Browsing by Author "Sereez, Mohamed"

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    Computational Ground Effect Aerodynamics and Airplane Stability Analysis During Take-off and Landing
    (EUCASS, 2017-09-22) Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.)
    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.
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    Computational Prediction of Stall Aerodynamics and Evaluation of Ground Effect for a Generic Transport Aircraft
    (De Montfort University, 2018-12) Sereez, Mohamed
    Flight safety of modern transport aviation depends to a large extent on the skills of the pilot in dealing with manual aircraft control in critical Flight situations.According to Boeing's document " Statistical Summary of Commercial Jet Air-plane Accidents, Worldwide Operations (1959-2016)" about 89 percent of all fatal accidents in aviation take place due to Loss of Control-In Flight (LOC-I), Con-trolled Flight into or Toward Terrain (CFIT), and Runway Excursion (RE). The major contribution to Flight fatalities is related to LOC-I situations when pilots are unable to handle control of an aircraft during an onset of aerodynamic stall at high angles of attack provoking almost unrecoverable Flight conditions. The second contributor to critical flight accidents is related to RE situations during landing and take-o phases of flight. It is now generally accepted that the reduction in accidents can be achieved via improved training of line pilots using modern flight simulators, which are now used for regular pilot training in normal flight conditions. Pilot training in extended flight envelope will soon become mandatory following new regulations from FAA, ICAA and EASA. Training of pilots for upset prevention and recovery in LOC-I critical conditions need flight simulators upgraded with aerodynamic models covering extended flight envelope including high angles of attack with separated low conditions. Flight accidents with RE require improved modeling of aerodynamics in close proximity to the ground considering cross-wind conditions. Data for aerodynamic models for normal and extended flight conditions are traditionally obtained from wind tunnel tests using different methods such as static, forced oscillation and rotary balance tests. The role of Computational Fluid Dynamics (CFD) methods in generating aerodynamic data for extended flight envelope has a significant potential in improving delity of aerodynamics models and reducing the cost of such models. Wind tunnel test results at high angles of attack are sensitive to the level of low turbulence in the tunnel and aero-elastic vibrations of the aircraft model, while computational simulation predictions are highly sensitive to the selection of turbulence model closing the Unsteady Reynolds Averaged Naiver-Stokes (URANS) equations. This Thesis is mostly focused on computational prediction of static stall hysteresis, ground effect and ice accretion effect on aerodynamics of flight which leads to upset of aircraft in the extended flight envelope. The ultimate motive is to generate reliable aerodynamic data which can be used to develop flight models that can be used to train pilots for loss of control of aircraft in critical flight situations.
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    Computational Simulation of Airfoils Stall Aerodynamics at Low Reynolds Numbers
    (Royal Aeronautical Society, 2016-07-19) Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.)
    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.
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    Evaluation of Aerodynamic Characteristics in Oscillatory Coning Using CFD Methods
    (EUCASS, 2022-09-28) Sereez, Mohamed; Goman, M. (Mikhail G.)
    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 𝑅𝑒 = 1 × 10^6 , low Mach number 𝑀=0.2 and the use of the obtained unsteady responses in aerodynamic modelling.
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    Impact of Ground Effect on Airplane Lateral Directional Stability during Take-Off and Landing
    (Scientific Research Publishing, 2018-01) Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.)
    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. 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.
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    Investigation of Aerodynamic Characteristics of a Generic Transport Aircraft in Ground Effect Using URANS Simulations
    (Royal Aeronautical Society, 2022-09-14) Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.)
    This paper focuses on computational prediction of aerodynamic and the flow field characteristics for NASA Common Research Model (CRM) in it’s High-Lift (HL) configuration in close proximity to the ground. The URANS simulation with the Spalart-Allmaras (SA) turbulence model is checked for the quality of the generated mesh and compared with the available wind tunnel data. The obtained simulation results in the immediate vicinity of the ground demonstrate significant changes in the longitudinal and lateral-directional aerodynamic characteristics in aircraft banked positions, which is important for a better understanding of aircraft landing in crosswind conditions.
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    A modified dual time integration technique for aerodynamic quasi-static and dynamic stall hysteresis
    (Sage, 2023-03-29) Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.)
    Simulation 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.
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    Prediction of aerodynamic characteristics of high-lift Common Research Model in ground effect
    (Cambridge University Press, 2023-10-20) Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.)
    Reynolds Averaged Navier-Stokes (RANS) simulations are performed to investigate the aerodynamic characteristics of the NASA Common Research Model (CRM) in its high-lift (HL) configuration in close proximity to the ground. The RANS simulations are conducted at a moderate Reynolds number of Re=5.49×106 and M=0.2 with the use of the Spalart-Allmaras (SA) turbulence model. out of ground effect (OGE) simulation results are validated against available wind tunnel data before proceeding to in ground effect (IGE) simulations. The obtained computational results in the immediate vicinity of the ground with asymmetric aircraft attitudes demonstrate significant changes in the longitudinal and lateral-directional aerodynamic characteristics, which should be taken into account in flight dynamics analysis of aircraft during take-off and landing in crosswind conditions.
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    Prediction Of Static Aerodynamic Hysteresis On A Thin Airfoil Using OpenFOAM
    (American Institute of Aeronautics and Astronautics, 2020-10-13) Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.)
    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 𝑅𝑒=6×106 and a Mach number of 𝑀=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.
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    Wing Rock Prediction in Free-to-Roll Motion Using CFD Simulations
    (Aerospace Europe Conference 2023 - 10th EUCASS - 9th CEAS, 2023-10-02) Sereez, Mohamed; Lambert, Caroline; Abramov, Nikolay; Goman, M. (Mikhail G.)
    The free-to-roll wing rock CFD simulation of a slender 80-degree delta wing is performed using the Dynamic Fluid-Body Interaction (DFBI) framework and the overlap/chimera mesh method. The purpose of the simulations carried out was to test the capabilities of the current CFD methods for predicting wing rock motion over a wide range of angles of attack, including strong conical vortex interactions and vortex breakdown phenomenon. The predictions of steady aerodynamic dependencies and the aerodynamic stability derivatives based on forced oscillation tests along with the time histories of the wing rock motion of an 80-degree delta wing are in good qualitative and quantitative agreement with the available wind tunnel experimental data demonstrating onset of the wing rock motion. At higher angles of attack with vortex breakdown CFD simulations demonstrated an excitation of the large amplitude regular oscillations or the low amplitude chaotic oscillations depending on the applied initial conditions.