Numerical Modelling of the 3D, Unsteady Flow of an Inlet Particle Separator for Turboshaft Engines

Authors

Marco Castaldi  - von Karman Institute for Fluid Dynamics, Belgium
Frank Eulitz - von Karman Institute for Fluid Dynamics, Belgium
Jacques Demolis - Safran Helicopter Engines, France
Ignacio Mayo Yague - von Karman Institute for Fluid Dynamics, Belgium

Abstract

Helicopter and turboprop engines are susceptible to the ingestion of debris and other foreign objects, such as dust and sand, especially during take-off, landing and hovering operation. The ingestion of small particles is a known issue for accelerated degradation and reduction of engine and components life. An Inlet Particle Separator (IPS) mounted in front of the compressor inlet represents one approach to prevent or reduce particle ingestion. The flow inside the IPS is highly 3D and unsteady, with fluctuations especially pronounced when choking conditions are reached in one or both of the flow channels of the IPS. Vital for design optimization of the IPS is a profound understanding of the flow physics. The purpose of this paper is to contribute to the sparse work on numerical modeling for the aerodynamic characterization of IPS, in support of experimental campaigns and future work on design improvement.A set of models with increasing granularity is developed starting from simple analytical models to 3D Large Eddy Simulation. The analytical models are based on the inviscid compressible flow theory, considering the IPS bifurcating duct as a system of nozzles. The first model receives in input the inlet total pressure, the pressure ratios and the pressure losses in the outlet channels as main parameters. The algorithm is able to provide preliminary information on choking, Reynolds number, Mach number, bypass ratio and other fundamental design characteristics. The second model receives in input the bypass ratio and the mass flow rate in one of the channels as main parameters, and it is validated with CFD simulations and with experimental data from a previous campaign executed at the von Karman Institute. The analytical models along with the Reynolds-Averaged Navier-Stokes (RANS) simulation provide for a computationally economic characterization during a preliminary design process.To gain insights on the unsteady flow features, Detached Eddy Simulations have been carried out. Two test cases are considered, defined by high and low values of Reynolds number and inlet total pressure. The grid size and the sampling of the unsteady data are obtained through a systematic sensitivity analysis of mesh and time step resolution. We compare the results of RANS and DES with a LES, identifying the weaknesses of the RANS modeling, and the high accuracy reached with time-resolved simulations. As a last step, we focus on the two-way coupling between solid and gaseous phase, i.e. how the air turbulent structures are perturbed by the presence of large particles, and how the separation efficiency is affected by the increased unsteadiness.