FLOW AND HEAT TRANSFER CHARACTERISTICS IN RIBBED CHANNEL USING LATTICE BOLTZMANN METHOD

摘要

In order to improve the efficiency of the gas turbines and power plants, researchers have aimed to reach higher turbine inlet temperatures. There is always a metallurgical limit for highest temperature, as the materials pertaining to turbine cannot withstand very high temperature due to change in material properties. Deformation, creeping and even melting of turbine blades may occur. To alleviate these, researchers have been trying to evolve the cooling systems for turbine blades. Two major cooling strategies involve (a) external cooling and (b) internal cooling. In case of internal cooling, a layer of air or some coolant is made to flow through small passages inside the blade. Both the systems remove heat from the blade and keep the blade temperature under the metallurgical limit. The present work is aimed at modeling the internal cooling passages of the gas turbine blades. The same geometry can throw light on the performance of cooling passages used in electronic devices. Taking these two applications into consideration, it becomes necessary to study flow and heat transfer past bluff-bodies and in ribbed channels. In the present work, the fluid flow behavior and heat transfer characteristics in a rectangular channel with staggered ribs mounted on both walls are analyzed using the lattice Boltzmann method (LBM). This study is carried out for the fluid with Prandtl number Pr = 0.7 and a wide range of Reynolds numbers (10 ≤ Re ≤ 120). The computational strategy is applied in various test cases and validated with the results reported in the literature. The unsteady flow behaviors, such as, instantaneous streamlines, vortex shedding frequency and phase plots are reported. For the ribbed channel (with staggered ribs), the heat transfer is predicted with the help of isotherms, local Nusselt number distribution and average Nusselt number.