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The time averaged wake structure of a realistically dimensioned quarter scale automobile model was studied in a wind tunnel on the basis of flow visualization, wake surveys, force and pressure measurements. Through a systematic variation of base slant angle in the range of 0 to 40 deg, the ensuing changes in the wake structure were observed and the wake structure present at lowest value of aerodynamic drag is shown. Experimental data were obtained at a model length based Reynolds number of 4.29 million. Correlation of wake structure with drag, pressure distribution, and kinetic energy content of vortex motion in wake is addressed.

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The time averaged wake structure of three characteristic vehicle shapes viz. Estate, Fastback and Notchback was studied on the basis of flow visualization and wake surveys behind smooth quarter scale models in a wind tunnel. The models differed through their upper rear-end shape. Flow in the separation bubble at vehicle base and the subsequent formation of a pair of longitudinal vortices aft of this region is analysed. The kinetic energy of the rotational motion in the wake is evaluated to give a “vortex drag” rating for the vehicle shapes investigated. Effect of body details was assessed by a parallel set of experiments with detail models of same principal dimensions. Force measurements supplemented the investigations.

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High quality polymer free CO 2 foam possesses unique properties that make it an ideal fluid for fracturing unconventional shales. In this paper, the viscosity of polymer free fracturing foam and its empirical correlations at high pressure high temperature (HPHT) as a function of surfactant concentration, salinity, and shear rate are presented. Foams were generated using a widely-used surfactant, i.e., alpha olefin sulfonate (AOS) in the presence of brine and a stabilizer at HPHT. Pressurize foam rheometer was used to find out the viscosity of CO 2 foams at different surfactant concentration (0.25-1 wt %) and salinity (0.5-8 wt %) over a wide range of shear rate (10-500 s −1 ) at 1500 psi and 80 • C. Experimental results concluded that foam apparent viscosity increases noticeably until the surfactant concentration of 0.5 wt %, whereas, the increment in salinity provided a continuous increase in foam apparent viscosity. Nonlinear regression was performed on experimental data and empirical correlations were developed. Power law model for foam viscosity was modified to accommodate for the effect of shear rate, surfactant concentration, and salinity. Power law indices (K and n) were found to be a strong function of surfactant concentration and salinity. The new correlations accurately predict the foam apparent viscosity under various stimulation scenarios and these can be used for fracture simulation modeling.