The effect of rib orientation on flow and heat transfer in a four-pass square channel with skewed ribs in nonorthogonal-mode rotation was numerically studied by using omega-based Reynolds stress model (SMC−ω). Two cases are examined: in first case, the ribs are oriented with respect to the main flow direction at an angle of −45 deg in the first and third passage and at an angle of +45 deg in the second passage. The second case is identical to the first case with the ribs oriented at angle of +45 deg in the three passages. The calculations are carried out for a Reynolds number of 25,000, a rotation number of 0.24, and a density ratio of 0.13. The results show that the secondary flows induced by −45 deg ribs and by rotation combine partially destructively in the first and third passage of first case. In contrast, for second case, the secondary flows induced by +45 deg ribs and by rotation combine constructively in the first passage, while the flow is dominated by the vortices induced by +45 deg ribs in the third passage. In first case, a significant degradation of the heat transfer rate is observed on the coleading side of the first passage and on both cotrailing and coleading sides of the third as compared to second case. Consequently, the rib orientations at +45 deg are preferred in the radial outward flowing passage with an acceptable pressure drop. The numerical results are in agreement with the available experimental data.

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Convective heat transfer in a rotating two-pass square channel with 45 deg ribs is numerically investigated to simulate turbine blade cooling operation under extreme design cooling conditions (high rotation number, high density ratio, and high buoyancy number). Two channel orientations are examined β = 0 deg and β = 45 deg in order to determine the effects of passage orientation on flow and heat transfer. For a reference pressure of 10-atm and a Reynolds number of 25,000, the results show that at low buoyancy number and for both channel orientations, the combined effect of Coriolis and centrifugal buoyancy forces generates an important thermal gradient between low- and high-pressure surfaces of the first passage, while the second passage remains almost unchanged compared to the stationary cases. At high buoyancy number, and unlike low buoyancy number, the interaction of Coriolis-driven cells, rib-induced vortices, and buoyancy-driven cells are destructive, which degrade the heat transfer rate on trailing and leading surfaces in the first passage for β = 0 deg. In contrast, for β = 45 deg, this interaction is constructive, which enhances the heat transfer rate on co-trailing and co-leading surfaces. In the second passage, the interaction of rib-induced vortices and buoyancy-driven cells deteriorates significantly the heat transfer rate in case of β = 0 deg than in case of β = 45 deg compared to low buoyancy number. The computations are performed using the second-moment closure turbulence model and the numerical results are in fair agreement with available experimental data.