# Miguel R. Visbal's research while affiliated with Air Force Research Laboratory and other places

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## Publications (403)

This paper presents a computational study of unsteady transonic effects on a pitching supercritical laminar airfoil using high-order implicit large-eddy simulation. A CAST10-2 airfoil operating at a chord-based Reynolds number of [Formula: see text], a transonic freestream Mach number of [Formula: see text], and a small nominal angle of attack of [...

Large-eddy simulations (LES) are employed to investigate the pitch-plunge equivalence of an SD7003 airfoil undergoing constant ramp motions at Reynolds number Re 6 × 10 4. The equivalence is constructed based on the geometric effective angle of attack according to the quasi-steady thin-airfoil theory. Two rates of descent (or pitch up) are analyzed...

The role of aspect ratio on the dynamic stall process of an unswept finite wing is investigated using high-fidelity large-eddy simulations. Three aspect ratios (AR=4, 8, and 16) are explored for wings (NACA 0012 cross section) at chord Reynolds number Rec=2×105 and freestream Mach number M∞=0.1. The wings pitch sinusoidally from initial incidence o...

View Video Presentation: https://doi.org/10.2514/6.2022-3634.vid Large Eddy Simulations (LES) of coflow jet (CFJ) active flow control on a NACA 6421 airfoil were performed to examine the effects of angle of attack and magnitude of the jet momentum coefficient. The flow conditions for the current work were a free stream Mach number of 0.1 and a Reyn...

This paper presents a computational study of unsteady transonic effects on a supercritical laminar airfoil using high-order implicit large-eddy simulation. The unsteady transitional flow behavior on a static CAST10-2 airfoil operating at a chord-based Reynolds number of Rec=2×106, a transonic freestream Mach number of M∞=0.73, and several small ang...

A low-amplitude high-frequency flow control strategy for mitigation of transient tip stall is demonstrated for the case of a finite swept wing using high-fidelity wall-resolved large-eddy simulations. A wing of aspect ratio =4 and NACA 0012 section is considered at freestream Mach number M∞=0.1 and chord Reynolds number Rec=2×105. The wing undergoe...

The onset and evolution of the dynamic stall vortex (DSV) are analysed by means of large eddy simulations of an SD7003 aerofoil undergoing periodic plunging motion in a transitional Reynolds number flow ( $Re =6\times 10^{4}$ ). Interactions between upstream propagating Kelvin–Helmholtz instabilities and a shear layer formed at the leading edge tri...

A high-fidelity numerical study is undertaken to expand the notion of pitch/plunge equivalence to finite, swept wings undergoing deep-dynamic stall and builds upon the analysis of straight wings in another paper by the authors [“Pitch/Plunge Equivalence for Dynamic Stall of Unswept Finite Wings,” AIAA Journal (submitted for publication)]. The wing...

Pitch/plunge equivalence for deep dynamic stall of a straight finite wing is considered by employing large-eddy simulations. The flowfields are computed with a well-established time-implicit high-fidelity large-eddy simulation approach. The wing has a moderate aspect ratio of AR=4 and a NACA 0012 section incorporating a rounded tip. The flow parame...

View Video Presentation: https://doi.org/10.2514/6.2022-0043.vid This paper explores gust interactions on a supercritical, laminar CAST10-2 airfoil operating at a transonic Mach number of M = 0.73, transitional Reynolds number of Re = 2,000,000, and a low angle of attack of α = 0.9 deg. The airfoil is exposed to periodic transverse gusts generated...

View Video Presentation: https://doi.org/10.2514/6.2022-1376.vid Numerical simulations are carried out for supersonic flow over a rectangular cavity at a freestream Mach number of 1.5 and Reynolds of 1,000,000. The generic cavity configuration has a length-to-depth ratio of 4.5, and has been widely studied both computationally and experimentally. F...

View Video Presentation: https://doi.org/10.2514/6.2022-1949.vid Large Eddy Simulations (LES) were performed to study coflow jet (CFJ) active flow control on a NACA6421 airfoil. This is the first known LES simulating an airfoil applying CFJ flow control. Previous numerical studies of airfoils and wings using CFJ have relied on Reynolds Averaged Nav...

View Video Presentation: https://doi.org/10.2514/6.2022-0708.vid A novel passive flow control strategy for the mitigation of transient separation and dynamic stall is demonstrated by means of high-fidelity large-eddy simulations. The control technique is based on a properly-sized micro-cavity cut into a wing’s underside near the leading edge, ahead...

View Video Presentation: https://doi.org/10.2514/6.2022-0051.vid The objective of the current work is the development and comparative analysis of a novel, nonlinear, robust, closed-loop control of airfoil boundary-layer transition employing local dynamic surface modification as part of the control system design. Two approaches in the closed-loop co...

View Video Presentation: https://doi.org/10.2514/6.2022-2125.vid The occurrence of dynamic stall vortex is delayed via plasma actuation across various pitch rates for a NACA0012 at Re= 2 × 105 . The phenomenon is surveyed via flow visualization of a pitching airfoil and qualitatively compared to prior implicit large-eddy simulation. The plasma actu...

View Video Presentation: https://doi.org/10.2514/6.2021-2519.vid In the present work, we perform large eddy simulations (LES) to investigate the pitch-plunge equivalence of an SD7003 airfoil undergoing constant ramp motions at Reynolds number $\text{Re}=6\times10^4$. To this end, a new description of the ramp motion is proposed for the plunging cas...

View Video Presentation: https://doi.org/10.2514/6.2021-2948.vid The role of aspect ratio on the dynamic stall process of swept finite wings is investigated using high-fidelity, implicit large-eddy simulations. Two aspect ratios (4 and 8) are explored for a 30 degree swept wing with a NACA 0012 profile and rounded wing-tips. Following previous work...

High-fidelity large-eddy simulations are performed to study the unsteady boundary layer sensitivity of a natural-laminar-flow airfoil (NLF-0414) undergoing dynamic stall in comparison to two traditional airfoil sections (NACA 0012 and SD 7003). In this work, the natural-laminar-flow airfoil at Rec=5.0×105 and M∞=0.1 pitches with a constant nondimen...

Numerical calculations were carried out in order to investigate the delay of transition to turbulence on a wing section by means of local dynamic surface deformation. Physically, the deformation may be produced by piezoelectrically driven actuators located below a compliant aerodynamic surface, which have been explored experimentally. One actuator...

The compounding effects of panel flutter and oblique shock impingement are of great concern to the development of light-weight, high-speed vehicles. Shock-induced panel flutter response is investigated at M=2 and Re=120,000 using the Navier–Stokes equations closely coupled to the von-Kármán equations. A naturally occurring laminar inflow boundary l...

A low-amplitude, high-frequency flow control strategy for mitigation of transient tip stall is demonstrated for the case of a finite swept wing using high-fidelity wall-resolved large-eddy simulations. A wing of aspect ratio AR=4 and NACA 0012 section is considered at freestream Mach number M = 0.1 and chord Reynolds number Re = 200,000. The wing u...

The effects of compressibility on the onset of the dynamic stall vortex (DSV) over a wing section are analyzed by means of large eddy simulations. A SD7003 airfoil is considered at two different freestream Mach numbers, being $M_{\infty} = 0.1$ and $0.4$, and at a chord-based Reynolds numbers of $\mbox{Re}_c = 6 \times 10^4$. The profile undergoes...

This study compared two high-order solvers for a Large Eddy Simulations (LES) of supersonic flow over a wall-mounted hemisphere. The two high-order codes used for this comparison are FDL3DI and OVERFLOW. The FDL3DI solver employed a hybrid sixth-order compact spatial discretization and second-order Roe scheme. The OVERFLOW solver used a fifth-order...

This paper presents a number of high-order implicit large-eddy simulations (ILES) that show flow transition effects on a supercritical laminar airfoil undergoing small-amplitude pitch oscillations. A CAST10-2 airfoil operating at a Reynolds number of Re = 2,000,000, a transonic free stream Mach number of M = 0.73, and an angle of attack of α = 0.9...

Given the important role of transition to the dynamic stall process, high-fidelity large-eddy simulations are performed to study the unsteady boundary layer sensitivity of a natural-laminar-flow airfoil (NLF-0414) undergoing dynamic stall in comparison to two traditional airfoil sections (NACA 0012 and SD 7003). In this work, the NLF airfoil at $Re...

The role of aspect ratio on the dynamic stall process of an unswept finite wing is investigated using high-fidelity large-eddy simulations. Three aspect ratios ($AR = 4$, 8, and 16) are explored for a finite wing with a NACA 0012 profile and rounded wing-tips. Following previous work, the finite wing at chord-Reynolds number $Re_c = 2 \times 10^5$...

Numerical calculations were carried out in order to investigate the delay of transition to turbulence on a wing section by means of local dynamic surface deformation. Physically, the deformation may be produced by piezoelectrically driven actuators located below a compliant aerodynamic surface, which have been explored experimentally. One actuator...

Direct numerical simulations were carried out in order reproduce the generation and control of transition on a flat plate by means of local dynamic surface modification. The configurations and flow conditions duplicate those of previous numerical investigations, and are similar to an experimental arrangement, which employed piezoelectrically driven...

This paper presents high-fidelity implicit large-eddy simulations of counterclockwise-oriented parallel vortical gust interactions with a NACA0012 airfoil operating at a transitional chord-based Reynolds number of Rec=200,000. Both the angle of attack (α=4, 8, and 12 deg) and gust core size (rv/c=0.125, 0.25, and 0.50) are varied. In all cases, flo...

Large-eddy simulations of the onset of dynamic stall for a NACA 0012 airfoil, pitching at a constant rate, are performed for a chord Reynolds number of 1.0×10^6. Using four simulations, spanning M∞=0.1–0.4, the effects of compressibility are examined for constant Reynolds number. The interplay between the laminar separation bubble (LSB), separation...

A novel high-frequency flow control strategy for mitigation of dynamic stall is demonstrated for the case of a finite wing using high-fidelity wall-resolved implicit large-eddy simulations. A NACA 0012 wing of aspect ratio AR=4 is considered at freestream Mach number M∞=0.1 and chord Reynolds number Rec=2×105. The wing undergoes an oscillatory pitc...

This work explores self-sustained pitching oscillations of a NACA0012 airfoil operating at low-to-moderate Reynolds numbers in which the aerodynamic flow is in a transitional regime. One-degree of freedom (1-DOF) pitching oscillations are explored for chord-based Reynolds numbers of Rec=77,000 and 110,000, which fall on the lower end of the flutter...

A three-dimensional transitional shock boundary layer interaction (SWBLI) over a finite-span flexible panel is investigated by performing direct numerical simulations (DNS). The laminar inflow is at Mach 2, on which an oblique shock of turn angle 5.62∘ is imposed. The shock impinges at the mid-chord length of the panel, giving rise to flow separati...

A numerical study has been conducted to investigate the unsteady nature of afterbody vortices shed from an upswept region of a simple fuselage configuration. The upsweep angle considered is ϕ=28 deg, the Reynolds number based on the body’s diameter is ReD=2.0×105, and the freestream Mach number is M=0.1. These conditions have been selected followin...

This work explores the aerodynamics of an airfoil oscillating in a uniform-shear flow at chord Reynolds number of approximately 1.2×104 using complementary two-dimensional Navier–Stokes computations and direct force measurements. A NACA-0012 airfoil is pitched harmonically about its quarter-chord, with 2° amplitude and reduced frequency up to 12, i...

A recently proposed high-frequency control concept for dynamic-stall mitigation is demonstrated using large-eddy simulation of a pitching NACA 0012 airfoil at a chord Reynolds number of Rec=10^6. At this condition, dynamic stall occurs when the suction-surface laminar separation bubble (LSB) breaks down due to interaction with the turbulent separat...

Direct numerical simulations were carried out in order to reproduce the generation and control of transition on a flat plate by means of local dynamic surface modification. The configuration and flow conditions are similar to those of an experimental arrangement that employed piezoelectrically driven actuators to impart small-amplitude local deform...

Numerical calculations were carried out to investigate control of transition on a flat plate by means of local dynamic surface deformation. The configuration and flow conditions are similar to a previous computation which simulated transition mitigation. Physically, the surface modification may be produced by piezoelectrically driven actuators loca...

An investigation of the effect of moderate sweep on three-dimensional (3D) dynamic stall of a pitching finite-aspect-ratio wing is performed by means of large-eddy simulations. The wings have an aspect ratio AR=4 and a NACA 0012 section. Three values of sweep angle are considered, Λ=0°, 15°, and 30°. The flow parameters are freestream Mach number M...

Wall-resolved large-eddy simulations are carried out in order to explore the use of an overset nested-grid approach for computing high-Reynolds number turbulent aerofoil flows. By lowering the computational grid density as the distance from solid surfaces increases, a saving in computing resources may be realised. The configuration consists of a wi...

An investigation of dynamic stall on a pitching NACA 0012 aspect ratio 4 wing is performed by means of high-fidelity wall-resolved large-eddy simulations. The flow parameters are freestream Mach number M∞=0.1 and chord Reynolds number Rec=2×105. Three cycles of a sinusoidal pitching motion are considered with reduced frequency k=πfc/U∞=π/16 and min...

Oblique shockwaves may impinge on supersonic vehicles internally in an engine or externally on the outer mold line. They create a severe loading environment and may induce dynamic instabilities such as panel flutter. This study computationally explores the effect of shock-induced panel flutter response in 3D, inviscid, Mach 2 flow. Flutter behavior...

Previous experimental and numerical studies showed that two-dimensional roughness elements can stabilize disturbances inside a hypersonic boundary layer and eventually delay the transition onset. The objective of this paper is to evaluate the response of disturbances propagating inside a high-speed boundary layer to various two-dimensional surface...

Dynamic stall represents a challenge in a number of engineering applications including rotorcraft, maneuvering aircraft, gust encounters, and wind turbines. Delay of the onset of dynamic stall and mitigation of its undesirable transient loading effects have been sought in the past five decades employing a number of passive and active flow control t...

Previous experimental and numerical studies showed that two-dimensional roughness elements can stabilize disturbances inside a hypersonic boundary layer, and eventually delay the transition onset. The objective of this paper is to evaluate the response of disturbances propagating inside a high-speed boundary layer to various two-dimensional surface...

This paper presents high-fidelity implicit large-eddy simulations (ILES) of parallel vortical gust interactions with a NACA0012 airfoil operating at a transitional chord-based Reynolds number of Rec=200,000 and an angle of attack of α=4 deg. The gust is supplied upstream of the airfoil as a Taylor vortex. Three different initial vertical positions...

This paper presents high-fidelity implicit large-eddy simulations of parallel vortical-gust interactions with a NACA0012 airfoil operating at a transitional Reynolds number of Rec=200,000 and an angle of attack of α=4 deg. The gust is supplied upstream of the airfoil as a counterclockwise-oriented Taylor vortex. Upon impact with the leading edge, t...

This article explores the evolution of the unsteady flow structure for rigid and elastically mounted NACA0012 airfoils subject to a parallel vortical gust disturbance at a Reynolds number of Re=150,000 using implicit large-eddy simulation coupled with a structural dynamics model. A Taylor vortex is supplied upstream of the airfoil and shown to be s...

This work explores self-sustained pitching oscillations of a NACA0012 airfoil operating at low-to-moderate Reynolds numbers in which the aerodynamic flow is in a transitional regime. One-degree of freedom (DOF) pitching oscillations were explored over a range of Reynolds numbers (7.7×104<Rec≤2.0×105) using high-order implicit large-eddy simulation...

We present an investigation into the influence of upstream shear on the viscous flow around a steady two-dimensional (2-D) symmetric airfoil at zero angle of attack, and the corresponding loads. In this computational study, we consider the NACA 0012 airfoil at a chord Reynolds number $1.2\times 10^{4}$ in an approach flow with uniform positive shea...

Large-eddy simulations of the dynamic stall process on a pitching NACA 0012 airfoil at Re_c = 1.0x10^6 have been performed. Using a constant-rate pitch-up maneuver it is shown that the onset of dynamic stall occurs due to bursting of a very small laminar separation bubble located near the airfoil leading edge. This bursting is initiated by direct i...

The current work reports on the results of high-accuracy two-dimensional and high-fidelity three-dimensional Navier–Stokes simulations of an SD7003 airfoil interacting with canonical upstream flow disturbances at low and moderate Reynolds numbers corresponding to laminar and transitional flow regimes. Three deterministic forms of upstream flow dist...

Compressibility effects were numerically investigated for use of plasma-based flow control, which was applied to delay transition generated by excrescence on the leading edge of a wing. The wing airfoil section incorporates a geometry that is representative of modern reconnaissance air vehicles, and has an appreciable region of laminar flow at desi...

Effect of airfoil thickness on onset of dynamic stall is investigated using large eddy simulations at chord-based Reynolds number of 200,000. Four symmetric NACA airfoils of thickness-to-chord ratios of 9%, 12%, 15%, and 18% are studied. The 3-D Navier Stokes solver, FDL3DI is used with a sixth-order compact finite difference scheme for spatial dis...

A numerical study is conducted to characterize the tip vortex unsteady evolution on a rounded-tip NACA0012 wing of aspect ratio AR = 6 operating at a Reynolds number of Re = 2.0 × 10⁵ and an incidence of α = 8 deg. Stationary and plunging wing configurations are examined as representative problems of aircraft wandering, wing vibration, or structura...

This study addresses the flow structure and unsteady loading arising over a pitching low-aspect-ratio rectangular wing under low-Reynolds-number conditions of interest in small unmanned aerial vehicle operation and gust interactions. Simulations are performed employing a high-fidelity computational approach capable of accurately capturing the compl...

A numerical investigation was carried out to assess the effectiveness of plasma-based flow control for a swept-wing configuration. A single dielectric barrier discharge plasma actuator was used to delay transition generated by excrescence near the leading edge. Large-eddy simulations were performed for the configuration, which had a wing airfoil se...

## Citations

... Pressure is a thermodynamic property that plays a key role in fluid mechanics. It is of utmost importance in aerodynamic load prediction [1,2,3], noise generation [4,5], flow instability and turbulence [6,7,8], and flow control [9]. The increase of time resolution in velocity field measurements during the last decade has opened the path to obtaining instantaneous pressure fields by combining experimental data with the flow governing equations [10,11]. ...

... This can significantly constrain the design of an AUV by determining manufacturing costs, durability, mission envelope etc., and thus demonstrates the necessity of finite flipper analysis. Contemporary literature on finite wings of varying AR often focuses on single flapping configurations (Hammer, Garmann, & Visbal, 2021;Zhong, Han, Moored, & Quinn, 2021;Zurman-Nasution et al., 2021b) with only a few studies related to tandem arrangements (Arranz, Flores, & Garcia-Villalba, 2020;Jurado, Arranz, Flores, & García-Villalba, 2022). A key feature of the above is the presence of tip vortices that transform the 2-D wake into a complex chain of ring-like formations (Li, Pan, Zhao, Ma, & Wang, 2018;Shao et al., 2010). ...

... Strong lift oscillations, characteristic of buffet, can be seen for the free-transition cases with a peak observed in the PSD at = 0.11 and 0.15 for cases A5M7F and A5M735F, respectively (highlighted seen here is that the turbulent buffet frequency ( = 0.13) remains approximately the same as that of laminar buffet ( = 0.15) at these conditions. It can also be inferred from the temporal variations in Fig. 3a that the time-averaged is approximately the same at a given for both free-and forced-transition cases (see Table 1 [44], more recent experiments at ONERA † and LES in [45]). Interestingly, multiple shock waves were also observed in steady inviscid calculations by [45]. ...

... In fact, the peculiarities of the trailing-edge dynamics have also been reported in other cases besides the ramp motion [15,[32][33][34][35]. Naturally, the mismatch between pitch and plunge under certain conditions resulted in questioning the validity of the effective angle-of-attack definition [32,36]. Recently, Visbal and Garmann [37] attributed the differences between pitch and plunge to the rotation-induced apparent camber effect. After subtracting this contribution from the pitching airfoil, the previous authors were able to reconcile lift and moment coefficients for periodic maneuvers. ...

... Pressure is a thermodynamic property that plays a key role in fluid mechanics. It is of utmost importance in aerodynamic load prediction [1,2,3], noise generation [4,5], flow instability and turbulence [6,7,8], and flow control [9]. The increase of time resolution in velocity field measurements during the last decade has opened the path to obtaining instantaneous pressure fields by combining experimental data with the flow governing equations [10,11]. ...

... Flow separation initiates at the leading edge following LSB bursting that concentrates into a leading-edge vortex (LEV). Aside from the tip vortices (TVs) near the wingtips, the inception of unsteady separation for the finite wings develops similarly to that observed for 2-D sections (e.g., [37,43]). By α 20.6°↑ (Fig. 2a), the LEV remains nearly spatially uniform across the span at this angle, with the exception of two features. ...

... The capstone of the current work is performing Reynolds-Averaged Navier-Stokes (RANS) simulations of a single bell-loaded configuration to both support the Euler simulation results and provide motivation for future efforts. The planform selected is a stationary AR = 8 swept wing (Λ = 30 • ) depicted in Fig. 2. The choice of this configuration is based on previous work investigating the unsteady flow-structure of a high aspect ratio swept wing undergoing dynamic stall using high-fidelity implicit Large-Eddy Simulation (ILES) [25]. The bell-shaped lift distribution is achieved on the swept wing by a combination of aerodynamic and geometric twist. ...

... Although the numerical study of a panel clamped on all sides (making the interaction inherently 3D) has also been carried out in recent years, (see Shinde et al. 2019 andBoyer et al. 2021), most of the existing numerical researches consider quasi-2D interactions with panels that have free edges at the lateral sides (as in Pasquariello et al. (2015) and Visbal (2012)). Therefore, in this study a panel with free side edges has been investigated, predicting a nominally 2D character from both the flow (at least close to the panel centerline; see Bermejo-Moreno et al. (2014) for an analysis of confinement effects) and structural perspective. ...

... The Chimera overset technique with high-order interpolation [50] transfers information between connected grids. The flow for static airfoil and constant-rate pitchup conditions was computed on the baseline (fine) grid and two additional meshes of increasing coarseness to address the effect of grid resolution: the details of which are provided in Ref. [51]. Strong agreement was found between the fine-and medium-resolution grids, demonstrated by convergence of the loads, the pressure and skin friction at the surface, and the qualitative flow structure. ...

... Dynamic stall phenomenon will seriously change the fatigue loads of turbomachinery and affect its life. In order to study the mechanism of dynamic stall, Visbal (2014) (Visbal and Garmann, 2018) (Hammer et al., 2021) employed a high-fidelity implicit large-eddy simulations approach based on high-order compact schemes analysis the onset of unsteady separation and dynamic stall vortex formation over an intermediate Reynolds number constant-rate pitching NACA0012 airfoil. They analyzed the dynamic stall process of NACA0012 airfoil in detail through the fine flow field around the airfoil, especially the boundary layer so that we could intuitively analyze and understand the change of the flow field around the airfoil in the dynamic stall process. ...