Ground Effect Research Articles

Steady and Unsteady Hover Test of a Lift Compounding Rotorcraft

Compound rotorcraft can be a viable option to achieve moderately high speeds of 240 knots. However, there is no systematic wind tunnel test data in the public domain to understand the complex interactional aeromechanics involved. This work is part of a test campaign to conduct multiple high-speed wind tunnel tests of various compound configurations. The compound configuration consists of a single main rotor, a single wing on the retreating side for lift augmentation, and a single rear propeller for propulsive augmentation. In this paper, hover test results are presented. Hover tests were conducted for various configurations and at different tip Mach numbers with the maximum value of 0.5. Rotor and wing performances are measured separately using individual balances. Rotor blades are equipped with strain gauges for measuring flap, lag, and torsional moments at radial stations. The wing location is below the main rotor, and the measured wing download is only 2.8% of the rotor thrust. The wing provides a partial ground effect, making the rotor more efficient and almost compensates for the download with less than 1% reduction in net figure of merit. Blade structural loads correlate satisfactorily between the analysis and measurement except for lag bending moment. This discrepancy is a large 2/rev lag bending moment measured in the test, which needs further investigation. Propeller hover test was conducted up to 2500 revolutions per minute (tip Mach number of 0.25) at a single collective. Prediction correlates well and captures the low-Reynolds-number effect for lower revolutions per minute.

The impact of the ground on flow structure and aerodynamic characteristics of a double delta wing

The ground effect (GE) on the formation of the vortical flow over a double delta wing having sweep angles of Λ=70°/40° was examined using the Particle Image Velocimetry (PIV) and dye flow visualization methods in this study. Qualitatively and quantitatively measured results were demonstrated for angles of attack, α=15° and 25° cases in the side and cross-flow planes to reveal the detail of the flow structures. The distance, h between surfaces of the ground and the delta wing normalized with the chord length of the double delta wing, c, was selected as h/c=0.1, 0.25 0.55, and the ground-free case (GFC). The results demonstrated that the magnitudes of the strake and wing vortices at α=15° and the coiled-up vortex at α=25° progressively diminish when the delta wing moves from the free-stream region into the boundary layer region close to the ground surface, h/c=0.1. Also, the rate of the inboard movement of leading edge vortices towards the wing central axis increases on the pressure surface of the wing as the altitude of the double delta wing is gradually lowered towards the ground surface. The lift coefficient, CL of the delta wing enhances due to the development of air stagnation and ram pressure between wing and ground surfaces by lowering the level of the double delta wing from the free-stream region into the boundary layer flow region which is strongly influenced by the presence of the ground surface. Also, the drag coefficient, CD increases more than the lift coefficient, CL resulting in a deterioration of the lift to drag ratio, CL/CD under the ground effect (GE). Finally, an increment in CL/CD is much more prominent at lower angles of attack, α regardless of ground effect.

The effects of dry grinding and chemical conditioning during grinding on the flotation response of a Cu-Zn sulphide ore and a spodumene pegmatite silicate ore

Dry processing of metal containing ores is often easily discarded as a viable option because of the higher energy consumption of dry grinding and several other challenges introduced from the handling of the dry ore. However, possible positive aspects include improved surface properties, reduced wear of the grinding media, and improved efficiency of water usage, which will become increasingly important in the future due to the water scarcity and global warming.Laboratory scale flotation tests with various grinding and conditioning methods were conducted with the Pyhäsalmi massive sulphide ore (Cu-Zn) and the Syväjärvi spodumene pegmatite silicate ore (Li) to determine the effects of dry processing on the flotation performance of these ores. Products were characterized utilizing XRF and MP-AES, and metallurgical efficiency was assessed. EDTA-leaching of the grinding products, and electrochemical measurements were conducted to further assess the chemical conditions after various processing atmospheres.Dry grinding the Pyhäsalmi sulphide ore resulted in higher flotation mass recoveries compared to wet grinding, but at the cost of selectivity. Beneficial effects emerging from the chemical conditioning during grinding were observed regarding kinetics, selectivity, and overall performance. Conditioning the Syväjärvi spodumene ore with a fatty acid collector during dry grinding had a tremendous activating effect on the ore, and detrimental effect on the selectivity. Overall, the spodumene ore responded poorly to the dry processing conditions, but some potential applications were identified.These initial results showed clear differences in the separation performance between the various grinding and conditioning conditions, and future efforts will be focused on determining the effects of these different processing conditions on the mineralś surface properties in a more precise manner.

Experimental Study on Laser Ablation Texture-Assisted Grinding of Tungsten Alloy.

In order to machine the tungsten alloy with high efficiency, low damage and precision, laser ablation texture technology and precision grinding technology were combined to carry out grinding experiments of tungsten alloy and laser ablation texture-assisted grinding experiments. The advantages of laser ablation texture-assisted grinding tungsten alloy were investigated by comparing of the surface morphology, grinding force and surface roughness between ordinary grinding and laser ablative texture-assisted grinding. The results demonstrate that the surface morphology of ordinary grinding tungsten alloy was poor, the surface roughness was relatively high and the grinding force was relatively large. The surface morphology of the laser ablation texture-assisted grinding tungsten alloy processed by laser ablation texture was improved, the surface roughness decreased by 0.023 µm–0.204 µm, the normal force decreased by 49.91–59.46% and the tangent force decreased by 44.11–58.49%. Meantime, for the area ratio of texture A being the most, the grinding effect was related to the area ratio of texture, and the lowest grinding force and the best surface quality were observed on the tungsten alloy with the laser ablated texture A; the grinding forces and roughness of the other textures’ workpiece was similar and close because of their similar area ratios. The results demonstrate that laser ablation texture-assisted grinding of tungsten alloy could improve machining quality and reduce grinding force, which would provide guidance for realizing the high efficiency and precision machining of tungsten alloy.

Determination of Leaf pH without Grinding the Sample: Is It Closer to the Reality?

This study recommends a non-grinding measurement method of leaf pH which can reduce the destructive interference to the measured fresh-leaf pH values. To verify the accuracy of this method, we measured leaf pH with the non-grinding and grinding method and further assessed the dilution effect on leaf pH in the grinding process. Compared with the non-grinding method, the grinding method significantly increased the measured pH value; leaf pH increased with decreasing leaf–water ratio in the procedure of the grinding method, but gradually stabilized. The grinding effects of severe physical damage and thereafter oxidization of leaf samples, and the dilution effects according to the Debye–Hückel limiting law and acid-base ionization theory, may both contribute to the increased leaf pH measured with the grinding method. Thus, leaf pH measured with the non-grinding method was expected to be much closer to those of leaf sap in vivo and be more suitable to indicating the dynamic variation or instant response of leaf pH to the environmental changes. Finally, considering that non-significant difference had been proved in the measured leaf pH between dried, frozen, refrigerated, and fresh ground samples, a conversion equation was provided to facilitate mutual conversion of the results with non-grinding fresh samples (y) against those with grinding dried samples (as representative) (x): y = 1.097x − 0.722.

Effect of ground on aerodynamics and longitudinal static stability of a non-slender delta wing

In this paper, the effect of ground on aerodynamics and longitudinal static stability of a non-slender delta wing with sweep angle of 45 degree and thickness-to-chord ratio (t/c) of 5.9% was characterized at Reynolds number of 9×104 in a low-speed wind tunnel using force and pressure measurements. The measurements were conducted for angles of attack varying between 0≤α≤30 degrees and non-dimensional heights between 3%≤h/c≤107% and height stability of the wing based on aerodynamic center in pitch (Xa) and aerodynamic center in height (Xh) was constructed. The results indicate that the effect of ground has substantial impact on both aerodynamic performance and stability of the delta wing. As the height of the wing decreases, both drag and lift forces increases where these effects were observed to be more pronounced for higher angles of attack. The maximum aerodynamic performance with increasing ground effect intensity was measured around 7 degree. Center of pressure (Xp) as well as Xa travel in a limited range over the wing chord, whereas Xh exhibits back and forth movement on the longitudinal axis resulting in interchanging stability characteristics varying with both height and angle of attack. The pressure measurements showed that the effect of ground has significant and complex impact on both vortex reattachment and vortex strength with varying angles of attack and heights such that it might promote reattachment and increases vortex strength but might cause earlier stall.

Effect of superfine grinding on the physicochemical properties of straw mushroom (Volvariella volvacea) powders rich in vitamin D2

AbstractIn this study, straw mushroom (Volvariella volvacea) powders (SMPs) rich in vitamin D2 were prepared by ultraviolet‐B irradiation and superfine grinding. And effect of superfine grinding on the physicochemical properties of SMPs was investigated. Results indicated that the specific surface area, cell wall breakage ratio, hydration characteristics, and thermal stability of SMPs increased significantly with decreasing particle size, while the oil holding capacity, fluidity, and bulk density decreased. Superfine grinding did not destroy the main chemical structure of SMPs and improved the solubility of proteins, polysaccharides, vitamin D2, and ergosterol of SMPs. The results have positive implications for the resource development of straw mushroom and the promotion of food products containing vitamin D2.Novelty impact statementThe conversion of ergosterol into vitamin D2 in straw mushroom was promoted by ultraviolet (UV)‐B irradiation. Straw mushroom powders (SMPs) rich in vitamin D2 were prepared by superfine grinding. The effect of superfine grinding on the physicochemical properties of SMPs rich in vitamin D2 for the first time.

Assessing the impact of ground reflection on measurement of the overall sound power level and acoustic radiation efficiency of rocket launches

Determining the sound power levels of a rocket is the first step in characterizing its radiation efficiency. Because the sound radiation from a launch vehicle is anisotropic, well-calibrated ground measurement stations are used, along with trajectory data, to obtain sound power. Historically, the effect of ground reflections appears to largely have been neglected in the literature, despite the potential to inflate OAPWLs and therefore radiation efficiency. This study investigates the likely effect of a finite-impedance ground on spectra, overall sound pressure levels, and power levels. The single-parameter ground reflection model by Embleton et al. [J. Acoust. Soc. Am. 74, 1239–1244 (1983)] is used to obtain an estimate for change in OASPL for a model spectrum based on space vehicle launches. When the correction is applied to the OAPWL it produces in a nearly 3dB reduction in level and reducing the efficiency by a factor of 2. This indicates the possibility that the 0.5% radiation power efficiency assumed for rockets in the past is too high.

Sonic boom measurements: Practical implications considering ground effects, microphone installation, and weather hardening.

Sonic boom measurements from recent flight tests have provided an opportunity to investigate effects of microphone installation on sonic boom waveforms, spectra, and metric levels in support of NASA X-59 flight test planning. While those flight tests used N-wave aircraft (F-18s), modeling studies were also conducted using source characteristics for a shaped low-boom aircraft. Of particular interest were the effects of receiver height on boom waveforms and metrics at elevated receiver positions, microphone installation, and local ground cover type. Reductions of more than 2 dB in A-weighted sound exposure level and perceived level were shown for 1.6 ft (0.48 m) microphone heights for 35º ray elevation angle. Measured and modeled results are described in this letter.

In vitro prediction of the lower/upper-critical biofluid flow choking index and in vivo demonstration of flow choking in the stenosis artery of the animal with air embolism

<i>In vitro</i> prediction of the lower/upper-critical biofluid flow choking index and <i>in vivo</i> demonstration of flow choking in the stenosis artery of the animal with air embolism

EFFECTS OF GRINDING, POLISHING AND AGING ON PHASE TRANSFORMATION AND PHYSICAL PROPERTIES OF DENTAL TRANSPARENT CERAMICS

Purpose: This study investigated the effects of grinding, polishing and aging on physical properties using self-made zirconia and commonly used ultraclear ceramic materials and glass ceramics in the clinic. Methods: The samples were prepared using 3% yttria-stabilized zirconia ceramic (3Y-TZP) powder containing alumina, which was granulated by ball milling. Then, it is pressed into a circular sheet together with Upcera and Wieland materials. The glass ceramic materials are molded. Finally, all materials were subjected to hydrothermal aging. Results: The self-made zirconia had better permeability than the commonly used ultratransparent ceramic materials and glass ceramics. The polishing after grinding improved the surface morphology and roughness of tooth transparent ceramic materials; Polishing after grinding improved the aging resistance of zirconia materials. The bending strength of self-made samples was less than that of two kinds of ceramics commonly used in clinic, but greater than that of glass ceramics. Aging improved the bending strength of zirconia. Conclusions: The self-made zirconia had better permeability than ultratransparent all-ceramic materials and glass ceramics, and its bending strength was better than that of glass ceramics. Grinding and polishing could improve not only the surface morphology and roughness but also the strength and aging resistance.

Numerical simulation of propulsive aerodynamic profiles

The problem of creating high-lift propulsive aerodynamic is considered. A method was developed for constructing an aerodynamic profile by solving the inverse problem of aerodynamics. The dependence of the lifting force of this profile on the volume of air sucked from its upper surface and from the angle of attack is studied. The profile under study was developed on the basis of the well-known Griffin/Goldschmid profile with air suction at the upper critical point. Three aerodynamic profiles have been developed. The first profile has a flat lower surface to obtain the ground effect. The second profile is similar to the first but has a slit nozzle near the trailing edge. The third profile is similar to the second but has a non-flat bottom surface and increased thickness. The solution of the inverse problem of aerodynamics was used to construct aerodynamic profiles within the model of an ideal gas. The pressure distribution on the upper part of the profile, its construction height and the range of angles of attack are from 0° to 16°, as well as the degree of rarefaction up to 0.5 atm in the gap through which the air was taken were set. For the second and third profiles, the ratio of the amount of air ejected through the nozzle to the amount of air taken from the upper surface of the profile was set. This ratio ranged from 50 % to 200 %. Numerical calculations were performed for each variant using the Spalart-Allmaras turbulence models and the Transition Shear Stress Transport (SST) and Langtry model. The parameters of the turbulence models were adjusted according to known reference data. The Reynolds number was in the range of 1.5·105–1.5·106. The profiles have a high lift coefficient Cy = 3–3.4 which is achieved when creating a vacuum in the air intake of 0.5 atm. Cy depends on the angle of attack almost linearly up to the maximum values. The greater the air flow through the slot nozzle, the greater is the Cy at a vacuum in the air intake of 0.5 atm. Significance for practical application. The developed profiles have a large thickness and create traction. These profiles are convenient to use in aircraft with large internal volumes, for example, those running on hydrogen fuel.

Aerodynamic Characteristics of a Ducted Fan Hovering and Transition in Ground Effect

Ducted fans installed on vertical takeoff and landing vehicles experience significant ground effect during takeoff and landing. The aerodynamic characteristics of a ducted fan hovering and transitioning in the ground effect are studied using numerical simulations in this paper. The flowfields are obtained by solving Reynolds Averaged Navier–Stokes equations with the Multiple Reference Frame approach. When a ducted fan hovers in the ground effect, the blade thrust increases due to the combined effect of the increase in the effective angle of attack of the blade and the increase in ambient pressure; the duct thrust decreases due to the combined effect of the decrease in the effective angle of attack of the duct and the increase in ambient pressure. Stall occurs at a certain advance ratio and angle of attack when transitioning in the ground effect. The ground effect delays the occurrence of stall at some advance ratios. The ground effect is hardly detectable at angles of attack less than 30° even if the height drops to 0.5 times the duct exit diameter. At this height and high angles of attack, the different positions and influence regions of the ground vortex at different advance ratios contribute to the different variation trends in the ducted fan performance.

지면효과 속에 놓인 이중로터의 공력 특성에 대한 수치적 연구

Multi-copters are used in various fields as unmanned aerial vehicles. Consequently, the stability of the operation conditions of the unmanned aerial vehicle and the improvement of aerodynamic characteristics are required. Therefore, this study is intended to examine the effect of the wake interaction between rotors in ground effect when a set of double rotors is positioned adjacent to the ground through an unsteady numerical analysis. For this reason, the rotor is positioned adjacent to the ground, and the thrust ratio is measured while changing the distance between the rotors which are rotating at a fixed rotational speed. With the ground height as z and the rotor radius as R, the smaller the height ratio(z/R), the higher the thrust. As the distance between the rotors became smaller, the collision and interaction between wing tip vortices of the rotor blades got stronger, and the flow was not properly propagated into the direction of the wake. It is shown that when the rotor gets closer to the ground, the flow could not be fed back in after flowing along the ground, so the thrust ratio due to the ground effect tends to decrease. With these results and analysis, the effect of wake interference between rotors on the ground effect could be confirmed.

드론용 동축 반전 로터와 단일 로터의 지면효과에 따른 추력특성에 대한 수치 비교 연구

In this study it is attempted to compare the difference of increase rate of rotor thrust between coaxial counter-rotating rotor and single rotor due to ground effect by using computational fluid analysis. Rotor system was modeled with a commercial propeller usually used in small drones in both cases, and thrust was calculated with unsteady-state transient analysis by using Fluent 19.1 software. As a result, it is found that the rate of change of rotor thrust in accordance with the distance to the ground of coaxial rotor with a relatively large inter-propeller distance is quite different from the case of a single rotor.

A new one-step approach for the fabrication of microgrooves on Inconel 718 surface with microporous structure and nanoparticles having ultrahigh adhesion and anisotropic wettability: Laser belt processing

Two typical aspects of wettability on functional surfaces, namely, ultrahigh adhesion and anisotropic wettability, have attracted considerable interest for practical applications. A new and efficient method, laser belt processing, was proposed in this study for the preparation of Inconel 718 surfaces with ultrahigh adhesion and anisotropic wettability. The microgroove depth processed by the laser belt could be increased without changing the processing parameters, and microporous structures with nanoparticles were introduced. The results showed that the width and depth of the microgrooves increased with increasing laser power and processing times, whereas the depth decreased when the processing times was increased by eight times owing to the removal effect of belt grinding. The surface wetting state was between the Wenzel and Cassie wetting states, and van der Waals forces on the surface provided ultrahigh adhesion. The anisotropic wettability increased with increasing laser power, with a maximum contact angle of 121.3° and anisotropy of 34.9° at a laser power of 9.8 W. The microporous structure with nanoparticles enhanced the anisotropy. A new approach for the preparation of microgrooves was thus demonstrated. The prepared surface with ultrahigh adhesion and anisotropic wettability has promising applications in the field of droplet smart transport and microfluidic devices.

PREFACE: A SPECIAL SELECTION ON EMERGING TECHNIQUES FOR BIOMECHANICS–PART II

PREFACE: A SPECIAL SELECTION ON EMERGING TECHNIQUES FOR BIOMECHANICS–PART II

Efficient Al Recovery from Aluminum Dross with Simultaneous AlN Separation by a Mechanical Method

Aluminum dross (AD) is a hazardous waste that contains valuable metallic Al and reactive aluminum nitride (AlN). The intergrowth of Al and AlN presents a challenge to Al recovery and AlN removal. In the current work, a mechanical milling method was developed to separate Al and AlN. Steel bars and balls were used as grinding media. The AD particle size decreased after milling and was distributed in the ranges 0.425–2 mm, 0.15–0.425 mm, 0.08–0.15 mm, and &lt;0.08 mm. The particle size distribution was affected by the ball milling media and grinding time. Steel ball media had a better grinding effect on particles &gt; 2 mm. After ball milling, the Dp0.08–2 mm size fraction accounted for approximately 90%. With changes in particle size, the element content of AD varied: the fraction of metallic Al decreased, while the fraction of Si increased. Metallic Al mainly existed in particles with size &gt; 0.425 mm, accounting for 48.5%. AlN mainly existed in Dp0.15–0.425 mm, accounting for 64.9%. The optimal milling conditions achieved a 65% Al recovery rate and a 90% AlN separation efficiency. This work provides a promising approach for highly efficient pretreatment for AD recovery and AlN elimination in industrial applications.

Dietary Ground Flaxseed Increases Serum Alpha-Linolenic Acid Concentrations in Adult Cats.

Simple SummaryThe use of flaxseed in complete pet foods as a source of omega-3 fatty acids, and in particular alpha-linolenic acid, has been studied extensively in dogs. However, to date, no scientific published literature exists on the impacts of feeding whole ground flaxseed as an ingredient in cat food on nutrient digestibility, fatty acid bioavailability, and overall health in cats. In addition, dietary flaxseed inclusion has been challenged as providing little nutritional value for cats by not changing serum fatty acid levels and lowering nutrient digestibility. Therefore, the objective of this study was to directly evaluate the effects of adding ground flaxseed to dry cat food on fatty acid bioavailability, stool consistency, nutrient digestibility, and overall health in adult cats. These results clearly exhibit that a flaxseed-supplemented diet resulted in no changes in stool quality or nutrient digestibility, and elicited an increase in serum alpha-linolenic acid concentrations in healthy cats. Overall, these results clearly demonstrate that ground flaxseed can be used to modulate serum fatty acid concentrations and serve as a bioavailable source of alpha-linolenic acid in commercial cat food.We evaluated effects of dietary ground flaxseed on fecal and serum alpha-linolenic acid (ALA) concentrations, nutrient digestibility, and stool quality in female and male adult cats (n = 20 (8 males, 12 females); 3.95 ± 1.49 years of age (mean ± SD); 3.88 ± 0.82 kg BW). We hypothesized that adding ground flaxseed would increase serum ALA compared with feeding no flax, without changing nutrient digestibility. Cats were fed as-is 2.6% added-flaxseed (flax, n = 10) or no-flax (control, n = 10) diets (2.66 vs. 0.78% ALA of total fatty acids; crude protein 35%, fat 20%, fiber 3% as-fed) twice daily to maintain body weight for 28 days. Fecal collections were conducted on days 23–27 for total-tract nutrient digestibility, stool quality (scale 1–5; 1 = watery diarrhea, 5 = hard, dry, crumbly) and long-chain fatty acid (LCFA) analyses. Blood was collected on days 0, 14, and 28 for serum LCFA and chemistry analysis. Digestibility and fecal data were analyzed by ANOVA (SAS v9.4, Cary, NC, USA) and a repeated measures ANOVA for serum ALA. Flax-fed cats, compared with control-fed, had greater (p < 0.05) serum ALA after 14 days (4.00 vs. 0.71 µg/mL) and 28 days (7.83 and 3.67 µg/mL). No differences were observed in stool quality, and dry matter, protein, fat, and ALA digestibility. However, metabolizable energy was greater in the flax vs. control diet (4.18 vs. 3.91 kcal/g; p < 0.05). Overall, these data demonstrate that ground flaxseed added to cat diets increases serum ALA within 14 days, with no detriments to nutrient digestibility. We conclude that flaxseed can be used as a bioavailable source of ALA in cat diets.

Aqueous carbonation of peridotites for carbon utilisation: a critical review.

Peridotite and serpentinites can be used to sequester CO2 emissions through mineral carbonation. Olivine dissolution rate is directly proportional with temperature, presence of CO2, surface area of mineral particles and presence of ligands and is inversely proportional to pH. Olivine dissolution is better under air flow and increases seven times when rock-inhibiting fungus (Knufia petricola) is used. Olivine dissolution retards as silica layers form during reaction. Sonication, acoustic and concurrent grinding using various grinding medias have been used to artificially break these silica layers and achieve high magnesium extraction. Wet grinding using 50 wt.% ethanol enhanced CO2 uptake of dunite 6.9 times and CO2 uptake of harzburgite by 4.5 times. The best economical process is single-stage concurrent grinding at 130 bar, 185 °C, 15 wt.% solids and 50 wt.% grinding media (zirconia) using 0.64 M NaHCO3. Ratio of grinding media to feed should not be less than 3:1. Yield increases with temperature, pressure, time of reaction, pH and rpm and using additives and grinding media and reducing particle size. This review aims to investigate the progress from 1970s to 2021 on aqueous mineral carbonation of olivine and its naturally available rocks (harzburgite and dunite). This paper comprehensively reviews all aspects of olivine carbonation including olivine dissolution kinetics, effects of grinding and concurrent grinding, thermal activation of olivine feedstock (dunites and harzburgites) as well as chemistry of olivine mineral carbonation. The effects of different reaction parameters on the carbonation yield, role of mineral carbonation accelerators and costs of mineral carbonation process are discussed.