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R.D. Mitchell

Bio: R.D. Mitchell is an academic researcher from Queen's University Belfast. The author has contributed to research in topics: Transonic & Airfoil. The author has an hindex of 3, co-authored 4 publications receiving 50 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors investigated the origin of shock oscillations on an 18% thick biconvex aerofoil using a thin-layer Navier-Stokes code.

26 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the origin of NACA0012 aerofoil shock oscillations using a moving grid thin layer Navier Stokes code and found that the shock induced bubble plays a leading role in the origin.
Abstract: The mechanism of the origin of shock oscillations on NACA0012 aerofoils is investigated using a moving grid thin layer Navier Stokes code. The method used to understand the mechanism is to initiate the shock oscillations on an aerofoil by moving the aerofoil from a regime of steady transonic flow into a regime of periodic flow by a change in airflow incidence. The results indicate that the shock induced bubble plays a leading role in the origin of shock oscillations and the trailing edge has an affect on its amplitude.

21 citations

Journal ArticleDOI
TL;DR: In this article, the results of a transonic computational fluid dynamics (CFD) study performed on a biconvex airfoil with a splitter plate extension or with surface cooling with a view to suppress the periodic motion were presented.
Abstract: We present some of the results of a transonic computational fluid dynamics (CFD) study performed on a biconvex airfoil with a splitter plate extension or with surface cooling with a view to suppress the periodic motion

5 citations

Proceedings ArticleDOI
01 Jan 1997
TL;DR: The results of numerical studies of Wells turbine aerodynamics are presented in this article, where the ability of a hybrid active/passive device to alleviate post-stall buffet of an isolated NACA0012 aerofoil at 18/spl deg/ is evaluated.
Abstract: The results of numerical studies of Wells turbine aerodynamics are presented. In the first study, the ability of a hybrid active/passive device to alleviate post-stall buffet of an isolated NACA0012 aerofoil at 18/spl deg/ is evaluated. The passive boundary layer control device is a porous surface/plenum chamber which covers the 1% to 10% chord portion of the aerofoil, and active control is provided by applying suction to the plenum chamber. It is shown that the unsteady load experienced by the solid aerofoil at post-stall incidence is indeed alleviated by the active device; while the passive device has minimal impact on performance at pre-stall angles. The second study uses a three-dimensional numerical method to predict the performance of typical Wells turbines with various numbers of blades and tip clearances. The effect of solidity on turbine performance is predicted well both qualitatively and quantitatively, and the effect of clearance is qualitatively correct.

2 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a review of the physical mechanisms of the periodic shock motion on airfoils at transonic flow conditions are associated with the phenomenon of buffeting, and various modes of shock wave motion for different flow conditions and airfoil configurations are described.

333 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a review of recent investigations in the field of transonic shock buffet and highlight the importance of these experiments for the development of physical models stressed with a particular emphasis on the emergence of frequency synchronisation phenomenon.

155 citations

Journal ArticleDOI
TL;DR: In this article, a study of the shock buffet onset and instability mechanism via Reynolds-averaged Navier-Stokes simulations on several airfoils is presented, and the numerical setup and the AUmaras turbulence closure are validated based on wind-tunnel data from NACA 0012 and RA16SC1.
Abstract: A study of shock-buffet onset and instability mechanism via Reynolds-averaged Navier―Stokes simulations on several airfoils is presented. The numerical setup and the Spalart―AUmaras turbulence closure are validated based on wind-tunnel data from NACA 0012 and RA16SC1 airfoils. The paper presents simulations of the flow past three • airfoils: the subsonic NACA 0012, the supercritical RA16SC1, and the thin, transonic/supersonic NACA 64A204, at pre- and postbuffet conditions, and within a cycle of developed shock buffet. The shock-buffet cycle is found to be »■• similar in nature for all airfoils, originating in unstable interaction of the shock and the separation bubble. Simulation results support the notion that buffet onset is not related to the bursting of the separation bubble behind the shock. Shock-buffet categorizing is posited as a transonic prestall instability phenomenon that depends on the shock strength and location. Shock-buffet onset conditions occur when the shock position is behind and sufficiently close to the upper-surface maximum curvature location. Additionally, it is suggested that offset conditions are when the shock is at an upstream location and the flow aft of it is fully separated.

109 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of three-dimensional flow, wing sweep, and span length on the shock-buffet characteristics were identified, and numerical validation was presented for OAT15A and RA16SC1 swept wings based on wind-tunnel experiments.
Abstract: The paper presents a computational study of the transonic shock-buffet flow instability phenomenon on three-dimensional wings. Reynolds-averaged Navier–Stokes simulations were conducted on three wing configurations, all based on the RA16SC1 airfoil, at shock-buffet flow conditions. Numerical validation is presented for the OAT15A and RA16SC1 swept wings based on wind-tunnel experiments. The simulated configurations include infinite-straight, infinite-swept, and finite-swept three-dimensional wing models of several sweep angles and span lengths. Based on the results, the effects of three-dimensional flow, wing sweep, and span length on the shock-buffet characteristics are identified. For small wing-sweep angles, the fundamental shock-buffet instability mechanism remains similar to the two-dimensional mechanism, which is characterized mainly by chordwise shock oscillations. For moderate sweep angles, a phenomenon of lateral pressure disturbance propagation is observed. This phenomenon is essentially differe...

103 citations

Journal ArticleDOI
TL;DR: In this paper, Lee et al. investigated the flow of the BauerGarabedianKorn No. 1 supercritical airfoil by the solution of the unsteady Reynolds-averaged NavierStokes equations with a two-equation lagged kωturbulent model.
Abstract: The flow of the BauerGarabedianKorn (BGK) No. 1 supercritical airfoil is investigated by the solution of the unsteady Reynolds-averagedNavierStokes equations with a two-equation lagged kωturbulent model.Two steady cases (M=0.71, α=1.396 deg and M=0.71, α=9.0 deg) and one unsteady case (M=0.71, α=6.97 deg), all with a far-stream Reynolds number of 20106, are computed. The results are compared with available experimental data. The computed shock motion and the evolution of the concomitant flow separation are examined. Space-time correlations of the unsteady pressure field are used to calculate the time for pressure waves to travel downstream within the separated region from the shock wave to the airfoil trailing edge and then back from the trailing edge to the shock outside the separated region. The reduced frequency so calculated agrees well with the computed buffet frequency, supporting the signal propagation mechanism for buffet proposed by Lee (Lee, B. H. K., Oscillation Shock Motion Caused by Transonic Shock Boundary-Layer Interaction, AIAA Journal, Vol. 28, No. 5, 1990, pp. 942944).

99 citations