Dynamics of structures

Turbulence, Coherent Structures, Dynamical Systems and SymmetryP. Holmes, J. L. Lumley, G. Berkooz, and C. W. Rowley, 2nd ed., Cambridge University Press, Cambridge, England, U.K., 2012, 386 pp., $90

Effects of large computational time steps on the computed turbulence were investigated using a fully implicit method. In turbulent channel flow computations the largest computational time step in wall units which led to accurate prediction of turbulence statistics was determined. Turbulence fluctuations could not be sustained if the computational time step was near or larger than the Kolmogorov time scale.

Effects of the computational time step on numerical solutions for turbulent flow

Recent advances in the shock wave/boundary layer interaction and its control in internal and external flows

Flying airplanes in extended formations, with separation distances of tens of wingspans, significantly improves safety while maintaining most of the fuel savings achieved in close formations. The present study investigates the impact of roll trim and compressibility at a fixed lift coefficient on the benefits of extended-formation flight. An Euler solver with adjoint-based mesh refinement combined with a wake propagation model is used to analyze a two-body echelon formation at a separation distance of 30 spans. Two geometries are examined: a simple wing and a wing-body geometry. Energy savings, quantified by both formation drag fraction and span efficiency factor, are investigated at subsonic and transonic speeds for a matrix of vortex locations. The results show that, at fixed lift and trimmed for roll, the optimal location of vortex impingement is about 10% inboard of the trailing airplane’s wing tip. Interestingly, the improvement in drag fraction is relatively robust in the vicinity of the optimal pos...

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Inviscid Analysis of Extended-Formation Flight

Transitional shock wave boundary layer interaction over a flexible panel

On the role of flow transition in laminar separation flutter

Features of shock-induced panel flutter in three-dimensional inviscid flow

This paper explores the flow structure of a corrugated airfoil using a high-fidelity implicit large eddy simulation approach. The first three-dimensional simulations for a corrugated wing section are presented considering a range of Reynolds numbers of Rec = 5 × 103 to 5.8 × 104 bridging the gap left by previous numerical and experimental studies. Several important effects are shown to result from the corrugations in the leading-edge region. First, interaction between the detached shear layer and the first corrugation peak promotes recirculation upstream and enhances transition to turbulence due to flow instabilities. Thus, early transitional flow develops on the corrugated wing which helps to delay stall even at Reynolds numbers as low as Rec = 1 × 104. Transition is shown to occur as early as Rec = 7.5 × 103 and quickly advances toward the leading-edge as Reynolds number is increased. Modification of the first corrugation peak height produces significantly reduced separation and improved aerodynamic for...

Numerical exploration of the origin of aerodynamic enhancements in [low-Reynolds number] corrugated airfoils

This investigation addresses the impingement of the trailing vortex provided by a leader-wing upon a follower-wing operating in close proximity. Exploration of the relative spacing between the two wings reveals several distinct flow regimes occur within a small range of lateral positions of the incident vortex. These changes effectively alter the evolution of the follower-wing wake via mutual induction between the incident and trailing vortices. Several unsteady mechanisms impact the general flow field in each regime. The incident vortex for an inboard impingement rapidly decays over the wing due to transition to turbulence. A tip-aligned vortex results in a highly unsteady interaction and generates enhanced surface pressure fluctuations beneath the tip vortex. Placing the incident vortex outboard elicits mutual instability between the leader and follower-wing trailing vortices. While lift-enhancement was found to be dominated by an inviscid increase in effective angle of attack, viscous effects in the near-tip region alter the local surface force distribution and influence the rolling moment coefficient. These flow variations which occur over a small range of lateral positions could generate buffeting loads in the presence of a wandering streamwise vortex.

Caleb J. Barnes

Papers

Transitional shock wave boundary layer interaction over a flexible panel

On the role of flow transition in laminar separation flutter

Features of shock-induced panel flutter in three-dimensional inviscid flow

Numerical exploration of the origin of aerodynamic enhancements in [low-Reynolds number] corrugated airfoils

Analysis of streamwise-oriented vortex interactions for two wings in close proximity