Effect of contraction on screen-generated turbulence

An experimental study was conducted to determine the relative agreement with test data of the rapid distortion theories proposed for the effect of screens and contraction in wind tunnels. It was found that when the natural rate of decay of turbulence is low ahead of contraction, the increase in longitudinal turbulence kinetic energy can be observed for a contraction ratio as low as four. The transfer of energy from the lateral to the longitudinal kinetic energy component, as a consequence of the tendency to isotropy, is inadequate to account for the large increase in the longitudinal component observed in contractions. It is concluded that a modification of the strain term in turbulence models is needed in order to account for an increase that appears to be proportional to a power of mean velocity at a station/mean velocity ahead of contraction.