A modified dual time integration technique for aerodynamic quasi-static and dynamic stall hysteresis

open access articleSimulation of the aerodynamic stall phenomenon in both quasi-static and dynamic conditions requires expensive computational resources. The computations become even more costly for static stall hysteresis using an unsteady solver with very slow variation of angle of attack at low reduced frequencies. In an explicit time-marching solver that satisfies the low Courant number condition, that is, CFL<1, the computational cost for such simulations becomes prohibitive, especially at higher Reynolds numbers due to the presence of thin-stretched cells with large aspect ratio in the boundary layer. In this paper, a segregated solver method such as the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) is modified as a dual pseudo-time marching method so that the unsteady problem at each time step is reformulated as a steady state problem. The resulting system of equations in the discretized finite volume formulation is then reduced to zero or near-zero residuals using available convergence acceleration methods such as local time stepping, multi-grid acceleration and residual smoothing. The performance and accuracy of the implemented algorithm was tested for three different airfoils at low to moderate Reynolds numbers in both incompressible and compressible flow conditions covering both attached and separated flow regimes. The results obtained are in close agreement with the published experimental and computational results for both quasi-static and dynamic stall and have demonstrated significant savings in computational time

Computational Simulation of Airfoils Stall Aerodynamics at Low Reynolds Numbers

Experimental results for aerodynamic static hysteresis at stall conditions obtained in the TsAGI's T-124 low-turbulence wind tunnel for NACA0018 are presented and analysed. Computational predictions of aerodynamic static hysteresis are made using the OpenFOAM simulations considering di erent grids, turbulence models and solvers. Comparisons of compu- tational simulation results with experimental wind tunnel data are made for 2D NACA0018 and NACA0012 airfoils at low Reynolds numbers Re = (0.3-1.0) millions. The properties of the proposed phenomenological bifurca- tion model for simulation of aerodynamic loads at the existence of static hysteresis are discussed

Computational Simulation of Airfoils Stall Aerodynamics at Low Reynolds Numbers

Experimental results for aerodynamic static hysteresis at stall conditions obtained in the TsAGI's T-124 low-turbulence wind tunnel for NACA0018 are presented and analysed. Computational predictions of aerodynamic static hysteresis are made using the OpenFOAM simulations considering di erent grids, turbulence models and solvers. Comparisons of compu- tational simulation results with experimental wind tunnel data are made for 2D NACA0018 and NACA0012 airfoils at low Reynolds numbers Re = (0.3-1.0) millions. The properties of the proposed phenomenological bifurca- tion model for simulation of aerodynamic loads at the existence of static hysteresis are discussed

Impact of Ground Effect on Airplane Lateral Directional Stability during Take-Off and Landing

Open Access journalComputational simulations of aerodynamic characteristics of the Common Research Model (CRM), representing a typical transport airliner are conducted using CFD methods in close proximity to the ground. The obtained dependencies on bank angle for aerodynamic forces and moments are further used in stability and controllability analysis of the lateral-directional aircraft motion. Essential changes in the lateral-directional modes in close proximity to the ground have been identified. For example, with approach to the ground, the roll subsidence and spiral eigenvalues are merging creating the oscillatory Roll-Spiral mode with quite significant frequency. This transformation of the lateral-directional dynamics in piloted simulation may affect the aircraft responses to external crosswind, modify handling quality characteristics and improve realism of crosswind landing. The material of this paper was presented at the Seventh European Conference for Aeronautics and Space Sciences EUCASS-2017. Further work is carried out for evaluation of the ground effect aerodynamics for a high-lift configuration based on a hybrid geometry of DLR F11 and NASA GTM models with fully deployed flaps and slats. Some aspects of grid generation for a high lift configuration using structured blocking approach are discussed

Computational Ground Effect Aerodynamics and Airplane Stability Analysis During Take-off and Landing

Computational simulations of aerodynamic characteristics of the Common Research Model (CRM), representing a typical transport airliner, are conducted using CFD methods in close proximity to the ground. The obtained dependencies on bank angle for aerodynamic forces and moments are further used in stability and controllability analysis of the lateral-directional aircraft motion. Essential changes in the lateral-directional modes in close proximity to the ground have been identified. For example, with approach to the ground, the roll subsidence and spiral eigenvalues are merging creating the oscillatory Roll-Spiral mode with quite significant frequency. This transformation of the lateral-directional dynamics in piloted simulation may affect the aircraft responses to external crosswind, modify handling quality characteristics and improve realism of crosswind landing

Synthetic Turbulence Modeling for Evaluation of Ultrasonic Cross-Correlation Flow Measurement

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI linkPerformance of an ultrasonic cross-correlation flow measurement instrument may be significantly affected by turbulence at the location of the ultrasonic sensors. In this paper, a new method of generating Synthetic Turbulence is presented, to provide an effective tool for creating a variety of turbulent fields, which can be used to model and analyze instrument performance under different flow conditions. In the proposed method, a turbulent field is presented as a Fourier time-series in each point in space. Turbulence structures are defined by a spatial distribution of phase functions for each harmonic. Principles of designing a phase function to achieve the desirable distribution of turbulence scales, and two-point correlations, are outlined by considering the example of Uniform Isotropic Turbulence. One application of this method, presented in this work, is the mathematical modeling of ultrasonic cross-correlation flow measurement. Results predicted by the proposed mathematical model show good agreement with experimental data

Prediction Of Static Aerodynamic Hysteresis On A Thin Airfoil Using OpenFOAM

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.The paper presents computational prediction of aerodynamic hysteresis loops in static conditions for a two-dimensional aerofoil that was used as a cross-section profile for a rectangular wing with an aspect ratio of five, tested in the TsAGI T-106 wind tunnel at a Reynolds number of =6×106 and a Mach number of =0.15. Tests in the wind tunnel showed that minor changes in the curvature of the leading edge of the thin aerodynamic profile lead to a significant increase in the maximum lift coefficient when significant hysteresis loops appear in the aerodynamic characteristics of the wing. The computational predictions of stall aerodynamics presented in this paper are made for a two-dimensional profile using the OpenFOAM open-source code to simulate a flow based on the unsteady Reynolds-averaged Navier–Stokes equations using the Spalart–Allmaras turbulence model. The calculation results confirm the existence of loops of static aerodynamic hysteresis and bistable structures of the separated flow, and the results are qualitatively similar to the results observed experimentally on the wing with a finite aspect ratio

Evaluation of Aerodynamic Characteristics in Oscillatory Coning Using CFD Methods

This paper contributes to the methodology of the REF2021 Impact Case Study "Enhancing Pilot Training and Flight Safety Through Improved Aerodynamic Modelling and Prediction of Nonlinear Flight Dynamics" submitted by De Montfort University (rated 3*).The wind tunnel rotary-balance testing is widely used in aircraft dynamics to characterise aerodynamics at moderate and high angles of attack during stall and spin regimes. In such experiments an aircraft test model is rotated along the wind-tunnel free-stream velocity vector allowing the measurement of aerodynamic characteristics in steady rotational flow conditions with constant angle of attack and sideslip. In modified tests named as oscillatory coning, the rotation vector is tilted from the free-stream velocity vector making flow conditions with periodic variations in angle of attack and sideslip. This allows evaluation of unsteady aerodynamic responses superimposed on steady conical rotation. The use of CFD methods for prediction of aerodynamic characteristics in rotary-balance and oscillatory coning conditions may significantly complement experimental data via extrapolation of data for higher Reynolds numbers, elimination of interference effects from supporting system, extraction of unsteady aerodynamic derivatives affecting aircraft dynamic stability. This paper presents CFD simulation results obtained in rotary-balance and oscillatory coning motions for the NASA Common Research Model (CRM) in its wing-body configuration at moderate = 1 × 10^6 , low Mach number =0.2 and the use of the obtained unsteady responses in aerodynamic modelling