Abstract
The unsteady surface pressure distribution and aerodynamic loads on a pitching airfoil are determined non-intrusively using PIV measurements. An experimental test case is considered where the flow around the airfoil is mostly attached while the unsteady effects on the aerodynamic loads are significant. The surface pressure is calculated from the flow velocity measurements in the vicinity of the airfoil surface, that are obtained with a robotic PIV system, by using relations from unsteady potential flow and thin airfoil theory. The proposed approach is a robust and computationally efficient approach to obtain non-intrusive measurements of the unsteady surface pressure distribution and the aerodynamic loads, that are in good agreement with reference data from installed pressure transducer sensors.
Highlights
Unsteady fluid-structure interaction (FSI) experiments are necessary for generating reference data to validate computational models, for example in the design of novel aircraft configurations.An important parameter in the characterization of FSIs is the magnitude and distribution of the aerodynamic load
The chordwise surface pressure difference distribution that is obtained by using the quasi-steady and the unsteady pressure formulations are shown for four phase instants in figure 5
The phase shift is negative for the lift and positive for the moment. This can be explained by the fact that the unsteady term affects the load distribution mostly in the region downstream of the reference axis for the pitching moment computation that is located at xr/c = 0.3125, as it is observed in figure 5
Summary
Unsteady fluid-structure interaction (FSI) experiments are necessary for generating reference data to validate computational models, for example in the design of novel aircraft configurations.An important parameter in the characterization of FSIs is the magnitude and distribution of the aerodynamic load. The use of installed pressure transducers for the measurement of the unsteady surface pressure and aerodynamic loads in these experiments is challenging, because the integration of the sensors in the experimental model is associated with significant costs, possibly intrudes the experimental measurements and it suffers from a relatively low spatial resolution. An alternative approach is to infer the aerodynamic loads from flow field measurements that are obtained non-intrusively with particle image velocimetry (PIV). A straightforward and computationally efficient method to determine the surface pressure on moving airfoils in unsteady flow conditions based on non-intrusive PIV measurements, for instance in large-scale aeroelasticity experiments, is still missing. A popular method for the PIV-based surface pressure determination is the numerical solution of the Poisson equation for the pressure in incompressible flow, after the pressure gradient throughout the flow field has been calculated from the flow velocity measurements using the momentum equation in its differential form [1].
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