An investigation of a jet in a crosswind

Taylor, Paul (1976) An investigation of a jet in a crosswind. PhD thesis, University of Glasgow.

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Wind tunnel experiments were conducted to determine the complete longitudinal interference characteristics of a turbulent jet exhausting from a flat plate into a turbulent subsonic freestream. The apparatus was designed so that the trends from systematic variations in one parameter, while the others remain fixed, could be established. The variable parameters were jet inclination, the plate Incidence and the ratio of the jet exit velocity to the freestream velocity (the velocity ratio.) The angles of jet inclination, measured from the normal to the plate surface, varied from 0 to 60 degrees downstream in increments of 15 degrees. The angle of incidence of the plate to the freestream direction varied from 0 to 8 degrees in increments of 2 degrees. The values of the velocity ratio ranged from 4 to 12, values that are pertinent to the range of interest for V/STOL aircraft in transitional flight, The surface pressure distribution about the jet and the jet trajectory, defined as the locus of the maximum total pressure, were measured for each configuration. In addition, the surface pressure distribution was integrated numerically to provide a surface force distribution about the jet, a suction force coefficient, a pitching moment coefficient and the centre of pressure. The results are summarised by presenting the variation of the suction force coefficient, centre of pressure, pitching moment coefficient and jet trajectory with the velocity ratio for a given jet inclination and plate incidence. These curves can be crossplotted to provide the variation of these quantities with the jet inclination or the plate incidence as the independent variable In addition, selected isobar plots are presented. The extent of the low pressure field in the lateral and forward regions was reduced as the jet inclination increased. The contribution from these regions to the lift loss and the magnitude of the lift loss decreased. The centre of pressure moved downstream accordingly. The jet penetrated the freestream less and was deflected less as the jet inclination increased. These observations were attributed to a change in the entrainment rate of the jet. The jet entrainment rate decreased as the jet inclination increased. The changes in the surface pressure distribution resulting from a change in incidence of the plate were detailed rather then gross. The variation of the lift loss with incidence exhibited a maximum between 40 and 60 incidence. The change in jet penetration and. deflection was small. The centre of pressure appeared to be independent of incidence. A change in incidence appeared to cause an effective change in the inclination of the jet. The entrainment rate of the jet was only moderately affected by a change in incidence. The low pressures spread to the lateral and forward region as the velocity ratio-increased. The contribution of these regions to the lift loss increased while that from, the wake region decreased. The magnitude of the lift loss increased as the velocity ratio increased. The centre of pressure moved upstream accordingly. Both the lift loss and the centre of pressure showed a weak dependence on the velocity ratio for large values of the velocity ratio. The jet penetrated the freestream more and suffered a less severe initial deflection as the velocity ratio was increase. These observations were attributed to an increase in the entrainment rate of the jet as the velocity ratio increased, A two-dimensional potential flow model was proposed to predict the surface pressure distribution, the surface force distribution and the suction force coefficient on the flat plate for the normal jet at aero incidence. The model successfully predicted the surface pressures and surface forces close to the jet in the lateral and forward regions, for velocity ratios less than 10, The agreement between the predicted and experimental value of the suction force coefficient was particularly good for velocity ratios less than 10, The model was unable to allow for the increasing three-dimensional effects at high ratios. The trends in the variation of the model parameters with the velocity ratio agreed well with the experimentally observed trends of the physical characteristics which they represented.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: A W Babister
Keywords: Aerospace engineering
Date of Award: 1976
Depositing User: Enlighten Team
Unique ID: glathesis:1976-72945
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06

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