Détermination du terme de déficit du sillage dans la loi de paroi des écoulements turbulents de couche limite

Abstract

In atmospheric flows, turbulence plays an important role and it is the basis of the transport and dispersion of solid particles and pollutants by turbulent energy. Pollutant emissions in the atmosphere degrade air quality. Transport of solid particles constitute soil erosion and hence desertification. Knowledge of the mechanisms that underlie these phenomena is now needed to quantify and reduce the appropriate environmental impact. In fact, in the boundary layers, turbulence is a dominant parameter. As developed turbulence in the wall, so it is directly dependent on the roughness. The laboratory experiments allow the creation of a database for the validation of computer codes and modeling the gradient of the mean velocity very near to the wall, represented by the log law. In this context, the log law is very dependent on the roughness as reported by the scientific community, and the study of the roughness turbulent boundary layer is of great interest. For this purpose, tests were performed in the atmospheric wind tunnel of LMFA ECLyon. Series of measurement was carried out for three regimes on rough wall, the roughness is obtained by sand grains stuck to the same wall, which allowed the distinction of three different turbulent Reynolds number ks+ . The flow characteristics are obtained by the use of particule image velocimetry (PIV). The law governing the evolution of the mean velocity profile proposed in the literature is + +  + l * U 1 U = = ln z + A - ΔU u κ in all works the value of A1=5, the term U+ is modeled according to the expression ΔU = ln k - 3 + + 1  s  κ in our case and only for a range of turbulent Reynolds transition from 4 to 20 we get ΔU = ln 0.21 k + 0.42 + + 1  s  κ ,this difference is due to the fact that the expression of the bibliography has been proposed for a range of turbulent Reynolds from 1 to 180. Numerical analysts in their computational code, need the gradient of the average velocity in near wall. For modeling, represented by the log law.