Abstract
A new experimental study is presented for a combustor with a double-wall cooling design. The inner wall at the hot gas side features effusion cooling with 7-7-7 laidback fan-shaped holes, and the outer wall at the cold side features an impingement hole pattern with circular holes. Data are acquired to asses the thermal and aerodynamic behavior of the setup, using a new, scaled up, engine similar test rig. Similarity includes Reynolds, Nusselt and Biot numbers for hot gas and coolant flow. Different geometrical setups are studied by varying the cavity height between the two walls and the relative alignment of the two hole patterns at two different impingement Reynolds numbers. This article focuses on the aerodynamic performance of the setup. Instationary flow data are acquired, using a high speed stereo PIV setup. For each geometrical configuration, approximately 20 planes are recorded with a data rate of 1000 Hz by traversing the flow region of interest in the cavity between the two specimen. This fine resolution allows the reconstruction of 3D flow fields for the mean data values and an extensive analysis of transient phenomena at each plane. Time averaged data and jet-center plane transient data are presented in detail. The results show a complex flow field with a hexagonal vortex pattern in the cavity, which is mainly influenced by the cavity height and the relative alignment of the two walls. The jet Reynolds number shows small influence when analyzing normalized data. Small cavity heights show a less developed flow field with less stable vortex systems. The alignment shows a similar influence on vortex system stability, with the aligned case performing better. Additionally, statistical analysis of the jet flow and frequency domain analysis of the jet and the effusion flow are presented, showing the damping capability of the cavity, especially at increased cavity heights, and a residual low frequency pulsation of the effusion cooling inflow.
Highlights
The results show a major influence of effusion cooling especially downstream on the test surface
Two main geometrical variations are identified and studied: the change in cavity height as a main design parameter and the relative alignment of effusion to impingement specimen, which can occur due to thermal expansion in the real engine
The results are discussed : initially, time-averaged velocity data are analyzed to show jet profiles for different configurations, the effects of cavity height and longitudinal alignment on the flow patterns inside the cavity
Summary
The continuous development of aero-gas turbines leads to constant improvements that benefit air passengers and the environment. A commonly used combustion technology to reduce the formation of NOx is the RQL combustor, describing the three major combustion regions—Rich, Quench and Lean—in an annular combustor. The air from the compressor is divided into two major flow paths. A small amount of the compressor air is used to create an air-assisted fuel spray, providing a minimal amount air for burning that fuel spray in a rich environment (red arrow). The remaining air is guided around the combustor liner and used for consecutive mixing, dilution and, mainly, for the cooling of the liner walls
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