Study of the Effects of the Blowing Ratio of Vortex Generator Jets in a Low Pressure Turbine

Low air density at high altitude can result in very low Reynolds number flow through the low pressure turbine section of aircraft gas turbine engines. At these low Reynolds numbers flow over the aft portion of the low pressure turbine blades is laminar and the very prone to laminar separation which can lead to increased pressure losses and reduced loading. Small jets of air, called Vortex Generator Jets (VGJs), injected through the airfoil surface, have been shown to successfully suppress separation and maintain attached flow. Pulsing these jets has been shown just as effective as steady jets and can reduce the amount of mass flow needed to maintain control. An experiment using Particle Image Velocimetry (PIV) has been performed to study the interaction of the VGJ flow with the flow around the airfoils. A cascade of low pressure turbine blades was mounted in the test section of a low speed wind tunnel. The middle six blades were fitted with rows of 1mm VGJ holes located at 45% and 63% axial chord. Jet velocity blowing ratios of 0.5, 1.0, and 2.0 were studied for a pulsing frequency of 10Hz and a 50% duty cycle. The purpose of this study is to examine the influence of the blowing ratio on the response of the bounday layer to the VGJs. The blowing ratios chosen represent cases where jet momentum is dominated by, roughly matches, and dominates the crossflow momentum. Results show that the b owing ratio of 1.0 case effectively suppresses separation for the entire pulsing cycle The blowing ratio of 2.0 case also suppresses separation, but the jets penetrate well through the boundary layer, indicating excess momentum. The blowing ratio of 0.5 case still keeps the boundary layer attached, but there is evidence of re-emergence of the separation between jet pulses.