Influence of the thermal boundary conditions on the heat transfer of a rib-roughened cooling channel using LES

Abstract

Internal cooling channels of turbine blades are rib-roughened to increase the heat transfer between the wall and the coolant. A large effort has been made in simulating these flows with large eddy simulations to have a better understanding of the flow physics. This contribution focuses on the thermal prediction capabilities of large eddy simulations for such cooling channels. Of particular interest to this study is the influence of the thermal boundary condition on the heat transfer coefficient. If important, this strongly indicates that conjugate effects exist that would need to be modeled resulting in significant additional computational cost. Studies were carried out for Reynolds numbers of 40,000 at different thermal uniform heat flux boundary conditions. The results are compared with experimental aerodynamic and thermal data obtained at the von Karman Institute for Fluid Dynamics. The main outcomes are: first, the results show the dependence of the heat transfer coefficient on the imposed thermal boundary condition, even though it is usually assumed in experimental and numerical studies to depend only on the aerodynamics; this assumption may not be valid. Second, the dependence of the heat transfer coefficient on the thermal boundary condition implies that conjugate heat transfer is important for the current configuration and can be captured numerically, although research on fully coupled, efficient large eddy simulations based conjugate heat transfer algorithms is still needed.

Dependence of Conjugate Heat Transfer in Ribbed Channel on Thermal Conductivity of Channel Wall: An LES Study

“…The difference observed between experimental and LES results at the edge of the rib indicates the possibility of an optical problem involving infrared camera images [22]. Additionally, the possibility of solid/fluid time disparity [23] caused by Scholl et al [20,21] using the conduction-convection linkage as the heat transfer coefficient forward temperature back method was raised. Recently, Oh et al [24] performed a fully coupled LES using the IBM (Immersed Boundary Method) for the same problem [13,14].…”

“…Furthermore, mechanisms for generating local peaks can be elucidated by observing instantaneous flow and thermal fields [18,19]. For studying the conjugate heat transfer of ribbed channels [14,15], Scholl et al [20,21] performed a LES. The LES predicted that the heat transfer of the channel wall was in good agreement with the experiment, but the heat transfer coefficient at the front edge and back of the rib was higher than those observed in the experiment [20].…”

“…In the above studies [14,15,20,21,24], the blockage ratio was 0.3 and the thickness of the channel wall was the same as the rib height. In actual turbine blades, the typical blockage ratio is about 0.1, and the wall thickness is usually 2 to 7 times the rib height [25,26].…”

Fully Coupled Large Eddy Simulation of Conjugate Heat Transfer in a Ribbed Channel with a 0.1 Blockage Ratio

“…Cukurel et al [15,16] provided the temperature distribution inside the rib obtained from experimental data. Scholl et al [17,18] performed LES considering conjugate heat transfer under conditions tested by [15,16]. LES predicted the experimental results well on the channel wall; however, the local heat transfer distribution at the front and rear sides of the rib indicated some variation [17,18].…”

“…Scholl et al [17,18] performed LES considering conjugate heat transfer under conditions tested by [15,16]. LES predicted the experimental results well on the channel wall; however, the local heat transfer distribution at the front and rear sides of the rib indicated some variation [17,18]. Scholl et al [17,18] pointed out that, as a result of this variation, optical problems occur at the edges.…”