1 Copyright © 2008 by ASME Proceedings of the 9th Biennial ASME Conference on Engineering Systems Design and Analysis ESDA08 July 7-9, 2008, Haifa, Israel ESDA2008-59509 ACTIVE CONTROL OF AN INCOMPRESSIBLE AXISYMMETRIC JET D. Greenblatt Faculty of Mechanical Engineering Technion – Israel Institute of Technology Technion City – Haifa 32000, Israel Y. Singh, C.N. Nayeri and C.O. Paschereit Institute of Fluid Mechanics & Technical Acoustics Technical University of Berlin 10623 Berlin, Germany N. K. Depuru Mohan Department of Aerospace Engineering Indian Institute of Technology Madras Chennai 600036, India ABSTRACT An experimental investigation was conducted to compare the active generation and management of streamwise vortices in an incompressible jet flow using different flow control methods. The lip of the jet was equipped with a small flap deflected away from the stream at an angle of 30°, that incorporated a flow control slot through which steady suction, oscillatory suction and zero mass-flux perturbations were introduced. Data acquired were compared on the basis of momentum addition to the jet, the generation of streamwise vorticity and the generation of turbulent stresses. All active control methods produced an increase in jet momentum, stronger streamwise vortices and higher turbulence levels than those produced by a simple tab. The increase in jet momentum, combined with the generation of strong streamwise vortices and elevated turbulence levels, indicates potential for improvements in propulsion efficiency, mixing and possibly jet noise reduction. 1. INTRODUCTION An understanding of the mixing of turbulent flows is vital for the design and analysis of many engineering systems. Mixing governs processes such as the energy release-rate during combustion, the noise generated by high-speed jets and the infrared signature produced by hot plumes. Common passive techniques that have been used to enhance mixing include lobed mixers, serrated nozzles, chevrons and tabs (e.g. Stone et al, 2003; Calkins and Butler, 2004; Bradbury and Khadem, 1975; and Zaman et al, 1991). In essence, these techniques aim to increase the interfacial area between the jet and the ambient fluid, thereby producing an increase in streamwise vorticity and turbulent stresses. Active approaches to jet control generally involve low amplitude perturbations intended to excite preexisting flow instabilities that strengthen large-scale structures (Crow and Champagne, 1971) and regulate vortex paring (Zaman and Hussain, 1980; Reynolds and Bouchard, 1981). Simultaneous excitation of axial and azimuthal modes (Lee and Reynolds, 1985) leads to significant changes in the flow field of circular jets. The effect of excitation amplitude was investigated by Parekh, Reynolds, and Mungal (1987), which impacts on the spreading angle of the jet. A different approach uses high amplitude forcing that can be on the order of the base flow, at frequencies that are not necessarily related to the base flow stability characteristics (Parekh et al. 1996). 2. NOMENCLATURE A area of the circular jet C Q dimensionless volumetric suction rate C μ dimensionless momentum coefficient C p coefficient of pressure D diameter of the circular jet D t turbulent diffusion coefficient f excitation frequency F + dimensionless excitation frequency J momentum of the jet L flap length M a mixing augmentation p pressure measured at the pressure tap p ∞ reference pressure Q volumetric suction rate Re Reynolds number U 0 exit velocity of the jet u,v,w mean velocity components