Experimental and Numerical Investigation of the Subsonic Flow Field inside and near a Weapons Bay

Tomer Rokita
Work towards Ph.D. degree under the supervision of Prof. B. Greenberg, Prof. R. Arieli, and Dr. Y. Levy
Faculty of Aerospace Engineering
Technion – Israel Institute of Technology

Motivated by the development of recent military aircraft that carry weapons internally (for improved stealth and aerodynamic efficiency), this research provides a detailed experimental and numerical investigation of the subsonic flow field inside and near a weapons bay. The weapons bay configuration is represented by a plate with a rectangular cutout (cavity) immersed in a fluid moving parallel to the plate. Despite its simple geometry, a cavity generates complicated flow that contains a wide range of physical phenomena like unsteady shear-layer, vortex shedding, recirculation eddies, instabilities and three dimensional effects. Characterization and understanding of these phenomena are challenging tasks, especially in high Reynolds number turbulent regimes.
The experimental investigation includes the design and implementation of a designated wind-tunnel model, which allows various measurements of flow properties inside and near the cavity, and, in particular, simultaneous measurements of pressures and velocities. The numerical investigation includes time-accurate, three-dimensional numerical flow simulations, utilizing a hybrid RANS/LES approach, which is extensively validated, thereby allowing us to study three dimensional spatial-temporal patterns of cavity flow in depth.
Special attention is paid to the cavity shear-layer whose characteristics and stability are analyzed by application of Linear-Hydrodynamic-Stability-Theory (LHST). Cavity shear-layer LHST results will be presented and an analogy to a free shear-layer will be discussed. In addition, a new linear empirical correlation between shear-layer thickness and shear-layer turbulence intensity is proposed.
The mean and unsteady flow structure is first examined qualitatively by advanced flow visualizations techniques and vortex tracking in time and space and then quantitatively by calculation of spatial velocity cross-correlation fields and application of Proper-Orthogonal-Decomposition (POD) in both two-dimensions and three-dimensions. Fully three-dimensional POD analysis of cavity flow has been rarely done in other studies, mainly due to computational cost and the ability to obtain high fidelity three-dimensional flow fields. It will be shown that two-dimensional POD analysis could be misleading without the insight afforded by three-dimensional POD analysis. This type of analysis sheds new light on three-dimensional cavity flow by disclosing novel non-intuitive dominant structures and modes.

The talk will be given in Hebrew

Wed, 11-06-2014, 16:30 (Gathering at 16:00)

Classroom, ground floor, Library, Aerospace Eng.

Light refreshments will be served before the lecture

Experimental and Numerical Investigation of the Subsonic Flow Field inside and near a Weapons Bay