The flow around bluff bodies at subsonic speeds exhibit regions of flow separation and shear layer attachment, vortical structure formation and vortex shedding. The overall focus of the proposed effort is to characterize the dynamics of flows past bluff bodies with upswept base regions. The study involves experimental measurements to be carried out at FSU and simulations will be performed at Ohio State University. At FSU, the flowfield will be characterized in substantial detail using an array of conventional and advanced diagnostic tools. At a qualitative level, the evolution of the surface flow topology with compressibility and Reynolds number will be explored through surface flow visualizations. Careful application of this method can provide significant infomiation about the three-dimensional flow since it represents the surface footprint. Even though the relationship is not one-to-one, some of the key features of the spanwise/crossflow can be discerned through the mean surface topology. In particular, the location, orientation, and evolution of various lines of coalescence and divergence, together with associated clitical points (nodes/foci and saddle points) provide a framework for a clear description of different regimes that arise with parametric change. In addition to surface visualizations, mean and unsteady surface measurements will be obtained. These high-resolution measurements can be distilled to analyze some of the unsteady dynamics that drive the flow evolution. At a more advanced level, we will leverage optical methods which have seen substantial advances in flowfield illumination (lasers), image acquisition and processing algotithms and hardware. This facilitates the acquisition of highly resolved spatial, and to a more limited extent, temporal, measurements of the flowfield. Particle Image Velocimetry (PIV) has particularly benefitted from these recent advances. We will use increasingly advanced PIV methods to document and elucidate dynamics of this flowfield, its relationship with the surface features and the evolution with geometry (upsweep angle, compressibility and Reynolds number). In the initial stages, planar or 2-Component PIV will be obtained along appropliate streamwise planes of symmetry to map the most relevant flow features and identify significant transition points in its evolution, if any. Once the basic structure is identified, stereoscopic/3-Component PIV (S-PJV) will be employed to provide all three components of the velocity field in a plane. Tomographic PIV (TPIV), an extension of SPIV, enables measurement of all three velocity components in a 3-D volume. A standard TPIV system requires a 4-camera arrangement; FCAAP-FSU has the requisite hardware and software to obtain such measurements. TPJV will enable us to examine the properties and spatial evolution of complex 3-D flow features such as the development of the dual, counter-rotating vortices along the up sweep plane and in the wake of the model. Time-resolved PIV will be deployed to explore flow features identified in either surface pressure measurements or the accompanying simulations. There are two broad ways explore the evolution of temporally coherent feature: either use "real-time" high repetition rate PIV or make conditional measurements based on pertinent flow events. FSU is acquiring IO - 20/cHz PIV systems that can be used to obtain "time-series" PIV data, from which coherent and stochastic flow field properties can be extracted, at least in the lower speed regime, where the time scales are relatively large. For higher speeds, the above acquisition rates will not adequately resolve the temporal behavior, given the speeds and time-scales associated with this flow. A more promising approach is then to obtain phase-conditioned velocity field measurements. Using an unsteady pressure sensor, critical events, can be used to conditionally sample the flow and thus study the spatio-temporal evolution of such features. This data will result in an improved understanding of the role of compressibility while also providing additional flow properties for more robust validation of the companion simulations at OSU. The Pis at FSU have extensive experience in acquiring PIV and similar measurement data over a range of flowfield at different scales and high-speed flows The experiments will be carried out in both the FSU Low-Speed Wind Tunnel (LSWT) and the Polysonic Wind tunnel, PSWT. The LSWT is an open circuit facility with a square test section measuring 30-in x 30-in that extends 60-in in the flow direction. The facility is driven by an axial fan powered by a 150HP, direct drive AC induction motor. The motor is controlled by a Toshiba variable frequency drive that outputs a constant frequency power signal between 2 and 50 Hz. The range of freestream velocity is 2 m/s to 80 m/s and a corresponding maximum Reynolds number of 2.4 million/ft. To achieve flow uniformity and low-turbulence (< 0.05%), the facility is designed and equipped with 9: I contraction ratio, honeycomb inlet and three stainless steel meshes of appropriate porosity. The PSWT has a 12-in x 12-in cross-section, capable of operating in the Mach number regime of 0.2 to 5 including transonic speeds. The facility produces a unit Reynolds number of 30 million/ft. The PSWT features two separate test sections: I) 12-in x 12-in x 24-in test section with solid walls for sub/supersonic Mach number testing, and 2) 12-in x 12-in x 48-in with slotted walls for testing in the transonic speed regime. This facility allows us to cover a large range of the main interaction parameters, such as Mach and Reynolds number. The wind tunnel is equipped with required instrnmentation including six component strain gauge balances to measure aerodynamic forces and moments, electronic pressure scanners (ESP) for steady pressure distributions and Kulite pressure transducers for unsteady pressures. The facility is designed for maximum optical access and with flow diagnostic capabilities such as Schlieren, shadowgraph, surface oil flow visualizations, Particle Image Velocimetry and the Pressure Sensitive Paint technique. The side windows in the transonic test section are fitted with optical quality glass. Test models can be either supported by a sting and pitch /roll mechanism capable of pitch (cr = -10° to +45°) and roll (±180°) during the blowdown or roof/floor-mounted to mitigate sting interference effects. The polysonic wind tunnel is designed to produce excellent flow quality, an important requirement for the present study. This is achieved through a 10: I inlet contraction ratio, five fine mesh flow conditioning screens, flow straightener and settling chamber acoustic treatment. The tunnel floor noise levels at the sub/transonic Mach numbers ( = 0.2 -- 1.1) measured in tenns of root mean square pressure fluctuations, Cp rms is <= 1 %.