Drag Ratio Research Articles

Wind turbine blade design for low rotational inertia materials at variable speeds with different twisting angle using Q-Blade

In this current investigation, the comparison and analysis of two-dimensional model for aerodynamic characteristics of the wind turbine blade was studied. The aero profiles of NACA0008 and NACA0012H compared and simulate. NACA0012H aero profiles were transformed to three-dimensional model with variable twisting angles and compared with exhaustive literature. The blade element momentum (BEM) method was used for the calculations of aero profile’s lift, drag, pressure coefficients using Q-blade software. Coefficient of lift, coefficient of lift and drag ratio and Coefficient of moment is getting better result of NACA0012H from NACA008 this may be due more chord thickness. Power and coefficient of power is better in NACA0012H with 30° twisting angle with TSR and Thrust. A parametric report generated here showed advanced estimations of cutting edge aero foil and twist speed in Q-Blade programming. Power coefficient increase up to blade in three airfoils with different twist angle and finds the maximum power near to 10.0 TSR value.

The real Oaxaca decomposition: convergence within Mexico’s Oaxaca region in the twenty-first century—Do types of crime and religious belief matter?

The paper empirically examines municipality convergence within Mexico’s southern Oaxaca region. We find municipalities are converging more rapidly than the “iron law” of 2% with up to 8% β convergence. Though homicides from the Drug War have negatively impacted growth, overall crime perhaps through strengthening local institutions has a positive but weak impact. Higher income inequality and Catholic belief are associated with higher per capita GDP growth in Oaxaca overall and within two microregions. The positive impact of a higher share indigenous population on growth in the relatively urban Valles Centrales microregion suggests a cultural element to policy making with the dependency ratio drag on growth suggesting a need for policies that give more attention to how retirees can continue to participate in the economy as well.

Aerodynamic optimization of propellers for High Altitude Pseudo-Satellites

The propulsion system of High-Altitude Platform Stations or High-Altitude Pseudo-Satellites (HAPS) is commonly based on propellers. The properties of the atmosphere at those high altitudes and the characteristic speed of HAPS entail that the flight is performed at very low Reynolds numbers. Hence, the aerodynamic behavior of the propeller sections changes substantially from the hub to the tip of the blades. Under those circumstances, the ordinary methods to develop optimized propellers are not useful and must be modified. We present a method of propeller design adapted to HAPS features. It combines traditional solutions with modern numerical tools. Specifically, Theodorsen analytical theory is used to minimize induced drag. This process leaves one free parameter that it is fixed optimizing a cost function depending on the Reynolds number with a viscous-potential numerical code. It leads to an optimal determination of the geometrical characteristics of the propeller, i.e., chord and pitch distribution, increasing its total efficiency. The resulting algorithm has low computational requirements what makes it very appropriate for the preliminary design of HAPS missions, when it is necessary to simulate many different cases. That methodology has been applied to a relatively small HAPS airship with a wind speed of 10 m/s and required thrust of 100 N. The propeller is assumed to be made up of NACA4412 airfoils and the cost function to be minimized is given by the ratio of the 2D drag and lift coefficients. With those conditions we perform a parametric analysis where different combinations of diameters, thrust coefficients, and propeller advance ratios are considered. Over a Reynolds number range from 103 to 106, the new method provides a gain about 5% in the propeller efficiency when compared with the ordinary design procedure that employs a constant Reynolds number. That gain is of utmost importance for HAPS operations, since, for example, it allows an increase in the payload of up to 25% for a 90 meters long airship.

Variable Leading Edge with Adaptive Thermal Barriers and Its Heat Transfer Behaviour

At present, the hypersonic vehicles cannot be adapted to all the flight phases perfectly, and the aerodynamic heating and lift - to - drag ratio are contradictory to the shape of the vehicles. From the perspective of aerodynamic heating, a blunt shaped body is desired to reduce the heat flow of the hypersonic vehicles. However, the lift - to - drag ratio demands a sharp leading edge. In this paper, a scheme of variable leading edge which could satisfy with both the requirements of aerodynamic heating and lift-to-drag ratio was investigated, and an adaptive thermal barrier was proposed based on the features of the variable leading edge hot structure. According to the heat flux calculated from a certain trajectory by computational fluid dynamics, the heat transfer behaviour of the variable leading edge with adaptive thermal barriers was analyzed by the finite element method. The results indicated that the temperature peak of the panel reached 1428.2 K at 400 s, temperature of the adaptive thermal barriers approached 1418.4 K at 420 s, and the temperature of the internal insulation increased to 667.86 K finally. At the end of trajectory, temperature distribution in the thermal barrier and internal insulation tended to be balanced respectively, which exhibited an excellent thermal property and a promising prospect in complex environment..

The Interplay between Flow Field, Suspended Sediment Concentration, and Net Deposition in a Channel with Flexible Bank Vegetation

This paper investigates the interplay between the flow, suspended sediment concentration (SSC), and net deposition at the lateral interface between a main channel and riverbank/floodplain vegetation consisting of emergent flexible woody plants with understory grasses. In a new set of flume experiments, data were collected concurrently on the flow field, SSC, and net deposition using acoustic Doppler velocimeters, optical turbidity sensors, and weight-based sampling. Vegetation largely affected the vertical SSC distributions, both within and near the vegetated areas. The seasonal variation of vegetation properties was important, as the foliage strongly increased lateral mixing of suspended sediments between the unvegetated and vegetated parts of the channel. Foliage increased the reach-scale net deposition and enhanced deposition in the understory grasses at the main channel–vegetation interface. To estimate the seasonal differences caused by foliation, we introduced a new drag ratio approach for describing the SSC difference between the vegetated and unvegetated channel parts. Findings in this study suggest that future research and engineering applications will benefit from a more realistic description of natural plant features, including the reconfiguration of plants and drag by the foliage, to complement and replace existing rigid cylinder approaches.

LES of Flow Through and Around a Finite Patch of Thin Plates

AbstractLarge eddy simulations (LESs) are performed for turbulent flow through and around a porous patch of thin vertical plates at a plate Reynolds number of Rep=5,800. The plates are arranged in a staggered pattern, presenting an elliptical planform and mimicking streamwise‐oriented blades of emergent vegetation. The immersed boundary method is employed to explicitly resolve the interaction between flow and plates. Three flow cases, each with a different number of plates within the same planform area, that is, different patch density, are studied. The Reynolds number based on freestream velocity and plate length is the same in all cases. Inspection of the distribution of velocity and vorticity in the horizontal plane reveals that downstream plates are significantly impacted by the wakes from upstream plates. It is therefore proposed that the plates can be divided into two groups based on the local flow characteristics, which are a function of position within the patch: a free group and a wake group. This classification is subsequently used in the quantitative analysis of boundary layer development and drag force at plate scale. The thickness and character of the simulated boundary layers on the plates differ significantly from predictions based on analytical or empirical relationships, which is due to wake effects and the finite length of the plates. The simulations demonstrate the so‐called sheltering effect; that is, the drag forces acting on downstream plates (in the wake group) are significantly lower than those acting on upstream plates, a result of the lower approach flow speed. Although the front‐area‐to‐lateral‐area ratio of the plates is low (1/40), pressure drag is observed to be larger than friction drag for each plate. The ratio of pressure drag to the total drag at patch scale shows only very little dependence on the plate density of the patch.

Robust adaptive divided difference filter based on forgetting factors and its applications

SummaryThis paper proposes robust and adaptive divided difference filters (RADDFs) based on forgetting factors which are robust to dynamic systems with biases or uncertainties. The RADDFs are founded on the principle of covariance matching. The robustness of RADDFs is reflected in that it amplifies the innovation covariance to compensate the effect of dynamic biases or uncertainties. The forgetting factor is adjusted adaptively. Then, the scalar forgetting factor is further extended to multiple forgetting factors. The proposed RADDFs are illustrated by Mars entry navigation system with atmospheric density uncertainty, lift over drag ratio uncertainty, and ballistic coefficient uncertainty. To validate the filter performance by multiple forgetting factors, a typical tight coupling nonlinear system with abrupt biases is used.

Aerodynamic layout optimization design of a barrel-launched UAV wing considering control capability of multiple control surfaces

Owing to the size limitations of launchers, foldable main wings and foldable vertical tails are usually used in the design of barrel-launched unmanned aerial vehicles (UAVs), and the folding mechanisms are complex and bulky. Further, the coupling effect between aerodynamic performance and control capability is not typically considered in the aerodynamic layout design of traditional drum-launched UAVs; thus, the overall performance is often improved by serial design and multi-turns optimization, which result in low design efficiency. Based on the available research on barrel-launched UAVs, this paper presents an optimal design scheme for non-vertical tail aerodynamic layout considering the control capability of multiple control surfaces. A flying-wing configuration, with two groups of ailerons and one group of all moving tips, is employed in the design, and its control capability and aerodynamic performance are quantitatively described in terms of the volume of attainable moment subset and lift–drag ratio. The focus of the current design is shifted from improvement of single aerodynamic performance to optimization of overall performance. To overcome the computational complexity observed in direct optimization, the number of design variables is reduced by identifying the key test factors. The concept of a surrogate model matrix comprising cell surrogate models is proposed to effectively fit the aerodynamic characteristics and control capability of the wing. A multi-objective optimization based on the surrogate model matrix is carried out using the neighborhood cultivation genetic algorithm, which effectively improves the optimization efficiency. The entire process is implemented on an ISIGHT platform for automatic optimization design of the wing. At two design points selected on the pareto frontier, the results show that the lift–drag ratio is increased by 28.36%, reachable torque space is increased by 64.29% in state 1, lift–drag ratio is increased by 23.11%, and reachable torque space is increased by 164.29% in state 2. These results provide a reference for the aerodynamic layout design of barrel-launched UAVs for practical control requirements.

Design of small horizontal axis wind turbine for low wind speed rural applications

Abstract In this study, a 2 kW small scale horizontal axis wind turbine with rotor radius of 1.8 m and Tip Speed Ratio of 6 was designed to work at low wind speed for rural applications. Aerodynamic analysis was performed on 10 airfoils, viz Aquila, BW-3, E387, FX63-137, NACA0012, NASA LS-0413, RG-15, S1223, SD7080 and SG6043 using QBlade software. These airfoils were used to analyze Lift Coefficient, Lift to Drag ratio, with different angles of attack and compared with one another. From Numerical simulation, SD7080 was the most suitable airfoil to start producing high power in low wind speed applications.

CHAMP and GOCE thermospheric wind characterization with improved gas-surface interactions modelling

The CHAMP and GOCE satellites provided high-resolution thermosphere data between 2000 and 2013, improving our knowledge of atmosphere dynamics in the thermosphere-ionosphere region. However, the currently available data sets contain inconsistencies with each other and with external data sets and models, arising to a large extent from errors in the modelling of aerodynamic forces. Improved processing of the wind data for the two satellites would benefit the further development and validation of thermosphere models and improve current understanding of atmospheric dynamics and long-term trends. The first step to remove inconsistencies has been the development of high-fidelity models of the satellite surface geometry. Next, an improved characterization of the collisions between atmospheric particles and satellite surfaces is necessary. In this article, the effect of varying the energy accommodation coefficient, which is a key parameter for describing gas-surface interactions (GSI) is investigated. For past versions of the thermosphere density and wind data from these satellites a value of the energy accommodation coefficient of αE=0.93 was selected. The satellite accelerometer measurements, from which the thermospheric data are derived, have now been reprocessed using high-fidelity geometries and a wide range of αE values. Lowering the αE value used in the processing leads to an increase in the lift over drag ratio for those satellite panels that are inclined to the flow. This changes the direction of the modelled acceleration, and therefore the interpretation of the measured acceleration in terms of wind. The wrong choice of αE therefore leads to the introduction of satellite attitude-dependent wind errors. For the CHAMP and GOCE satellites, we have found that values of the energy accommodation coefficient significantly lower than 0.93 (0.85 for CHAMP and 0.82 for GOCE) result in increased consistency of the wind data. A comparison between the two missions and an overview of the influence on the results of filtering for solar activity and seasonal and diurnal variations is presented.

Effects of step configuration on hydrodynamic performance of one- and doubled-stepped planing flat plates: A numerical simulation

Categorized as one of high-speed marine vehicles, stepped planing hulls have the potential to reach relatively high speed in the sea by decreasing wetted surface. There were and still are some challenges in modeling of these vessels and design of ideal situation of steps. In the current study, a numerical-based method has been used to provide understanding about the effect of step height and its location on hydrodynamic characteristics of double-stepped planing plates. At the first step, one-stepped planing plate is numerically simulated. Results are compared against exiting numerical data, suggesting that results of the current numerical simulation are similar to results of previous numerical simulations. Then, double-stepped planing plates are modeled and pressure distribution, wetted length, free surface elevation and drag over lift ratio are computed. It is seen that, ventilation length behind the step and pressure coefficient are increased when step height of one- and a double-stepped planing plates are increased. It has been shown that, unlike an one-stepped planing plate, drag coefficient of a double-stepped planing plate can be increased when the step height is increased. The effects of the location of the second step on the performance of the planing plate have been explored, showing that this position plays a critical role on hydrodynamic forces. It is demonstrated that when the smallest possible lift force is produced by the middle-body, the plate shows the best performance (highest lift over drag ratio).

Optimization design of axial fan blade

ABSTRACTA series airfoil was obtained through optimization design which aimed to promote lift–drag ratio, and the new airfoil series was used to construct a blade. The chord length and installation angle of the blade along the blade height were optimized by using orthogonal optimization. Three design options (straight blades, C-type blades and forward swept blades) are examined in this paper. Taking an axial fan as the research object, the whole 3D numerical simulation was conducted by using Ansys-CFX. Axial fans with three kinds of blades are discussed and compared under design and off-design conditions. The present results show that: under design conditions, the total pressure efficiency of the axial flow fan with the forward swept blade is the highest, and the C-type blade has slightly lower efficiency while the straight blade has the lowest efficiency. Under off-design conditions, the aerodynamic performance of the forward-swept blade and C-type blade fans are better than that of the straight-blade fans.

Computational Analysis of Air Wings to Evaluate Downforce and Lift-Drag Ratio: Technical Note

Air wings with NACA air foil profiles are designed and analysed for their aerodynamics at 40m/s. More than one air profile has been analysed to find the suitable air wing meeting the requirement and efficiency. An air wing in an automobile experiences aerodynamic forces and act as an inverted air foil. The efficiency of an air wing can be determined by down force - drag ratio i.e., it has to produce more down force with least possible drag caused by its frontal area of cross section.

Aerodynamic effects of varying solid surface area of bristled wings performing clap and fling

The smallest flying insects with body lengths under 2 mm show a marked preference for wings consisting of a thin membrane with long bristles, and the use of clap and fling kinematics to augment lift at Reynolds numbers (Re) of approximately 10. Bristled wings have been shown to reduce drag forces in clap and fling, but the aerodynamic roles of several bristled wing geometric variables remain unclear. This study examines the effects of varying the ratio of membrane area (AM) to total wing area (AT) on aerodynamic forces and flow structures generated during clap and fling at Re on the order of 10. We also examine the aerodynamic consequences of scaling bristled wings to Re = 120, relevant to flight of fruit flies. We analyzed published forewing images of 25 species of thrips (Thysanoptera) and found that AM/AT ranged from 14% to 27%, as compared to 11% to 88% previously reported for smaller-sized fairyflies (Hymenoptera). These data were used to develop physical bristled wing models with AM/AT ranging from 15% to 100%, which were tested in a dynamically scaled robotic clap and fling model. At all Re, bristled wings produced slightly lower lift coefficients (CL) when compared to solid wings, but provided significant drag reduction. At Re = 10, largest values of peak lift over peak drag ratios were generated by wing models with AM/AT similar to thrips forewings (15% to 30%). Circulation of the leading edge vortex and trailing edge vortex decreased with decreasing AM/AT during clap and fling at Re = 10. Decreased chordwise circulation near the wing tip, vortex shedding, and interaction between flow structures from clap with those from fling resulted in lowering CL generated via clap and fling at Re = 120 as compared to Re = 10. Clap and fling becomes less beneficial at Re = 120, regardless of the drag reduction provided by bristled wings.

Application of Impulsive Aero-Gravity Assisted Maneuvers in Venus and Mars to Change the Orbital Inclination of a Spacecraft

Thse powered aero-gravity-assist is an orbital maneuver that combines three basic components: a gravity-assist with a passage by the atmosphere of the planet during the close approach and the application of an impulse during this passage. The mathematical model used to simulate the trajectories is the Restricted Three-Body Problem including the terms coming from the aerodynamic forces. The present paper uses this type of maneuver considering that the trajectory of the spacecraft is in the ecliptic plane and the presence of the atmospheric Drag and Lift forces. The maneuver in the ecliptic plane can be done due to technologies that provides spacecraft with high values for the Lift to Drag ratio. The main advantage is that this maneuver allows the modification of the semi-major axis of the orbit of the spacecraft using the gravity of the planet and, at the same time, to change the inclination, using the high Lift that is perpendicular to the ecliptic plane. So, it is a combined maneuver that changes two important orbital parameters at the same time. The Lift is applied orthogonal to the initial orbital plane to generate an inclination change in the trajectory of the spacecraft, which is a very expensive maneuvers when made using propulsion systems. The Lift to Drag ratio used in the present paper goes up to 9.0, because there are vehicles, like waveriders, designed to have these values. When the spacecraft is passing by the periapsis of its orbit, an instantaneous impulse is applied to increase or decrease the variation of energy given by the aero-gravity-assist maneuver. The planets Venus and Mars are selected to be the bodies for the maneuver, due to their atmospheric density and strategic location in the Solar System to provide possible uses for future missions. Results coming from numerical simulations show the maximum changes in the inclination obtained by the maneuvers, as a function of the approach angle and direction of the impulse; the Lift to Drag ratio and the ballistic coefficient. In the case of Mars, inclination changes can be larger than 13°, and for Venus larger than 21°. The energy and inclination variations are shown for several selected orbits. The powered aero-gravity-assist maneuver generates inclination changes that are higher than the ones obtained from the powered maneuver and/or the aero-gravity maneuver.

Experimental and numerical analysis on the hydrodynamic behaviors of permeable microbial granules

The microbial granules are found to be porous and permeable, which leads to a different drag force coefficient from the rigid sphere granules. Discrete element method (DEM) was employed to establish geometric models of porous microbial granules for the first time in this study. And computational fluid dynamics (CFD) was applied to simulate the effects of porosity and Reynolds number on the fluid flow, shear stress, pressure and drag force based on the established geometric models. The results showed that both the Reynolds number and the porosity of microbial granules significantly affect the fluid velocity distribution inside the granules. The porosity shows less effect on maximum shear stress than Reynolds number. It s well known that drag force consists form drag and skin drag. The ratio of form drag to drag force increased, while the skin drag force ratio decreased with the increasing Reynolds number. The porosity will enhance the skin drag and weaken the form drag at the same Reynolds number. A drag force coefficient equation was established based on the simulated results in order for engineering application. The correctness of the equation was confirmed by comparing with experimental results. The results from this study may provide valuable information for operation and designing of a granule-based bioreactor in wastewater treatment.

Multivariable Analysis of Aerodynamic Forces on Slotted Airfoils for Wind Turbine Blades

Improvement of the aerodynamic performance for cambered airfoils with leading-edge slots is investigated in this work. This concept is proven both computationally and experimentally in recent years. Five design variables of interest are slot's length, slot's width or thickness, inlet angle, exit angle, and the vertical position. The objective is to perform design of experiment and optimization studies on these variables and evaluate the behavior of the objective functions, namely lift and lift over drag ratio (LoD), within the appropriate ranges of the independent variables. Simulations are mainly carried out at the Reynolds number of 1.6 × 106 and the angles of attack (AoA) of 6 deg for NACA 4412 airfoil. However, some of the analyses are repeated at Reynolds number of 3.2 × 106 and AoA of 0 and 8 deg to show the scalability of the results. Results indicate that the proper selection of three of the design variables, i.e., length, inlet angle, and vertical position, can have a significant impact on both lift and LoD, while the other two variables seem less influential. For the combination of the operating conditions and the values of the design variables considered in this investigation, a LoD improvement as large as 11% is observed.

Blade dynamics in combined waves and current

Submerged aquatic vegetation (SAV), such as seagrass, is flexible and reconfigures (bends) in response to waves and current. The blade motion and reconfiguration modify the hydrodynamic drag. The modified drag can be described by an effective blade length, le, which is defined as the length of a rigid blade that results in the same drag as a flexible blade of length l. In many natural settings SAV is exposed to combinations of waves and current. This study derived and used laboratory measurements to validate new predictions of effective blade length for combined waves and current based on a Cauchy number, which describes the ratio of hydrodynamic drag to the restoring force due to rigidity of blade. Force measurements on and digital images of blades exposed to waves with a 2-s period and with a range of wave velocity (Uw) and current speed (Uc) were used to estimate the effective blade length. The measurements were also used to validate a numerical simulation of blade motion. Once validated, the simulation was used to expand the investigated parameter space to a wider range of wave conditions, and in particular longer wave periods. ForUc<14Uw, the blade motion and hydrodynamic drag were wave-dominated. For Uc>2Uw, the blade motion and hydrodynamic drag were current-dominated.

First-principles calculations of solute transport in zirconium: Vacancy-mediated diffusion with metastable states and interstitial diffusion

Zirconium alloys are the most widely used nuclear fuel cladding materials for light water power reactors where irradiation damage causes solute redistribution, leading to degradation of alloy properties such as corrosion resistance. Designing radiation-tolerant zirconium alloys requires a thorough understanding of the atomic-scale transport behavior of the alloying elements in Zr. We perform density function theory calculations to investigate the diffusion of Sn, Cr, Fe, Be, Al, and Ni in the hexagonal close-packed (HCP) Zr matrix. We develop a methodology to accurately model the metastable vacancy states along the basal migration path, known to occur in group IV metals. We compute the vacancy-mediated solute diffusion coefficients and drag ratios using the kinetic Monte Carlo method and an analytic Green's function method---the agreement between the two validates our methodology. The computed diffusion coefficients of Sn and Al show good agreement with the experimental data and we expect these solutes to diffuse via the vacancy-mediated mechanism. We use a Green's function approach, parameterized with data from density functional theory calculations, to compute the interstitial diffusion coefficients of Cr, Fe, Be, and Ni in the HCP Zr lattice. The computed diffusion coefficients of Cr, Ni, and Be agree with the experimental measurements within one order of magnitude, while those of Fe are within two orders of magnitude of the experimental measurements. The drag ratios for Cr, Fe, Be, and Ni are positive up to 1235 K, which suggests that nonequilibrium vacancy fluxes could drag these solutes toward sinks such as dislocation loops and grain boundaries. We also compute the transport coefficients without including the metastable states, and using the eight- and thirteen-frequency model. Our results show significant differences in drag ratio for the eight- and thirteen-frequency model predictions compared with the Green's function methodology, but smaller errors in the solute diffusivity. Combining interstitial and vacancy-mediated diffusivities, we predict the unusual result that increased vacancy concentration slows down solute diffusivity, while a sufficiently high vacancy concentration can change the dominant mechanism to an accelerated vacancy-mediated diffusion.

Experimental and Numerical Analysis of the Effect of Vortex Generator Height on Vortex Characteristics and Airfoil Aerodynamic Performance

To explore the effect of the height of vortex generators (VGs) on the control effect of boundary-layer flow, the vortex characteristics of a plate and the aerodynamic characteristics of an airfoil for VGs were studied by both wind tunnel experiments and numerical methods. Firstly, the ratio of VG height (H) to boundary layer thickness (δ) was studied on a flat plate boundary layer; the values of H are 0.1δ, 0.2δ, 0.5δ, 1.0δ, 1.5δ, and 2.0δ. Results show that the concentrated vortex intensity and VG height present a logarithmic relationship, and vortex intensity is proportional to the average kinetic energy of the fluid in the height range of the VG. Secondly, the effects of height on the aerodynamic performance of airfoils were studied in a wind tunnel using three VGs with H = 0.66δ, 1.0δ, and 1.33δ. The stall angle of the airfoil with and without VGs is 18° and 8°, respectively, so the VGs increase the stall angle by 10°. The maximum lift coefficient of the airfoil with VGs increases by 48.7% compared with the airfoil without VGs, and the drag coefficient of the airfoil with VGs is 84.9% lower than that of the airfoil without VGs at an angle of attack of 18°. The maximum lift–drag ratio of the airfoil with VGs is lower than that of the airfoil without VGs, so the VGs do not affect the maximum lift–drag ratio of the airfoil. However, a VG does increase the angle of attack of the best lift–drag ratio.