TED-AJ03-562 LES AND EXPERIMENT OF FULLY DEVELOPED FLOW AND HEAT TRANSFER IN A RECTANGULAR CHANNEL WITH ANGLED RIBS

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Numerical and experimental investigations were conducted in order to clarify the characteristics of fully developed flow and heat transfer in a rectangular channel with periodic angled ribs, installed in the internal cooling system of the gas turbine blades. Large eddy simulations (LES) and measurements were carried out with the same flow configurations as each other. The channel height to width ratio H/W was 0.5. The square-sectional ribs (rib height e=0.1H) with an angle-of-attack of 60 degrees were periodically mounted on the two opposite walls (bottom and top walls) with a cross arrangement. Reynolds number based on the hydraulic diameter was set to around 1.0×(10)^5,simulating the actual blades. In the LES, continuity, momentum and energy equations for the filtered incompressible flow at the grid-resolved scale were solved. A dynamic procedure was used for modeling the sub-grid scale (SGS) eddy viscosity. A gradient diffusion approximation was applied to the SGS turbulent heat flux in the energy equation, in which the SGS turbulent Prandtl number was set as a constant. Those governing equations in non-orthogonal coordinates were discretized based on the finite volume method with the collocation grid arrangement. The second-order central difference scheme and the Clank-Nicholson scheme were applied in time and space, respectively. The computational domain was one pitch between the middle of the ribs and a periodic condition was applied to the inlet/outlet boundary assuming fully developed flow. Uniform heat flux was set for one of the two ribbed walls and the other walls were adiabatic. In the experiments, a suction-type wind tunnel with the rectangular test channel was used. The velocity field was measured by using a constant temperature anemometer with an X-probe and a split-film probe, and the pressure drop through the channel was also measured. As a result, the predicted and measured average pressure loss Cp and average Nusselt number ratio Nu_a/Nu_s of the channel agreed well (Table A-1). Here, Nu_a and Nu_s are the Nusselt numbers for the present ribbed channel and a smooth circular tube, respectively. It was shown that the present LES can handle thermal engineering problems of such a complex field. The mechanisms that promote local heat transfer in the channel with the crossed angle ribs were clarified (e.g. Fig. A-1).[figure]

TED-AJ03-562 LES AND EXPERIMENT OF FULLY DEVELOPED FLOW AND HEAT TRANSFER IN A RECTANGULAR CHANNEL WITH ANGLED RIBS

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