Session: 04-15: Combustor Flows

Paper Number: 78404

78404 - Effect of Compressor Unsteady Wakes on a Gas Turbine Combustor Flow 

The understanding and correct prediction of the aerodynamic interactions occurring at the compressor-combustor interface are crucial to guarantee the desired performance of a gas turbine, ensuring high combustion efficiency and low emissions. In aircraft engines, combustor inlets are characterised by significant levels of circumferential and radial unsteady distortions due to the remnants of wakes and secondary flows generated from the outlet guide vanes (OGVs), together with additional radial gradients caused by prediffuser end-wall aerodynamic loading. These features have been linked to the development of non-uniform velocity distributions across the fuel injector (Barker and Carrotte, J. Eng. Gas Turbines Power, 2002), although the exact mechanism of interaction, and the effects it has on the downstream air-fuel mixing characteristics, is complex and not yet fully understood.

 

This paper investigates the flow behaviour in an annular isothermal rig, which includes a 1.5 stage axial compressor, diffuser, and a realistic fully featured rich-burn combustor model (Cha et al., J. Eng. Gas Turbines Power, 2012), for which five-hole probe traverses and scalar mixing measurements are available at several locations. A single sector of the rig is simulated using a compressible turbomachinery code and unsteady RANS for the compressor, while the combustor flow is solved with a low-Mach code using LES. The two sub-domains virtually overlap across a small interface region, where the solvers are coupled, and synchronous two-way data exchange between them is established using the interpolation library CWIPI (Duchaine et al., Int. J. Fluid Flow, 2009). The mixing characteristics in the flame tube are investigated using a passive scalar injected from the fuel feed. A standalone LES of the combustor is also presented for comparison; for this last case inlet boundary conditions are defined using the 1D experimental velocity profile at prediffuser exit and synthetic turbulence.

 

Validation against rig data shows that the coupling method can correctly predict compressor distortions and their propagation across the prediffuser, with no significant discontinuity of the solution at the coupling interface. In addition, unsteady information is preserved across the two codes, with the OGV wakes showing periodic lateral shedding, and generating velocity fluctuations within the innermost injector passage (pilot). Spectral analysis carried out on the standalone simulation reveals the presence of a high-energy peak downstream of the fuel injector due to the induced swirling motion. In comparison, for the coupled simulation peak power is halved and distributed across a broader frequency range, due to the additional turbulence introduced by the wakes. This has an effect on both the time-averaged and unsteady air–passive scalar mixing characteristics.

Presenting Author: Alessandro Soli Loughborough University

Presenting Author Biography: Alessandro Soli is a postgraduate researcher in Aeronautical Engineering at Loughborough University. He holds a MSc degree in Thermal power from Cranfield University (2016), a MSc degree in Aerospace Engineering from Politecnico di Torino (2017), and a MRes in Gas Turbine Aerodynamics from the University of Cambridge (2018). His research interests include compressor-combustor interactions, off-design gas turbine performance, and the numerical simulation of unsteady and reacting flows.

Authors:

Alessandro Soli Loughborough University
Richard Adoua Rolls-Royce plc
Ivan Langella Delft University of Technology
Paul Denman Loughborough University
Andrew Garmory Loughborough University
Gary Page Loughborough University