Towards a method for measuring heat transfer in complex 3-D flow

The objective of this work is to develop an improved method of describing and measuring heat transfer in complex flow fields with highly non-uniform thermal boundary conditions. The intended application is to gas turbine and electronics cooling type flows. Typically, experiments are done with some convenient thermal boundary condition and data are presented in terms of h, the conventional definition of the heat transfer coefficient. These data are often used in a finite element model to predict hardware temperatures, as though independent of thermal boundary conditions. There is a need for a description of convective heat transfer that is independent of thermal boundary condition. Hacker and Eaton (1995) introduced the Discrete Greens Function, DGF, as a compact and practical way of describing the heat transfer independent of the thermal boundary condition. This study extends the DGF approach. A simple and straightforward experiment was used to quantify the DGF for a turbulent boundary layer with and without freestream turbulence. The 1-D DGF of Hacker and Eaton is extended to a 2-D DGF which can be used to describe the heat transfer in a 3-D flowfield. The first iteration of a device for measuring the 2-D DGF was built and tested in the cylinder flowfield. The results are compared to the conventional results and indicate that enhancement levels are in part determined by the thermal boundary condition.;The case of a cylinder in a wall bounded crossflow is examined with both the conventional and the DGF approaches. This flow is a simplification of the flow which exists at the intersection of the hub and endwall in a gas turbine. Conventional heat transfer results are obtained with and without freestream turbulence. Freestream turbulence is found to decrease the level of heat transfer enhancement, defined as the ratio of the heat transfer at a given location to the heat transfer at the same location in the undisturbed boundary layer flow. Surface flow visualizations indicate that freestream turbulence causes separation to occur at a location closer to the cylinder leading edge along the centerline.