Improvements to a tightly coupled viscous–inviscid procedure for three-dimensional unsteady transonic flow

Abstract

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 flow equations hold. These two zones are tightly coupled to each other, allowing conservation 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 zones is allowed to adjust its position relative to blade based on an investigation of the instantaneous flow physics. The effects of rotor trim, aeroelasticity, and far wake induced inflow are included in the analysis through a coupling with a comprehensive rotor analysis. The methodology 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 experimental 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 accuracy of unsteady shock motion. The shock structure is examined to determine whether inaccuracies are introduced by the presence of the interface.