Static Aeroelasticity.- Dynamic Aeroelasticity.- Nonsteady Aerodynamics of Lifting and Non-Lifting Surfaces.- Stall Flutter.- Aeroelasticity in Civil Engineering.- Aeroelastic Response of Rotorcraft.- Aeroelasticity in Turbomachines.- Modeling of Fluid-Structure Interaction.- Experimental Aeroelasticity.- Nonlinear Aeroelasticity.- Aeroelastic Control.- Modern Analysis for Complex and Nonlinear Unsteady Flows in Turbomachinery.

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A Modern Course in Aeroelasticity

Nomenclature AR = aspect ratio; amplitude ratio B = probability density function of velocity c = root chord length f = frequency k = reduced frequency; axial wave number n =w ave number in angular direction P = probability p = pressure fluctuation Re =R eynolds number based on chord length S = spectral density s = local semispan T = period t = time U∞ = freestream velocity u = axial velocity v = swirl velocity x = streamwise distance xbd = breakdown location y = spanwise distance z =v ertical distance above wing surface α = angle of attack � = circulation δ = flap angle � = sweep angle ν = kinematic viscosity τ = time constant � =fi nangle ω =v orticity; radial frequency

Review of Unsteady Vortex Flows over Slender Delta Wings

Pressure-sensitive luminescent coating on porous anodized aluminium (AA-PSP) was applied to measure non-periodic unsteady pressure distribution on a wind-tunnel model. A high-speed digital video camera was used to capture the PSP signal. The pressure-sensitive dye was tris(4,7-diphenylphenanthroline) ruthenium(II) ([Ru(dpp)3]2+). The coating has a short response time of O(10 µs), although it exhibits temperature and humidity sensitivities. A hydrophobic coating was applied on the anodized aluminium surface to suppress the humidity sensitivity. A temperature sensitive paint was used to obtain the temperature distribution instantaneously with the pressure. The temperature data were used to correct the PSP response. An appropriate data acquisition procedure as well as digital image processing algorithm was established to compensate for the error from the temperature and humidity sensitivities. The present system was applied to measure the pressure distribution on a delta wing at a high angle of attack in transonic flow, whose flow is unsteady due to the interaction between shock waves and leading edge vortices. The non-periodic unsteady pressure distribution on the delta wing was successfully measured with the sampling rate of 1 kHz and within a few per cent error in absolute pressure level.

Image measurements of unsteady pressure fluctuation by a pressure-sensitive coating on porous anodized aluminium

The impact of leading-edge extension (LEX) modifications on aerodynamic and vertical tail buffet characteristics of a 16-percent scale F/A-18 model has been investigated in the NASA Langley 30-foot by 60-foot tunnel. Modifications under consideration include variations in LEX chord and span, addition of upper surface fences, and removal of the LEX. Both buffeting and high-angle-of-attack aerodynamics are found to be strongly dependent upon the LEX geometry, which directly influences the strength, position, and breakdown characteristics of the vortex flow field. Concepts aimed at influencing the development of vortical flow field are considered to have much greater potential in design application than those geared toward altering already established flow fields. It is recommended that configuration effects on structural and aerodynamic characteristics be evaluated in parallel, so that trade-off studies can be conducted to ensure adequate structural fatigue life and desired high-angle-of-attack stability and control characteristics in the design of future high performance aircraft.

Wind tunnel investigation of aerodynamic and tail buffet characteristics of leading-edge extension modifications to the F/A-18

Experimental evidence suggests that vortex breakdown is not the only source of buffeting of delta wings and fins. Other unsteady flow phenomena that contribute to buffeting at high angles of attack are fluctuations of vortex breakdown location and vortex shedding. Flow visualization and velocity measurements were carried out over a delta wing, over a wide range of angles of attack, to understand the transition between the helical mode instability and the vortex shedding. It was found that this transition is abrupt, as indicated by a jump in the frequency parameter, and that it occurs at the angle of attack at which breakdown reached the apex. The unsteady nature of vortex breakdown location was investigated by flow visualization for the interaction of vortex breakdown with a rigid flat plate. Although there are indications of a feedback effect on vortex breakdown, the amplitude of the fluctuations of breakdown location is smaller for impinging flows

D.G. Mabey

Papers

Some aspects of aircraft dynamic loads due to flow separation