Mechanical Engineering Thesis Defense: Mr. Jonathan Kenney

Date(s): 11/17/2009 10:00 AM - 11/17/20091:00 PM
Location: Textile Building, Room 101E
Contact: Sue Cunha scunha@umassd.edu 508-999-8492
www.umassd.edu/engineering

The Mechanical Engineering Department is pleased to announce the MS Thesis Defense of Mr. Jonathan Kenney entitled "Investigation of Vortex Generators to Manipulate the Boundary Layer and Control Droplet Impingement in a Low Pressure Steam Turbine."

Abstract:
In the L-1 stage of a steam turbine, water droplets are formed and cause damage to the rotor blades. The use of vortex generators on the stator blades is investigated in order to control droplet impingement. Several published papers show the effectiveness of vortex generators with respect to the reduction of separation and boundary layer manipulation. Assuming that the work developed at each stage is equal, the boundary conditions of the L-1 stage are found by using thermodynamic property tables. A mechanical drawing of the stator blades is used to abstract a single turbine blade. Using Fluent, a commercial CFD software package, a velocity field of the full blade is generated and validates the use of a cross section. The boundary conditions are applied to this model at the inlet and outlet, and the width of the model is based on an optimum distance for a single pair of rectangular contra-rotating vortex generators. Periodic boundary conditions are set above and below the blade to simulate the full set of blades. Periodic boundary conditions are also set on the sides of the model to represent repeating cross sections of the blade. Several turbulence models are compared based on their ability to model flow near a wall. The k-e realizable turbulent model with enhanced wall treatment is chosen. Once single phase solution is found, water droplets are released from the inlet using a rake function. The droplets are tracked and by visual inspection, show that they follow the flow away from the suction surface. Applying a single pair of vortex generators at a distance along the chord of 20% of the chord length, and using a height of 4.5% of the chord length, the same droplets are tracked using the same rake function. By visual inspection, the droplets are pulled into the flow nearer the suction side and stay close to the surface. This will change the velocity vector of the droplets and effectively lessen the damage caused to the tip of the subsequent rotor blade. The size of the droplets are doubled and investigated in the same manner, resulting in slightly less effectiveness due to the higher momentum of the droplets. Vortex generator heights of 3.0% and 6.0% of the chord length are applied and the simulations are run with the same boundary conditions. The shortest VG case resulted in much less influence on the water droplets. The largest set of VGs had similar results as the 4.5% case. Based on the amount of drag associated with each set of vortex generators, the 4.5% chord height would be recommended for the stator blades in order to reduce the damage inflicted on the rotor blades.