An Investigation of Turbulence Mechanisms in V/STOL Upwash Flow Fields.
Annual rept. 15 Mar 83-15 Jun 84,
GRUMMAN AEROSPACE CORP BETHPAGE NY RESEARCH AND DEVELOPMENT CENTER
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This study investigated the two-dimensional upwash region formed by collision of opposed two-dimensional wall jets. Extensive measurements were made in the 2-D wall jet to establish the starting conditions of the upwash. Evaluation of these measurements showed classical wall jet behavior, and fully developed mean and turbulence profiles at the collision zone. A unique set of velocity profiles was obtained at seven upwash locations. Two components of the velocity were found simultaneously using an X-probe anemometer. By rotating the probe and repeating the profiles, all three velocity components were measured. While mixing layer growth rates were larger than those found in a free two-dimensional jet, these values were less than those previously reported. These data are presented in similarity form. Higher moments and some of the terms in the turbulence kinetic energy equation were also measured. As part of the study of the effect of various initial conditions, a series of measurements was taken in the upwash formed by collision of unequal wall jets. These are compared to a very simple theory. By choosing a coordinate system aligned with the upwash, these data can be characterized in a pattern similar to the equal wall jet case. Obstacles of various heights were placed at the collision point of equal wall jets. Away from the influences of the obstacles wake, the upwash exhibited increasing decay rates with decreasing obstacle heights. This behavior asymptotes to the no-obstacle case for small obstacles and to twice the wall jet growth for large obstacles. Keywords include Jet fountains, and VSTOL upwash flow field.
- Fluid Mechanics