Reynolds number effects in the near-wall region of turbulent channel flows

The continuity and momentum equations do not imply a Reynolds number depend ence of turbulence data when wall variables are used for normalization. How ever, experimental and numerical results show a Reynolds number dependence of turbulence intensity very close to the wall. The cause of this is explai ned. It results from the behavior of a sink term in the dissipation rate eq uation which shows a Reynolds number dependence in the limit of two-compone nt two-dimensional turbulence as it exists close to walls. Away from the ne ar-wall region the Reynolds number dependence originates from the streamwis e pressure gradient which enters into the equations for the turbulent kinet ic energy and turbulent dissipation rate through the gradient production pr ocesses. The low-Reynolds number effects in turbulent channel flow were inv estigated experimentally using the laser Doppler anemometry (LDA) measuring technique. A new method was used to eliminate the influence of the limited spatial resolution of the LDA measuring control volume. Results are presen ted for the limiting behavior of the turbulent intensity near the wall and its variation with the Reynolds number. The present LDA measurements confir m the trend in the data of direct numerical simulations. (C) 2001 American Institute of Physics.