Experimental study of the characteristics of the wake and drag coefficient changes of a car model in unsteady flow

Authors

Department of Mechanical Engineering, Hakim Sabzevari University

Abstract

In this study, changes in velocity, turbulence intensity and drag coefficient in the wake of a notch-back car modelling steady and unsteady flow is measured and evaluated. The blow open circuit wind tunnel is used to simulate fluid flow. Turbulence intensity and nominal maximum speed of the device is measured to be 0.01% and 30m/s, respectively. The speed has been continuously increased by an inverter causing changes in rotational speed of the electromotor. In the near location to the model, the results showed three different regimes in the velocity profile of the model’s wake. With increasing distance from the model and with increasing the speed, three regimes in the wake are close to each other. Drag coefficient for several velocities is measured, where the result shows that decreasing in drag coefficient is proportional with increasing velocity. In addition, the changing trends of higher order velocity of parameters like flatness and skewedness are depicted. 

Keywords


[1]        Barlow, J. B., Rae, W. H., and Pope, A., “Low-Speed Wind Tunnel Testing”, John Wiley & Sons, 1999. Kumagai, S., and Isoda, H., Proc. Combust, Inst. 5, 1984, pp. 129-137.
[2]       Ahmed‚ S. R.‚ Ramm‚ R. and Faltin‚ G., “Some Salient Features of the Time Averaged Ground Vehicle Wake”, SAE Technical Paper Series 840300‚ Detroit, 1998.
[3]      Gilli, P., Chometon, F., “Modelling of Stationary Three-Dimentional Separated Air Flows around an Ahmed Reference Model”, Third International Workshop on Vortex, ESAIM Proceedings, Vol. 7, No.10, 1999, pp. 124.
[4]      Hanaoka, Y., Kiyohira A., “Vehicle Aerodynamic Development using PAMFLOW”, 2003.
[5]      Gillieron, P., Spohn, A., “Flow Separations Generated by a Simplified Geometry of an Automotive Vehicle”, 2007.
[6]      Lienhart, H., Stoocks, C., “Flow and Turbulence Structures in the Wake of a Simplified Car Model (Ahmed Model)”, DGLR FachSymp. Der AG STAB, Stuttgart UNIV., 15-17 Nov, 2010.
[7]      Khalighi, B., Zang, S., Koromilas, C., Balkanyi, S., Bernal, L. P., laccarino, G. and Moin, P., “Experimental and Computational Study of Unsteady Wake Flow behind a Body with a Drag Reduction Device”, SAE PPR. 2006-01-1042.
[8]      Javareshkiyan, M. H., Shayesteh Sadafiyan, R., and Azarkhish, A., “Numerical and Experimental investigation of Aerodynamics forces on the base model of vehicle”, SID, Vol. 18, No. 1, pp. 49-64, (1385 in Persian).
[9]      Javareshkiyan, M. H, Zehsaz, M., and Azarkhish, A., “ExprimentalOptimazation of Aerodynamcs forces on the base model of vehicle”, 9th Fluid Dynamics Conference, Shiraz University, (Esfand 1383 in Persian).
[10]   Watkins, S., Vino, G., “The Effect of Vehicle Spacing on the Aerodynamics of Representative Car Shape”, J. of Wind Engineering and Industrial Aerodynamics 96 1232-12393ED., Vol. 96, No. 3, 2011, pp. 1232-1239.
[11]   Watkins, S., Vino, G., “The Effect of Vehicle Spacing on the Aerodynamics of Representative Car Shape”, J. of Wind Engineering and Industrial Aerodynamics 96 1232-12393ED., Vol. 96, No. 3, 2011, pp. 1232-1239.
[12]   Salari. M., Ardakani. M. A., and Taghavi Zonnor. R., “Experimental Study for Effect of Free Flow Temperature Changes and Hot Wire Anemometer on sensors calibration and Velocity measurement”, Journal of Mechanics and AeroSpace, Vol. 1, No. 3, 1384, pp. 49-59 (in Persian).
[13]   Ardakani, M. A., “Hot Wire Anemometer”, Vol. 1, KhajeNasiroddinTosi University, 1385(in Persian).
[14]   Morelli, A., “General Layout Characteristic and Performance of a new wind Tunnel for Aerodynamics”, SAE Paper No. 710214, Society of Automotive Engineers, Warrendale, Pa., 1971.
[15]   Wolf-Heinrich Hucho., “Aerodynamics of Road Vehicles”, 4th Edition, SAE, Society of Automotive Engineers Inc Warrendale, Pa, 1998.
[16]   Saha, A. K., Muralidhar, K., and Biswas, G. “Experimental Study of Flow Past a Square Cylinder at High Reynolds Numbers”, Experiments in Fluids, Vol. 29, No. 4, 2008, pp. 553-563.
[17]   Shadaram, A., Azimifrad, M., and Rostami, N., “Study of characteristic flow at the near wake of square cylinder”, J. of Mechanical- aerospace Vol. 3, No. 4 1386 in persain.
[18]   Goldstein, S., “A Note on the Measurement of Total Head and Static Pressure on a Turbulent Stream”, Proceedings of the Royal Society of London, Series A, Vol. 155, No. 32, 1936, pp. 570-575.
[19]   LU, B., Bragg, M. B., “Experimental Investigation of the Wake-Survey Method for a Bluff Body with Highly Turbulent Wake”, AIAA-3060, 2002.
[20]   LU, B., Bragg, M. B., “Experimental Investigation of Airfoil Drag Measurements with Simulated Leading-Edge Ice Using the Wake-Survey Method”, AIAA3919, 2000.
[21]   LU, B., Bragg, M. B., “Airfoil Drag Measurement with Simulated Leading Edge Ice Using the Wake-Survey Method”, AIAA1094, 2003.
[22]   Van Dam, C. P., “Recent Experience with Different Methods of Drag Prediction”, Progress in aerospace. Science, Vol. 35, No.8, 1999, pp. 751-798.
[23]   Chowdhury, H., Moria, H., Iftekhar Khan, A., Alam, F., Watkins, S., “A study on aerodynamic drag of a semi-trailer truck”, Procedia Engineering 56, 2013, pp. 201-205.