Helicopter Flow Field Analysis

Abstract : A computer program has been developed which allows the flow around general aircraft configurations to be modeled, including the effects of regions of separated flow. The program, although developed specifically to handle the regions of separated flow associated with the typically bluff helicopter airframes, retains the capability to model the more slender shapes associated with fixed-wing aircraft. The flow around the specified configuration is calculated iteratively, the first step being the solution of the basic potential flow. This is followed by the definition of the potential flow streamlines over the surface, the calculation of boundary layer growth along the streamlines, the identification of the separated flow region and the eventual recalculation of the potential flow, including the effects of boundary layer growth and separated flow. The iterations between potential and viscous flow may be repeated as often as desired. During its development, the program has been exercised on a number of helicopter and aircraft configurations. This experience has shown that the program can be used to model the flow about the involved shapes typical of the new generation of rotocraft now going into service without any increase in difficulty, either in preparing the input data or in executing the solution, when compared with earlier purely potential flow solutions.