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This study presents the first 3D two-way coupled fluid structure interaction (FSI) simulation of a hybrid anechoic wind tunnel (HAWT) test section with modeling all important effects, such as turbulence, Kevlar wall porosity and deflection, and reveals for the first time the complete 3D flow structure associated with a lifting model placed into a HAWT. The Kevlar deflections are captured using finite element analysis (FEA) with shell elements operated under a membrane condition. Three-dimensional RANS CFD simulations are used to resolve the flow field. Aerodynamic experimental results are available and are compared against the FSI results. Quantitatively, the pressure coefficients on the airfoil are in good agreement with experimental results. The lift coefficient was slightly underpredicted while the drag was overpredicted by the CFD simulations. The flow structure downstream of the airfoil showed good agreement with the experiments, particularly over the wind tunnel walls where the Kevlar windows interact with the flow field. A discrepancy between previous experimental observations and juncture flow-induced vortices at the ends of the airfoil is found to stem from the limited ability of turbulence models. The qualitative behavior of the flow, including airfoil pressures and cross-sectional flow structure is well captured in the CFD. From the structural side, the behavior of the Kevlar windows and the flow developing over them is closely related to the aerodynamic pressure field induced by the airfoil. The Kevlar displacement and the transpiration velocity across the material is dominated by flow blockage effects, generated aerodynamic lift, and the wake of the airfoil. The airfoil wake increases the Kevlar window displacement, which was previously not resolved by two-dimensional panel-method simulations. The static pressure distribution over the Kevlar windows is symmetrical about the tunnel mid-height, confirming a dominantly two-dimensional flow field.
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Acoustic emission from one-dimensional vibrating porous panels in a single-sided flow
The acoustic far-field pressure is determined for one-dimensional finite-chord panels with uniform porosity in a single-sided uniform flow. The unsteady, non-circulatory pressure on the panel is computed using a previously established analysis method. The acoustic field is computed using the Green’s method. Results from this acoustic analysis identify the sensitivity of the far-field pressure magnitude and directivity to changes in flow Mach number, the reduced frequency of the panel vibration, and the panel porosity level characterized by a Darcy-type porosity boundary condition.
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- Award ID(s):
- 1805692
- PAR ID:
- 10091957
- Date Published:
- Journal Name:
- 2018 AIAA/CEAS Aeroacoustics Conference
- Page Range / eLocation ID:
- AIAA Paper 2018-2962
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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A thin compliant panel was tested in a Mach 2 wind tunnel. The panel was mounted flush with the tunnel floor and was of dimensions L=121.9 mm (chord), W=63.5 mm (span) and h=0.254 mm (thickness). A 20 degree compression ramp was placed 5 mm downstream of the model, which induced a shock/boundary layer interaction with fully separated flow over parts of the panel. Full-field deformation was measured using Digital Image Correlation and the surface pressure field was obtained from fast-response pressure-sensitive paint. Analysis of the shock foot motion was performed using a curve-fitting method. Comparison of the shock motion between a rigid and compliant panel case showed no difference in the size of the intermittent region but found that the shock motion over the compliant panel is affected by the panel vibration. Proper Orthogonal Decomposition revealed that the surface pressure is dominated by low-frequency unsteady shock motion, in both cases (rigid and compliant panel). The sixth POD mode clearly shows the streamwise shock foot motion oscillates at the first panel vibration frequency. The surface pressure field upstream of the shock foot is dominated by piston-theory aerodynamics and thus correlated to the slope of the compliant panel. The Sparse Identification of Nonlinear Dynamic Systems algorithm was employed to find low-order representations of the system dynamics. Linear stiffness matrices could be consistently recovered. The measurement noise however prevented extraction of additional relations, such as linear damping matrices or forcing terms from the surface pressure.more » « less
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null (Ed.)Flight vehicles that operate in the supersonic regime can be subject to adverse fluid-structure interactions due to their lightweight design. The presence of geometric obstructions such as control surfaces or fins can induce compression shocks that can interact with the boundary layer, leading to flow separation. The interaction of flow, compression shock and structural dynamics is very difficult to model and currently only poorly understood. This work investigates experimentally the interaction between a compliant panel in a Mach 2 flow under a ramp-induced shock-wave/boundary layer interaction (SWBLI). Brass panels of length 4.8" and width 2.5" and different thicknesses (h=0.020", 0.016", 0.012" and 0.010") are investigated. Tests are performed both with and without a compression ramp installed. This direct comparison allows characterization of the effect of the SWBLI on the system dynamics. High-speed stereoscopic digital image correlation (DIC) and fast-response pressure sensitive paint (PSP) are used to obtain simultaneous full field deformation and surface pressure of the panels. The results show that the shock induced by the 20compression ramp leads to separation of the turbulent boundary layer close to the ramp starting at about 80% of the panel length. This results in a region of large pressure fluctuations which primarily increase the vibration amplitude of the second panel mode. Analysis of the fundamental mode, which contains most of the vibration energy of the panel, shows that the SWBLI does not lead to changes of this mode, neither in frequency, amplitude or mode shape. On the other hand, analysis of the shock foot motion shows that the shock primarily oscillates at the fundamental frequency of the panel. This means that while the shock and panel oscillate at the same frequency, it is not two-way coupling. The panel vibration dictates the motion of the shock, but the shock (or rather the SWBLI) does not modify the fundamental panel vibration beyond the forcing provided by the turbulent boundary layer. Full field surface pressure predictions are made using linearized potential flow theory, which relates the local slope of the panel to the surface pressure. Results are found to be in good agreement in the region of attached flow.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.2514/6.2018-2962
