Doctoral Dissertations

Date of Award

12-1987

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Aerospace Engineering

Major Professor

Jain-Ming Wu

Committee Members

John Steinhoff, John Caruthers, K. C. Reddy, Trevor Moulden

Abstract

In the computation of helicopter rotor flow fields, wake effects can be very important since each blade passes close to the wake produced by the preceding ones, causing a large local effect. Also, the vortical flow from the wake of a number of blade passages causes a large global effect. Extensive work has been done on helicopter rotor flows using integral methods to follow the vortex wake. These generally cannot treat compressibility effects. Also, they have difficulty attaining stable solutions, particularly in hover, where a large number of interacting vortex sheets must be treated.

A new method has been developed which like integral methods does not constrain or spread the wake. Also, like finite difference methods, it can treat compressibility effects. This method has been developed into a computer program for the computation of rotor flow fields in hover with free wakes. The method utilizes a finite volume potential flow technique. The basic approach involves modifying the potential flow wake treatment so that, within the numerical approximation, the momentum is conserved there as in the rest of the flow field. The internal structure of the vortex is not solved for, but is modeled and spread over several grid points. The wake position and vorticity strength are computed so that the momentum over the wake is balanced in an integral sense. Results computed by this approach for the circulation and wake geometry are compared with experimentally measured data. Cases treated include subsonic and transonic flows, high and low aspect ratios, and two and four-bladed rotor configurations.

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