This thesis reports upon a second phase of research into the effects of free-stream turbulence quantities on heat transfer to impermeable gas turbine blading. It describes the development of a novel form of turbulence generator, to control separately the turbulence quantities intensity and frequency upstream of a cascade of blades at levels typical of the gas turbine. The turbulence generator was calibrated for these individual quantities, with a hotfilament anemometer system combined with on-line analog and digital signal processing. Blade heat transfer coefficients measured by two independent techniques are compared. A large quantity of data is presented, taken from a first stage high pressure rotor blade and a nozzle guide vane. These were subjected to steady flow and turbulent streams induced by both the novel turbulence generator and by more conventional turbulence grids. Surface pressure measurements have also been made, to predict the heat transfer rates by applying formulae derived from simple geometries. Much of the boundary layer over the two blades was apparently laminar. For the laminar regions, the simple formulae for heat transfer (flat plate for example) multiplied by a turbulence term, will provide as good a correlation as any. The intensity Tu is the most important turbulence quantity, but there is some evidence that the frequency of the perturbations can effect heat transfer. Other evidence presented would s'uggest that profile geometry is an overriding factor, which dictates the development of the turbulence, whatever its origin, as well as controlling its interaction with the boundary layer. None of the correlations available for the prediction of boundary layer transition are applicable. On both blade suction surfaces separation seems to have occurred, and the analysis indicates that transition on the pressure surfaces of modern blades will be inhibited by the high free-stream accelerations. Beyond transition, heat transfer is little affected by turbulence. It is now clear, that measurements of the turbulence as it develops through the cascade must be performed before a successful prediction procedure for all of the boundary layer regions can emerge.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:291250 |
| Date | January 1980 |
| Creators | Priddy, W. J. |
| Publisher | University of Sussex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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