A Prediction Model for Separated-Flow Transition

Hatman, Anca; Wang, T.

doi:10.1115/1.2841357

Cited by 77 publications

(28 citation statements)

References 17 publications

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“…velocities are also plotted in figure 12(b,c) for comparison. The behaviour of the exponential growth for (v /U ∞ ) max is similar with that for (−uv/U 2 ∞ ) max , suggesting that the boundary layer transition over the airfoil at this Reynolds number is dominated by K-H instability (Hatman & Wang 1999).…”

Section: Flow Separation and Reattachmentsupporting

confidence: 48%

Flow control over an airfoil using virtual Gurney flaps

2015

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Flow control over a NACA 0012 airfoil is carried out using a dielectric barrier discharge (DBD) plasma actuator at the Reynolds number of 20 000. Here, the plasma actuator is placed over the pressure (lower) side of the airfoil near the trailing edge, which produces a wall jet against the free stream. This reverse flow creates a quasi-steady recirculation region, reducing the velocity over the pressure side of the airfoil. On the other hand, the air over the suction (upper) side of the airfoil is drawn by the recirculation, increasing its velocity. Measured phase-averaged vorticity and velocity fields also indicate that the recirculation region created by the plasma actuator over the pressure surface modifies the near-wake dynamics. These flow modifications around the airfoil lead to an increase in the lift coefficient, which is similar to the effect of a mechanical Gurney flap. This configuration of DBD plasma actuators, which is investigated for the first time in this study, is therefore called a virtual Gurney flap. The purpose of this investigation is to understand the mechanism of lift enhancement by virtual Gurney flaps by carefully studying the global flow behaviour over the airfoil. First, the recirculation region draws the air from the suction surface around the trailing edge. The upper shear layer then interacts with the opposite-signed shear layer from the pressure surface, creating a stronger vortex shedding from the airfoil. Secondly, the recirculation region created by a DBD plasma actuator over the pressure surface displaces the positive shear layer away from the airfoil, thereby shifting the near-wake region downwards. The virtual Gurney flap also changes the dynamics of laminar separation bubbles and associated vortical structures by accelerating laminar-to-turbulent transition through the Kelvin-Helmholtz instability mechanism. In particular, the separation point and the start of transition are advanced. The reattachment point also moves upstream with plasma control, although it is slightly delayed at a large angle of attack.

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Section: Flow Separation and Reattachmentsupporting

confidence: 48%

Flow control over an airfoil using virtual Gurney flaps

2015

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“…Tests at K = -10 xlO" 7 separate a little sooner, near a local Reynolds number of 1.69 xlO"\ and also reattach turbulent shortly downstream. This agrees with a previous AFOSR supported study on separated flow transition by Hatman and Wang (1998). Data plotted in Figure 13 appears to match previous data well, and falls into the region predicting laminar separation, short bubble transition.…”

Section: Effects Of Pressure Gradientsupporting

confidence: 91%

“…A strong adverse pressure gradient is shown above. Transition onset under strong adverse pressure gradient compared with previous study by Hatman and Wang (1998). Data falls into region of laminar separation, short bubble transition.…”

Section: Effects Of Pressure Gradientmentioning

confidence: 72%

Turbulent Spot Characterization and the Modeling of Transitional Heat Transfer in Turbines

LaGraff¹

2001

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PuBic reportinf burden for this collection of information is estimated to average 1 hour per response, inclui Gathering and maintaining the data needed, and completing and reviewing the college «-^formation, be collection of information, including suggestions for reducing this burden, to Was,^n AbstractOptimum design of gas turbine blades depends on accurate prediction of boundary layer transition. The purpose of this research is to obtain more information on the generation, propagation, and coalescence of turbulent spots in a transitional boundary layer, and examine the effects of freestream turbulence, pressure gradient, and crossflow. Experimental data from this study may be used to improve existing CFD models, allowing designers to make more accurate predictions of transitional heat transfer in turbines.Time (

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“…Once the laminar kinetic energy is created in the separated shear layer, it must be transferred to the turbulence field to trigger the transition process, as shown by numerical [26] and experimental investigations [27]. The laminar and turbulent kinetic energy equations can be written in a general form as follows…”

Section: Transition and Turbulence Modellingmentioning

confidence: 99%

An assessment of the laminar kinetic energy concept for the prediction of high-lift, low-Reynolds number cascade flows

Pacciani

Marconcini

Arnone

et al. 2011

Proceedings of the Institution of Mechanical Engineers, Part A:

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Abstract:The laminar kinetic energy (LKE) concept has been applied to the prediction of lowReynolds number flows, characterized by separation-induced transition, in high-lift airfoil cascades for aeronautical low-pressure turbine applications. The LKE transport equation has been coupled with the low-Reynolds number formulation of the Wilcox's k À ! turbulence model. The proposed methodology has been assessed against two high-lift cascade configurations, characterized by different loading distributions and suction-side diffusion rates, and tested over a wide range of Reynolds numbers. The aft-loaded T106C cascade is studied in both high-and low-speed conditions for several expansion ratios and inlet freestream turbulence values. The front-loaded T108 cascade is analysed in high-speed, low-freestream turbulence conditions. Numerical predictions with steady inflow conditions are compared to measurements carried out by the von Kármán Institute and the University of Cambridge. Results obtained with the proposed model show its ability to predict the evolution of the separated flow region, including bubble-bursting phenomenon and the formation of open separations, in high-lift, low-Reynolds number cascade flows.

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A Prediction Model for Separated-Flow Transition

Cited by 77 publications

References 17 publications

Flow control over an airfoil using virtual Gurney flaps

Flow control over an airfoil using virtual Gurney flaps

Turbulent Spot Characterization and the Modeling of Transitional Heat Transfer in Turbines

An assessment of the laminar kinetic energy concept for the prediction of high-lift, low-Reynolds number cascade flows

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