Abstract: A patched viscous-inviscid interaction method is used to predict the subsonic and transonic flow over an axisymmetric circular-arc boattail with a solid jet plume simulator. The complicated flow field in the vicinity of nozzle afterbodies was divided into two parts, namely an outer inviscid flow, and an inner viscous boundary - layer. Different computational methods are then applied to each region and the models are coupled into an overall interactive scheme by applying matching conditions consistent with weak - interaction theory. The outer inviscid flow is described by the finite -difference solution for the full potential equation, and the inner boundary - layer flow by the integral method. The numerical results are found to be in fair agreement with the available experiments.