Abstract
The structural motion and unsteady aerodynamic loads of a pitching airfoil model that features an actuated trailing edge flap are determined experimentally using a single measurement and data processing system. This integrated approach provides an alternative to the coordinated use of multiple measurement systems for simultaneous position and flow field measurements in large-scale fluid–structure interaction experiments. The measurements in this study are performed with a robotic PIV system using Lagrangian particle tracking. Flow field measurements are obtained by seeding the flow with helium-filled soap bubbles, while the structural measurements are performed by tracking fiducial markers on the model surface. The unsteady position and flap deflection of the airfoil model are determined from the marker tracking data by fitting a rigid body model, that accounts for the motion degrees of freedom of the airfoil model, to the measurements. For the determination of the unsteady aerodynamic loads (lift and pitching moment) from the flow field measurements, two different approaches are evaluated, that are both based on unsteady potential flow and thin airfoil theory. These methods facilitate an efficient non-intrusive load determination on unsteady airfoils and produce results that are in good agreement with reference measurements from pressure transducers.
Highlights
The characterization of unsteady fluid–structure interactions (FSIs) is relevant for the design of deformable lifting structures in unsteady conditions, such as flexible flapping wings (Platzer et al, 2008; Heathcote and Gursul, 2007; Bleischwitz et al, 2017), rotor blades with unsteady periodic inflow (Wei et al, 2019; Strangfeld et al, 2016), or fixedwing aircraft subjected to gusts (Perrotta and Jones, 2017; Tang et al, 2010)
A particular focus is placed on the determination of the instantaneous geometry and aerodynamic load, which serve as coupling interfaces between fluid and structure in numerical FSI solvers (Kamakoti and Shyy, 2004)
The present study aims to relieve this complication by using a single data acquisition and processing system to obtain non-intrusive position measurements of an unsteady airfoil with actuated flap as well as measurements of the unsteady flow and the aerodynamic response in terms of the lift, pitching moment and surface pressure distribution
Summary
The characterization of unsteady fluid–structure interactions (FSIs) is relevant for the design of deformable lifting structures in unsteady conditions, such as flexible flapping wings (Platzer et al, 2008; Heathcote and Gursul, 2007; Bleischwitz et al, 2017), rotor blades with unsteady periodic inflow (Wei et al, 2019; Strangfeld et al, 2016), or fixedwing aircraft subjected to gusts (Perrotta and Jones, 2017; Tang et al, 2010). The ongoing development of sophisticated computational methods for simulating these FSI problems requires validation data from wind tunnel experiments. This data is challenging to obtain because it requires the simultaneous measurement of a variety of quantities of different nature, which may explain why only a limited number of parameters has been typically used for validation purposes in the past (Tang and Dowell, 2001). A particular focus is placed on the determination of the instantaneous geometry and aerodynamic load, which serve as coupling interfaces between fluid and structure in numerical FSI solvers (Kamakoti and Shyy, 2004).
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