The effect of roughness element thermal conductivity on turbulent convection.

Many flows of engineering interest occur over surfaces that exhibit roughness with thermal conductivities much lower than common metals and alloys. This is especially true of in-service gas turbine blades with surface depositions. Depending on the local convection coefficients, low thermal conductivity deposits may create situations where temperature changes along the heights of the elements are important and must be considered in predicting the overall surface convection coefficient. Using four test plates constructed with hexagonal distributions of hemispheres or cones made of either aluminum or ABS plastic, a series of experiments were performed in the Baylor University Subsonic Wind Tunnel to investigate the effects of roughness element thermal conductivities on turbulent convection. Results indicate that the packing density of the elements and the enhancement on the floor of the roughness distribution compete with the roughness element thermal conductivity in determining the overall convection enhancement.