Effects of turbulator profile and spacing on heat transfer and friction in a channel

Abstract

Turbulators in cooling passages of small turbine blades often have geometric constraints placed upon them due to casting limitations associated with small dimensions. Problems such as core die wear, cavity fill imperfections, and casting tolerance variations change turbulator profiles in their final form. This change of turbulator geometry affects, often in the wrong direction, the heat transfer coefficient and friction factor in the cooling cavity. Liquid crystals are used in this experimental investigation to study the effects of turbulator profile and spacing on heat transfer coefficient. Friction factors are also measured, and both heat transfer and friction factor results for 15 turbulator geometries are compared. For all test configurations, the turbulators are positioned on two opposite walls of a rectangular test section in a staggered arrangement with an angle of attack to the mainstream flow, a = 90 deg. A range of turbulator blockage ratios e/Dh, pitch-to-height ratios S/e, and Reynolds numbers are tested. It is concluded that while turbulators with aspect ratios (ARf = turbulator height/ turbulator width) greater than unity produce higher heat transfer coefficients at the expense of higher pressure losses, trapezoidal-shaped turbulators, spaced properly, are very effective in heat removal with moderate pressure losses. Low aspect ratio (ARt < 1) turbulators, especially with round corners, produce lower heat transfer coefficients. Furthermore, an optimum pitch-to-height ratio for 90-deg square turbulators is found to be around 8.