Fluid structure interaction modelling on flapping wings

Flapping wings display complex flows which can be used to generate large lift forces. Flexibility in wings is widely used by natural flyers to increase the aerodynamic performance. The influence of wing flexibility on the flow can be computed using numerical analysis with Fluid Structure Interaction (FSI). The influence of inertial, elastic and aerodynamic forces is quantified using a 2D wing. A sinusoidal flapping motion is imposed on the leading edge of the vertical wing. The inertial force on the wing dominates for high mass ratios and the wing deflection is rather independent of the flow. For a low mass ratio, the wing deformation scales with the increasing elasticity. The maximum lift and lowest drag were found for the wing with large flexibility and low mass so the passive deformation by aerodynamic forces creates a favourable shape for lift production. Flexible translating and revolving wings at an angle of attack of 45 degrees show that chordwise flexibility decreases both lift and drag, however the lift over drag ratio is increased. The flow around both wings forms a coherent structure with a Root Vortex (RV), Tip Vortex (TV), Leading Edge Vortex (LEV) and Trailing Edge Vortex (TEV). The LEV on the revolving wing is stable for approximately up to half the span because vorticity is transported outward in the vortex core. The flowfield and LEV breakdown are consistent with experimental data of the same wing. The translating wing builds up circulation but the LEV detaches quickly near the centre of the wing. Chordwise bending reduces the angle of attack which decreases the distance to the core of the shed LEVs

Incipient Separation in Shock Wave Boundary Layer Interactions as Induced by Sharp Fin

The incipient separation induced by the shock wave turbulent boundary layer interaction at the sharp fin is the subject of present study. Existing theories for the prediction of incipient separation, such as those put forward by McCabe (1966) and Dou and Deng (1992), can have thus far only predicting the direction of surface streamline and tend to over-predict the incipient separation condition based on the Stanbrook's criterion. In this paper, the incipient separation is firstly predicted with Dou and Deng (1992)'s theory and then compared with Lu and Settles (1990)' experimental data. The physical mechanism of the incipient separation as induced by the shock wave/turbulent boundary layer interactions at sharp fin is explained via the surface flow pattern analysis. Furthermore, the reason for the observed discrepancy between the predicted and experimental incipient separation conditions is clarified. It is found that when the wall limiting streamlines behind the shock wave becomes\ aligning with one ray from the virtual origin as the strength of shock wave increases, the incipient separation line is formed at which the wall limiting streamline becomes perpendicular to the local pressure gradient. The formation of this incipient separation line is the beginning of the separation process. The effects of Reynolds number and the Mach number on incipient separation are also discussed. Finally, a correlation for the correction of the incipient separation angle as predicted by the theory is also given.Comment: 34 pages; 9 figure

Nonintrusive determination of aerodynamic pressure and loads from PIV velocity data (Invited)

Traditionally in aerospace research, pressure is measured with pressure probes or wall-mounted sensors, while integral loads are obtained by means of balance systems. Recent years have seen the emerging and development of an alternative approach, which exploits Particle Image Velocimetry (PIV) data as a source for the nonintrusive determination of pressure fields and fluid-dynamic loads. The essential working principle underlying this approach is that, through invoking the momentum equation, the pressure gradient can be derived from the measured flow acceleration, yielding the pressure field upon spatial integration. Important potential benefits of this approach are, amongst others, that full field pressure data can be obtained and that no instrumentation is required for surface pressure mapping. In addition, it permits velocity and pressure data to be acquired simultaneously, which is relevant in, for example, aero-elastic and aero-acoustic areas. The presentation will address the operating principles and implementation of this method, as well as discuss some applications in areas that are of relevance to the aerospace technology domain

PIV-based pressure measurement

The topic of this article is a review of the approach to extract pressure fields from flow velocity field data, typically obtained with particle image velocimetry (PIV), by combining the experimental data with the governing equations. Although the basic working principles on which this procedure relies have been known for quite some time, the recent expansion of PIV capabilities has greatly increased its practical potential, up to the extent that nowadays a time-resolved volumetric pressure determination has become feasible. This has led to a noveldiagnostic methodology for determining the instantaneous flow field pressure in a non-intrusive way, which is rapidly finding acceptance in an increasing variety of application areas. The current review describes the operating principles, illustrating how the flow-governing equations, in particular the equation of momentum, are employed to compute the pressure from the material acceleration of the flow. Accuracy aspects are discussed in relation to the most dominating experimental influences, notably the accuracy of the velocity source data, the temporal and spatial resolution and the method invoked to estimate the material derivative. In view of its nature of an emerging technique, recently published dedicated validation studies will be given specific attention. Different application areas are addressed, including turbulent flows, aeroacoustics, unsteady wing aerodynamics and other aeronautical applications.Aerodynamic

Investigations of an aeroelastic oscillator: Analysis of one-degree-of-freedom galloping with combined translational and torsional effects

Aerospace Engineerin

Nonintrusive determination of aerodynamic pressure and loads from PIV velocity data (Invited)

Traditionally in aerospace research, pressure is measured with pressure probes or wall-mounted sensors, while integral loads are obtained by means of balance systems. Recent years have seen the emerging and development of an alternative approach, which exploits Particle Image Velocimetry (PIV) data as a source for the nonintrusive determination of pressure fields and fluid-dynamic loads. The essential working principle underlying this approach is that, through invoking the momentum equation, the pressure gradient can be derived from the measured flow acceleration, yielding the pressure field upon spatial integration. Important potential benefits of this approach are, amongst others, that full field pressure data can be obtained and that no instrumentation is required for surface pressure mapping. In addition, it permits velocity and pressure data to be acquired simultaneously, which is relevant in, for example, aero-elastic and aero-acoustic areas. The presentation will address the operating principles and implementation of this method, as well as discuss some applications in areas that are of relevance to the aerospace technology domain.Aerodynamic

Development of an aeroelastic oscillator: Design and initial results of an experimental set-up

Aerospace Engineerin

Principles and application of velocimetry-based planar pressure imaging in compressible flows with shocks

Aerospace Engineerin