Experimental Validation of the Kinematic Theory of Unsteady Separation

Peacock, Thomas; Coral, Raul; Haller, George

doi:10.2514/6.2005-4903

Cited by 4 publications

(4 citation statements)

References 18 publications

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“…A thorough investigation of deep transition and unsteady separation, including a comparison between asymptotics and numerics, can be found in Bowles et al (2003). The narrow eruptive spires are clearly observable in recent careful experiments and direct numerical simulations by Peacock et al (2005). All these analytical, numerical and experimental findings lend credence to our view that viscous/inviscid interaction controls transition up to the position where intermittency gets close to 1 owing to the spreading and ensuing amalgamation of spiking wave packets.…”

Section: Correlationmentioning

confidence: 72%

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Transition length in turbine/compressor blade flows

Ryzhov

2006

Proc. R. Soc. A.

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High Reynolds number mathematical models for convected vortex impinging against a local hump and sound scattering into Tollmien–Schlichting eigenmodes are introduced to simulate basic mechanisms of the disturbance excitation typical of turbomachinery environments. The streamwise dimension of the transitional flow on the suction side of a blade is evaluated on the assumption that the transition length is of equal order with the extent of viscous/inviscid interaction controlling the boundary-layer response. The triple-deck theory gives a simple power law correlation to express a value of the Reynolds number based on the transition length in terms of the Reynolds number calculated with the blade cord. Precisely the same correlation stems from processing experimental data for both smooth and rough surfaces. The computation shows the explosive development of highly modulated wave packets and their rapid breakdown brought about by erratic short-scaled wiggles riding on the primary long-scaled oscillation cycles. The filling-up of distant parts of the wavenumber spectrum is at the heart of the signal distortion. This process heralds the start of deep transition terminating in fully developed turbulent flow well before reaching the upper stability branch. With the time-harmonic excitation broadly used in experiments, transition requires a much longer distance to complete. An agreement between theoretical predictions based on the assumption of indefinitely large Reynolds numbers and experimental findings from wind-tunnel observations at finite Reynolds numbers is encouraging.

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Section: Correlationmentioning

confidence: 72%

“…Thus, the final phase of transition does not appreciably change its length, primarily determined by viscous/inviscid interaction and a singularity arising in the velocity field (Smith 1988). The formation of eruptive spires is seen in dye visualization of material spikes by Peacock et al (2005).…”

Section: Discussionmentioning

confidence: 99%

Transition length in turbine/compressor blade flows

Ryzhov

2006

Proc. R. Soc. A.

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“…The criterion gives a linear approximation for the separation profile (straight line), which notably differs from the separation line inferred from instantaneous streamlines (curve on the right). See [7] for details; joint work with Tom Peacock (MIT).…”

Section: Approachmentioning

confidence: 99%

Control of Unsteady Separation: A Dynamical Systems Approach

Haller¹

2005

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'Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for revriewing instruO t needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect ofl to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jeffa should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a coltecq number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

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“…While such manifolds remain hidden in instantaneous streamline, vorticity, and pressure plots, they are readily seen in flowvisualization experiments as sharp material spikes emanating from the wall. 19 Using the above kinematic theory, one can construct a closed-loop algorithm for controlling unsteady separation in two-dimensional time-periodic Stokes flows. 20 The algorithm includes a delay effect arising from the finite distance between the wall-based actuators and the intended separation point.…”

Section: Introductionmentioning

confidence: 99%

Closed-loop separation control: An analytic approach

2006

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We develop an analytic approach to two-dimensional flow separation control by feedback. With two wall-based actuators enclosing an array of distributed wall-shear sensors, we control the wall-shear evolution equation through its boundary values at the actuators. Using this approach, we induce separation at prescribed locations in steady and unsteady channel flows, and reduce the recirculation length behind a backward-facing step to a prescribed value.

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Experimental Validation of the Kinematic Theory of Unsteady Separation

Cited by 4 publications

References 18 publications

Transition length in turbine/compressor blade flows

Transition length in turbine/compressor blade flows

Control of Unsteady Separation: A Dynamical Systems Approach

Closed-loop separation control: An analytic approach

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