Predicting the characteristics of turbulent flow and heat transfer (or turbulent mixing) originating from complex configurations in fluid and heat systems is a crucial issue, since it affects the operating condition and efficiency of mechanical devices. We perform numerical studies (DNS and LES) for turbulent flow and heat transfer in basic flow configurations such as channel, pipe, boundary layer, and Couette systems as well as complex geometries of fluid machineries and heat exchangers. It is expected that 1) the physical mechanisms associated with the turbulent flow and heat transfer will be clarified and 2) the efficient methods to control the flow and heat transport as well as to enhance the performance of the system will be established.