Three components of mean velocity and the corresponding Reynolds shear stresses have been measured in fully developed concentric and eccentric annulus flows of a Newtonian fluid at bulk-flow Reynolds numbers of 8900 and 26600 and a weakly elastic shear-thinning polymer at effective bulk-flow Reynolds numbers of 1150, 6200 and 9600. The diameter ratio was 0.5 with eccentricities of 0, 0.5 and 1.0, and the use of a Newtonian fluid of refractive index identical to that of the Perspex working section facilitated the measurements by laser velocimetry.With the Newtonian fluid, the distribution of static pressure measurements on the outer wall is shown to be linear, with friction factors for concentric-annulus flows some 8% higher than in a smooth round pipe and for the eccentric flows of eccentricities of 0.5 and 1.0 it was lower by, respectively 8 and 22.5% than that of the concentric-annulus flow. In the former case, the law of the wall was confirmed on both inner and outer walls of the annulus at both Reynolds numbers. This was also the case for the outer wall in the eccentric-annulus flows, except in the smallest gap, but the near-inner-wall flow was not represented by a logarithmic region particularly in the smallest gap. The locations of zero shear stress and zero velocity gradient were displaced by amounts which were, like the secondary flows measured in the eccentric annulus of 0.5, almost within the measurement precision. In the eccentric-annulus flow with eccentricity of 1.0, there was a secondary flow with two circulation cells on each side of the plane of symmetry and with a maximum velocity of 2.2% of the bulk velocity.The measurements with the non-Newtonian fluid were less detailed since refraction limited the flow accessible to the light beams. The average wall shear stress coefficient was similar to that for the Newtonian fluid in the laminar region of the concentric-annulus flow and higher for the two eccentric-annulus flows. Transition was extended to an effective Reynolds number well above that for the Newtonian fluid with a drag reduction of up to 63%. The near-outer-wall flows had logarithmic forms between the Newtonian curve and that of the maximum drag-reduction asymptote, and all fluctuation levels were less than those for the Newtonian fluid, particularly the radial and tangential components.
Experimental and numerical investigations were performed to determine the pressure distributions and the drag forces on a passenger car model. Experiments were carried out with 1/5th scale model FIAT Linea for 20% and ~ 1% blockage ratios in the Uludag University Wind Tunnel (UURT) and in the Ankara Wind Tunnel (ART), respectively. Computational fluid dynamics (CFD) analysis for 1/5th scale model with 0%, 5%, and 20% blockage ratios was performed to validate various blockage correction methods supplementary to the experimental results. Three-dimensional, incompressible, and steady governing equations were solved by STAR-CCM+ code with realizable k–ε two-layer turbulence model. The calculated drag coefficients were in good agreement with the experimental results within 6%. Pressure coefficients on the model surfaces have shown similar trends in the experimental and numerical studies. Some of the existing blockage correction methods were successfully compared in this study and predicted drag coefficients were within ± 5%. The authors propose the continuity and the Sykes blockage correction methods for passenger car models because they are very simple and practical and they can be used economically for engineering applications.
Experimental and computational studies were performed to study the drag forces and the pressure distributions of a one-fifth scale model FIAT Linea at increasing yaw angle and two-vehicle platoon. Experiments were performed in the Uludag University Wind Tunnel (UURT) only for the yaw angles of 0 deg, 5 deg, and 10 deg due to the test section dimensional restriction. Supplementary tests were performed in the Ankara Wind Tunnel (ART) to evaluate the aerodynamic coefficients up to yaw angle of 40 deg. The test section blockage ratios were 20% and 1%, respectively, in the UURT and ART tunnels. The blockage effects for the yaw angles up to 10 deg were studied by the comparison of two wind tunnel results. The aerodynamic tests of two-vehicle platoon were performed in the ART tunnel at spacings of “x/L” 0, 0.5, and 1. Static pressure distributions were obtained from the model centerline and three vertical sections. In the numerical study, three-dimensional, incompressible, and steady governing equations were solved by star-ccm+ code with realizable k-ɛ two-layer turbulence model. Experimental and numerical Cp distributions and Cd values were found in good agreement for considered yaw angles and two-vehicle platoon. Maximum drag coefficient was obtained at yaw angle of 35 deg for both experimental and numerical calculations. The two-vehicle platoon analysis resulted with the significant drag coefficient improvement for the leading car at spacings of x/L = 0 and 0.5, while for the tail car drag coefficient remained slightly above the vehicle in isolation.
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