Cinematic particle image velocimetry of high-Reynolds-number turbulent free shear layer

Oakley, Thomas R.; Loth, Eric; Adrian, Ronald J.

doi:10.2514/3.13064

Cited by 32 publications

(13 citation statements)

References 27 publications

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“…For entrainment along the free-shear layer itself, the ow can be considered as fully developed turbulent in a small fraction of a step height downstream of the separation point for the Reynolds numbers considered herein. 20 Therefore the entire free-shear layer and reattachment regions were modeled as turbulent.…”

Section: Numerical Implementationmentioning

confidence: 99%

Computational Investigation of Simulated Large-Droplet Ice Shapes on Airfoil Aerodynamics

Dunn

Loth

Bragg

1999

Journal of Aircraft

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The objective of this research was to study numerically the effects of simulated spanwise-step-ice accretions (resulting from supercooled large-droplet icing conditions) on subsonic aircraft aerodynamics. The investigation was performed with a high-resolution full Navier-Stokes code with a solution-adaptiveunstructured grid for both non-iced and iced con gurations. The airfoil investigated was a modi ed NACA 23012 with a simple ap. Simulated ice shapes were tested on the airfoil to determine the sensitivity of ice shape size on airfoil performance and control. Predictions of sectional aerodynamic characteristics for quarter-round ice shape heights of 0.0083 and 0.0139 chords are presented and compared with experimental data. Signi cant reductions in lift were noted for these relatively small protuberances, which were consistent with experimental ndings. The results also indicate good predictive performance for drag, pitching-moment, and hinge-moment variations.

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Section: Numerical Implementationmentioning

confidence: 99%

Computational Investigation of Simulated Large-Droplet Ice Shapes on Airfoil Aerodynamics

Dunn

Loth

Bragg

1999

Journal of Aircraft

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“…Use of a triple pulse ͑instead of just a double͒ eliminates the need for precise synchronization between the shutter and the scanning mirror and increases the signal-to-noise ratio of the PIV correlation ͑Keane and Adrian 17 ͒. Further details of this design, as well as the results of both the single-phase shear layer and bubbly flows, can be found in Oakley 20 and Oakley et al 13,21 The seeding particles used in this study are 8 hollow glass sphere tracer particles ͑specific gravityϭ1.1͒ manufactured by Potters Industries. The particle concentration was approximately 0.002 g/l, which is enough to ''contaminate'' the water but an order of magnitude below the minimum value which denotes ''grossly contaminated'' systems.…”

Section: Cinematic Piv Systemmentioning

confidence: 99%

“…less than 5 mm/s. 20 ͑The error due to interpolating the fluid velocity vector onto the bubble centroid location is discussed later.͒…”

Section: Cinematic Piv Systemmentioning

confidence: 99%

“…Then, these curve fits were differentiated to give the x and y components of bubble velocity (V B ) and acceleration (dV B /dt) as well as the wavelength, amplitude, and frequency of the quasisinusoidal trajectories. The uncertainty in the bubble velocity was estimated to be 0.021 m/s by Oakley,20 which is 4% of the mean streamwise velocity of the bubble. The maximum bubble acceleration uncertainty was estimated by Oakley 20 to be 0.34 m/s 2 , which included effects of bubble centroid uncertainty and the leading-order error assuming a three-point finite difference formulation ͑the latter is conservative since a ninth-order polynomial curve fit was actually used͒.…”

Section: Bubble Diameter Position and Trajectory Determinationmentioning

confidence: 99%

“…The FOR-TRAN code specifically used for these calculations is listed in Oakley. 20 The Auton et al 8 bubble dynamic equation is herein generalized to include a drag force as follows:…”

Section: E Computation Of Instantaneous Bubble Dynamic Forcesmentioning

confidence: 99%

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Forces on ellipsoidal bubbles in a turbulent shear layer

Ford

Loth

1998

Physics of Fluids

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The objective of this research was to gain fundamental knowledge of the drag and lift forces on ellipsoidal air bubbles in water in a turbulent flow. This was accomplished by employing a cinematic two-phase particle image velocimetry ͑PIV͒ system to evaluate bubbly flow in a two-stream, turbulent, planar free shear layer of filtered tap water. Ellipsoidal air bubbles with nominal diameters from 1.5 to 4.5 mm were injected directly into the shear layer through a single slender tube. The cinematic PIV allowed for high resolution of the unsteady liquid velocity vector field. Triple-pulsed bubble images were obtained in a temporal sequence, such that the bubble size and bubble trajectory could be accurately determined. The bubble's oscillation characteristics, velocity, acceleration, and buoyancy force were obtained from the trajectory data. A bubble dynamic equation was then applied to allow determination of the time-evolving lift and drag forces acting upon bubbles within the shear layer. The results indicate that for a fixed bubble diameter ͑and fixed Bond and Morton numbers͒, the drag coefficient decreases for an increasing Reynolds number. This is fundamentally different than the increasing drag coefficient trend seen for ellipsoidal bubbles rising in quiescent baths for increasing diameter ͑and increasing Bond number͒, but is qualitatively consistent with the trend for spherical bubbles. A new empirical expression for the dependence of the drag coefficient on Reynolds number for air bubbles in tap water for both quiescent and turbulent flows is constructed herein. Finally, the instantaneous side forces measured in this study were dominated by the inherent deformation-induced vortex shedding of the bubble wake rather than the inviscid lift force based on the background fluid vorticity.

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