139**

gas dispersion process.

**Figure 17.**

**Figure 18.**

observed [24].

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

One practical application of this type of development is presented next. Wind tunnel tests were realized to evaluate some characteristics of the Alcântara Launch Center (ALC), which is the Brazilian gate to the space located at the north coast of Maranhão State, close to the Equator. Topographical local characteristics modify the parameters of incident atmospheric winds, and it can cause great influence on the

*Concentration profiles* K*, at* x/H *= 0.60, 1.20, and 1.80 and comparison with the Gaussian profile.*

The topographical scale models were built to measure mean and fluctuating flow characteristics in order to understand the real behavior of ALC winds, and then, physical simulations of the effluent dispersion process were made using these scale models. The wind velocity was measured by a hot-wire anemometer, and the concentration fields in the proximities of a gas emission source were analyzed by an

The dispersion process of the gases emitted from the launch center is illustrated in **Figure 19**. Different effluent conditions were tested to reproduce the emission caused by a rocket. Helium gas was used at the emission source to simulate the turbulent diffusion process. The results obtained were compared with previous full-scale measurements and computational evaluations considering the emission at ground level. A coherent behavior with the physics of the phenomena was

The interaction between the incident wind and wind turbines in a wind farm causes mean velocity deficit and increased levels of turbulence in the wake. The turbulent flow is characterized by the superposition of wind turbine wakes. A research work that included a series of wind tunnel tests to evaluate experimentally the spectral characteristics of turbulence in the wake of a wind turbine. Longitudinal

aspirating probe connected to the same anemometer system [23].

**4.5 Wind tunnel tests of the flow in the wake of wind turbines**

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

*Isolated emission source model in the test section of the UFRGS wind tunnel.*

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

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

in the return section of the wind tunnel Prof. Joaquim Blessmann. The simulation devices and roughness elements are similar to those described in Section 2.2.

*Sectional model and full-aeroelastic model of the Octávio Frias de Oliveira cable-stayed bridge in the wind* 

The concentration fields in the proximities of a local gas emission source were experimentally analyzed in several combinations of wind incidences and source emissions. Concentration measurements were performed by an aspirating probe in a boundary layer wind tunnel. The analysis included the mean concentration values and the intensity of concentration fluctuations in a neutral atmospheric boundary

To perform atmospheric diffusion studies, it is usual to consider full-scale wind speeds in the range of 5–20 m/s [21]. Thus, in order to fulfill the Froude number similarity, the wind tunnel modeling must be performed at low free-stream mean velocities. Atmospheric boundary layer developed with low mean velocities similar to the full-depth simulations described in Section 3.1 was used in the UFRGS wind tunnel. The hot-wire anemometer, by incorporating the aspirating probe, becomes a density measurement system, and when binary gas mixtures are used, the system measures instantaneous concentrations. A gas mixer was used to provide known air-helium mixtures to calibrate the probe [22]. This type of probe produces a wide useful bandwidth of frequency response, and it allows the evaluation of the plume fluctuating concentration near the source in a turbulent wind. At each measurement point, a sample of 1 min was taken at a sampling frequency of 1024 Hz. Different configurations were tested in the wind tunnel of Prof. Joaquim Blessmann of the UFRGS, but in this work only the case of an isolated stack in a homogeneous terrain is shown in partial form (**Figure 17**). The results obtained are presented as profiles of concentration coefficient *K* and intensity of the concentra-

concentration and the standard deviation (rms) of the concentration fluctuations,

at the emission source height (stack height), and *z* is the vertical coordinate mea-

**Figure 18** presents vertical profiles of concentration coefficient *K* and *Ic* for a specific condition of emission where plume velocity ratio is 0.66, plume momentum is 0.060, and the buoyancy parameter is −0.031. The experimental mean concentration values are contrasted with Gaussian profiles. It was possible to highlight the observation of the plume vertical asymmetry in the case of an isolated emission source and different probabilistic behavior of the concentration fluctuation data in

*/Q0* and *Ic* = *σc/C*, where *C* and *σc* are the mean

/s), *UH* is the wind velocity

**4.4 Study of atmospheric dispersion by means of scale model**

**138**

layer flow [18–20].

**Figure 16.**

*tunnel Prof. Joaquim Blessmann.*

tion fluctuations *Ic*, being *K = CUHH2*

sured from the wind tunnel floor.

respectively, *Q0* is the total exhaust volume flow rate (m3

a cross-sectional measurement plane inside the plume.

**Figure 17.** *Isolated emission source model in the test section of the UFRGS wind tunnel.*

**Figure 18.** *Concentration profiles* K*, at* x/H *= 0.60, 1.20, and 1.80 and comparison with the Gaussian profile.*

One practical application of this type of development is presented next. Wind tunnel tests were realized to evaluate some characteristics of the Alcântara Launch Center (ALC), which is the Brazilian gate to the space located at the north coast of Maranhão State, close to the Equator. Topographical local characteristics modify the parameters of incident atmospheric winds, and it can cause great influence on the gas dispersion process.

The topographical scale models were built to measure mean and fluctuating flow characteristics in order to understand the real behavior of ALC winds, and then, physical simulations of the effluent dispersion process were made using these scale models. The wind velocity was measured by a hot-wire anemometer, and the concentration fields in the proximities of a gas emission source were analyzed by an aspirating probe connected to the same anemometer system [23].

The dispersion process of the gases emitted from the launch center is illustrated in **Figure 19**. Different effluent conditions were tested to reproduce the emission caused by a rocket. Helium gas was used at the emission source to simulate the turbulent diffusion process. The results obtained were compared with previous full-scale measurements and computational evaluations considering the emission at ground level. A coherent behavior with the physics of the phenomena was observed [24].
