Experimental and analytical investigation of local heat transfer in high aspect ratio cooling channels

Large scale (M=25:l) model laboratory experiments with air as test fluid have been performed in order to investigate both local and global flow and heat transfer phenomena in rectangular cooling channels of a cryogenic rocket combustion chamber. The focus was put on high aspect ratio channels with asymmetrical , i.e. one-sided heating including channel wall fin effects. The investigations were performed for different model configurations with different channel curvature arrangements including a double curvature characteristic for real combustion chamber cooling channel geometries. Similar investigations had been performed before restricted however to symmetrical heating and single curvature set-ups. Physical field parameters within the fluid and the channel wall structure were determined experimentally for various different operational conditions, in order to identify 3-dimensional phenomena and to provide a broad, tailored data base for 3D-CFD code validation. Expected secondary flow phenomena and significant redistribution effects of mass fluxes at different channel locations, which are both expected to influence the heat transfer considerably, were identified experimentally. Both effects together may cause depending on the channel location relative to the curvature orientation either an increase or even a reduction of heat transfer, compared to undisturbed straight channel sections. Additionally, 3-dimensional simulations were carried out with the 3D-CFD code VADUCT, using boundary conditions derived from the conducted experiments. The results of these simulations are in good agreement with the experimental results, validation the code for chamber cooling design analyses. Both the secondary flow vortex structures and the mass flux redistribution effects were successfully predicted.