Local Heat Transfer Dependency on Thermal Boundary Condition in Ribbed Cooling Channel Geometries

Abstract

The present study is geared toward quantifying the effects of imposed thermal boundary condition in cooling channel applications. In this regard, tests are conducted in a generic passage, with evenly distributed rib type perturbators at 90deg, with a 30% passage blockage ratio and pitch-to-height ratio of 10. Uniform heat-flux is imposed on the external side of the slab which provides Biot number and solid-to-fluid thermal conductivity ratio around I and 600, respectively. Through infrared thermometiy measurements over the wetted surface and via an energy balance within the solid, conjugate heat transfer coefficients are calculated over a single rib-pitch. The local heat extraction is demonstrated to be a strong function of the conduction effects, observed more dominantly in the rib vicinity. Moreover, the aero-thermal effects are investigated by comparing the flndings with analogous aerodynamic literature, enabling heat transfer distributions to be associated with distinct flow structures. Furthermore, the results are contrasted with the iso-heat-flux wetted boundary condition test case. Neglecting the thermal boundary condition dependence, and thus the true thermal history of the boundary layer, is demonstrated to produce large errors in heat transfer predictions.

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

“…4 of the channel and shows a good agreement with the experimental results of Cukurel. 5,15 The overall level of the EF in the experiments and simulation is in very good agreement. Moreover, the effect of the secondary vortical structures on the EF is well visible in the EF contour plot.…”

“…The applied configuration models the experimental facility of Ç akan, 14 Cukurel,5,15 which was a simplified model of an internal rib-roughened aircraft gas turbine blade cooling passage with a pitch to rib ratio of 10 and a blockage ratio of 0.3 (Table 1 summarizes dimensions). The cooling passage was scaled up by a factor of 15 with respect to real engine conditions.…”

“…The relative bulk flow temperature (or temperature ratio) T 1 ÁT was assumed to have only a small effect on the heat transfer in the experiments 5,15 and it is assumed that the Nusselt number depends only on the Reynolds number, the conductivity ratio between fluid and solid and the Biot number:…”

“…Experimental studies did recently indicate a conjugate effect. 5 An objective of this study is whether this experimental observation can be found to be true numerically via LES, while bypassing real conjugate computations by applying different flux boundary conditions and thus reducing the computational cost.…”

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

“…They also imposed an iso-flux condition on the channel wall, despite conduction between the rib and the channel wall existing in actual cooled blades. Subsequently, studies conducted experiments on conjugate heat transfer including channel walls [14,15]. When conduction was considered, the average heat transfer coefficient decreased by 26% in the rib and 10% in the channel wall compared with the case of pure convection [15].…”