An experimental investigation into the effect of initial conditions on simultaneous amplitude and phase modulation of fluctuations in the transition of a planar turbulent jet
Abstract
The result of an experimental investigation into the effect of initial conditions on the simultaneous amplitude and phase modulation of fluctuations characterizing the transition of a planar turbulent jet at moderate Reynolds number is presented. Instantaneous amplitude and phase modulates are computed directly from hot-wire velocity fluctuation data which allows their respective role in the jet transition process to be quantified. Very low level periodic acoustic excitation is applied upstream of the nozzle exit in order to introduce an organized carrier wave into the flow. Two categories of applied acoustic excitation are considered: in the 'tuned case' the ratio of the thin, shear layer instability frequency to the jet column frequency is an integer power of two so that a sequence of shear layer vortex pairing events is fully capable of yielding the jet column mode near the end of the potential core. This is contrasted with the 'untuned case' in which the jet shear layer instability must undergo more dramatic frequency and phase adjustments in order to satisfy the downstream jet column constraint.
- Publication:
-
Forum on Turbulent Flows - 1990
- Pub Date:
- 1990
- Bibcode:
- 1990ftf..proc...91T
- Keywords:
-
- Acoustic Excitation;
- Hot-Wire Anemometers;
- Transition Flow;
- Turbulence Effects;
- Turbulent Jets;
- Boundary Value Problems;
- Flow Stability;
- Jet Nozzles;
- Shear Layers;
- Vortices;
- Fluid Mechanics and Heat Transfer