IMPROVEMENTS TO A TIGHTLY COUPLED VISCOUS-INVISCID PROCEDURE FOR 3-DIMENSIONAL UNSTEADY TRANSONIC FLOW

A tightly coupled procedure for solving three-dimensional compressible viscous flows has been developed. In this approach, the flow field is divided into two domains, a viscous domain surrounding viscous wakes and solid surfaces such as wings or rotor blades, and an outer domain where the inviscid, unsteady compressible potential how equations hold . These two zones are tightly coupled to each other, allowing conserva tion of mass, momentum and energy at the interface, and permitting the propagation of non-linear acoustic waves from one zone to another in a seamless fashion. The location of the interface dividing the two zon es is allowed to adjust its position relative to blade based on an inv estigation of the instantaneous flow physics. The effects of rotor tri m, aeroelasticity, and far wake induced inflow are included in the ana lysis through a coupling with a comprehensive rotor analysis. The meth odology has been applied to two cases which represent the flow physics typically encountered by modern helicopter rotors. A cruise condition for a UH-60 is analyzed and the results compared with both experiment al data and full Navier-Stokes results. Computer time savings realized by the zonal method over the full Navier-Stokes analysis are given. A non-lifting high speed case is also investigated to assess the accura cy of unsteady shock motion. The shock structure is examined to determ ine whether inaccuracies are introduced by the presence of the interfa ce. (C) 1998 Elsevier Science Ltd. All rights reserved.