Session: 01-08 Inlets, Nozzles, Mixers and Nacelles II

Paper Number: 126486

126486 - Cavity Impact on the Base Flow Unsteadiness for a High-Speed Exhaust System 

It is envisaged that future, advanced propulsion systems will be essential to enable sustainable high-speed flight, as well as more efficient space access. Such concepts usually feature rocket-like geometrical characteristics at the base and exhaust system, but their design is tailored to their mission. In specific, axially symmetric cavity regions are often employed in such systems to allow space for gimballing motion of the convergent-divergent nozzle which is embedded at the base. Such cavities are expected to have an impact on the propulsion and nozzle aerodynamics, and therefore, further analysis is required on such systems to quantify this effect. This paper presents a numerical investigation on a sub-scale, high-speed exhaust system, which is considered representative of future advanced concepts, and features a truncated, ideal contoured nozzle and a cavity region at the base. The full three-dimensional configuration, mounted on the test section of an ejector-driven, transonic wind tunnel is numerically investigated to facilitate an on-going experimental campaign. The Delayed Detached Eddy Simulation (DDES) approach is selected among hybrid Reynolds-averaged Navier-Stokes/Large Eddy Simulation (RANS/LES) methods, to investigate the flow at the base, owing to its global nature and reduced computational cost compared to pure LES for wall-bounded flows. Results of the experimental campaign are compared to the present numerical study to evaluate the validity of the solution. Additionally, the credibility of the solution is assessed on the basis of dominant flow features and non-dimensional frequency content of the flow for similar cases found in the public domain. The effect of the cavity region on the base flow unsteadiness is identified through a direct comparison to an identical, non-cavity configuration. This is facilitated by the spectral analysis of the base pressure fluctuations at several azimuthal locations for each configuration. Two nozzle pressure ratios of 10 and 20, corresponding to high degree of overexpansion and almost full-flowing nozzle state respectively, are examined for each configuration at fixed wind-tunnel conditions. This allows the identification of the cavity impact on the unsteady nozzle aerodynamics and base flow. Consequently, this work provides a quantification of the effect of axisymmetric cavities on the unsteady flow characteristics for future, high-speed exhaust systems, which has not been reported in previous studies.

Presenting Author: Spyros Tsentis Cranfield University

Presenting Author Biography: Spyros received his 5-year diploma (integrated MEng) in 2020 from the Aristotle University of Thessaloniki, Greece.
Following his graduation, he worked as a Researcher within a Horizon 2020, Research and Innovation Programme "Clean Sky 2", at the Laboratory of Fluid Mechanics and Turbomachinery, at the same university.
Currently, Spyros is undertaking his PhD on Aft-body Aerodynamics and base flows of Novel Propulsion Architectures within the Cranfield Air & Space Propulsion Institute.

Authors:

Spyros Tsentis Cranfield University
Ioannis Goulos Cranfield University
Simon Prince Cranfield University
Vassilios Pachidis Cranfield University
Vladeta Zmijanovic Reaction Engines Ltd.