Dr Nikolay Abramov

Job: Senior Research Fellow

Faculty: Computing, Engineering and Media

School/department: School of Engineering and Sustainable Development

Research group(s): Centre for Engineering Science and Advanced Systems (CESAS)

Address: De Montfort University, The Gateway, Leicester, LE1 9BH

T: +44 (0)116 207 8694

E: nabramov@dmu.ac.uk

W: http://dmu.ac.uk

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Research group affiliations

Centre for Engineering Science and Advanced Systems (CESAS)

Nonlinear Flight Dynamics Research Group (NFD)

Publications and outputs

Wing Rock Prediction in Free-to-Roll Motion Using CFD Simulations
dc.title: Wing Rock Prediction in Free-to-Roll Motion Using CFD Simulations dc.contributor.author: Sereez, Mohamed; Lambert, Caroline; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: 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.
A modified dual time integration technique for aerodynamic quasi-static and dynamic stall hysteresis
dc.title: A modified dual time integration technique for aerodynamic quasi-static and dynamic stall hysteresis dc.contributor.author: Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: 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. dc.description: open access article
Investigation of Aerodynamic Characteristics of a Generic Transport Aircraft in Ground Effect Using URANS Simulations
dc.title: Investigation of Aerodynamic Characteristics of a Generic Transport Aircraft in Ground Effect Using URANS Simulations dc.contributor.author: Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: 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. dc.description: This papers contributes to the methodology of the Impact Case Study submitted by De Montfort University to the REF2021 "Enhancing Pilot Training and Flight Safety Through Improved Aerodynamic Modelling and Prediction of Nonlinear Flight Dynamics" (rated 3*).
Prediction Of Static Aerodynamic Hysteresis On A Thin Airfoil Using OpenFOAM
dc.title: Prediction Of Static Aerodynamic Hysteresis On A Thin Airfoil Using OpenFOAM dc.contributor.author: Sereez, Mohamed; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: 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. dc.description: 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.
Aerodynamic Modeling for Post-Stall Flight Simulation of a Transport Airplane
dc.title: Aerodynamic Modeling for Post-Stall Flight Simulation of a Transport Airplane dc.contributor.author: Abramov, Nikolay; Goman, M. (Mikhail G.); Khrabrov, A. N. (Alexander N.); Soemarwoto, B. dc.description.abstract: The principles of aerodynamic modeling in the extended flight envelope, which is characterized by the development of separated flow, are outlined and illustrated for a generic transport airplane. The importance of different test techniques for generating wind tunnel data and the procedure for blending the obtained experimental data for aerodynamic modeling are discussed. Complementary use of computational fluid dynamics simulations reveals a substantial effect of the Reynolds number on the intensity of aerodynamic autorotation, which is later reflected in the aerodynamic model. Validation criteria for an extended envelope aerodynamic model are discussed, and the important role of professional test pilots with post-stall flying experience in tuning aerodynamic model parameters is emphasized. The paper presents an approach to aerodynamic modelling that was implemented in the project Simulation of Upset Recovery in Aviation (2009–2012), funded by the European Union under the seventh framework programme. The developed post-stall aerodynamic model of a generic airliner configuration for a wide range of angles of attack, sideslip, and angular rate was successfully validated by a number of professional test pilots on hexapod and centrifuge-based flight simulator platforms. dc.description: The file attached to this record is the author's final peer reviewed version.; open access article
Impact of Ground Effect on Airplane Lateral Directional Stability during Take-Off and Landing
dc.title: Impact of Ground Effect on Airplane Lateral Directional Stability during Take-Off and Landing dc.contributor.author: Sereez, M.; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: 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. dc.description: Open Access journal
Computational Ground Effect Aerodynamics and Airplane Stability Analysis During Take-off and Landing
dc.title: Computational Ground Effect Aerodynamics and Airplane Stability Analysis During Take-off and Landing dc.contributor.author: Sereez, M.; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: 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.
Computational Simulation of Airfoils Stall Aerodynamics at Low Reynolds Numbers
dc.title: Computational Simulation of Airfoils Stall Aerodynamics at Low Reynolds Numbers dc.contributor.author: Sereez, M.; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: 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.
Flight Envelope Expansion via Active Control Solutions for a Generic Tailless Aircraft
dc.title: Flight Envelope Expansion via Active Control Solutions for a Generic Tailless Aircraft dc.contributor.author: Abramov, Nikolay; Bommanahal, Mallesh; Chetty, S.; Goman, M. (Mikhail G.); Kolesnikov, E. N.; Murthy, P V Satyanarayana dc.description.abstract: Aircraft dynamics at high angles of attack due to loss of stability and control essentially limits its manoeuvrability. Modern control systems implement flight envelope protection at the cost of maneuverability to improve safety in these conditions. Flight envelope boundaries, which are set taking into account deterioration of stability and controllability due to separated flow, can be expanded by appropriate design of control laws. However, such a design requires extensive analysis of the maneuver envelope of the airframe and its utilization by the flight envelope protection laws. The reliability of this analysis depends on the adequate aerodynamic modeling which captures nonlinear unsteady variation of aerodynamic loads in these flight regimes. Two novel models for unsteady aerodynamics at low and high subsonic Mach numbers are described. These models and prototyping control laws are used for closed loop computational analysis. The computational methodology of clearing flight control laws for flight envelope expansion of a Generic Tailless Aircraft (GTA) is addressed
Synthetic Aerodynamics Modeling for Pilot Training in the Extended Flight Envelope
dc.title: Synthetic Aerodynamics Modeling for Pilot Training in the Extended Flight Envelope dc.contributor.author: Murthy, P V Satyanarayana; Abramov, Nikolay; Goman, M. (Mikhail G.) dc.description.abstract: Flight at high angles of attack is associated with a variety of types of aircraft departure and post stall behaviour. Every aircraft will exhibit specific set of flight characteristics in extended flight envelope. This work was motivated by the need for using flight simulator in training pilots in those high angles of attack conditions to give pilots awareness about nonlinear aircraft behaviours and peculiarities of flight at stall and above stall. Flight simulators, equipped with representative aerodynamic models covering normal and extended flight envelope can be utilised for this purpose. A special approach of building a synthetic aerodynamic model over an available high angle of attack aerodynamic model is discussed in this paper. The Synthetic modelling presented in this paper assumes complementary transformation of a number of key aerodynamic characteristics of the original aerodynamic model with an objective to diversify post stall dynamics.

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Research interests/expertise

Flight dynamics, aerodynamic modelling, unsteady aerodynamics at separated flow conditions, identification, nonlinear dynamical systems, mathematical modelling.

Areas of teaching

ENGD2005 - Engineering Science 2
ENGD3038 – Dynamics and Control
ENGD1005 – Mechanical Principles

Qualifications

Nikolay Abramov graduated from Moscow Institute of Physics and Technology, the Faculty of Aeromechanics and Flight Technology with MSc degrees in 1998 (http://phystech.edu/|) and received PhD degree in Aeronautical Engineering at De Montfort University in 2005.) and received PhD degree in Aeronautical Engineering at De Montfort University in 2005.

Membership of professional associations and societies

Member of the American Institute of Aeronautics and Astronautics (AIAA), www.aiaa.org| since 2012.

Conference attendance

Pushing Ahead - SUPRA Airplane Model for Upset Recovery. N. Abramov, M. Goman, A. Khrabrov, E. Kolesnikov, L. Fucke, B. Soemarwoto, H. Smaili. AIAA Modeling and Simulation Technologies Conference, Minneapolis, Minnesota, USA, 13-16 August 2012.

Aerodynamic Model Development for Simulation of Upset Recovery of Transport Airplane. N.Abramov, M.Goman, A.Khrabrov, B.Soemarwoto. RAeS Aerodynamics Conference - Applied Aerodynamics: Capabilities and Future Requirements. London, UK, 27 July 2010.

Externally funded research grants information

EU 7^th Framework Programme research project SUPRA (2009-2012) www.supra.aero|, Researcher.

National Aerospace Laboratories CSIR-NAL, Bangalore, India (2010-2013) www.nal.res.in|, Researcher