Swirl Impinging Cooling on an Airfoil Leading Edge Model at Large Reynolds Number

Jet impingement cooling has been extensively investigated due to its significant applications on the airfoil leading edge region; however, most of which are about normal jet impingement. The systematic research on swirl jet impinging cooling on leading edge is relatively rare. This study comprehensively investigated the heat transfer distribution of swirl jet impingement with one row of tangential jets. The location of the cross-over jets is offset from the centerline toward either suction or pressure side. Five jet Reynolds numbers varying from 10,000 to 80,000 are tested to reach real engine cooling condition. Jet plates with jet-to-jet spacing (s/d = 2, 4, and 8) and the ratio of surface diameter-to-jet diameter (D/d = 4, 6.6, and 13.3) are tested. We conducted the experiments with a test matrix of 45 cases. The optimum geometric parameters of the jet plate are revealed. Results indicate that for a given Reynolds number, the jet plate configuration with D/d = 4 and s/d = 2 provides the highest Nusselt number profile than the other jet plate configurations, while the jet plate configuration with D/d = 13.3 and s/d = 8 provides the lowest Nusselt number profiles. The best heat transfer region shifts by varying the jet plate configuration depending on the strength of swirl flow. Additionally, correlation of tangential jet impingement has been developed to predict the area-averaged Nusselt number, which is useful for airfoil leading edge cooling design and heat transfer analysis.

The Effect of Weak Crossflow on the Heat Transfer Characteristics of Short-Distance Impinging Cooling

This paper numerically and experimentally investigated the effect of weak crossflow on the heat transfer characteristics of a short-distance impinging jet. The Reynolds number of the impinging jet ranged from 6000 to 15,000, and the mass velocity ratio (M) between the crossflow and the jet varied from 0 to 0.15. The separation distance (H) between the exit of the jet nozzle and the impingement surface equals to the exit diameter (D) of the impinging jet. In the experiments, the temperature distribution on the impingement target surface was measured using a transient liquid crystal method. In the numerical simulation, a multiblock hexahedral mesh was applied to discrete the computational domain, and a commercial CFD package (Ansys cfx-12.0) with a standard k-ɛ turbulence model was used for computation. It was found that compared to the impinging cooling without crossflow, the heat transfer characteristics near the impinging stagnation point remained almost constant. At the same time, the presence of crossflow decreased the heat transfer rate in the upstream region of the impinging stagnation point, while increased that in the downstream of the impinging stagnation point. Taken together, crossflow has a complex influence on the impinging cooling, which is highly dependent on the mass velocity ratio between the crossflow and the jet.

Simulation of Impinging Cooling Performance with Pin Fins and Mist Cooling Adopted in a Simplified Gas Turbine Transition Piece

The gas turbine transition piece was simplified to a one-four cylinder double chamber model with a single row of impinging holes in the outer wall. Heat transfer augmentation in the coolant chamber was achieved through the use of pin fin structure and mist cooling, which could increase the turbulence and heat transfer efficiency. The present research is focused on heat transfer and pressure characteristics of the impinging cooling in the coolant chamber using FLUENT software. With the given diameter of impinging hole, pin fin diameter ratiosD/dhave been numerically studied in ranges from 1 to 2. Three different detachedLwere simulated. The impinging cooling performance in all cases was compared between single-phase and two-phase (imported appropriate mist) flow in the coolant chamber. All the simulation results reveal that the factors ofLandD/dhave significant effects on the convective heat transfer. After the pin fin structure was taken, the resulting temperature decrease of 38.77 K at most compared with the result of structure without pin fins. And with the mist injecting into the cooling chamber, the area weighted average temperature got a lower value without excess pressure loss, which could satisfy the more stringent requirements in engineering.