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1. A fully-coupled computational aeroelasticity model for transonic and supersonic flows

   https://doi.org/10.2514/6.2022-3600  

   Ilie, Marcel; Havenar, John (July 2022, AIAA AVIATION 2022 Forum)

   AIAA AVIATION Forum (Ed.)

   The aeroelastic phenomena of fixed-wing aircraft in transonic and supersonic flight regimes plays a critical role in the design of high-speed aircraft. The present research concerns the development of computationally efficient and accurate methods for the computation of aeroelastic systems containing transonic and supersonic flows. Therefore, we propose a fully- coupled, time-marching aeroelastic approach utilizing an URANS model. The computational studies are carried out to assess the effect of the freestream Mach number and angle of attack on the structural dynamics and stresses developed in the wing structure. The studies are carried out for a range of Mach numbers, 𝑴∞ = 𝟎. 𝟖 – 𝟏. 𝟒, and angles of attack, 𝜶 = {𝟐°, 𝟒°, 𝟔°}. The analysis reveals that the aeroelastic deformation of the wing and induced stress in the wing structure increase with the freestream Mach number. 

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2. Mach number effect on the aeroelastic phenomenon of fixed wing aircraft

   M. Ilie and J. Havenar (January 2022, AIAA SciTech Conference)

   AIAA SciTech (Ed.)

   The aeroelastic phenomenon plays a critical role in the aerodynamic performance and stability of fixed wing aircrafts. Aeroelastic phenomena may cause flow separation and large deformations of the wing, and implicitly high stresses into the structure. The computational study of aeroelasticity, in high-speed fixed wing, requires fully-coupled aeroelastic algorithms. Therefore, in the present research we propose a CFD based approach using the large-eddy simulation approach along with a finite-element method for the computations of the structural deformations. The analysis is performed for subsonic and transonic flows with Mach number . The analysis reveals that the elastic deformations of the wing and stresses in the wing increase with the Mach number. 

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3. Reynolds number dependency in supersonic spatially-developing turbulent boundary layers

   https://doi.org/10.2514/6.2020-0574  

   Araya, Guillermo; Lagares, Christian; Jansen, Kenneth E. (January 2020, 2020 AIAA SciTech Forum (AIAA 3247313) 6 - 10 January, Orlando, FL, 2020.)

   Direct Numerical Simulation (DNS) of compressible spatially-developing turbulent boundary layers (SDTBL) is performed at a Mach number of 2.5 and low/high Reynolds numbers over isothermal Zero-Pressure Gradient (ZPG) flat plates. Turbulent inflow information is generated via a dynamic rescaling-recycling approach (J. Fluid Mech., 670, pp. 581-605, 2011), which avoids the use of empirical correlations in the computation of inlet turbulent scales. The range of the low Reynolds number case is approximately 400-800, based on the momentum thickness, freestream velocity and wall viscosity. DNS at higher Reynolds numbers (~3,000, about four-fold larger) is also carried out with the purpose of analyzing the effect of Reynolds number on the transport phenomena in the supersonic regime. Additionally, low/high order flow statistics are compared with DNS of an incompressible isothermal ZPG boundary layer at similar low Reynolds numbers and the temperature regarded as a passive scalar. Peaks of turbulence intensities move closer to the wall as the Reynolds number increases in the supersonic flat plate. Furthermore, Reynolds shear stresses depict a much larger "plateau" (constant shear layer) at the highest Reynolds number considered in present study. 

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4. Nonlinear Aeroelastic Analysis for Highly Flexible Flapping Wing in Hover

   https://doi.org/10.4050/JAHS.67.022002  

   Yang, Xuan; Sudhir, Aswathi; Halder, Atanu; Benedict, Moble (April 2022, Journal of the American Helicopter Society)

   Aeromechanics of highly flexible flapping wings is a complex nonlinear fluid–structure interaction problem and, therefore, cannot be analyzed using conventional linear aeroelasticity methods. This paper presents a standalone coupled aeroelastic framework for highly flexible flapping wings in hover for micro air vehicle (MAV) applications. The MAV-scale flapping wing structure is modeled using fully nonlinear beam and shell finite elements. A potential-flow-based unsteady aerodynamic model is then coupled with the structural model to generate the coupled aeroelastic framework. Both the structural and aerodynamic models are validated independently before coupling. Instantaneous lift force and wing deflection predictions from the coupled aeroelastic simulations are compared with the force and deflection measurements (using digital image correlation) obtained from in-house flapping wing experiments at both moderate (13 Hz) and high (20 Hz) flapping frequencies. Coupled trim analysis is then performed by simultaneously solving wing response equations and vehicle trim equations until trim controls, wing elastic response, inflow and circulation converge all together. The dependence of control inputs on weight and center of gravity (cg) location of the vehicle is studied for the hovering flight case. 

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5. Implicit Subgrid-Scale Modeling of a Mach 2.5 Spatially Developing Turbulent Boundary Layer

   https://doi.org/10.3390/e24040555  

   Araya, Guillermo; Lagares, Christian (April 2022, Entropy)

   We employ numerically implicit subgrid-scale modeling provided by the well-known streamlined upwind/Petrov–Galerkin stabilization for the finite element discretization of advection–diffusion problems in a Large Eddy Simulation (LES) approach. Whereas its original purpose was to provide sufficient algorithmic dissipation for a stable and convergent numerical method, more recently, it has been utilized as a subgrid-scale (SGS) model to account for the effect of small scales, unresolvable by the discretization. The freestream Mach number is 2.5, and direct comparison with a DNS database from our research group, as well as with experiments from the literature of adiabatic supersonic spatially turbulent boundary layers, is performed. Turbulent inflow conditions are generated via our dynamic rescaling–recycling approach, recently extended to high-speed flows. Focus is given to the assessment of the resolved Reynolds stresses. In addition, flow visualization is performed to obtain a much better insight into the physics of the flow. A weak compressibility effect is observed on thermal turbulent structures based on two-point correlations (IC vs. supersonic). The Reynolds analogy (u′ vs. t′) approximately holds for the supersonic regime, but to a lesser extent than previously observed in incompressible (IC) turbulent boundary layers, where temperature was assumed as a passive scalar. A much longer power law behavior of the mean streamwise velocity is computed in the outer region when compared to the log law at Mach 2.5. Implicit LES has shown very good performance in Mach 2.5 adiabatic flat plates in terms of the mean flow (i.e., Cf and UVD+). iLES significantly overpredicts the peak values of u′, and consequently Reynolds shear stress peaks, in the buffer layer. However, excellent agreement between the turbulence intensities and Reynolds shear stresses is accomplished in the outer region by the present iLES with respect to the external DNS database at similar Reynolds numbers. 

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