Basic Study on Perfect Push-Pull Local Ventilation : 2nd Report, Turbulence Characteristics of Push-Pull Flow(Fluids Engineering)

Abstract

In the first report, we had investigated the characteristics such as the changes of the mean velocity component profiles, half-widths (b_<1/2>) of the mean velocity profile in the downstream direction of the Push-Pull flow. In this report, we have experimentally investigated the characteristics of the turbulence intensity, Reynolds shear stress, and intermittency of turbulence. Turbulence intensity √<<u'>^^^-^2>/U_1 in the axial direction is not affected by the flow rate ratio Q_3/Q_1 (Q_1 is jet flow rate from mozzle and Q_3 is suction flow rate produced by the hood.). At the same time, turbulence intensity √<<v'>^^^-^2>/U_1 in the lateral direction becomes greater as the hood is approached and the flow rate becomes larger. These results are in accord with the values of production term for <u'^2>^^^- and <v'^2>^^^-. Although the variation of √<<u'>^^^-^2>/u^^-_m with respect to dimensionless coordinate y_1/b_<1/2> becomes similar with that for completely developed two-dimensional jet, the value decreases in the downstream direction as the flow rate ratio becomes larger for Push-Pull flow. But the flow rate ratio do not affect √<<v'>^^^-^2/U_1. Reynolds shear stress becomes smaller as the flow rate ratio becomes larger near the hood. Dimensionless distance y_1/b_<1/2>, from the centre axis of the flow to the point where intermittency factory γ becomes constant value (γ=0.3 or 0.5), becomes narrower as the flow rate ratio becomes larger near the hood. At the same time, the distance becomes smaller than that for completely developed two-dimensional jet.