1,721,309 research outputs found
Preliminary Design of a Fixed-Wing UAV for the Martian Environment
No full textThe preliminary design of a vertical take-off and landing fixed-wing UAV for the large-scale aerial exploration of Mars is presented. This work aims to assess the effects of Martian environmental conditions on the design of fixed-wing UAVs. The Martian environment is characterized by low gravity, extremely low atmospheric density, and glacial temperatures. These conditions significantly affect the drone’s capability to generate sufficient lift and have a relevant impact on the overall performance of the UAV, which features reduced aerodynamic characteristics given the typical low-Reynolds regime
A deep neural network reduced order model for unsteady aerodynamics of pitching airfoils
Full text linkA machine learning framework is developed to compute the aerodynamic forces and moment coefficients for a pitching NACA0012 airfoil incurring in light and deep dynamic stall. Four deep neural network frameworks of increasing complexity are investigated: two multilayer perceptrons and two convolutional neural networks. The convolutional framework, in addition to the standard mean squared error loss, features an improved loss function to compute the airfoil loads. In total, five models are investigated of increasingly complexity. The convolutional model, coupled with the loss function based on force and moment coefficients and embedding the attention mechanism, is found to robustly and efficiently predict pressure and skin friction distributions over the airfoil over the entire pitching cycle. Periodic conditions are implemented to grant the physical smoothness of the model output both in space and time. An analysis of the training dataset point distributions is performed to point out the effects of adopting low discrepancy sequences, such as Latin hypercube, Sobol', and Halton, compared to random and uniform sequences. The current model shows improved performances in predicting forces and pitching moment in a broad range of operating conditions
Effects of Molecular Complexity and Reservoir Conditions on the Discharge Coefficient of Adapted Planar Nozzles
Full text linkThe transonic flow at throat section of a convergent-divergent nozzle is studied in adapted conditions to assess the influence of the fluid molecular complexity and total thermodynamic state on the discharge coefficient. The standard Sauer method is applied to solve the transonic perturbation potential equation in the vicinity of the nozzle throat. An analytic expression is derived that allows one to compute the discharge coefficient in terms of the nozzle curvature at the throat section and of the value of the fundamental derivative of gasdynamics at sonic conditions, which depends on the fluid molecular complexity and on the thermodynamic state in the reservoir. A linear dependence of the discharge coefficient on the sonic value of the fundamental derivative of gasdynamics is exposed
Reynolds and Mach Number Effects on the Aerodynamics and Design of Airfoils for the Martian Atmosphere
No full textA parametric study is carried out to assess numerically the flow dependence on the Reynolds and Mach numbers in the Martian atmosphere, under the RANS approximation. The Ishii airfoil at Re=23,000 is taken as a reference. The Laminar Separation Bubble (LSB) and large separations are identified as the leading cause for the small lift-to-drag ratio in the low-Reynolds regime. Numerical simulations highlight a strong sensitivity of the aerodynamic coefficients on these non-dimensional parameters, which influence the LSB. The reference Ishii airfoil is optimized for different flight conditions using global and local techniques. The output optimal geometries exhibit a strong dependence on the Reynolds number and a weak dependence on the Mach number. By reducing the Reynolds number, optimal airfoils are thinner, the leading edge radius gets smaller, the camber increases, and the geometry of the suction side exhibits a lower curvature
Unsteady Adjoint Optimization in SU2 Based on the Hybrid Harmonic Balance-URANS Approach
No full textAssessment of Icing Wind Tunnel Operational Uncertainties on Ice Protection System Performances
No full textNumerical simulations of icing wind tunnel testing of an Ice Protection System (IPS) for Appendix C and Appendix O conditions are carried out, accounting for the operational uncertainties in the Liquid Water Content (LWC), median volume diameter (MVD), and static air temperature (SAT) in the wind tunnel. Relevant variability was observed in relevant quantities such as surface temperature and run-back water mass flux in the three selected test cases—particularly in run-back ice formations. The uncertainties were significant, suggesting that under the specified conditions, the wind tunnel testing results may not be entirely conclusive in evaluating the effectiveness of the IPS. These findings highlight the importance of incorporating uncertainties in ice protection system design to prevent overly conservative or unsafe configurations
Nonclassical gasdynamics: thermodynamic modeling and numerical simulation of multidimensional flows of BZT fluids
No full textNozzle Design for Supersonic Flows of N2O at Supercritical and Close-to-Critical Conditions
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AVT-390: Outlook on Innovative Simulation Technologies Arising From Analyses of the DLR LK6E2 Airframe
No full textThe maneuverability and agility of missiles depend on the precise control of complex, vortex-dominated flows, which involve intricate interactions between vortices, airframe components, and shock waves. To reduce development costs and accelerate time-to-theatre, there is an increased reliance on Computational Fluid Dynamics (CFD) for missile design and performance assessment. This paper presents methodologies to enhance CFD predictions for these challenging flows, building on research initiated by the NATO Science and Technology Organization (STO) Applied Vehicle Technology (AVT) panel under Task Group AVT-316 and continued by AVT-390. The proposed approaches include utilizing the Eigenvalue Perturbation Method to quantify epistemic uncertainties in the closure models of the Reynolds-Averaged Navier-Stokes (RANS) equations, implementing Automatic Mesh Refinement (AMR) to eliminate errors due to grid discretization, and evaluating the potential of adjoint formulations for future application in stability and control predictions. This paper details these methods, highlighting their application to a specific test case, and concludes with a summary of findings and recommendations for future research directions
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