Vladimir V. Golubev

High-Accuracy Low-Re Simulations of Airfoil-Gust and Airfoil-Vortex Interactions

The current work completes a high-accuracy 2D study of nonlinear viscous interaction of SD7003 airfoil with nonuniform, unsteady incoming flow initiated in Ref. [1]. A laminar mean flow is considered with M=0.1 and Re=10,000 typical of MAV applications in which an encounter with upstream vortical flow structures may induce particularly significant aerodynamic and aeroelastic responses. Previous and new results obtained for the aerodynamic airfoil response to time-harmonic and sharp-edge gust perturbations with variable gust amplitude, frequency, dimension and duration are discussed in comparison with “equivalent” pitching simulations as well as corresponding predictions based on the linearized inviscid, incompressible unsteady aerodynamic theory. In addition, results obtained for the airfoil response to an upstream Taylor vortex are presented and compared against sharp-edge gust solutions. Preliminary 3D ILES computations of the vortex-airfoil interaction are also conducted and compared with 2D predictions in a transitional flow regime.

High-Fidelity Simulations of Transitional Airfoil Interacting with Upstream Vortical Structure

The paper discusses results of 2D and 3D high-fidelity viscous simulations of SD7003 airfoil’s unsteady aerodynamic response to impinging vortical structures in the transitional flow regimes characteristic of Micro Air Vehicle (MAV) applications. Following a thorough review of previous studies characterizing various scales and configurations of urban flow disturbances, the numerical work focuses on the airfoil-vortex unsteady interaction investigated in the parametric space of variable vortex strength, size, position, sense of rotation, as well as the airfoil steady loading and the mean flow Reynolds number. The analysis reveals numerous details of the unsteady interaction processes and elucidates a complex interplay of viscous and inviscid unsteady phenomena and their resulting effect on the airfoil unsteady aerodynamic lift, drag and moment responses.

Modeling Synthetic Jets for Low-Re Airfoil Unsteady Flow Control

Synthetic jet actuators (SJAs) may be carefully designed to alleviate the negative impact of impinging flow non-uniformities on the aircraft wing unsteady aerodynamic response. The current study investigates the effectiveness of SJAs for active control of unsteady flow over SD7003 low-Re airfoil in presence of a high-amplitude upstream flow disturbance characterized by a sharp-edge gust. In the adopted numerical procedure, the actuators dimensional scaling and excitation frequency effects are first examined for a specific SJA configuration using a Lumped Element Model. The next step employs a Reynolds-averaged Navier-Stokes analysis to determine simple fluctuating-velocity boundary condition at the bottom of the actuators orifice. The orifice with the properly defined boundary condition is then embedded into the airfoil surface for conducting high-accuracy viscous analysis of active flow control during gust-airfoil interaction process. Results of numerical simulations indicate that the SJA positive effe...

High-Accuracy Viscous Simulations of Gust-Airfoil Nonlinear Aeroelastic Interaction

The work develops a high-accuracy viscous analysis of the nonlinear aeroelastic interaction of a Micro Air Vehicle’s (MAV) wing section with a non-uniform, unsteady incoming flow. In the implemented iterative procedure, a set of governing Navier-Stokes equations is solved simultaneously with the nonlinear equations of motion for the structure, so that the fluid and structure are treated as a coupled dynamic system. The numerical procedure employs a high-order lowpass filter operator which selectively damps the poorly resolved high-frequency content to retain numerical accuracy and stability over a wide range of flow regimes. An efficient analytical model is developed to introduce an unsteady incompressible 2D vortical flow perturbation inside the computational domain through a source term in the momentum equations. Strongly coupled, nonlinear unsteady aerodynamic and structural responses of an elastically mounted airfoil subject to harmonic, high-amplitude vortical gust are examined in a test study, with emphasis on the wing section transition to limit cycle oscillations (LCO).

New Approach to Modeling Airfoil Interaction with Upstream Turbulence

The current work proposes a new method to introduce an upstream turbulence for high-fidelity numerical simulations of unsteady flow-structure interactions. In particular, the approach to generate a threedimensional, divergence-free, convected perturbation velocity field by prescribing a momentum source in an arbitrary region of the computational domain upstream of a solid body is discussed. It is shown that the method can be efficiently employed in conjunction with the random flow generation (RFG) procedures for numerical analysis of airfoil response to synthetically-generated upstream turbulence with prescribed integral characteristics. Details of the numerical implementation of the method are discussed. Preliminary two-dimensional test studies are conducted to illustrate application of the proposed technique for analysis of the airfoil interaction with convected disturbance fields.

High-Fidelity Simulations of Airfoil Interaction with Upstream Turbulence

This work complements a series of benchmark high-fidelity numerical studies investigating a low-speed airfoil response to canonical forms of impinging flow disturbances characteristic of unsteady urban environment. While previous parametric analyses examined aerodynamic effects induced by incident sharp-edge gust, time-harmonic gust, and Taylor vortex all representing deterministic perturbation models, the current study focuses on modeling airfoil interaction with upstream synthetic turbulence produced based on a random flow generation procedure. A previously introduced highly efficient approach is employed to generate a three-dimensional, divergence-free, convected turbulent velocity field with prescribed integral characteristics by means of a time-dependent momentum source located in an arbitrary region of the computational domain upstream of a solid body. In parametric 2D and 3D numerical studies, imposed and generated turbulence spectra as well as the resulting unsteady aerodynamic responses are examined for a set of parameters characterizing turbulent upstream flow conditions and airfoil loading.

High-Fidelity Simulations of Transitional Airfoil Interacting with Canonical Upstream Flow Disturbances

The current work reports on a comparison of high-fidelity 3D Navier-Stokes simulations of SD7003 airfoil interacting with canonical upstream flow disturbances against previous high-accuracy 2D simulations conducted for transitional flow regime. Three forms of upstream flow disturbance are considered including 1D and 2D time-harmonic gust, sharp-edge gust, and the Taylor vortex models. Results obtained for the airfoil unsteady aerodynamic responses to time-harmonic and sharp-edge gust perturbations with variable gust amplitude are discussed in comparison with linearized inviscid, incompressible unsteady aerodynamic theory. In addition, analysis of unsteady aerodynamic response for a large highamplitude Taylor vortex impinging on the airfoil is examined. It is shown that the less computationally expensive 2D simulations provide a sufficiently accurate analysis of the unsteady lift responses but fall short in drag and moment predictions.

High-Accuracy Simulations of Robust LCO Control Using Synthetic Jet Actuators

In the follow-up study to Ref. [1], we investigate a benchmark case of a robust nonlinear control of gustinduced limit-cycle oscillations (LCO) of an elastically-mounted transitional airfoil using synthetic-jet actuators (SJA) embedded in the airfoil design of a small-size unmanned air vehicle (UAV). The robust controller is particularly advantageous for high levels of uncertainty and nonlinearity present both in the UAV unsteady flight-path environment and the actuator’s response. In the adopted numerical procedure, the actuator is modeled through imposing a fluctuating-velocity boundary condition directly on the airfoil surface for conducting high-accuracy viscous analysis of SJA-based airfoil LCO control governed by the developed robust regulation law. The numerical studies conducted for selected SJA excitation parameters examine the thresholds of the actuator’s control authority to produce the desirable impact.

Robust Nonlinear Regulation of Limit Cycle Oscillations in UAVs Using Synthetic Jet Actuators

In this paper, a synthetic jet actuators (SJA)-based nonlinear robust controller is developed, which is capable of completely suppressing limit cycle oscillations (LCO) in UAV systems with parametric uncertainty in the SJA dynamics and unmodeled external disturbances. Specifically, the control law compensates for uncertainty in an input gain matrix, which results from the unknown airflow dynamics generated by the SJA. Challenges in the control design include compensation for input-multiplicative parametric uncertainty in the actuator dynamic model. The result was achieved via innovative algebraic manipulation in the error system development, along with a Lyapunov-based robust control law. A rigorous Lyapunov-based stability analysis is utilized to prove asymptotic LCO suppression, considering a detailed dynamic model of the pitching and plunging dynamics. Numerical simulation results are provided to demonstrate the robustness and practical performance of the proposed control law.

APPLICATION OF SPACE-TIME MAPPING ANALYSIS METHOD TO UNSTEADY NONLINEAR GUST-AIRFOIL INTERACTION PROBLEM

This paper is concerned with the application of a new Space-Time Mapping Analysis (STMA) method to a nonlinear, inviscid computation of unsteady airfoil response to an impinging, highintensity, vortical gust. The method solves the unsteady problem as a steady-state one by treating the time coordinate identically to the space directions. A high-order discretization scheme is provided to achieve time-accurate predictions of both unsteady aerodynamic and aeroacoustic responses. The obtained results show localized zones in the computational plane where nonlinear response effects become important.