CFD analysis of low pressure turbine blade using vortex generator jets
With the trend toward higher bypass ratios in turbofans, demands are increasing for the low pressure turbines (LPT) that drive the large fan assemblies. Also, many military and civilian applications use the LPT to power an ever increasing applications of onboard communication, diagnostic, and service hardware. Aerodynamic efficiency is a major concern in today's aerospace and aircraft industries. But the flow separation is one of the important factors that affect the aerodynamic efficiency. At very high altitudes the low Reynolds number flow through the low pressure turbine section of the gas turbine engine can drop below 25,000. At these low Reynolds numbers the flow is laminar and extremely susceptible to separation which can lead to increased losses and reduced lift. Small jets of air injected through the suction surface of the airfoil, called Vortex Generator Jets (VGJs), have been shown successful in suppressing separation and maintaining attached flow. We focused on designs of Low Pressure Turbine with the available L1A blade data to improve the performance of the aircraft, delay boundary layer separation and increase the lift forces and to analyze the performance of the turbine blade with vortex generator jet with the available fluent software. We conclude that flow separation can delayed by using vortex generator.
LARGE SCALE VISUALIZATION OF PULSED VORTEX GENERATOR JETS
The use of small jets of air has proved to be an effective means of flow control on low Reynolds number turbine blades. Pulsing of these jets has also shown benefits in reducing the amount of air needed to achieve the same benefits in flow control. An experiment using both hot wire anemometry and Particle Image Velocimetry (PIV) has been set up to investigate how these pulsed jets interact with the boundary layer to help stabilize it and keep the flow attached. A 25x scaled jet hole in a plate has been utilized. The 1” diameter jet has a pitch angle of 30° and a skew angle of 90°. Pitch angle is defined as the angle the jet makes with the surface of the plate, and the skew angle is the angle that the jet makes with the cross flow. A two-dimensional traverse was set up to obtain the hot wire data of the free jet, which serves as a baseline for the free jet PIV results. Measurement planes were taken along the centerline of the jet. The jet was pulsed at 4 Hz with varying pulse durations. The ratio of the pulse duration to the total cycle time is called the duty cycle. Duty cycles of 10, 25, and 50 percent were implemented for each plane. Velocity and vorticity planes were obtained from the hot wire method, and were used in the characterization of the jet flow and its interaction with the boundary layer.
The decay of longitudinal vortices shed from airfoil vortex generators
An experimental study is conducted to examine the crossplane structure and streamwise decay of vortices shed from airfoil-type vortex generators. The vortex generators are set in a counter-rotating array spanning the full circumference of a straight pipe. The span of the vortex generators above the duct surface, h, is approximately equal to the local turbulent boundary layer thickness, delta. Measurement of three-component mean flow velocity in downstream crossplanes are used to characterize the structure of the shed vortices. Measurements in adjacent crossplanes (closely spaced along the streamwise coordinate) characterize the interaction and decay of the embedded vortices. A model constructed by the superposition of Oseen vortices is compared to the data for one test case.