Active cancellation of pure tones in an excited jet

Arbey, H.; Williams, J. E. Ffowcs

doi:10.1017/s0022112084002743

Cited by 58 publications

(21 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Some of these studies focus on shear layer control and use excitation at the separation point [243][244][245][246][247][248][249][250], mechanical actuation [248,[251][252][253], or transverse excitation of the free stream by both standing waves [254] and traveling waves [237,[255][256][257]. Experiments…”

Section: Transverse Forcing Of Typical Combustor Flow Fieldsmentioning

confidence: 99%

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

O’Connor

Acharya

Lieuwen

2015

Progress in Energy and Combustion Science

304

View full text Add to dashboard Cite

Thermoacoustic oscillations associated with transverse acoustic modes are routinely encountered in combustion chambers. While a large literature on this topic exists for rockets, no systematic reviews of transverse oscillations are available for airbreathing systems, such as in boilers, aircraft engines, jet engine augmentors, or power generating gas turbines. This paper reviews work on the problem for air-breathing systems, summarizing experimental, modeling, and active control studies of transverse oscillations. It then details the key physical processes controlling these oscillations by describing transverse acoustic wave motions, the effect of transverse acoustic waves on hydrodynamic instabilities, and the influence of acoustic and hydrodynamic fluid motions on the unsteady heat release. This paper particularly emphasizes the distinctions between the direct and indirect effect of transverse wave motions, by arguing that the dominant effect of the transverse acoustics is to act as the "clock" that controls the frequency and modal structure of the disturbance field. However, in many instances, it is the indirect axial flow disturbances at the nozzles (driven by pressure oscillations from the transverse mode), and the vortices that they excite, that cause the dominant heat release rate oscillations. Throughout the review, we discuss issues associated with simulating or scaling instabilities, either in subscale experimental geometries or by attempting to understand instability physics using identical nozzle hardware during axial oscillations of the same frequency as the transverse mode of interest. This review closes with a model problem that integrates many of these controlling elements, as well as recommendations for future research needs.

show abstract

Section: Transverse Forcing Of Typical Combustor Flow Fieldsmentioning

confidence: 99%

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

O’Connor

Acharya

Lieuwen

2015

Progress in Energy and Combustion Science

304

View full text Add to dashboard Cite

show abstract

“…This seminal work initiated many experimental studies which revealed the large potential of active control techniques. [15][16][17][18][19][20][21][22][23] In this paper, we combine passive and active flow control techniques to rectangular turbulent jets, and analyse the resulting flow field. The former is obtained by using a rectangular shape with various aspect ratios of the jet and the latter is obtained by imposing at the jet inlet an excitation with a specific amplitude and frequency.…”

Section: Introductionmentioning

confidence: 99%

Controlled mixing enhancement in turbulent rectangular jets responding to periodically forced inflow conditions

Tyliszczak

Geurts

2015

Journal of Turbulence

View full text Add to dashboard Cite

We present numerical studies of active flow control applied to jet flow. We focus on rectangular jets, which are more unstable than their circular counterparts. The higher level of instability is expressed mainly by an increased intensity of mixing of the main flow with its surroundings. We analyse jets with aspect ratio A r = 1, A r = 2 and A r = 3 at Re = 10,000. It is shown that the application of control with a suitable excitation (forcing) at the jet nozzle can amplify the mixing and qualitatively alter the character of the flow. This can result in an increased spreading rate of the jet or even splitting into nearly separate streams. The excitations studied are obtained from a superposition of axial and flapping forcing terms. We consider the effect of varying parameters such as the frequency of the excitations and phase shift between forcing components. The amplitude of the forcing is 10% of the inlet centreline jet velocity and the forcing frequencies correspond to Strouhal numbers in a range St = 0.3-0.7. It is shown that qualitatively different flow regimes and a rich variety of possible flow behaviours can be achieved simply by changing aspect ratio and forcing parameters. The numerical results are obtained applying large eddy simulation in combination with a high-order compact difference code for incompressible flows. The solutions are validated based on experimental data from literature for non-excited jets for A r = 1 at Re = 1.84 × 10 5 and A r = 2 at Re = 1.28 × 10 5 . Both the mean velocities as well as their fluctuations are predicted with good accuracy.

show abstract

“…Many researchers have used active control methods to influence the generation and pairing of the primary vortex rings. [3][4][5] In most cases, the jet is ''forced'' by superposing oscillating components on the mean nozzle exit velocity. Control of the dimensionless forcing frequency or frequencies ͑Strouhal number͒ allows control of vortex ring spacing and axial pairing locations.…”

Section: Introductionmentioning

confidence: 99%

Bifurcating jets generated with stepped and sawtooth nozzles

Longmire

Duong

1996

Physics of Fluids

View full text Add to dashboard Cite

A simple round jet is perturbed by attaching either a stepped or a sawtooth trailing edge that acts as a form of passive control. Flow visualization, laser Doppler anemometer, and hot-wire measurements are used to document the flow behavior in both water and air for Reynolds numbers of 7600 and 22 000, respectively. When the jet is forced, the flow bifurcates. The bifurcation requires a low forcing frequency that encourages the formation of tilted primary vortex rings with significant vorticity and axial spacing. In the step nozzle flow, the rings result from closed vortex loops. In the sawtooth nozzle flow, they develop from sections of a helix. A powerful secondary jet initiates in straining regions between primary ring cores, where closed-loop or helical structures with opposite tilt are present. The radial momentum in this jet is large enough to divert the path of the primary jet in the opposite direction. The bifurcating effect was found to be strongest when the forcing frequency was less than or equal to one-third of the natural roll-up frequency.

show abstract

Active cancellation of pure tones in an excited jet

Cited by 58 publications

References 19 publications

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

Transverse combustion instabilities: Acoustic, fluid mechanic, and flame processes

Controlled mixing enhancement in turbulent rectangular jets responding to periodically forced inflow conditions

Bifurcating jets generated with stepped and sawtooth nozzles

Contact Info

Product

Resources

About