Ground Effect

It is well known that an aircraft experiences increasing lift and decreasing drag as it approaches the runway during landing. Therefore the aerodynamic efficiency of an aircraft, represented by its lift to drag ratio, increases considerably if it flies close to the ground . This fact has been taken advantage of, particularly in the design of WIG (Wing in Ground) Effect Crafts . Most articles concerned with WIG effect usually discuss the chordwise and the spanwise effects separately . The increase in lift is attributed to chordwise effect, whereas the decrease in induced drag is attributed to spanwise effect. In reality the chordwise and spanwise effects interact non-linearly. This interaction results on the wing's lift and drag having different values from those predicted by the individual effects considered separately. This paper describes the aerodynamic analysis of a wing, taking into account both chordwise and spanwise effects simultaneously. The computer program is based on Numeric Lifting Line Theory , where the solution is obtained iteratively rather than by assuming a lift distribution approximated by a Fourier Series and then solving the resulting system of equations simultaneously. Furthermore, the magnitude of the lift at each spanwise location on the wing is calculated taking into account the effect of wing's height above the surface. The ground effect is modeled by using image vortices located below the ground plane. Both lumped vortex and vortex panel methods with Neumann boundary conditions are used for the potential flow simulation, which is corrected for viscous effect using boundary layer integral approach.

The flow characteristics over a symmetrical airfoil--NACA 0015--are studied experimentally in a low speed wind tunnel. The pressure distribution on the airfoil surface was obtained, lift and drag forces were measured and mean velocity profiles were obtained over the surface. The wake region was also explored in detail and measurements of mean velocity and turbulence intensities were performed at two stations downstream of the trailing edge. Experiments were carried out by varying the angle of attack, a, from 0°to 10°and ground clearance of the trailing edge from the minimum possible value to one chord length. It was found that high values of pressure coefficient are obtained on the lower surface when the airfoil is close to the ground. This region of high pressure extended almost over the entire lower surface for higher angles of attack. As a result, higher values of lift coefficient are obtained when the airfoil is close to the ground. The flow accelerates over the airfoil due to flow diversion from the lower side, and a higher mean velocity is observed near the suction peak location. The pressure distribution on the upper surface did not change significantly with ground clearance for higher angles of attack. The upper surface suction causes an adverse pressure gradient especially for higher angles of attack, resulting in rapid decay of kinetic energy over the upper surface, leading to a thicker wake and higher turbulence level and hence a higher drag. The lift was found to drop at lower angles of attack at some values of ground clearance due to suction effect on the lower surface as the result of formation of a convergent-divergent passage between the airfoil and the ground plate. For the angle of attack of 12.5°, a very thick wake region was observed and higher values of turbulence intensity were recorded.

Some applications of the study of outdoor acoustics and sets of data for sound-level spectra obtained close to the ground are described. Measurements and models of ground effects arising from the interaction between sound traveling directly from source to receiver and sound reflected from the ground are emphasized. Details are given concerning the influences of porosity, layering, small-scale surface roughness, and tall vegetation. Areas of related current and future research are outlined.

In this paper, effects of flight altitude from ground surface and the thickness of the airfoils moving at ground proximity on the inception point of the transition phenomenon, the start of flow separation, and the boundary layer thickness have been analyzed. The amounts of drag force as well as the lift of the airfoil in viscous flows are influenced by these parameters. Included in this study are the effects of change in Reynolds number and angle of attack on the symmetric airfoils which are carefully investigated. Results of this aerodynamic analysis indicate that the motion at ground proximity is the cause of some changes in boundary layer properties. By close scrutiny of these changes, justifications are found for the behavior of the lift and drag forces at ground proximity.

In recent days people are dependent highly on transportation and the demand for
quicker modes of transportation are increasing day by day. Technological advances in
the areas of roadways, airways and waterways have led to development of faster and
efficient vehicles which has largely contributed in connecting people across the globe.
This study deals with finding the effect of different forces acting on Ground Effect
Vehicles. Initially three different tail models were considered and modeled in CATIA
and then imported to ANSYS for further analysis. It was observed that the higher
pressure at tips is a result of the shape of the GEV and it causes drag, since it is
opposing the inlet flow. Lift is generated due to difference in pressures between top
and bottom surfaces of the wing, which is a consequence of velocity difference. The
pressure at top is much lesser that than bottom of the GEV, so lift is also generated.
However, it was found from L/D ratio that V tail displayed higher response for the
considered process parameters and boundary conditions

The aerodynamic behavior of an inverted airfoil in ground effect under heaving motion was investigated numerically. A sinusoidal vertical movement perpendicular to a uniform freestream was imposed on the airfoil. The response showed a periodic pattern that repeated with the same frequency as the heaving motion. The effect of reduced frequency at several mean distances from the ground was examined. By analyzing the lag of the aerodynamic coefficients with respect to the vertical motion, the flow can be classified into different regimes. Three fundamental features that define these regimes have been identified: 1) ground effect, 2) incidence effect, and 3) added mass effect. At low frequencies, the airfoil can be assumed to be in a quasi-stationary motion and the ground effect governs the flow. The contribution of incidence effects becomes apparent at medium frequencies and can be explained by defining an effective angle of attack. The maximum downforce is obtained at high effective angles of attack. As the frequency is increased even further, the only apparent effect is that of added mass. In this regime, downforce is shown to be related to the vertical acceleration of the airfoil. These mechanisms are independent of Reynolds number.

this paper, experimental and analytical studies of the electromagnetic transient response of a buried bare wire and a ground grid are presented. The electromagnetic transient response of a ground grid has effects on induced surges in low-voltage and control circuits of power stations, substations and telecommunication stations. Therefore, the experimental and theoretical examinations for the electromagnetic transients response of a buried bare wire and a ground grid have been carried out. However, these examinations need verifications with field tests in practical use. To solve these problems, the measurements of the electromagnetic transient response of the buried bare wire and ground grid are carried out under various experimental conditions. The experimental results are compared with results calculated using Sunde's theoretical formulas, and the validity of the theoretical formulas is examined. Moreover, a calculation model based on both the theoretical formulas and ElectroMagnetic Transients Program (EMTP) is proposed. From these examinations, it is clearly shown that the results calculated using the theoretical formulas can reproduce the experimental results.

We apply space mapping to antenna design for the first time. We exploit a coarse-mesh method of moments (MoM) solver as the coarse model and align it with the fine-mesh MoM solution through space mapping. We employ two plans: (I) implicit and output space mapping, and (II) input and output space mapping. We propose a local meshing method which avoids inconsistencies in the coarse model. The proposed techniques are implemented through our user-friendly space mapping framework (SMF) system. In a double annular ring antenna example, the S-parameter is optimized. The finite ground size effect for the MoM is efficiently solved by space mapping plan I and the design specification is satisfied after only three iterations. In a patch antenna example, we optimize the impedance using both plans in separate optimization processes. Comparisons are made. Coarseness in the coarse model and its effect on the space mapping performance are also discussed.

A number of reference numerical models can be used to perform outdoor sound propagation prediction in a complex environment. Most of time, either they consume little computational time by not taking all phenomena into account at the same time, or they are more complete but their calculation times are prohibitive. This paper presents some principles which can be used in reference numerical models to reduce calculation times in predicting long-range outdoor sound propagation under complex environments. Limits, assumptions and approximations used to predict outdoor sound propagation are discussed here in terms of their impact on accuracy for typical road traffic configurations as a function of frequency, geometry of the site and atmospheric conditions.

Laser-Doppler measurements of the velocity characteristics of a ground vortex flow resulting from the collision of a wall jet with a boundary layer are presented and discussed together with flow visualization. In the present study velocity ratios between the boundary layer and the wall jet of 0.5 and 0.62 were considered. Two secondary vortices were found upstream the separation point for the highest velocity ratio. The angle of deflection of the upwash flow was found to decrease with the velocity ratio, while the wall jet penetration increases.

A water surface acts not only as an optic mirror but also as an acoustic mirror. Echolocation calls emitted by bats at low heights above water are reflected away from the bat, and hence the background clutter is reduced. Moreover, targets on the surface create an enhanced echo. Here, we formally quantified the effect of the surface and target height on both target detection and -discrimination in a combined laboratory and field approach with Myotis daubentonii. In a two-alternative, forced-choice paradigm, the bats had to detect a mealworm and discriminate it from an inedible dummy (20 mm PVC disc). Psychophysical performance was measured as a function of height above either smooth surfaces (water or PVC) or above a clutter surface (artificial grass). At low heights above the clutter surface (10, 20, or 35 cm), the bats' detection performance was worse than above a smooth surface. At a height of 50 cm, the surface structure had no influence on target detection. Above the clutter...

ABSTRACT For racing car configurations an inverted wing produces negative lift that allows increased levels of acceleration to be maintained through corners. Routine aerodynamic analysis, however, will typically be in the straight-line condition. A numerical analysis of the inverted T026 wing geometry through the curved path of a constant radius corner was conducted. The asymmetrical properties of the oncoming flow resulted in the introduction of a rolling and yawing moment along the span, as well as side-force. Yaw angle, flow curvature and a velocity gradient resulted in changes to the pressure distribution over the wing surface. Primary vortex behaviour was observed to differ significantly in both direction and structure.

A global model approach developed on the X-31 EFM data was recently improved during the experimental aircraft program X-31 VECTOR. The VECTOR program is briefly presented, focusing on extremely precise ESTOL (Extremely Short TakeOff and Landing) manoeuvre following a slow, thrust-vectored approach at high angle of attack. High accuracy navigation and inertial sensor systems enable onboard calculation of the height above runway with sufficient accuracy, which is also required to identify ground effect. System identification procedure utilises a global model to cover the entire flight regime including high lift configuration during power approach and landing. Analysis of specially designed flight tests led to aerodynamic increment tables for supplementary update of the original database. The wind-tunnel and CFD-predicted ground effect was incorporated into the highly accurate identified global model which was then used for conventional landings re-simulation to support the initial ESTOL to the ground flight clearance process. Recently an incremental ground effect model was implemented to supplement the original data set. First identification results from conventional and ESTOL landings show some improvements compared to the predictions at very low height above ground shortly before touch down.

A rigorous electromagnetic model has been used to analyze the scattering from two dielectric shallow objects buried under the two-dimensional (2-D) random rough ground (3-D scattering problem) as a means of predicting false alarms. The Method of Moments (MoM) accelerated by the Steepest Descent Fast Multipole Method (SDFMM) is used to compute the equivalent electric and magnetic surface currents on all scatterers (i.e., the rough ground and the two buried objects). The roughness parameters influence the scattering interference mechanism of the two objects, however, a large separation distance (e.g., several correlation lengths) showed stronger effect for small ground roughness.

Laser-Doppler measurements of the velocity characteristics of a ground vortex flow resulting from the collision of a wall jet with a boundary layer are presented and discussed together with flow visualization. In the present study velocity ratios between the boundary layer and the wall jet of 0.5 and 0.62 were considered. Two secondary vortices were found upstream the separation point for the highest velocity ratio. The angle of deflection of the upwash flow was found to decrease with the velocity ratio, while the wall jet penetration increases.

Abstract The objective of this paper is to show an alternative methodology to calculate transmission-line parameters per unit length. With this methodology, the transmission-line parameters can be obtained starting from impedances measured in one terminal of the ...

The present paper aims to the investigation of the methods used to minimize or maximize the values of the Corona onset and Breakdown voltage in small rod-plate air gaps when stressed by dc or impulse voltages. The geometry and the selection of grounding and charging of the electrodes, (ground effect), the gap length, the existence of barrier in the gap (barrier effect), and the Corona effects appearing in the gap prior to the breakdown are the main factors, which influence greatly the distribution of the electric field in the gap, and hence the above values. Combining theoretical, simulation and experimental work, it is resulted that: a) The electrode chosen to be ground, strongly influences the distribution of the field and the Corona effects and hence the values of the Corona onset and breakdown voltage. When the rod is grounded and the plate is negatively charged the value of Corona onset voltage is higher, the corona effects are less intense and dc breakdown voltage, without Corona, is higher. When the plate is grounded and the rod negatively charged the value of the Corona onset voltage is lower, the corona effects are more intense and hence the dc breakdown voltage is higher. b) A dielectric barrier, when placed in specific positions in the gap, decreases the Corona effects and raises the breakdown dc voltage. c) In air gaps stressed by impulse voltages the results are very different. The corona onset and the breakdown voltage are maximum when the rod is grounded and positive leading to more intense Corona effects.