This study presents the numerical study of transient conjugate heat transfer in a high turbulence air jet impinging over a flat circular disk. The numerical simulation of transient, two-dimensional cylindrical coordinate, turbulent flow and heat transfer is adopted to test the accuracy of the theoretical model. The turbulent governing equations are resolved by the control-volume based finite-difference method with a power-low scheme, and the well-known low-Re kappa-omega turbulence model to describe the turbulent structure. The SIMPLE algorithm is adopted to solve the pressure-velocity coupling. The parameters studied include turbulent flow Reynolds number (Re = 16,100-29,600), heated temperature of a circular disk (T-h = 373 K) or heat flux (q" = 63-189 kW/m(2)), and orifice to heat-source spacing (H/D = 4-10). The numerical results of the transient impinging process indicate that the jet Reynolds number has a significant effect on the hydrodynamics and heat transfer, particularly in the stagnation region of an impinging jet. High turbulence values lead to greater heat transfer coefficients in the stagnation region and cause a bypass of the laminar-to-turbulent transition region in the wall jet region. Induced turbulence from the environment around the jet also influences the variation of the stagnation heat transfer. The modeling approach used here effectively captures both the stagnation region behavior and the transition to turbulence, thus forming the basis of a reliable turbulence model. (c) 2006 Elsevier Ltd. All rights reserved.