Optimization study of a Coanda ejector
The Coanda effect has long been employed in the aerospace applications to improve the performances of various devices. This effect is the ability of a flow to follow a curved contour without separation and has well been utilized in ejectors where a high speed jet of fluid emerges from a nozzle in the ejector body, follows a curved surface and drags the secondary flow into the ejector. In Coanda ejectors, the secondary flow is dragged in the ejector due to the primary flow momentum. The transfer of momentum from the primary flow to the secondary flow takes place through turbulent mixing and viscous effects. The secondary flow is then dragged by turbulent shear force of the ejector while being mixed with the primary flow by the persistence of a large turbulent intensity throughout the ejector. The performance of a Coanda ejector is studied mainly based on how well it drags the secondary flow and the amount of mixing between the two flows at the ejector exit. The aim of the present study is to investigate the influence of various geometric parameters and pressure ratios on the Coanda ejector performance. The effect of various factors, such as, the pressure ratio, primary nozzle and ejector configurations on the system performance has been evaluated based on a performance parameter defined elsewhere. The performance of the Coanda ejector strongly depends on the primary nozzle configuration and the pressure ratio. The mixing layer growth plays a major role in optimizing the performance of the Coanda ejector as it decides the ratio of secondary mass flow rate to primary mass flow rate and the mixing length.
KeywordsCoanda ejector compressible mixing layer flow dragging mixing length induced flow
Unable to display preview. Download preview PDF.
- Gilchrist, A. R. and Smith, D. G. G.: Compressible Coanda Wall Jet: Predictions of Jet Structures and Comparison with Experiment, Intl. J. Heat and Fluid Flow, Vol.9, no.3, (1988)Google Scholar
- Smith, D. G. G. and Gilchrist, A. R.: The Compressible Coanda Wall Jet — An Experimental Study of Jet Structure and Breakaway, Intl. J. Heat and Fluid Flow, Vol.8, (1987)Google Scholar
- Smith, D. G. G. and Senior, P.: The Effect of Base Steps and Axisymmetry on Supersonic Jets over Coanda Surfaces, Intl. J. Heat and Fluid Flow, Vol.15, no.4, (1994)Google Scholar
- Morison, J. F and Smith, D. G. G.: Calculation of an Axisymmetric Turbulent Wall Jet over a Surface of Convex Curvature, Intl. J. Heat and Fluid Flow, Vol.5, (1984)Google Scholar
- Kim, H. D., Raghunathan, S., Setoguchi, T. and Matsuo, S.: Experimental and Numerical Studies of Coanda Wall Jet, AIAA-2000-0814, 38th Aerospace Sciences Meeting & exhibit, Reno, Nevada, (2000)Google Scholar
- Ameri, M.: An Experimental and Theoretical Study of Coanda Ejectors, Ph. D thesis, Case Western Reserve University, (1993)Google Scholar
- Guerriero, V., Baldas, L. and Caen, R.: Numerical Solutions of Compressible Flow Mixing in Coanda Ejectors,” Proc. The Eighth Symposium on Fluid Control, Measurement and Visualization, China Society of Theoretical and Applied Mechanics, Chengdu, China, (2005)Google Scholar
- Bogdanoff, D. W.: Compressible Effects in Turbulent Shear Layers, AIAA Journal, Vol. 21, (1989)Google Scholar
- Barre, S., Quine, C. and Dussauge, J. P.: Compressibility Effect on the Structure of Supersonic Mixing Layers: Experimental Results, Journal of Fluid Mechanics, Vol. 259, (1994)Google Scholar