Turbulent flow and endwall heat transfer analysis in a 90° turning duct and comparisons with measured Data - Part II: Influence of secondary flow, vorticity, turbulent kinetic energy, and thermal boundary conditions on endwall heat transfer

Fundamental character of forced convection heat transfer to the endwall surface of a gas turbine passage can be simulated by using a 90° turning duct. Elevated operating temperatures in gas turbines require a thorough understanding of the turbulent thermal transport process in the three-dimensional end-wall boundary layers. The current study uses an in-house developed three-dimensional viscous flow solver to computationally investigate the heat transfer character near the endwall surfaces. Extensive heat transfer experiments also illuminate the local heat transfer features near the endwall surface and form a baseline data set to evaluate the computational method used. Present experimental effort at Re = 342,190 employs a prescribed heat flux method to measure convective heat transfer coefficients on the end-wall surface. Local wall temperatures are measured with liquid crystal thermography. Local convective heat flux is determined by solving the electric potential equation with constant uniform potential that is applied along the inlet and exit boundaries of the end-wall. The viscous flow and heat transfer computation algorithms are based on the same methods presented in Part I. The influence of the two primary counter-rotating vortices developing as a result of the balance of inertia and pressure forces on the measured and computed endwall heat transfer coefficients is demonstrated. It is shown that the local heat transfer on the endwall surface is closely related to the structure of the three-dimensional mean flow and the associated turbulent flow field. A comparison of the molecular/turbulent heat diffusion, wall shear stress, visualization of local turbulent kinetic energy are a few of the tasks that can be performed using a numerical approach in a relatively time efficient manner. The current numerical approach is capable of visualizing the near wall features that can not be easily measured in the flow field near the end-wall surfaces.