Qiulin Qu

Numerical Study of Aerodynamics of a Wing-in-Ground-Effect Craft

The flow around a wing-in-ground-effect craft flying at α=3  deg and α=9  deg over flat and wavy ground is simulated and investigated by using ANSYS FLUENT, employing the compressible Reynolds-averaged Navier–Stokes equations and the Spalart–Allmaras turbulence model. The sliding mesh technology is used to simulate the relative motion between the wing-in-ground-effect craft and wavy ground. The effects of the wavy ground, flight height, and angle of attack on the aerodynamic characteristics and flowfield are analyzed in detail. The aerodynamic forces are found to be periodic when the wing-in-ground-effect craft flies over wavy ground. The aerodynamic forces over both flat and wavy ground vary with flight height in the same pattern. As the flight height reduces, the lift, drag, and nose-down pitching moment all increase at both angles of attack (α=3  deg and α=9  deg); however, the lift-to-drag ratio increases for all flight heights at α=3  deg, while it first increases and then decreases at α=9  deg. Redu...

Numerical Simulation of the Flowfield of an Airfoil in Dynamic Ground Effect

A = area of the channel between the lower surface of the airfoil and the ground CL = lift coefficient Cp = pressure coefficient c = airfoil chord length h = ride height; that is, the distance from the trailing edge of the airfoil to the ground p = pressure Re = Reynolds number based on chord length V = flow velocity W = compression work done by the airfoil x, y = body-fixed Cartesian coordinates α = angle of attack γ = flight-path angle θ = pitch angle

Study of Ditching Characteristics of Transport Aircraft by Global Moving Mesh Method

This paper numerically investigates the ditching characteristics of the NACA TN 2929 model. In the simulation method, the Reynolds-averaged Navier–Stokes equation and realizable k-e turbulence model are solved by the finite volume method; the volume-of-fluid method is used to capture the water–air interface; the six-degree-of-freedom model and the global-moving-mesh method are used to deal with the relative motion between the water and the object. Global moving mesh is a new dynamic-mesh method, which is proposed to simulate water-entry problems. In global moving mesh, the whole computational domain and boundaries move together with the object to avoid the high computational expense and low-quality mesh in the traditional mesh-deformation method. This numerical method is applied to simulate the water impact of a two-dimensional cylinder in free fall, and the results show a good agreement with the experimental data. The effect of each aerodynamic part of the NACA TN 2929 model on the ditching behavior is s...

Numerical Simulation of Water Spray Caused by a Rolling Airplane Tire

The meshless method of smooth particle hydrodynamics is used to simulate the water spray caused by a rolling airplane tire, which is a complex physical problem. Graphics of the spray at a certain tire speed and water film thickness are given to describe the whole process in detail. Flowfields at different tire speeds demonstrate that, as the tire speed increases, splashes as well as the scroll effect of the rolling movement become more pronounced. Furthermore, the angles between the runway and main jet flowfields at both sides increase. Results are also presented on splashes through the water film with different thicknesses. In this paper, for the first time in literature, detailed results of the whole water spray process are given and the effects of tire speed and water film thickness on water spray are quantified.

Numerical Simulation of Aircraft Tire-Generated Spray and Engine Ingestion on Flooded Runways

The aircraft water spray test on water-contaminated runways is of great significance in the civil aircraft airworthiness certification. It is a very complex strongly nonlinear multiphysics process involving tire-generated water spray and engine ingestion. In this paper, an integrated simulation platform that combines the smoothed particle hydrodynamics method and the discrete phase model in a finite volume framework is developed to predict the complex physical interactions and processes. The smoothed particle hydrodynamics method is used to accurately predict the tire-generated water spray pattern, and the discrete phase model method is used to predict the droplets motion in the airflow field around the airplane. The initial conditions of the droplets in the discrete phase model method are provided by the smoothed particle hydrodynamics computations. The results of the numerical simulations are validated using NASA’s tire-generated water spray experiments and the water spray and engine ingestion tests on ...

Studying atmospheric turbulence effects on aircraft motion for airborne SAR motion compensation requirements

It is necessary to study the influence of atmospheric disturbance on aircraft motion for the motion compensation sensitivity requirements of airborne SAR. Most motion compensation study for airborne SAR is focusing on the effects of assuming motion errors on SAR images from the early years of airborne SAR development. In this paper, based on power spectra density (PSD) method, the spectra of aircraft motion that containing all the response motion information due to atmospheric disturbance can be calculated from the given spectra of the atmospheric turbulence and the transfer function between aircraft motion and atmospheric turbulence. As an example, one common atmospheric turbulence model is applied to get the lateral/longitudinal uncontrolled and controlled aircraft motion. At low frequency domain, our results show that the controlled aircraft motion is suppressed in comparison with the uncontrolled aircraft motion as wished; whereas, at high frequency domain, there is no difference between the spectra of controlled and uncontrolled aircraft motion, i.e., each has a scaling behavior with a scaling exponent corresponding exactly to the atmospheric turbulence model. Based on these aircraft motion analysis, an acceptable residual motion error is predicted from the motion compensation requirements, which suggests that motion compensation for airborne SAR is unavoidable and should pay more attention on the medium frequency range.

Near-field Wingtip Vortex Characteristics of a Rectangular Wing in Ground Effect

The aerodynamics and near-field wingtip vortex characteristics of a rectangular wing with NACA4412 section in ground effect (GE) are studied in this paper. The steady compressible Reynolds-Averaged Navier-Stokes (RANS) equations with the SpalartAllmaras (SA) turbulence model are discretized using the finite volume method. Based on the pressure and lift variations in GE, a 3D rectangular wing can be divided into two parts along the span-wise direction: the quasi-2D inner part of the wing (away from wing tip) in which the lift increases monotonously, and the second part near the wingtip in which the lift decreases. In GE, the wingtip vortex moves outward along the span-wise direction due to the ground mirror effect, and rebounds in the vertical direction due to the induction from the secondary vortex generated from the ground boundary layer. In GE, the strength of the near-field wingtip vortex along the flow direction depends not only on the initial vortex strength and the shear layer developing from the trailing edge of the wing, but also due to the generation of secondary vortex in the ground boundary layer, and the interaction between the wingtip vortex and the secondary vortex.

Numerical Investigation of the Aerodynamics of an Airfoil in Mutational Ground Effect

The numerical investigation of the landing and take-off processes of the NACA4412 airfoil on a platform is conducted to study the mutational ground effect. The incompressible Unsteady Reynolds-Averaged Navier-Stokes (UNRANS) equations and the Shear Stress Transport k-ω (SST k-ω) turbulence model are discretized using the finite volume method. The dynamic layering technology is adopted to deal with the relative movement between the airfoil and the platform. The landing and take-off processes can be divided into four regions based on the lift characteristics and flow physics. Except for the static ground effect, the airfoil undergoes the upwash flow in landing and the downwash flow in take-off condition. It should be noted this study on mutational ground effect is first of its kind reported in the gound effect literature for the first time.

Numerical Study of Transient Deformation and Drag Characteristics of a Decelerating Droplet

A numerical study of the transient deformation and drag properties of impulsively started decelerating drops in axisymmetric flows is conducted. The incompressible Navier–Stokes equations coupled with the volume of fraction method are solved. The differences in the deformation and drag characteristics between the accelerating and decelerating drops are elucidated. The Weber number We has a significant influence on the drag properties of the round drops; however, the effect of the Ohnesorge number Oh is small. A dynamic droplet drag model is provided based on the computational fluid dynamics results to predict the drag coefficient of a decelerating drop. In addition, the flow of liquid drops past an RAE2822 airfoil is considered, and its drag is evaluated using the drag model.

Effect of Sideslip on High-Angle-of-Attack Vortex Flow over Close-Coupled Canard Configuration

The aerodynamic response to sideslip is crucial for an aircraft’s lateral stability, especially for configurations incorporating vortex flow, on which sideslip causes asymmetric vortex behavior and brings extra complexity. In this work, vortex flow over a close-coupled canard configuration under sideslip is simulated using delayed detached-eddy simulation, with the angle of attack varying up to the poststall regime. Sideslip-induced distinctions in both vortex dynamics and canard/wing-vortex interaction are analyzed to explain the nonlinear response of the configuration. The results reveal that the effect of sideslip differs significantly upon different angle-of-attack regimes. At a medium angle of attack, the spanwise extension of the low-pressure area due to windward vortex core expansion results in superior windward lift against the leeward side, but the relatively low pressure retained due to delay of the leeward vortex breakdown is the main motivation that leeward lift surpasses windward at a high an...