1 3 Exp Fluids (2016) 57:60 DOI 10.1007/s00348-016-2145-5 RESEARCH ARTICLE Experimental characterization of turbulent subsonic transitional–open cavity flow T. Rokita 1 · Y. Elimelech 1 · R. Arieli 1 · Y. Levy 2 · J. B. Greenberg 1 Received: 23 October 2015 / Revised: 17 February 2016 / Accepted: 25 February 2016 © Springer-Verlag Berlin Heidelberg 2016 aircraft (payload bay). Flow over these cavities causes undesirable effects, such as self-sustaining oscillations and high-intensity tones (as high as 160–180 dB; Shaw 1995), which can significantly reduce the life of aerostructures in the bay and can damage sensitive electronic components (primarily in deep cavities). Flow over cavities is encountered in many other indus- trial applications. A few examples are window or sunroof of a running car, electronic chips on a circuit board, adja- cent buildings, etc. Growing interest in many cavity appli- cations in aerospace gave rise to major research regarding cavity flow and the related aeroacoustics. Through many experiments and computations, a great deal has been learned about the flows in and around rectangular cavities. However, the physics behind these complex flows is not fully understood yet. Despite its simple geometry, a cavity generates compli- cated flow that is rich in unsteady flow features and flow- acoustic interactions. The complex flow field generated in and around a cavity may be studied in various ways, and the results may be combined to create a complete flow pic- ture. Cavity flows are highly unsteady and three dimen- sional, even for a cavity of a low length-to-width ratio (L/W) as observed by Maull and East (1963). However, it is common in the literature to study and characterize the type of cavity flow by its time-averaged two-dimensional features (as originally introduced by Charwat et al. 1961). Three-dimensional structures of cavity flows have been studied and characterized to a lesser extent due to difficul- ties in definitively identifying less steady flow behavior. Flow field patterns observed using flow visualiza- tion techniques and studying time-averaged static pres- sure distributions along cavity centerlines have lead to the identification of three main flow types entitled, “open,” “closed,” and “transitional” (Charwat et al. 1961; Tracy Abstract Turbulent subsonic “transitional–open” cavity flow was investigated by wind-tunnel tests. The investigated cavity configuration had a length-to-depth ratio of 6.25 and a width-to-depth ratio of 2. The cavity was exposed to a free-stream Mach number of 0.40 and a Reynolds num- ber (based on cavity depth) of 1.6 × 10 6 , with a turbulent incoming boundary layer. Measurements of velocity and wall pressures were taken simultaneously, which enabled the analysis of velocity–pressure cross-correlations. Spe- cial attention is paid to the shear layer that develops over the cavity and an emphasis is placed on the analysis of its characteristics and its stability. Application of linear hydro- dynamic stability theory, together with examining veloc- ity–pressure cross correlations, revealed that the behavior of the cavity shear layer is analogous to a free shear layer, approximately up to mid-length of the cavity, where further downstream nonlinear interactions occur. 1 Introduction 1.1 Background The phenomenon of flow over cavities has become the focus of much research interest recently due to the impor- tance of noise reduction of commercial aircraft (wheel well) and of stealth and aerodynamic efficiency of military * T. Rokita rokita.tomer@gmail.com 1 Faculty of Aerospace Engineering, Technion - IIT, 32000 Haifa, Israel 2 Israeli CFD Center, Caesarea Industrial Park, 38900 Caesarea, Israel