The flow around a pitching NACA0015 airfoil with an oscillating trailing-edge flap is experimentally investigated to characterize the influence of the flap kinematics on the development of dynamic stall. We specifically focus on the timing of the stall development and critical values of the leading-edge suction parameter as potential stall triggers. In general, static or dynamic trailing-edge flap

Magnetohydrodynamic (MHD) aerobraking experiments were conducted in the large-scale X3 expansion tunnel at the University of Queensland. The test gas was argon flowing at approximately 5.7 km⋅s−1 for a quasi-steady period of 500 μs. A neodymium spherical permanent magnet, suspended by string and enclosed within a 65-mm-diameter spherical forebody, was used to generate the magnetic field. An accelerometer

This paper shows that N-degree-of-freedom generic unstable potential systems, whose potential matrices have an even number of negative eigenvalues and which are gyroscopically stabilized, can always be made exponentially stable through the use of an uncountably infinite number of indefinite damping matrices. A step-by-step methodology is provided for gyroscopic stabilization of such unstable potential

The three-dimensional (3-D) shock-wave/boundary-layer interaction (SBLI) between a fin-generated shock and a turbulent boundary layer is examined using plenoptic particle image velocimetry (PIV): a 3-D diagnostic technique that uses a single camera to obtain direct 3-D velocity measurements. A sharp, unswept fin at a 15 deg angle of attack in Mach 2 flow generates a 45 deg oblique shock that interacts

This paper proposes a probabilistic framework for assessing the consistency of an experimental dataset, i.e., whether the stated experimental conditions are consistent with the measurements provided. In case the dataset is inconsistent, our framework allows one to hypothesize and test sources of inconsistencies. This is crucial in model validation efforts. The framework relies on Bayesian inference

This paper reviews the development of the space–time conservation element and solution element (CESE) method and summarizes its applications in various research areas. The CESE method is a special finite-volume-type method that provides an alternative approach to numerical solutions of fluid-dynamic equations and conservation laws in various physical systems. Based on a unified treatment of time and

The present investigation shows that a triad of three vortices is behind the quasi-periodic self-sustained low-frequency flow oscillation phenomenon. Large-eddy simulations are carried out at Rec=5×104, M∞=0.4, and sixteen angles of attack at near-stall conditions. It is shown that the best description of the underlying mechanism is that of a button whirligig. A globally oscillating flow whirls around

This Paper introduces a generic force decomposition method derived from mechanical energy conservation. A transformation from relative to absolute reference frame captures the power transfer from pressure and skin-friction forces on aircraft surfaces to mechanisms in the flowfield. A unique flow-feature extraction procedure isolates these mechanisms into different regions including the jet-plume substructures

Streamwise-coherent structures were observed in schlieren images of a Mach 2.5 flow in an empty supersonic wind tunnel with a rectangular cross section. These features are studied using Reynolds-averaged Navier–Stokes computations in combination with wind-tunnel experiments. The structures are identified as regions of streamwise vorticity embedded in the sidewall boundary layers. These vortices locally

AIAA Journal, Ahead of Print.

Maintenance of engineering assets (for example, aircraft, jet engines, and wind turbines) is a profitable business. Unfortunately, building models that estimate remaining useful life for large fleets is daunting due to factors such as duty cycle variation, harsh environments, inadequate maintenance, and mass production problems that cause discrepancies between designed and observed lives. We model

AIAA Journal, Ahead of Print.

The paper discusses the development of a nonlinear aeroelastic coupled trim model of a twin cyclocopter in forward flight. The twin cyclocopter consists of two cycloidal rotors as main thrusters and a conventional nose rotor for pitch-torque balance. It is shown that five control inputs [mean and differential revolutions per minute (RPM), mean and differential phase offset of cycloidal rotors, RPMs

The stress and strain tensors in maneuvering aircraft are affected not only by the aerodynamic and propulsive forces but also by the body translational and angular velocities and high rate temperature distributions. The structural design of flexible aircraft requires the elastic fields to be evaluated at high accuracy. For this, new models that couple the aeroelasticity equations with the heat and

The spectral proper orthogonal decomposition method, which extracts spatially and temporally coherent modes in stationary flowfields, is used in the current paper to analyze high-speed broadband chemiluminescence and shadowgraph videos taken the internal and external flowfields, respectively, of multiple pulsejet engine geometries. By comparing the modes of highest energies across geometric variations

The vortex force map (VFM) method is a promising low-cost technique for predicting unsteady aerodynamic load from the vorticity field. Developed under potential flow assumption and applied to high-resolution computational fluid dynamics (CFD) data, the original VFM method needs to be further explored for viscous flows, especially at low Reynolds numbers and with incomplete knowledge of the flow data

AIAA Journal, Ahead of Print.

The aerodynamic performance of conventional high-lift systems is typically achieved using multi-element flap configurations with cross-stream gaps that necessitate the use of complex positioning mechanisms with significant penalties in terms of weight, part count, and fabrication cost. In the present investigation, the performance of a high-lift airfoil in Fowler flap and simple flap configurations

AIAA Journal, Ahead of Print.

Unstructured grid techniques have the potential of minimizing discretization errors for production analysis workflows where the control of errors is critical to obtaining reliable simulation results. Recent progress has matured a number of independent implementations of flow solvers, error estimation methods, and anisotropic grid adaptation mechanics. Here, the interoperability of several separately

The effect of the eddy viscosity length scale on the accuracy of large-eddy simulation (LES) is investigated for several commonly used subgrid models. Multiple types of length scales are considered, both purely geometric length scales (including the cube root of the cell volume and the maximum cell dimension) and length scales that depend on both the grid and the flow. The assessment focuses on how

A novel approach to reduce the peak lift and pitching moment on a plunging airfoil is investigated through force, moment, and velocity measurements. This approach, unlike previous investigations of delayed flow separation and leading-edge vortex suppression, uses forced separation through deployment of a minitab near the leading edge. The device can be activated for short time intervals during a gust

Large-eddy simulations (LESs) of low-Reynolds-number flow (Re=50,000) over a NACA0018 airfoil are performed to investigate flow control at the stall angle of attack (15 deg) by low-amplitude surface waves (actuations) of different types (backward/forward traveling and standing waves) on the airfoil’s suction side. It is found that the backward (toward downstream) traveling waves, inspired from aquatic

Supersonic flow over a cavity, such as the open internal bay of a tactical aircraft, involves a variety of fluid dynamics mechanisms and different types of instabilities, including those associated with the shear layer, flow-induced resonance, and turbulence. The current study presents experimental data on the response of cavity dynamics to the introduction of various store configurations mounted at

Hypersonic argon flows over circularly blunt flat plates in near-continuum regime are numerically investigated in this study. The flows are, respectively, simulated using the direct simulation Monte Carlo (DSMC) method, the Navier–Stokes–Fourier (NSF) equations, and the DSMC data-improved Navier–Stokes (DiNS) model that is an improved continuum model with consideration of local shear nonequilibrium

Within a scramjet, the location of the shock train will change as the backpressure changes. When the shock train leading edge moves out from the entrance of the isolator, the engine usually goes into unstart. A precise shock train leading edge detection technique is indispensable for controlling the shock train within the isolator. In this Paper, a reconstruction-flowfield-based shock train leading

This paper shows that a potential system with one multiple eigenvalue of multiplicity two or more can assuredly be made unstable by infinitesimal positional perturbations. The explicit nature of these pertubatory forces is provided. It is shown that the matrices that describe these perturbatory forces are not required to commute with the potential matrix. The general positional perturbatory forces

An investigation is carried out to evaluate how an external uniform stream affects turbulent-jet coherent structures. The presence of this uniform stream outside the jet represents the effect of forward flight on the velocity field. Coherent structures are modelled as wave packets, and the flight effect is studied using the parabolized stability equations (PSEs). Measurements of mean base flows and

An experimental study on the propagation mode of H2–air rotating detonation waves (RDWs) under atmospheric backpressure in a hollow combustion chamber was performed. Experiments were conducted by holding the equivalent ratio at ∼0.90 and the mass flow rate m˙ of 101.5–805.7 g/s, that is, mass flow rate per unit area of 68.02–539.92 kg/(s⋅m2). High-frequency pressure results indicated that increasing

Compressive sensing (CS) based fan noise mode detection methods have been developed recently by taking advantage of the fact that the fan noise sound field is usually dominated by a limited set of modes. It has been shown that the CS based methods require remarkably few measurements and can improve mode detection capability. However, the mode sparsity would be easily destroyed either due to strong

Spatially and temporally resolved wave fronts were collected in flight using Airborne Aero-Optics Laboratory at varying subsonic Mach numbers through both the naturally developing boundary layer and an artificially generated shear layer. Dispersion analysis was used to separate the wave fronts into the downstream and upstream-traveling components. The upstream propagating component was associated with

This experimental study explored the effects of axisymmetric sinusoidal excitation on structural and mixing characteristics in the equidensity jet in crossflow (JICF). Planar laser-induced fluorescence imaging of acetone seeded in the jet fluid was used in this quantification, where the jet Reynolds number was fixed at Rej=2300 and crossflow velocity was varied. Jet-to-crossflow momentum-flux ratios

Modifications to the quadratic constitutive relations (QCRs) of Spalart (“Strategies for Turbulence Modelling and Simulation,” International Journal of Heat and Fluid Flow, Vol. 21, 2000, pp. 252–263) and Mani et al. (“Predictions of a Supersonic Turbulent Flow in a Square Duct,” AIAA Paper 2013-0860, Jan. 2013) are proposed. These modifications result from computational fluid dynamics (CFD) studies

The paper presents the results of an experimental and numerical study on the combustion characteristics of a supersonic combustor operation enhanced by pilot hydrogen and air throttling, including ignition and combustion. Wall pressure measurements, schlieren images, and hydroxyl-radical planar-laser-induced-fluorescence (OH-PLIF) are used to obtain information on the flowfield and flame development

Rotating detonation engines (RDEs) are characterized by extremely high temperatures and pressures, with operating frequencies on the order of several kilohertz. This creates an environment that is challenging to implement research diagnostics. The two most common diagnostics implemented in RDEs operating at speeds capable of defining the detonation wave are dynamic pressure transducers and ion probes

This paper presents the investigation of the starting flow in association with pitch acceleration using transient laminar-flow computation and an unsteady inviscid-flow theory. A thin flat-plate foil pitched at the leading edge is modeled in a two-dimensional incompressible fluid at chord Reynolds numbers of the order of 103. Several acceleration amplitudes (1.1≤αm′′tc2≤17.0) and acceleration durations

Counter-rotating open rotors (CRORs) have the potential to reduce environmental emissions thanks to their high propulsive efficiency. However, there are a number of concerns surrounding their acoustic emissions. This contribution presents a novel multiconfiguration CROR that offers considerable noise reductions. In particular, locking either the fore or aft rotor during takeoff is considered, with

This paper describes the effects of vibrational relaxation on sonic boom waveforms in a stratified atmosphere. Full-field direct simulations with vibrational nonequilibrium are performed over uniform and stratified atmospheres, extending from a supersonic body to the ground level. The governing equations are the three-dimensional Euler equations, combined with the conservation equations for vibrational

Surrogate-based optimization has been used in aerodynamic shape optimization, but it has been limited due to the curse of dimensionality. Although a large number of variables are required for the shape parameterization, many of the shapes that the parameterization can produce are abnormal and do not add meaningful information to a surrogate model. To improve the efficiency of surrogate-based optimization

The flow physics governing the shock-buffet phenomenon on swept wings remain disputed without an unequivocal description. Herein is a contribution to the ongoing discussion that addresses the inherent dynamics near the onset of unsteadiness, complementing experimental data of a large aircraft wing geometry with scale-resolving simulation. Specifically, delayed detached-eddy simulations are performed

This paper presents an experimental study of laminar-to-turbulent boundary-layer transition in a circular duct at high supersonic Mach number. The experiments were conducted as an essential precursor for scramjet drag reduction studies using a direct-connect scramjet combustor. The experiments were carried out at the University of Queensland T4 shock tunnel using a 33.2-mm-diam and 500-mm-long circular

AIAA Journal, Ahead of Print.

A landmark set of measurements of high-temperature O2 relaxation under strong shock heating conditions, conducted in 2013 by Ibraguimova et al. (“Investigation of Oxygen Dissociation and Vibrational Relaxation at Temperatures 4000–10800 K,” Journal of Chemical Physics, Vol. 139, No. 3, 2013, Paper 034317) using ultraviolet (UV) absorption converted to time-dependent vibrational temperature profiles

This paper describes an automated approach to deform an analysis mesh applied to a computer-aided design (CAD) model in response to a change in the shape of the CAD model. The process has been used to overcome a key issue that occurs during the shape optimization process. It is an advance over existing techniques because it works even when the boundary topology of the CAD model changes during the shape

We design, construct, and test a device for controlled boiling by means of local vapor bubble formation in a cavity that injects vapor bubbles in a capillary crossflow. The outcome of the device is a regular slug flow of approximately monodisperse bubbles that can be used for a variety of applications. The setup is designed to be independent of gravity level and is tested succesfully both in normal

Studying the vibratory behavior of inherently damped laser powder bed fused (LPBF) specimens has led to an improved damping performance assessment via a multifactor correlation model. The damping demonstrated in LPBF (additively manufactured) specimens is an artifact of 1–3% unfused volume of powder that is capable of suppressing vibration 95% compared to a fully fused part. The original model associates

Overset meshes have a unique advantage in handling moving boundary problems as remeshing is often unnecessary. Recently, overset Cartesian and strand meshes were used successfully to compute complex flow over rotorcraft. Although it is quite straightforward to deploy a high-order finite difference method on the Cartesian mesh, the near-body solver for the strand mesh is often limited to second-order

The wake of a circular cylinder was forced with a temporally modulated and spatially segmented dielectric-barrier-discharge plasma actuator. The temporal modulation was achieved by modulating the applied voltage signal with a square wave whose frequency was twice the vortex shedding frequency. The spatial segmentation was implemented by locating the buried electrodes only at certain spanwise locations

The fluid–structure interaction of a flexible panel exposed to a ramp-induced shock-wave/boundary-layer interaction (SWBLI) at Mach 6 is investigated experimentally for transitional and turbulent incoming boundary layers. Panel deformations are measured using photogrammetry enabled by a new marker-tracking routine, whereas pressure fluctuations are obtained with fast-response piezoresistive pressure

This paper investigates the dynamics of a pitching and heaving aeroelastic wing undergoing large-amplitude limit-cycle oscillations influenced by a vortical wake from an upstream rectangular cylinder bluff body. The results show that under certain conditions, the limit cycle is annihilated. The conditions in which annihilation occurs are dependent on the limit-cycle frequency, bluff-body shedding frequency

AIAA Journal, Ahead of Print.

In this research, a loop-separation concept (LSC) is applied to a very flexible aircraft. Appealing features of this control architecture include decoupled control logic and the use of high-order models for controller design, thus not requiring model order reduction. The LSC consists of two control loops. The inner loop employs a linear quadratic regulator capable of stabilizing the aircraft while

Dynamic stall often occurs under conditions of simultaneous unsteady pitching and surging (e.g., rotorcraft and wind turbines), but many models employ a dimensionless time base that implicitly assumes that surging is superimposed, in a quasi-steady manner, on dynamic pitching. An unsteady wind tunnel was used to examine this assumption, where a technique was developed to quantify the unsteady effects

AIAA Journal, Ahead of Print.

AIAA Journal, Ahead of Print.

This paper proposes a method to derive the upper-bound vibration spectrum of a membrane structure from a few selected point measurements. The upper-bound spectrum exceeds the measured spectra by a certain proportion. Three types of square membranes subjected to corner tension loads, namely, flat, wrinkled, and composite membranes, were tested. Full-field surface shape measurements via the grating projection

The effectiveness of closed-loop flow control using a deep Q network (DQN), such as deep reinforcement learning algorithm, was experimentally researched for a NACA0015 airfoil. The system used a dielectric barrier discharge plasma actuator as the flow control device, and the experiment was conducted at the chord Reynolds number of 6.3×104. The closed-loop control system selected a nondimensional burst

Laminar–turbulent transition downstream of a backward-facing step (BFS) in a two-dimensional zero-pressure-gradient boundary layer is investigated computationally for step-height–to–local-displacement-thickness ratios of 0

Dynamic mode decomposition (DMD) yields a linear, approximate model of a system’s dynamics that is built from data. This paper seeks to reduce the order of this model by identifying a reduced set of modes that best fit the output. A model selection algorithm from statistics and machine learning known as least angle regression (LARS) is adopted. LARS is modified to be complex-valued, and LARS is used

A recently developed vibration suppressing design approach that leverages the laser powder bed fusion (LPBF) additive manufacturing process is under investigation for damping performance improvement. To date, this approach has demonstrated the ability to design inherent damping capability in LPBF parts that can suppress vibration by 88–95% compared to fully fused counterparts, and the damping capability