Vicinity Of Ground Research Articles

Ground Effect Investigation on the Aerodynamic Airfoil Behavior Using Large Eddy Simulation

Abstract The underlying physics ever behind the aerodynamics of an airfoil in ground effect (GE) are still not fully resolved. In this work, the aerodynamics for an airfoil in GE is investigated computationally for both transitional and turbulent flow regimes. Large eddy simulation (LES) is employed to explore the flow physics around a NACA0012 airfoil in ground vicinity, which is commonly used in wind energy applications. The angle of attack (AoA) is fixed at AoA = 10 deg, while the flight height to chord ratio (h/c) is variable. An analysis is conducted for the aerodynamic forces, i.e., the lift (CL), and the drag (CD). The behavior for the skin fiction drag (CDf) is explored in the light of the flow physics near the ground. In addition, the vortex shedding behavior is estimated at different height (h/c) for the transitional and turbulent flow regimes. At h/c = 0.2, the friction drag (CDf) is improved by 9.6% and 16.3% for the transitional and turbulent flow regimes, respectively. The results show that the frequencies for the vortex shedding decline significantly near the ground. This decline is correlated with the larger vortical structures and vortex developing mechanism.

Aerodynamic Effects of Ceiling and Ground Vicinity on Flapping Wings

The combined ceiling and ground effect on the aerodynamics of a hovering flapping wing is investigated using numerical simulations. In the simulations, the wing was located between the ceiling and the ground. Simulations were carried out for different wall clearances at two Reynolds numbers (Re = 10 and 100). Special efforts were paid to whether there exists aerodynamic coupling between the ceiling effect and the ground effect. At Re = 10, the combined ceiling and ground effect increases the aerodynamic forces monotonically through two effects, namely the narrow-channel effect and the downwash-reducing effect. Additionally, there exists a coupling effect of the ceiling and the ground for the combined case at Re = 10, where the force enhancement of the combined effect is much more significant than the sum of the ceiling-only effect and the ground-only effect. At Re = 100, the combined effect of ceiling and ground causes three non-monotonic force regimes (force enhancement, reduction and recovery) with increasing wall clearance. The narrow-channel effect at Re = 100 leads to a monotonic force trend, while the downwash-reducing effect results in a non-monotonic force trend. The two effects eventually lead to the three force regimes at Re = 100. Unlike the Re = 10 case, the coupling effect at Re = 100 is small.

Numerička analiza elise u blizini zemlje

Detailed studies of propeller flows are regaining both interest and significance worldwide, as the number of their different design and applications (particularly for futuristic urban air vehicles) continues to grow. An additional distinctive characteristic of small-scale unmanned air vehicles (UAV) propellers is that they are meant to operate in a wide range of (previously considered atypical) operating conditions, including backward flight, flight in the vicinity of obstacles, hard/ground surfaces, etc. These specific requirements raise the issue of the effects of ground proximity on their aerodynamic performance. This paper computationally investigates flows around a small-scale, custom-made propeller in ground effect. Different ground distances are considered and novel thrust and power relations (dependencies) on them are proposed. In order to obtain sufficiently reliable and accurate results and capture the most significant flow features, Reynolds-averaged Navier-Stokes (RANS) equations are solved by finite volume method. In addition, interesting flow visualizations are presented. Although the obtained thrust trend correlates well with the conventionally used semi-empirical formula, more realistic estimations are obtained for small ground distances. Furthermore, the positive effects of ground vicinity on rotor aerodynamic performances are once again confirmed and quantified.

Outwash flow measurement around the subscale tandem rotor in ground effect

Numerous issues are yet to be discovered about the small tandem rotor aerodynamics in the vicinity of ground. In this paper, a multipurpose test rig has been used to test outwash patterns of a sub-scale model of a generic tandem rotor helicopter in ground effect using two total-static rakes at different positions ahead and aft of the rotor(s). The results showed that in tandem rotor, the change in the rakes distance from the rotors has mild influence on the outwash flow velocity. The interaction between rotor wakes and formation of the fountain flow impressed the outwash of the rotors and changed their behavior in comparison with a single rotor. For the elevation higher than z/2R = 0.8, the outwash averaged velocity of the rotors due to flow recirculation was negative. As the rotor elevation decreased, outwash accelerated by moving away from the rotor within the measurement area. Comparing the results of present study with the experiments for the CH-47D helicopter indicated that the overlap between the rotors was caused the outwash velocity be more than non-overlapping rotors. Tuft flow visualizations showed the evidences of a fountain flow between the rotors and that, in the vicinity of tandem rotors, the resultant outwash velocity was inward due to formation of the fountain flow and the consequent suction.

Apparent Explosion Moments fromRgWaves Recorded on SPE

Abstract Seismic moments for the first four chemical tests making up phase I of the Source Physics Experiments (SPE) are estimated from 6‐Hz Rg waves recorded along a single radial line of geophones under the assumption that the tests are pure explosions. These apparent explosion moments are compared with moments determined from the reduced displacement potential method applied to free‐field data. Light detection and ranging (lidar) observations, strong ground motions on the free surface in the vicinity of ground zero, and moment tensor inversion results are evidence that the fourth test SPE‐4P is a pure explosion, and the moments show good agreement, 8×10 10 N·m for free‐field data versus 9×10 10 N·m for Rg waves. In stark contrast, apparent moments for the first three tests are smaller than near‐field moments by factors of 3–4. Relative amplitudes for the three tests determined from Rg interferometry using SPE‐4P as an empirical Green’s function indicate that radiation patterns are cylindrically symmetric within a factor of 1.25 (25%). This fact assures that the apparent moments are reliable even though they were measured on just one azimuth. Spallation occurred on the first three tests, and ground‐based lidar detected permanent deformations. As such, the source medium suffered late‐time damage. Destructive interference between Rg waves radiated by explosion and damage sources will reduce amplitudes and explain why apparent moments are smaller than near‐field moments based on compressional energy emitted directly from the source.

Deposition Measurements From the Full-Scale Radiological Dispersal Device Field Trials.

In 2012, Defence Research and Development Canada led a series of experiments, titled the Full-Scale Radiological Dispersal Device Field Trials, in which short-lived radioactive material was explosively dispersed and the resulting plume and deposition were characterized through a variety of methods. Presented here are the results of a number of measurements that were taken to characterize the radioactive ground deposition. These included in situ gamma measurements, deposition filter samples, and witness plate measurements that were taken in situ with handheld beta survey meters. The results from the different measurement techniques are compared to each other and to a simple deposition model. Results showed that approximately 3% of the original source activity was deposited in the immediate vicinity of ground zero, and an additional 15-30% of the original activity was deposited within 450 m of ground zero. Implications of these results for emergency response are discussed.

Multiple Jet/Wall/Crossflow Interactions

This paper summarizes thirty years of research on ground vortex and upwash flows generated by single and multiple impinging jets in a crossflow with relevance to vertical/Short Take-Off and Landing Aircrafts (V/STOL). Laser Doppler measurements and flow visualization are presented for turbulent circular jets emerging into a low-velocity cross-stream and, then, impinging on a flat surface perpendicular to the geometrical jet-nozzle axis. The experiments were performed for single, twin side-by-side., twin in tandem, and three jets through a crossflow for velocity ratios between the jet exit and the crossflow VR =Vj /Uo of 7.5 to 90. The multiple jets configurations include interject spacings of S=5D and L=6D. The impinging heights were varied from 5 to 20 jet diameters and include mean and turbulent velocity characteristics along the two normal directions parallel to the nozzle axis. The largest velocity ratios are characterized by a large penetration of the impinging jets, giving rise to a ground vortex due to the collision of the radial wall jet and the crossflow that wraps around the impinging point like a scarf. The results help to understand the flow around a V/STOL aircraft operating in ground vicinity with front wind or small forward movement that may result in enhanced negative pressures in the underside of the aircraft causing a pitching moment and suction down force towards the ground.

An iterative boundary element method for a wing-in-ground effect

In this paper, an iterative boundary element method (IBEM) was proposed to solve for a wing-in-ground (WIG) effect. IBEM is a fast and accurate method used in many different fields of engineering and in this work; it is applied to a fluid flow problem assessing a wing in ground proximity. The theory and the developed code are validated first with other methods and the obtained results with the proposed method are found to be encouraging. Then, time consumptions of the direct and iterative methods were contrasted to evaluate the efficiency of IBEM. It is found out that IBEM dominates direct BEM in terms of time consumption in all trials. The iterative method seems very useful for quick assessment of a wing in ground proximity condition. After all, a NACA6409 wing section in ground vicinity is solved with IBEM to evaluate the WIG effect.

EXPERIMENTAL STUDY OF GROUND EFFECT ON THREE-DIMENSIONAL INSECT-LIKE FLAPPING MOTION

This paper focuses on an experimental investigation aimed at evaluating the aerodynamics force characteristics of three-dimensional (3D) insect-like flapping motion in the vicinity of ground. The purpose is to establish whether flapping wing insects can derive aerodynamic benefit from ground effect similar to that experienced by a fixed wing aircraft. To evaluate this, force measurements were conducted in a large water tank using a 3D flapping mechanism capable of executing various insect flapping motions. Here, we focus on three types of flapping motions, namely simple harmonic flapping motion, hawkmoth-like hovering motion and fruitfly-like hovering motion, and two types of wing planforms (i.e. hawkmoth-like wing and fruitfly-like wing). Results show that hawkmoth-like wing executing simple harmonic flapping motion produces average lift to drag ratio [Formula: see text] similar to that of fruitfly wing executing the same motion. In both cases, they are relatively independent of the wing distance from the ground. On the other hand, a hawkmoth wing executing hawkmoth flapping motion produces [Formula: see text] characteristic different from that of fruitfly wing executing fruitfly motion. While the [Formula: see text] value of the former is a function of the wing distance from the ground, the latter is minimally affected by ground effect. Unlike fixed wing aerodynamics, all the flapping wing cases considered here do not show a monotonic increase in [Formula: see text] with decreasing wing distance from the ground.

Experimental Study of Two Impinging Jets Aligned With a Crossflow

Laser Doppler measurements provide information on the flowfield created by twin impinging jets aligned with a low velocity crossflow. The experiments were carried out for a Reynolds number based on the jet exit conditions of Rej = 4.3 × 104, an impingement height of 20.1 jet diameters and for a velocity ratio between the jet exit and the crossflow VR = Vj/Uo of 22.5, and an inter-jet spacing of S = 6D. The results show a large penetration of the first (upstream) jet that is deflected by the crossflow and impinges on the ground, giving rise to a ground vortex due to the collision of the radial wall and the crossflow that wraps around the impinging point like a scarf. The second jet (located downstream) is not so affected by the crossflow in terms of deflection, but due to the downstream wall jet that flows radially from the impinging point of the first jet it does not reach the ground. The results indicate a new flow pattern not yet reported so far, that is most relevant for a VSTOL aircraft operating in ground vicinity with front wind or small forward movement may result in enhanced under pressures in the aft part of the aircraft causing a suction down force and a change of the pitching moment towards the ground.

Study on the Aerodynamic Brake of Small Gyro-Mill Type Vertical Axis Wind Turbine (1st Report, Method of the Rotational Speed Continuous Control under the Strong Wind)

The vertical axis wind turbine can correspond to the wind direction change in principle and is possible to increase the output by stack it up vertically. However, it is pointed out that the control is difficult, because the self-start is weak and the rotational speed rises rapidly. In this study, we report on the method by which the generating operation can be continued at ease when the wind of the mean speed from 12m/s to 15m/s blows to the small giro-mill type vertical axis wind turbine and under the situation with large wind speed fluctuation in the vicinity of ground. In this method, firstly, the slide shaft is installed squarely to the rotation axis of the vertical axis wind turbine. The flat plate wing in the tip of this slide shaft is parallel to the plane of rotation under a usual rotational speed, and the axial resistance torque is small. However, the flat plate wing begins to tilt when the rotational speed exceeds a certain value, and it becomes finally right-angled to the plane of rotation, and large axial resistance torque is generated. By this method, the runaway of the vertical axis wind turbine is prevented. In the paper, various problems on this are clarified and are verified through the wind tunnel experiment, and the practicable method has been clarified.

Identification and Quantification of Polar Nitroaromatic Compounds in Explosive-Contaminated Waters by means of HPLC-ESI-MS-MS and HPLC-UV

In the area of former ammunition plants, contaminations caused by explosives and their degradation products are of great environmental relevance because of the immediate vicinity of ground- and drinking water reservoirs. Beside the determination of selected explosive-related compounds by means of HPLC with UV detection, a LC-MS-MS coupling utilizing electrospray ionisation was developed, which is particularly suited for the determination of highly polar compounds. Therewith, 12 different explosive-related compounds were identified and quantified on the basis of specific precursor-/ product-ion traces using the high selectivity and sensitivity of multiple reaction monitoring mode (MRM) of a triple quadrupole mass spectrometer. The LC-MS-MS-technique was applied to water samples from the area of a former ammunition plant. In addition to dinitrophenols and aminodinitrotoluenes which could be determined also by HPLC-UV, some highly polar compounds were found in the contaminated water, for example 3,5-dinitrobenzoic acid and 2-amino-4,6-dinitrobenzoic acid. The highest concentrations (14–40 µg L−1) were found for two isomers of dinitrotoluenesulfonic acids. In order to assure the quantitative determination of polar substances in real samples with different composition, external calibration and standard addition method were compared. The presented LC-MS-MS-method is suited for screening and quantification of polar and hydrophilic explosive-related compounds from different classes of substances in a single analytical protocol.

送電線下地表面近傍の電界分布の比較方法

送電線下地表面近傍の電界分布の比較方法

Ground reflection effects upon radiated and received signals as viewed via image theory

The ground surface affects radiated and received signals of antennas near the surface of ground. By considering spatially extended current distributions, we obtain both positive and negative image results for both horizontal and vertical antennas. We present numerical results for HF with ground surfaces of soil, seawater, and a perfect electrical conductor. To illustrate the angle and frequency-to-height dependence of the constructive and destructive interference, we plot contours (of equal amplitude) of the four different image factors in terms of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\theta</tex> and height/wavelength ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">h/\lambda</tex> ). These results provide insight into design considerations involving antennas in the near vicinity of ground.