Several Angles Of Attack Research Articles

Wingtip vortex structure in the near-field of swept-tapered wings

Wingtip vortices are an important phenomenon in fluid dynamics due to their complex and negative impacts. Despite numerous studies, the current understanding of the inner vortex is very limited; thus, a basis for the design of effective wingtip geometry and vortex manipulation is narrow. This work examines the structure of the trailing vortex shed from a swept-tapered wing, analogous to a commercial aircraft topology. Stereoscopic particle imaging velocimetry has been utilized to compare the vortex structure and development through several angles of attack at various downstream stations for a fixed Reynolds number (Re = 1.5 × 106). After correcting for vortex meander through helicity-based spatial localization of the vortex core, relationships between the vortex core velocity/vorticity fields, core shape, and turbulent properties have been examined. Subsequently, the vortex is found to exhibit a layered structure with slow linear rates of dissipation indicative of laminar diffusion mechanisms, despite being a turbulent vortex. The turbulent kinetic energy distribution in the vortex signals that relaminarization of the inner core occurs. Consideration of the streamline curvature around the core, via examination of the local Richardson number, indicated that a laminar core structure had formed within which large-scale turbulent eddies could not contribute to the turbulent diffusion of vorticity away from the core. The normalized circulation within the vortex core has been shown to exhibit self-similar behavior typical of the fully developed axisymmetric vortices.

Improvement of Defogging Performance of Automobile Defroster using Vortex Generators

Fog on the automotive windshield interferes with the sight of the driver and causes serious safety problems; thus, removing it rapidly has been a longstanding goal in the automobile industry. In this study, we propose a novel method for improving the defogging performance of the defroster without its structural alteration by using vortex generators (VGs). To optimize the performance of the VGs, we performed particle image velocimetry experiments, an evaporation measurement experiment, and a numerical simulation for visualizing the airflow from the defroster inlet. The dimensions of the VG (height h = δ and length l = 5δ) were selected according to the boundary-layer thickness, δ, of the lowest-flow rate (ulow = 0.33 m/s) used in the defroster inlet. We employed a dimensionless parameter, i.e., the secondary flow intensity (Se), to quantify the intensity of vortices for several angles of attack (30°, 45°, and 60°). The results indicated that the vortices generated from VGs with a 30° angle of attack retained their maximum intensity until they reached the vision area of the driver. Additionally, we explored two different configurations of VGs—co-rotating and counter-rotating—and concluded that the counter-rotating configuration had higher performance than the co-rotating configuration. The optimized VGs were directly inserted in the defroster inlet and improved the defogging performance by approximately 10%. The proposed method is applicable to various automobile models for enhancing the performance of the defroster regardless of the interior volume, air-ventilation performance, and other conditions, such as the number of passengers and outside temperature.

The Effect of Aspect Ratio on Wall Pressure Fluctuations at a Wing-Plate Junction

AbstractMeasurements of the wall pressure fluctuations near a wing-plate junction were made for wings with three different aspect ratios (AR) of 0.2, 0.5, and 1.0 at several angles of attack. The chord-based Reynolds number for each wing was 274,000. The results show that the wall pressure fluctuations are a function of wing AR for cases where AR≤ 1.0. For each wing, the pressure fluctuations are highest upstream of the wing leading-edge due to three-dimensional flow separation; wings with AR = 1.0 and 0.5 show comparable levels, while those with AR = 0.2 show lower fluctuation levels over a wide frequency range. Downstream of the leading-edge, the pressure fluctuations decay rapidly on both sides of the wing until the maximum thickness location after which little variation is observed. The pressure fluctuations downstream of the leading-edge on the suction-side were observed to be comparable for AR = 0.2 and 0.5, while those for AR = 1.0 were higher in magnitude. On the pressure-side, the pressure fluctuations near the leading-edge are a weak function of AR; however, those further downstream remain independent of AR. The pressure fluctuations aft of the wing on the suction-side are more coherent for lower ARs and show higher convection velocity, possibly due to an interaction between the tip and the junction flows for lower ARs.

Numerical investigations of the compressible turbulent flow past wavy-axis cylinder

The compressible turbulent flows past wavy-axis cylinder have been studied numerically using the large-eddy simulation technique. The free-stream Mach number and Reynolds number based on the diameter are 0.75 and 2 × 105, respectively. To investigate the effects of angle of attack on force behaviors and wake characteristics, several angles of attack are adopted, i.e., α = 0°, 15°, 30°, 45°, 60°, 75° and 90°. Results show that there are two different force behaviors, as well as wake characteristics around the critical angle of attack about 45°. One is the effective drag reduction and suppression of fluctuating force with vortex shedding vanishing for α < 45°. The other is obvious rises of drag and fluctuating force with the appearance of vortex shedding for α > 45°. In particular, at α = 90°, force behaviors and wake characteristics of a wavy-axis cylinder are identical to that of a circular cylinder. Furthermore, the mechanisms relevant to different force behaviors and wake characteristics have also been revealed. The first flow state is associated with wave-like separation along the spanwise direction and symmetric flow mode. The attenuated wave-like separation and asymmetric flow mode can give an interpretation for the second flow state.

CFD Analysis of NACA 2421 Aerofoil at Several Angles of Attack

In this paper NACA 2421 Aerofoil is analyzed at several angles of attack ranging from -200 to 200 and with the Reynolds number at 1.8 × 105 and the velocity are 20 m/s. The co-efficient of lift and drag are compared with the standard values in the literature. Variation of pressure co-efficient is plotted in the form of contour. The aerofoil is designed in ANSYS and it is imported to Computational Fluid Dynamics and the variations of CL and CD with respect to various angles of attack is analyzed.

Image-guided chemistry altering biology: An in vivo study of thermoembolization.

RationaleAdvances in image-guided drug delivery for liver cancer have shown a significant survival benefit. However, incomplete treatment is common and residual disease is often found in explanted liver specimens. In addition, the need to treat a malignancy from multiple mechanisms at the same time for optimal outcomes is becoming more widely appreciated. To address this, we hypothesized that an exothermic chemical reaction could be performed in situ. Such a strategy could in principle combine several angles of attack, including ischemia, hyperthermia, acidic protein denaturation, and metabolic modulation of the local environment.MethodsThe University of Texas MD Anderson Cancer Center Institutional Animal Care and Use Committee approved this study. Outbred swine (25–35 kg, 5 control and 5 experimental) were treated under general anesthesia. Embolization was performed with coaxial microcatheter technique in a segmental hepatic arterial branch using either ethiodized oil as control or with thermoembolic solutionBlood samples were obtained before, immediately after, and the day following the procedure just before CT scans and euthanasia. Livers were explanted and samples were obtained for histologic analysis.ResultsAll animals survived the procedure and laboratory values of the control and experimental groups remained within normal limits. The control group had a diffuse or cloudy pattern of attenuation on follow-up CT scan the day after, consistent with gradual antegrade sinusoidal transit of the embolic material. The experimental group had clearly defined vascular casts with some degree of peripheral involvement. At histology, the control group samples had the appearance of normal liver, whereas the experimental group had coagulative necrosis in small pale, punctate areas extending several hundred microns away from the treated vessels and a brisk inflammatory response just outside the margins.ConclusionIn situ chemistry via thermoembolization shows early promise as a fundamentally new tactic for image-guided therapy of solid tumors.

An explicit power-law-based wall model for lattice Boltzmann method–Reynolds-averaged numerical simulations of the flow around airfoils

In this paper, an explicit wall model based on a power-law velocity profile is proposed for the simulation of the incompressible flow around airfoils at high Reynolds numbers. This wall model is particularly suited for the wall treatment involved in Cartesian grids. Moreover, it does not require an iterative procedure for the friction velocity determination. The validation of this power-law wall model is assessed for Reynolds-averaged Navier-Stokes simulations of the flow around a two-dimensional airfoil using the lattice Boltzmann approach along with the Spalart-Allmaras turbulence model. Good results are obtained for the prediction of the aerodynamic coefficients and the pressure profiles at two Reynolds numbers and several angles of attack. The explicit power-law is thus well suited for a simplified near-wall treatment at high Reynolds numbers using Cartesian grids.

Numerical simulation of aerodynamic characteristics and heating for grid fin missiles

A grid fin is an unconventional missile control surface comprising an outer frame supporting an inner grid of lifting surfaces. Although the topic of grid fin aerodynamics has been studied by many researchers, only a few have considered aerodynamic heating, generating a high-quality structured grid that remains to be a difficult task. An effective method of grid partition and an aerodynamic prediction method to simulate the viscous flow fields of grid-fin configurations at supersonic Mach numbers have been developed. Multi-block and H-O-type grid treatments are developed for complex grid fin configurations. The viscous flow over a tail-controlled missile with grid fins at a Mach number of 2.5 and several angles of attack is calculated using computational fluid dynamics. Additionally, the heat flux distribution of grid fins is investigated, and the effects of shock wave interaction on heat flux are analyzed. The numerical results show good agreement with the measured data, and confirm that this method is an effective way to numerically simulate viscous grid fin flow fields. Furthermore, the aerodynamic heating results show that, because the peak heat flux on the shock wave interaction region is lower than that on the leading edge of the grid fin, it does not affect the thermal protection of the grid fin.

A COMPUTATIONAL STUDY OF THREE-DIMENSIONAL LAMINAR SEPARATION ON A PROLATE SPHEROID AT INCIDENCE

This paper presents a computational study of three-dimensional laminar separation on a prolate spheroid at incidence. The fully- elliptic Navier-Stokes and continuity equations are solved using the regular grid, finite-analytic discretization, a PISO-type velocity- pressure coupling algorithm, and method of lines. An O-O type body-conforming grid, which is suitable for the detailed study of the problem, is used in the computation. An overview of the approach is given, and numerical results are presented and discussed for a 6:1 prolate spheroid for several angles of attack. The latter includes comparisons with available experimental data. The computational results display detailed flow structures in the post-separation region and near wake, such as the generation and development of the girthwise and longitudinal vortices or the separation patterns which cannot be classified by the conventional open- and closed-type separation models.

Vortex force map method for viscous flows of general airfoils

In a previous paper, an inviscid vortex force map approach was developed for the normal force of a flat plate at arbitrarily high angle of attack and leading/trailing edge force-producing critical regions were identified. In this paper, this vortex force map approach is extended to viscous flows and general airfoils, for both lift and drag forces due to vortices. The vortex force factors for the vortex force map are obtained here by using Howe’s integral force formula. A decomposed form of the force formula, ensuring vortices far away from the body have negligible effect on the force, is also derived. Using Joukowsky and NACA0012 airfoils for illustration, it is found that the vortex force map for general airfoils is similar to that of a flat plate, meaning that force-producing critical regions similar to those of a flat plate also exist for more general airfoils and for viscous flow. The vortex force approach is validated against NACA0012 at several angles of attack and Reynolds numbers, by using computational fluid dynamics.

Identifying Opportunities for Reducing Nacelle Drag

The accurate prediction of drag caused by bluff bodies present in aerospace applications, particularly at high angles of attack, was a challenge. An experimental and numerical investigation of a nacelle intended for fuselage-mounted aircraft engines was completed at several angles of attack between 0 deg and 45 deg with a Reynolds number of 6 × 105. Steady-flow simulations were conducted on hybrid grids using ANSYS fluent 15.0 with preference given to the realizable k–ε turbulence model. Both total drag and the pressure-to-viscous drag ratio increased with angle of attack as a consequence of greater flow separation on the suction surface. Near-field and far-field drag predictions had grid uncertainties below 2.5% and were within 10% of experiment, which were less than the uncertainties of the respective force balance and outlet traverse data at all angles of attack. Regions were defined on suction-side x-pressure force plots using the validated computational fluid dynamics (CFD) data-set that showed where and how much drag could be reduced. At 20 deg angle of attack, there was a potential to reduce up to 20% drag contained within the separated flow region.

Wind induced vibrations of a high tapered obelisk: wind tunnel tests, numerical analysis and design of countermeasures

The structure studied in this paper is a 85 meters high tapered obelisk, made of reinforced concrete for the first 9 meters and of steel welded plates for the upper 76 meters. Its bluff cross section consists of two closely spaced triangular sections that are scaled linearly with the height from ground. Having a complex bluff section and being a light structure, aerodynamic instabilities and vortex induced vibrations were investigated using a mixed experimental-numerical approach, in order to define wind loads for the structural design, and possible interventions aimed at mitigating the dynamic effects due to wind action. Exploiting the regular tapering of the obelisk section, a rigid sectional model with constant section was initially tested in wind tunnel: static aerodynamic coefficients and vortex-induced response as a function of the Scruton number were measured for several angles of attack. The experimental sectional results were successively used to assess numerically the response of the structure considering tapering, the gradient of wind speed, the modal shapes, and the correlation of wind actions. Even though the numerical analysis showed that the tapering drastically reduces aerodynamic issues, the achieved results underlined the pressing need to increase the damping of the structure in order to avoid galloping and vortex induced vibrations for wind speeds within the design range; to this aim tuned mass dampers were designed.

Tonal noise of a controlled-diffusion airfoil at low angle of attack and Reynolds number

The acoustic signature of a controlled-diffusion airfoil immersed in a flow is experimentally characterized. Acoustic measurements have been carried out in an anechoic open-jet-wind-tunnel for low Reynolds numbers (from 5 × 10(4) to 4.3 × 10(5)) and several angles of attack. As with the NACA0012, the acoustic spectrum is dominated by discrete tones. These tonal behaviors are divided into three different regimes. The first one is characterized by a dominant primary tone which is steady over time, surrounded by secondary peaks. The second consists of two unsteady primary tones associated with secondary peaks and the third consists of a hump dominated by several small peaks. A wavelet study allows one to identify an amplitude modulation of the acoustic signal mainly for the unsteady tonal regime. This amplitude modulation is equal to the frequency interval between two successive tones. Finally, a bispectral analysis explains the presence of tones at higher frequencies.

Numerical assessment of an L-shaped Gurney flap for load control

The aerodynamic performance of a novel trailing edge L-shaped flap design is characterized numerically by means of computational fluid dynamics. The device is primarily thought for aerodynamic load adaptation to flight conditions. The device could be applied on a broad range of flying vehicles, like rotorcraft, for which it has been primarily designed, and also fixed wing aircraft and wind turbines. The operation of this movable surface is twofold. On one side, when the device is deployed downward, it acts as a Gurney flap, allowing the increase of the aerodynamic lift, without severe drawbacks in terms of drag rise. On the other side, when it is deflected upward, it is found capable to significantly alleviate the negative effects of stall. Simulations are carried out on a NACA 0012 airfoil equipped with the present L-shaped device at several angles of attack, both in linear and stall regimes. The reliability of numerical computations is supported by comparisons with pressure measurements and PIV surveys. Moreover, for small angles of attack, a Mach sensitivity analysis is performed, to assess the effects of compressibility on the L-shaped flap. Additionally, this work highlights how such device, when designed appropriately, can even delay the static stall onset.

Aerodynamic performance of a circulating airfoil section for Magnus systems via numerical simulation and flow visualization

The lift to drag ratio is the most determining factor in power efficiency of wind conversion systems such as wind turbines. The lift to drag ratio can be enhanced considerably using circulating airfoil shapes. In this research, the NACA0021 airfoil is modified and manufactured to form a treadmill like circulating shape. Aerodynamic performance of the treadmill shape is computationally and experimentally investigated. In the experiment, the smoke flow visualization is conducted in a small wind tunnel to study flow features such as separation and stagnation points. Computational method is based on the finite volume discretization of RANS (Reynolds Averaged Navier–Stokes) equations and the shear stress transport (k–ω SST (shear-stress transport)) turbulence modeling. Magnus effects are investigated under various speed ratios (speed of circulating surface to the wind speed) and several angles of attack. The numerical and flow visualization results reveal some main changes to flow features including full removal of separation zone above moving surfaces. At the speed ratio of 3, zero angle of attack and flow Reynolds number of 94,000, an impressive lift to drag ratio of 130 is obtained for the circulating airfoil whilst the maximum attainable value is merely 45 for the original NACA0021 airfoil.

NUMERICAL INVESTIGATION OF WINGLET ANGLES INFLUENCE ON VORTEX SHEDDING

Wingtip devices are usually intended to improve the efficiency of fixed-wing aircraft. There are several types of wing tip devices, and although they function in different manners, the intended effect is always to reduce the aircraft's drag by partial recovery of the tip vortex energy. Wingtip devices can also improve aircraft handling characteristics and enhance safety for following aircraft. Such devices increase the effective aspect ratio of a wing without materially increasing the wingspan. The purpose of this project is to analyse different types of winglets using Auto CAD, GAMBIT and FLUENT and then, to find out what happens when winglets are linked to wingtips and to study about the aerodynamic properties of spiroid winglets which are still under research. One wing model without winglet and three wing models with winglets were created and drawn in Auto CAD and they were meshed in GAMBIT using geometry data gathered from research papers. Those models were read into Fluent where flow boundary conditions were applied. The wing without winglet, the wings with spiroid winglets and the wings with other kinds of winglets performance were analyzed in several angles of attack and the drag coefficient was compared when the aircraft is taking off. Wingtip vortices from models were checked, studied and compared. The best winglet model reduces drag coefficient and wingtip vortices from wing without winglet model and it will be pointed out at the end of this project. --------------------------------------------------------------------***----------------------------------------------------------------------

Lift Augmentation Based on Flap Deflection With Dielectric Barrier Discharge Plasma Flow Control Over Multi-Element Airfoils

The effect of the lift augmentation of multi-element airfoils with increased flap deflection and dielectric barrier discharge (DBD) plasma flow control on the flap at several angles of attack (AOAs) is investigated numerically and experimentally. A phenomenological body force model is employed to simulate the DBD actuators at Re = 1.03 × 106. The simulation results show that the atmospheric plasma generated by the DBD actuators completely suppresses the flow separation over the flap at several AOAs, and consequently, the lift augmentation of a multi-element airfoil can be achieved over the entire prestall AOA range. A corresponding flow control experiment on a multi-element airfoil performed in a low-speed wind tunnel at a freestream velocity of 30 m/s is presented; in this experiment, particle image velocimetry (PIV) was employed for flow visualization over the upper surface of the flap. The PIV results demonstrate that the flow separation on the flap is suppressed completely by the same DBD actuators used in the simulation.

Passive control of pitch-break of a BWB UCAV model using vortex generator

To examine the effect of vortex generator on pitch-break control for a BWB model having lambda wing configuration, wind tunnel experiments were conducted. Tests were carried out at two freestream velocities of 30 m/s and 60 m/s. Experimental results of the BWB model, which was modified slightly from UCAV 1303, at various angles of attack are presented. Aerodynamic force and moment coefficients and chordwise pressure distributions at several spanwise stations are included. Spanwise location of a vortex generator was selected based on pressure distributions of the BWB model at several angles of attack and through a preliminary test. Well known pitch-break or pitch-up phenomenon was identified to occur at a specific angle of attack for the case without vortex generator. When the vortex generator was installed, this pitch-break was found to be delayed to a much larger angle of attack, which might well be adopted for efficient flight control.

Screening-based translation of public research encounters painful problems.

Whether identified through high throughput screening or in silico screening, and whether target-based or phenotypic, sets of hits will contain chemical con artists. Such pan-assay interference compounds (PAINS) and other subversive compounds continue to pollute the scientific literature. There are several angles of attack to aid identification of such nonprogressable molecules. One of these rules above all, and this is a demonstration of genuine structure-activity relationships. Recognition of this, which will require a greater effort in medicinal chemistry, will be of general benefit.

Static loads to simulate dynamic effects of wind on hyperbolic paraboloid roofs with square plan

The main international standards do not report any specific information (e.g. pressure coefficients) for wind-induced loads on tensile suspended roofs with hyperbolic paraboloid shape, that require therefore ad hoc wind tunnel tests or CFD analyses even in the preliminary design stage. This motivated a wide and parametric investigation aimed to explore the general trend of their aerodynamic behaviour, and experimental tests on in-scale models were performed in the CRIACIV boundary layer wind tunnel (see Rizzo, 2009; Rizzo et al., 2011, 2012), to measure pressure fields for several angles of attack of the incoming wind on different models of hyperbolic paraboloid roofs. On the base of experimental results and of finite element analyses for the sample case of square footprint, this paper explores the possibility of defining equivalent static pressure fields able to reproduce the envelope of dynamic displacements of the cables net.