Top PDF Formation and near-field dynamics of a wing tip vortex

Formation and near-field dynamics of a wing tip vortex

Formation and near-field dynamics of a wing tip vortex

161 Effects of Boundary Layer and Tip Geometry Vortex lines of opposite sign annihilate each other Vortex lines coming from the wing surface boundary layer Rectangular Tip Case Vortex li[r]

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Mean flow and turbulence measurements in the near field of a fighter aircraft wing-tip vortex at high Reynolds number and transonic flow conditions

Mean flow and turbulence measurements in the near field of a fighter aircraft wing-tip vortex at high Reynolds number and transonic flow conditions

The model construction involved the assembly of three major components: a stainless steel central section with a one piece wing box, an aluminium alloy forebody with integral leading edge extensions (LEX) and a stainless steel rear fuselage. These components were assembled through bolted and spigotted joints. Through-flow air inlets were fitted without using any internal chokes (ie. fully open). Vertical fins were bolted to the rear fuselage. Due to mechanical interference with the articulated sting used to support the measurement probe, the horizontal stabilators were removed. However, since all measurements were well upstream of the location of the stabilators, this was not expected to have any effect on the results. Boundary layer transition strips were placed on the wings, LEX, vertical fins and forebody of the model. Due to the particular wing geometry, the flow structure in the vicinity of the wing-tip can be expected to be considerably more complex than that typically investigated in tip vortex studies using rectangular half- wings of symmetrical profile. AIM-9 sidewinders were mounted on the wing-tips as shown in Figure 2, and thus the resulting flow was due to the interaction of the wing-tip vortex, the wake of the main body of the missile (similar to an ogive cylinder), and the additional vortical flow generated by the canards and fins of the AIM-9. The underwing of the model was clean (ie. no stores or pylons were installed). Wing flaps were bolted to the wing box and set to zero deflection.
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Detached-Eddy Simulation of a Wing Tip Vortex at Dynamic Stall Conditions

Detached-Eddy Simulation of a Wing Tip Vortex at Dynamic Stall Conditions

The structure of the tip vortex generated by a square NACA0015 wing was numeri- cally studied using RANS and DES methods. The problems considered include the stationary wing fixed at various angles of attack (AOA) and the wing in pitching os- cillations. These problems were experimentally investigated by Birch and Lee [3, 2]. They measured velocity components at grid points with uniform spacing of 3.2 mm on a rectangular plane located at x/c = 1. In our numerical study, we interpolated the velocity components on the similar grid points from the simulated flow filed. Our purpose is to compare the performance of RANS and DES models to predict the near-field structure of the tip vortex and the onset of the static and dynamic stall. For the vortex visualization in the 3D flow field, we adopted the λ 2 method
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A vortex-based tip/smearing correction for the actuator line

A vortex-based tip/smearing correction for the actuator line

Abstract. The actuator line (AL) was intended as a lifting line (LL) technique for computational fluid dynamics (CFD) applications. In this paper we prove – theoretically and practically – that smearing the forces of the actuator line in the flow domain forms a viscous core in the bound and shed vorticity of the line. By combining a near-wake representation of the trailed vorticity with a viscous vortex core model, the missing induction from the smeared velocity is recovered. This novel dynamic smearing correction is verified for basic wing test cases and rotor simulations of a multimegawatt turbine. The latter cover the entire operational wind speed range as well as yaw, strong turbulence and pitch step cases. The correction is validated with lifting line simulations with and without viscous core, which are representative of an actuator line without and with smearing correction, respectively. The dynamic smearing correction makes the actuator line effectively act as a lifting line, as it was originally intended.
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Experimental investigation of wing tip vortices in the near-field

Experimental investigation of wing tip vortices in the near-field

The vortex core obtained from Q-criterion is depicted in Figure 3(b). Here, only the region, satisfying the condition Q>80000, is shown for clarity to eliminate small descrete regions of vorticity in the vicinity of the vortex core. As can be seen from Figure 3(b), the vortex origin obtained from CSL-method corresponds to the maximum value of Q. However, the vortex core origin is displaced from the geometric center, which is sometimes used for preliminary vortex identification from low density areas of the seeded tracer particles. A similar analysis for other angles of attack and different distances from the trailing edge has shown that vortex position obtained using CSL-method correspond to maximum value of Q, and that low density of seeded tracer particles can be used only as an estimate of the vortex origin.
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Computational Prediction of Tip-Vortex of a Swept Wing

Computational Prediction of Tip-Vortex of a Swept Wing

Abstract: The near-field flow structure of a wing tip vortex behind a sweptback and tapered NACA 0015 wing was investigated using Computational Fluid Dynamics (CFD) code at Re of 1.81 x 105. In this paper, Numerical simulations of the tip vortices was carried out at a geometric angle of attack 8° and the numerical results of tangential velocity of tip vortex is compared with the experimental result done by P. Gerontakos and T. Lee at McGill University low speed wind tunnel at the velocity equal to 35 m/s. The numerical result that was obtained by using CFD code shows a good agreement with the experimental result. The coordinates of the vortex-core location are closely captured along the downstream of flow and the variation of the vortex flow quantities with different angle of attack are investigated. Also circulation at three different downstream location of the trailing edge are calculated.
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Vortex formation and recirculation zones in left anterior descending artery stenoses: computational fluid dynamics analysis

Vortex formation and recirculation zones in left anterior descending artery stenoses: computational fluid dynamics analysis

Flow patterns may affect the potential of thrombus formation following plaque rupture. Computational fluid dynamics (CFD) were employed to assess hemodynamic conditions, and particularly flow recirculation and vortex formation in reconstructed arterial models associated with ST elevation myocardial infraction (STEMI) or stable coronary stenosis (SCS) in the left anterior descending coronary artery (LAD). Results indicate that in the arterial models associated with STEMI, a 50% diameter stenosis immediately before or after a bifurcation creates a recirculation zone and vortex formation at the orifice of the bifurcation branch, for most of the cardiac cycle, thus allowing the creation of stagnating flow. These flow patterns are not seen in the SCS model with an identical stenosis. Post-stenotic recirculation in the presence of a 90% stenosis was evident at both the STEMI and SCS models. The presence of 90% diameter stenosis resulted in flow reduction in the LAD of 51.5 % and 35.9 % in the STEMI models, and 37.6% in the SCS model, for a 10 mmHg pressure drop. CFD simulations in reconstructed model of stenotic LAD segments indicate that specific anatomic characteristics create zones of vortices and flow recirculation that promote thrombus formation and potentially myocardial infarction.
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Formation number of confined vortex rings

Formation number of confined vortex rings

[3, 22] that each vortex ring generator has a specific rate for feeding the flow with the kinetic energy, impulse, and circulation, resulting in specific values for E VR ∗ . Figure 7 shows that E ∗ VR is almost constant after the pinch-off and during the entire post-formation phase. This result will be useful in the next section which focuses on the theoretical prediction of the formation number. The time evolution of E VR ∗ for the NS case decreases slightly and displays larger values than those obtained with the PS program for all confinement ratios. We can conclude that the confinement has little effect on the value of the non-dimensional energy E VR ∗ of the pinched-off vortex for confinement ratios D w /D ≥ 4. The values of E VR ∗ obtained for low confinements (D w /D = 8) for both PS and NS injection programs
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Vortex formation by unstable oceanic jets

Vortex formation by unstable oceanic jets

Finally, the modal analysis of the nonlinear evolution is shown in Fig.2b. To perform it, the zonally averaged jet is substracted from the total flow at each instant. Until 32 days, the exponential growth of the fundamental wave k = 0.75 follows the linear instability prediction. The second growing wave (after 16 days) is the first harmonic k = 1.5, which results from the self interaction of the k = 0.75 wave. After 38 days, a second stage begins: long waves (k = 0.25, 0.5) amplify, feeding on the fundamental wave whose energy is depleted. Vortices start detaching (near 56 days) when very long waves amplify to finally dominate.
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Vortex formation with a snapping shrimp claw

Vortex formation with a snapping shrimp claw

Snapping shrimp use one oversized claw to generate a cavitating high speed water jet for hunting, defence and communication. This work is an experimental investigation about the jet generation. Snapping shrimp (Alpheus-bellulus) were investigated by using an enlarged transparent model reproducing the closure of the snapper claw. Flow inside the model was studied using both High-Speed Particle Image Velocimetry (HS-PIV) and flow visualization. During claw closure a channel-like cavity was formed between the plunger and the socket featuring a nozzle-type contour at the orifice. Closing the mechanism led to the formation of a leading vortex ring with a dimensionless formation number of approximate DT*<4. This indicates that the claw might work at maximum efficiency, i.e. maximum vortex strength was achieved by a minimum of fluid volume ejected. The subsequent vortex cavitation with the formation of an axial reentrant jet is a reasonable explanation for the large penetration depth of the water jet. That snapping shrimp can reach with their claw- induced flow. Within such a cavitation process, an axial reentrant jet is generated in the hollow cylindrical core of the cavitated vortex that pushes the front further downstream and whose length can exceed the initial jet penetration depth by several times.
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Suppression of tip vortex cavitation noise of propellers using PressurePoresTM technology

Suppression of tip vortex cavitation noise of propellers using PressurePoresTM technology

Before the pressure-relieving holes implementation, different methods in the literature were reviewed for the mitigation of cavitation and resulting noise. Firstly, the studies of blade geometry modification were investigated. According to [6], the main source of the noise, the pressure fluctuations, can be reduced with propeller geometry modifications. For example, larger skew angles can affect the cavitation dynamics reducing pressure fluctuations, noise and vibration [7–9]. Another solution for cavitating noise reduction is by increasing the number of blades which can also reduce the unsteady force on each propeller blade [10]. By improving the finishing of the blade surfaces, modifying the trailing edge [11], changing the blade area, or optimisation of blade pitch distribution might also be further solutions for the mitigation of cavitation noise.
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Tracking a Tip Vortex with Adaptive Vorticity Confinement and Hybrid RANS LES

Tracking a Tip Vortex with Adaptive Vorticity Confinement and Hybrid RANS LES

In the following section the simulation results will be analysed and compared to the experimental data. The simulation results are evaluated after 0.6 s time each, by then the flow has passed the measurement region ( x c ∈ [ 0,30 ] ) more than three times. The presented velocities are averaged values over a time period of 0.1 s. Before showing results, the way how the velocity profiles are extracted from the simulation data is presented. These profiles will later be compared to tangential and axial velocity profiles through the core provided by Devenport et al . The procedure how the experimental data is processed to gain the velocity profiles is explained in Section 4. The corresponding procedure for the simulation data is described in the following. Therefore, it is important to state that the presented simulation results show the absence of vortex wandering. The temporal change of the vortex centre is at least several orders of magnitude smaller than the actual core radius. Even a reduction of the time step by a factor of eight showed no wandering effects on the medium mesh. This supports the conclusions given by Devenport et al ., that wandering may originate from unsteady effects in the wind tunnel. Not all of these effects are captured by the model and setup, this refers e.g. to the inflow condition or the modelling of the wing with a completely fixed grid.
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Reflection mode scanning near field optical microscopy: Influence of sample type, tip shape, and polarization of light

Reflection mode scanning near field optical microscopy: Influence of sample type, tip shape, and polarization of light

As was explained in previous sections, surface topogra- phy without associated strong optical contrast complicates the issue of resolution in R-SNOM. Several systems contain optical contrast without any associated topography. One of these is single-molecule detection, which has previously been demonstrated with SNOM; 21 another is magneto-optics. Faraday effect SNOM imaging has already been demonstrated, 22 but little work has been done to date on Kerr effect SNOM 23,24 which is potentially more useful as most conventional magneto-optic materials are relatively opaque. Here we show that Kerr effect SNOM imaging is indeed possible on flat samples, and with a resolution of 60 nm or more. The sample used for these experiments was a magnetic Co/Pt multilayer 25 with a series of tracks of prewritten bits of dimension and spacing in the range 400–800 nm, depending on the particular area of the sample. This sample is magne- tized out of plane, and the polar Kerr rotation for normally incident light at 635 nm is ; 0.25°. It is known that SNOM fiber tips may reach temperatures of over 500 K 26 due to the light within the tip being absorbed by the metal coating. As the Curie point of our sample was 650 K, there was the possibility of unintentionally erasing the bit pattern while trying to image it. To avoid this, we coupled the minimum comfortable amount of light into the tip, resulting in a de- tected signal of 1.5 nW. The aperture diameter was of the
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Vortex dynamics, combinatorics and statistics

Vortex dynamics, combinatorics and statistics

This report represents an overview of the interconnections between the dynamics of large vortex systems, combinatorics, n-body problems and statistical mechanics. The combinatorial perturbation method for the 2D vortex problem is discussed the essential combinatorial sym- plectic transformations to Jacobi-type variables which are based on a binary tree algorithm, is introduced and extended to the 3D vortex problem. Combinatorial and graph-theoretic results which are motivated by the computational needs of the vortex problem, are mentioned. They include new results on sign-nonsingular patterns and noneven digraphs. A simplied singular limit of the 3D Hamiltonian for vortex dynamics is derived and its basic properties discussed. The 2- and 3-body problems in this simple model is studied.
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Energization of Boundary Layer Over Wing Surface By Vortex Generators

Energization of Boundary Layer Over Wing Surface By Vortex Generators

Abstract— The issue taken into consideration is sudden increase in drag over an aircraft wing due to three dimensional flow, tip vortices and flow separation. When flow separates its displacement thickness increases sharply this modifies the outside potential flow and pressure field. The pressure field modification results in an increase in pressure drag, and if severe enough will also result in loss of lift and stall. This study presents computational analysis results of a prototype wing with and without vortex generators of two different shapes located at leading and trailing edges of a linear wing. Here both wind tunnel testing and computational fluid dynamic analysis is carried out. The effect of the vortex generators are studied in four different cases. Nine sets of rectangular shaped vortex generators inclined at 15 degree were placed in the leading edge and trailing edge of the wing, nine sets of ogive shaped vortex generators inclined 15 degree were placed in the leading edge and trailing edge of the wing, are the cases analyzed. The studies also focus on prevention of downstream flow separation and improve overall performance by reducing drag. Both analytical and experimental results are compared where it shows that the pressure over the upper surface increases, so that the boundary layer is reenergized and attached with the body surface thus reducing the drag.
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Potassium dynamics in the soil and yield formation in a long term field experiment

Potassium dynamics in the soil and yield formation in a long term field experiment

Soil testing has to provide a basis for the proper ferti- liser recommendation for maximum yields and best qual- ity simultaneously minimising unproductive losses. As K fixation and buffer capacity can vary considerably be- tween sites due to different mineral composition and site history, choosing the right amount of K fertiliser is not an easy task. For this reason a long-term field experiment was established on Luvisol derived from loess, which is representative for the region close to Cologne (Germa- ny), to examine the efficiency of kainite, potash magne- sia, muriate of potash and potash sulphate as K fertilisers in a rotation of crops. According to Kick and Poletschny (1974) the higher K supply increased the K concentration in beets and potatoes and in the straw of cereals, irre- spectively of the K fertiliser form. The K concentration of the grain remained unchanged. Beets and potatoes reacted to the higher KCl supply immediately by in- creased K concentrations. The low K application rates were not sufficient to compensate K removal, and thus the fraction of the lactate soluble K decreased. In the case of the high K application rates, the fraction of lac- tate soluble K increased slightly.
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The field testing of a vortex sewage overflow

The field testing of a vortex sewage overflow

The samples show no significant difference between inflow and spill flow, which means the overflow has little or no effect upon the pollutants gathered by the samplers. These will be the dissolved material and the fine suspended matter with densities close to that of water. Very little floating matter was observed in the samples, and only small quantities of fine settled material. Other matter in the storm sewage is perhaps filtered out by the coarse inlet filters on the sample pipes, or does not reach the sampler since it floats near the soffit or runs along the floor of the sewer (samples were taken from the middle of the flow). The lack of floating matter ties in with the results from analysing the gross solids caught in a sack from the dry weather flow. These suggested only about 5% of the material floated.
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Dynamics of vortex fronts in type II superconductors

Dynamics of vortex fronts in type II superconductors

Superconductors are materials characterized not only by a perfect conduc- tance below a critical temperature, as was first discovered by Kamerlingh Onnes in 1911 in Leiden, but also by the diamagnetic property of expelling an external magnetic field, the so called Meissner-Ochsenfeld effect [1]. In type II superconductors for external fields between the two temperature-dependent values H c1 and H c2 , flux penetration occurs in the form of quantized flux lines or vortices, with a quantum flux φ 0 = hc/2e [2]. These are elastic and interacting objects, whose fascinating physics has attracted many scientists in the last decades. After the discovery of the high-T c superconductors, the richness of the phenomenology of vortices, both in their static and dynam- ical properties, has led to the introduction of the new concept of “vortex matter” as a new state of matter [3]. From the technological point of view, the intense research activity on type II superconductors was also stimulated and motivated by the fact that, when vortices move they induce dissipation, due to the normal nature of the cores, and therefore the superconducting property of perfect conductivity is lost.
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Geometry and dynamics of vortex sheets in 3 dimensions

Geometry and dynamics of vortex sheets in 3 dimensions

associated with g. We may indicate the degree of a homogenous form, homogenous chain or homogenous distribution by writing it underneath the form, chain or distribution. The interior, or contraction, operation on a form α, taken with respect to the vector field X, is denoted ι X α. Most tensor

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A new non linear vortex lattice method : applications to wing aerodynamic optimizations

A new non linear vortex lattice method : applications to wing aerodynamic optimizations

The theory and the mathematical model behind the nonlin- ear VLM are detailed in Section 2. Then, in order to test the validity of the method, multiple test cases are performed. Sec- tion 3 begins with a grid convergence study to establish the sur- face mesh requirements. The linear implementation of the VLM code is verified using two reference cases. Validation tests for the new nonlinear VLM formulation are performed considering three wings of different planform shapes. Numer- ical results expressed in terms of lift, drag and pitching moment coefficient obtained with our code and with a well- known VLM code are compared against wind tunnel experi- mental data. Section 4 includes two applications of the nonlin- ear VLM for wing design and optimization. The first application concerns the redesign of an UAS wing in order to increase its lift-to-drag ratio. The advantage of the new method is that it allows to modify the wing airfoil in addition to changes in wing planform. The second application concerns the determination of the performance improvements obtained through upper surface morphing for an industrial morphing wing technology demonstrator.
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