Active flow control of a precessing jet is the focus of this work. A round jet confined by a concentric round cavity exhibits a self-excited rotational motion, precession, for a specific range of cavity lengths. Active flow control of this unstable flow provides the ability to control near-field mixing of the precessing jet. This work is a collaboration between Dr. Koch and Dr. Nobes.
Twelve micro-jets on the periphery of the nozzle inlet are used as actuation and near-field pressure data is measured by four pressure probes at the chamber exit to monitor the flow behavior.
Figure 2: Schematic
Figure 2: Schematic
Experimental Results - phase plane
A phase plane, based on pressure signals, is used to find a Reynolds number and actuation frequency range where actuation stabilizes the flow motion.
Figure 3: the influence of frequency and Reynolds number on Standard deviation of phase of the triggered pressure data for chamber length L to chamber diameter D of: 2:0 < L/D < 3.5, without center body.
Experimental Results - phase locked PIV
Phase-locked stereoscopic PIV, triggered by actuation signals, is also used to validate the 4 pressure measurements.
Figure 4: An example Instantaneous outflow (out of plane) velocity and in-plane velocity vector field at Re=62,000 with CW actuation, triggered by injector 10
Figure 5: An example Instantaneous outflow (out of plane) velocity and in-plane velocity vector field at Re=62,000 with CW actuation, triggered by injector 10
The results confirm the pressure measurement and micro-jet actuation can be employed to develop a future closed-loop flow control on precessing jet.
Video showing jet center exiting shroud - first without actuation and then with actuation turned on.
C. R. Koch - Website
D. N. Nobes - Website
H. Babazadeh, C. R. Koch, and D. S. Nobes. Investigation of micro-jet active control of a precessing jet using PIV. Experiments in Fluids, 51:1709-1719, 2011. 10.1007/s00348-011-1193-0.
H. Babazadeh. Active flow control of a precessing jet. M.Sc. thesis, University of Alberta, 2010.