Journal of Fluid Mechanics

Response of a turbulent boundary layer to a step change in surface heat flux

R. A.  Antonia a1, H. Q.  Danh a2 and A.  Prabhu a3
a1 Department of Mechanical Engineering, University of Newcastle, New South Wales 2308, Australia
a2 Department of Mechanical Engineering, University of Sydney, New South Wales 2006, Australia
a3 Department of Aeronautics, Indian Institute of Science, Bangalore 560012

Article author query
antonia ra   [Google Scholar] 
danh hq   [Google Scholar] 
prabhu a   [Google Scholar] 


Measurements of both the velocity and the temperature field have been made in the thermal layer that grows inside a turbulent boundary layer which is subjected to a small step change in surface heat flux. Upstream of the step, the wall heat flux is zero and the velocity boundary layer is nearly self-preserving. The thermal-layer measurements are discussed in the context of a self-preserving analysis for the temperature disturbance which grows underneath a thick external turbulent boundary layer. A logarithmic mean temperature profile is established downstream of the step but the budget for the mean-square temperature fluctuations shows that, in the inner region of the thermal layer, the production and dissipation of temperature fluctuations are not quite equal at the furthest downstream measurement station. The measurements for both the mean and the fluctuating temperature field indicate that the relaxation distance for the thermal layer is quite large, of the order of 1000θ0, where θ0 is the momentum thickness of the boundary layer at the step. Statistics of the thermal-layer interface and conditionally sampled measurements with respect to this interface are presented. Measurements of the temperature intermittency factor indicate that the interface is normally distributed with respect to its mean position. Near the step, the passive heat contaminant acts as an effective marker of the organized turbulence structure that has been observed in the wall region of a boundary layer. Accordingly, conditional averages of Reynolds stresses and heat fluxes measured in the heated part of the flow are considerably larger than the conventional averages when the temperature intermittency factor is small.

(Published Online April 11 2006)
(Received June 26 1975)
(Revised May 27 1976)