Ground Effect with Special Reference to Pitching Moments

Aerodynamic characteristics of an airfoil, NACA 6409, flying over a wavy wall is investigated numerically. An Euler code based on the LU-factored algo rithm and higher-order upwind scheme is constructed and its accuracy is tested on two benchmark problems : NACA 4412 airfoil moving over a level ground and NACA 0012 airfoil in free-flight pitching oscillation. The calculated flow about NACA 6409 airfoil over the wavy ground represented by a moving sine function indicates that the aerodynamic property of the airfoil becomes sensitive if the wave number or amplitude of the wavy ground is increased, and/or if the proximity of the airfoil to the ground is smaller. Introduction When an aircraft flies near the ground, the aerodynamic performance of the wing is much changed from that of the free flight. In particular, a wing in proximity to the ground manifests reduced upwash, downwash, and tip vortices which cause enhancement of lift and pitching moment, and reduction of induced drag. These effects, in overall, are called ‘the ground effect’ whereas the wing taking advantage of these effects is called ‘wing in the ground effect’ or WIG, in short. There has been recently considerable interest in development of WIG crafts in such countries as Russia[1,2], Japan[3,4], Germany[5,6], and China[7] due to its energy saving feature as a means of passenger and cargo transportation. Preliminary design of a WIG airplane is under progress in South Korea[8] and the present research is motivated by this particular program. The gain in the lift-todrag ratio might be achieved by a WIG craft at the cost of stability due to the increased pitching moment. The flight properties of a WIG hence need to be investigated thoroughly during the aircraft development process. Recently, a few reports have appeared on the aerodynamic performance of WIG wings and airfoils[4-7,9] flying over a level *Doctoral candidate, Dept. of Aerospace Engineering. tprofessor, Dept. of Aerospace Engineering, Member AIAA. Copyright @ 2000 by YEHOO” Im. Kcun-Shik Chmg. Publidld by the Americ-n Institute of Aeronautica md Aatronautica. Inc. with permhion. ground. NACA Cdigit airfoils are, in general, known to have positive ground effect. However, a symmetric airfoil with large thickness, NACA 0012, for example, can exhibit negative ground effect at a small angle of attack[4,7]. The WIG craft operated over the sea is quite often expected to face with rough wavy surfaces. This rather periodic terrain will cause ground effect different from that of the level ground. In the literature, the unsteady flow past a twodimensional airfoil moving over a wavy ground has been investigated with the lifting surface theory by Ando et al.[lO], and with the unsteady panel method by Morishita and Ashihara[ll]. Mizutani and Suzuki[l2] used Rankine source and boundary element method to compute the wing aerodynamics over the coastal free surface. Their results have certainly offered some useful data for fundamental study of the lifting airfoils. However, the solutions of Euler and Navier-Stokes equations are still wanted in order to study the possible compressibility and viscosity effect of the WIG craft. In this paper we have numerically solved the Euler equations with the LU-factored algorithm[l3] and high-resolution upwind scheme for the unsteady WIG airfoil moving over a wavy wall. Fortunately, Mizutani and Suzuki[l2] have found that deformation of the free surface caused by the proximate flight of a WIG craft is only negligible. We verified accuracy of the present computer code by reproducing two earlier results : NACA 4412 airfoil over a level ground[l4], and the NACA 0012 airfoil in pitching oscillation[l5]. Various parameter effects on NACA 6409 airfoil flying over a wavy wall with a subsonic flight Mach number, M, = 0.3, is elaborated in this paper. Governing Equations We consider unsteady twodimensional Euler equations in the computational domain (t, 5, n), 1 OF 8 aQ ai aF z+-+-=O ac 877 with the flux vectors (1) AMERICAN INSTITUTE OF AERONAUTICS AND ASTRONAUTICS PAPER 2000-0657

This article presents and discusses the results of experimental and numerical aerodynamic analysis of the flow around a surface-air platform by using the near-surface effect – ground effect – for flight. The experimental tests have been conducted in the low-speed wind tunnel of the Military University of Technology, while numerical simulations of the flow have been performed in the Ansys Fluent software. Both experimental and numerical tests have been performed for the object without taking into account the presence of the engine. The results of the tests in the wind tunnel have been compared with the numerical results. The obtained results have been presented in the form of characteristics of the coefficients of aerodynamic forces and moments as a function of the angle of attack, in tables and in the form of raster graphs. Particular attention has been paid to the influence of the ground effect on the aerodynamic characteristics of the initially designed object. This influence has been analyzed by referring the results obtained for the variants of flight near the surface to the results obtained for the so-called free flight, without taking into account the ground effect.

Effects of ground and load on upper trapezius, biceps brachii muscle and hand forces in one- and two-wheeled wheelbarrow pushing

The study of the fixed-pitch small-scale propeller in ground/ceiling effect is extended to forward flight conditions. Force-based experiment and smoke flow visualization is conducted at the University of Dayton Low Speed Wind Tunnel. The propeller is mounted at different incidence angles to simulate the transition to forward flight from hover and forward flight conditions. The effect of propeller incidence angle seems to be negligible at J=0. The power required at constant thrust shows an increasing trend after a threshold advance ratio for each h/D and then decreases steeply upon further increase in advance ratio. Smoke flow visualization revealed the presence of three distinct zones separated by the onset of the fountain vortex and the onset of the ground vortex at each ground distance. At advance ratios below the onset of the fountain vortex lies the optimal ground effect zone. An increase in advance ratio beyond this threshold will result in power increment due to the fountain vortex. Further increase in advance ratio initiates the onset of the ground vortex where the ground effect is significantly reduced. The onset of the fountain vortex and the ground vortex occurs at lower advance ratios for a propeller at an incident angle to the ground.

Recently a new transport system "Aerotrain" has been proposed, and test using the first and second stage models are conducted in a 3 km guide way of old MAGLEV test facility in Miyazaki prefecture. "Aerotrain" has wings, and flies close to the ground of an open channel to take advantage of the ground effect. Characteristics of wing in ground effect (WIG) have been investigated using conventional wind tunnels. But this type of experiment cannot estimate the ground effect correctly because of the existence of boundary layer developed between bottom of the wings and the ground surface. Therefore, it is necessary to experiment using a towing wind tunnel to clarify characteristics of wing in the real ground effect. The aerodynamic charactersistis of two kinds of aerofoil sections: NAGA 4412 and circular arc aerofoil were clarified by the experriment towing the aerofoils in 3 km guide way of MAGLEV test facility. In addition, we examined problems to utilize the guide way of old MAGLEV as a towing wind tunnel.

This paper focused on the development of a model to represent longitudinal aerodynamics of a wing and/or flight vehicle in ground effect when height is a function of time including high angles of attack. A general aerodynamic model of a wing and/or airplane in ground effect which includes high angles of attack was created. The aerodynamic coefficients of wings studied herein were obtained by the unsteady vortex lattice method with Kirchhoff-based correction (UVLM-K). Wind tunnel measurements presented in the literature were used to validate the UVLM-K. Then, a rectangular wing was simulated at high angles of attack in takeoff and flare, and the aerodynamic characteristics at different heights aboveground were obtained along with the h derivatives during these maneuvers. The mathematical model presented herein is capable to model unsteady aerodynamic phenomena in ground effect at high angles of attack. When this model was used in static ground effect, values of R2 equal to and greater than 0.999, 0.981, 0.993 were obtained for lift, induced drag, and pitching moment coefficient, respectively. In dynamic ground effect, the model can adjust the aerodynamic coefficient during the maneuvers.

Effect of bleeding on aerodynamics of non-slender delta wing in ground effect

Investigation of a new high-speed zero-emission transportation “Aerotrain” is proceeded mainly in Tohoku University and Miyazaki University. Since the aerotrain utilizes the ground effect, researches of the aerofoil section which can harnesses the ground effect effectively are important. The aerotrain moves along U-shaped guide way which has a ground and side walls, so it has many viscous interference elements. In an analysis of ground effects on aerodynamic characteristics of aerofoils, it must be considered boundary layers on the aerofoil surface. At first, velocity distributions on surfaces of aerofoils in potential flows are computed using the vortex method, then the momentum integration equations of boundary layer is solved with experimental formulas. This procedure has following advantages : modifications of aerofoil section are easy because it is not necessary to make complicated computational grids, a boundary layer transition and separation can be predicted using empirical procedures. The aerodynamic characteristics of four kinds of aerofoil sections is investigated to clarify the relation between aerofoil sections and ground effects. Computational results are compared with experiments results by the towing wind tunnel to verify computational precisions. In addition, aerofoil characteristics at actually cruise speed are analyzed.

Experimental parametric study of rectangular bodies with radiused edges in ground effect

HERE has been renewed interest recently in the calculation of the aerodynamic characteristics of a wing flying in proximity to the ground. In fact, some vehicles have been designed to take advantage of the positive aspects of ground effect. For the idealized problem of two-dimension al steady potential flow past a flat plate airfoil in the presence of a plane wall, Tomotika et al.l and Havelock2 used conformal mapping to obtain an exact solution. Green3 obtained a solution for an airfoil of general shape in ground effect. In Refs. 1-3, expansions are also given in chord-to-wall clearance ratio. More recently, accurate numerical solutions using panel methods (surface singularity distributions) are readily obtainable. An early example of this approach is given by Giesing.4 In the case where the airfoil disturbance and the chord-towall clearance ratio are small, analytical results can be obtained directly using the higher-order thin airfoil theory of Van Dyke.5 For a wide range of the chord-to-wall clearance ratio, an approach due to Keldysh and Lavrentiev6 for the corresponding hydrofoil problem is appropriate. Plotkin7'8 used this method, which involves a series expansion in the chord-to-wall clearance (submergence depth) ratio, to study the first-order effects of thickness, angle of attack, and camber. In this paper the effect of the thickness of the airfoil on the lift coefficient will be calculated to the second order in the thickness ratio. Analytical results will be presented for the Joukowski airfoil. The first-order angle-of-attack solution for the flat plate will also be given.

Influence of metal foam thickness on the conduction and convective heat transfer for a flat plate with metal foam impinged by a rectangular slot jet

The transition of the boundary layer from the laminar to the turbulent state on a smooth flat plate at a zero angle of attack is studied in the range of Mach numbers M∞ = 2–6. It is demonstrated that the results measured at the end of the transition region can be approximated by a simple dependence suitable for applications, which does not require additional measurements, is valid in the range of Mach numbers M∞ = 2–10, and, with an error lower than 20 %, can be used to estimate the location of the transition region on a flat plate in geometrically similar wind tunnels.

Infrared thermography is applied to measurement of turbulent heat transfer in order to investigate its applicability under near-ambient conditions. Natural convection along a vertical smooth flat plate and forced convection along a smooth flat plate are realized in a large darkroom, where individual heat transfer coefficients are quantitatively measured using infrared thermography in the laminar, transition and turbulent regions. The measurement error is then estimated using ANSI/ ASME PTC 19.1-1985 measurement uncertainty to confirm the accuracy. It is obvious from a series of application experiments and error analyses that the present technique is useful for estimating turbulent heat transfer quantitatively and dynamically. Infrared thermography is an appropriate measurement procedure for engineering applications because it can be applied to diagnose a twodimensional and dynamical temperature field instantaneously and nondestructively.

Infrared thermography was applied to measurement of turbulent heat transfer in order to investigate its applicability under near-ambient conditions. Natural convection along a vertical smooth flat plate and forced convection along a smooth flat plate were realized in a large darkroom, where individual heat transfer coefficients were quantitatively measured using infrared thermography in the laminar, transition, and turbulent regions. The measurement error was then estimated using ANSI/ASME PTC 19.1-1985 measurement uncertainty to confirm the accuracy. It is obvious from a series of application experiments and error analyses that the present technique is useful for estimating turbulent heat transfer quantitatively and dynamically. Infrared thermography is an appropriate measurement procedure for engineering applications because it can be applied to diagnose a two-dimensional and dynamical temperature field instantaneously and nondestructively. © 1999 Scripta Technica, Heat Trans Asian Res, 28(6): 442–455, 1999

In the present study, we deal with one of the most fundamental and common topics related with the ground effect: that is, a sliding flat plate (or thin aerowing) just above the stationary ground surface. Specifically speaking, by using a moving-belt system, we investigate the ground effect in such a simple model. Namely, we put a two-dimensional thin flat plate above the belt in a wind-tunnel test section, and conduct flow visualizations with particle-image-velocimetry PIV analyses, together with flow-velocity measurements using a hot-wire anemometer HWA. As a result, we have shown the influence of the gap between the flat plate and the moving wall. Furthermore, we have confirmed that, the antisymmetric alternating vortex street past the flat plate tends to be broken and weakened, due to the existence of the moving wall below the flat plate, if the gap becomes less than a critical value.