The counteractive flow and heat transfer in a narrow straight channel with sidewall bleeding slots

In the internal cooling passages of the first stage turbine blade in the modern advanced gas turbines, the dense bleeding holes are arranged in order to supply the cold air for the external film cooling. The fluid extractions dramatically vary the flow field and convective heat transfer in the internal channels. In the current work, the flow and heat transfer in a high aspect ratio channel (AR = 4) with the side wall bleeding slots are investigated. Unlike the traditional single inlet channel, the cooling air is supplied into the channel from two entrances located at the both ends of the long straight channel. Therefore, a counteractive flow pattern is generated. The effects of the flow rate ratio of the two streams (MR = m ₂/m ₁) on the flow and heat transfer inside the channel are investigated, where m ₁ and m ₂ are the flow rate of the two streams at the two entrances. The local heat transfer is found to be zigzagging with an increase in the flow rate ratio. Interestingly, once a local flow ratio, MR_x, is defined, which is based on the predicted local flow rate, all the data at different locations are converged to the same trend in the Nu/Nu₀ - MR_x space, where Nu is the measured local Nusselt number normalized with the Dittus-Boelter correlation, Nu₀. Based on the numerical simulations, the detailed flow structure is analyzed and reported. The thermal boundary conditions in the simulations mimic the heating scheme in the experiments, where the channel wall is segmented into a matrix of copper plates which are separated by the insulations. It shows that the segmental heating scheme influences the heat transfer significantly.