Numerical modeling of separated flows in three-dimensional diffusers and application of synthetic jets for separation control

Abstract

Solving the problem of creating an environmentally friendly “green plane” implies development and implementation of several actions aimed at increasing airplane performance and reducing environmental contamination. One possible way to solve this problem is to reduce the powerplant weight, in particular, by decreasing its length. The airplane engine flowpath comprises transition ducts: those between the low- and high-pressure compressors, between the compressor and combustor, and between the high- and low-pressure turbines. In a modern high-bypass turbofan, the flowpath varies in the streamwise direction. Shorter transition ducts have greater curvature. Because of this, intensive separation may occur, which leads to increased losses in the flowpath and to significant growth of nonuniformity of flow parameters. Vast experience of numerical and experimental studies of unsteady separated flows has been accumulated by now. In many cases, however, these investigations are performed in a two-dimensional (2D) formulation, which is primarily caused by the high cost of three-dimensional (3D) unsteady calculations. The numerical and experimental work [1] shows that flows in diffuser ducts can have an essentially unsteady 3D structure. This is valid even for ducts modeling 2D configurations. This paper describes the results of a numerical study of the flow structure and its features in model S-shaped transition ducts, as well as the results of using a synthetic jet generator for flow control and for reduction of total pressure losses. Three-dimensional flows are numerically modeled by the unsteady Reynolds-averaged Navier-Stokes (URANS) / RANS methods. The calculations show that the use of the synthetic jet generator can lead to duct loss reduction by 45%.