A method for analyzing dynamic stall

Crimi, Peter; Reeves, Barry L.

doi:10.2514/6.1972-37

Cited by 15 publications

(7 citation statements)

References 5 publications

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“…Much of this work has been surveyed by Ward (1963). Recently, Crimi & Reeves (1972) and McCroskey & Philippe (1975) have combined semi-empirical theories for separation bubbles with inviscid flow theories and finite-difference calculation procedures for unsteady Iaminar and turbulent boundary layers, in efforts to predict dynamic stall. There does not appear to have been any previous attempt, however, to compute a transitional separation bubble in detail.…”

Section: Introductionmentioning

confidence: 99%

Numerical prediction of incompressible separation bubbles

Briley¹,

McDonald²

1975

J. Fluid Mech.

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A method is presented for performing detailed computations of thin incompressible separation bubbles on smooth surfaces. The analysis consists of finite-difference solutions to the time-dependent boundary-layer or Navier-Stokes equations for the flow in the immediate vicinity of the bubble. The method employs the McDonald-Fish turbulence model, to predict the development of the time-mean flow field, as influenced by the free-stream turbulence level. It also employs a viscous-inviscid interaction model, which accounts for the elliptic interaction between the shear layer and inviscid free stream. The numerical method is based on an alternating-direction implicit scheme for the vorticity equation. It employs transformations, to allow the free-stream boundary to change in time with the shape of the computed shear layer, and to ensure an adequate resolution of the sublayer region. Numerical solutions are presented for transitional bubbles on an NACA 663-018 airfoil at zero angle of incidence with chordal Reynolds numbers of 2·0 × 106 and 1·7 × 106. These have a qualitative behaviour similar to that observed in numerous experiments; they are also in reasonable quantitative agreement with available experimental data. Little difference is found between steady solutions of the boundary-layer and Navier-Stokes equations for these flow conditions. Numerical studies based on mesh refinement suggest that the well-known singularity at separation, which is present in conventional solutions of the steady boundary-layer equations when the free-stream velocity is specified, is effectively removed when viscous-inviscid interaction is allowed to influence the imposed velocity distribution.

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Section: Introductionmentioning

confidence: 99%

Numerical prediction of incompressible separation bubbles

Briley¹,

McDonald²

1975

J. Fluid Mech.

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Section: Methods Of Solutionmentioning

confidence: 99%

“…Finite difference calculations of time-dependent boundary layers around oscillating airfoils have been performed by Crimi and Reeves [42], Scruggs et al [43] and McCroskey and Philippe [30]. In references [42] and [43] the primary objective is the analysis of airfoil dynamic stall whereas in [30] the emphasis is on the investigation of viscous flow around both stalled and unstalled airfoils. The numerical method of [30] (based on the implicit finite difference scheme of Dwyer [23], [24]) will be used in the present study because it is simple, is more directly applicable to the present situation and, most importantly, permits the rapid solution of the boundary layer equations.…”

Section: Methods Of Solutionmentioning

confidence: 99%

“…The error damped out slightly faster when the above procedure was used as compared to the situation in which the computations were started at For two-dimensional incompressible flows there are several, mostly empirical, methods [27], [42], [46], [47] available for predicting transition due to the growth of laminar instabilities. However, none of the methods take into account unsteady effects.…”

Section: Finite Difference Schemementioning

confidence: 99%

“…by several investigators [51], [42], [30], [52], In all of these com- The number of streamwise locations around the airfoil was kept at 105 (for the completely laminar case there were only 45 such locations).…”

Section: Unsteady Flow Calculations Based On This Model Have Been Per...mentioning

confidence: 99%

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Drag on an Oscillating Airfoil in a Fluctuating Free Stream

Kottapalli

Pierce

1979

Journal of Fluids Engineering

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An analytical study is presented regarding the unsteady skin friction drag of an oscillating airfoil exposed to a fluctuating free stream speed. Both laminar and turbulent conditions are covered in the analysis. The unsteady potential flow pressure and velocity distributions required for the subsequent boundary layer analysis are obtained by an approximate development. The time-dependent boundary layer is solved by a finite difference scheme. It was found that depending on the values of the phase difference between free stream fluctuations and airfoil oscillations, reduced frequency, and amplitude of free stream fluctuations, the drag can either lead or lag the free stream.

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Prediction of leading-edge-vortex initiation using criticality of the boundary layer

Ramanathan

Gopalarathnam

2023

Theor. Comput. Fluid Dyn.

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The initiation of leading-edge-vortex formation in unsteady airfoil flows is governed by flow criticality at the leading edge. While earlier works demonstrated the promise of criticality of leading-edge suction in governing LEV shedding, this criterion is airfoil and Reynolds number dependent. In this work, by examining results from Navier-Stokes computations for a large set of pitching airfoil cases at laminar flow conditions, we show that the onset of flow reversal at the leading edge always corresponds to the boundary-layer shape factor reaching the same critical value that governs laminar flow separation in steady airfoil flows. Further, we show that low-order prediction of this boundary-layer criticality is possible with an integral-boundary-layer calculation performed using potential-flow velocity distributions from an unsteady panel method. The low-order predictions agree well with the high-order computational results with a single empirical offset that is shown to work for multiple airfoils. This work shows that boundary-layer criticality governs LEV initiation, and that a low-order prediction approach is capable of predicting this boundary-layer criticality and LEV initiation.

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A method for analyzing dynamic stall

Cited by 15 publications

References 5 publications

Numerical prediction of incompressible separation bubbles

Numerical prediction of incompressible separation bubbles

Drag on an Oscillating Airfoil in a Fluctuating Free Stream

Prediction of leading-edge-vortex initiation using criticality of the boundary layer

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