摘要 :
Streamwise vorticity in viscous, compressible, steady flow about aircraft is analysed on the basis of the steady Reynolds-averaged Navier-Stokes equations. It is shown, that Streamwise vorticity can develop in the presence of stre...
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Streamwise vorticity in viscous, compressible, steady flow about aircraft is analysed on the basis of the steady Reynolds-averaged Navier-Stokes equations. It is shown, that Streamwise vorticity can develop in the presence of stream-normal vorticity and can be non-negligible only inside e.g. boundary layers, shock layers, viscous (turbulent) wakes, jet exhausts and propeller slipstreams, but also along streamlines leaving such viscous and heat conduction dominated flow regions on their downstream side (e.g. downstream of shock layers). However, the actual development of Streamwise vorticity then still depends on such local flow characteristics as e.g. streamline curvature and streamline convergence or divergence. Two illustrative examples are discussed.
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The present experimental work is concerned with "twin jets in crossflow" (TJICF) concentrating upon the vorticity distribution and turbulent vorticity transport associated with the dominant vortical structure of the TJICF. The con...
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The present experimental work is concerned with "twin jets in crossflow" (TJICF) concentrating upon the vorticity distribution and turbulent vorticity transport associated with the dominant vortical structure of the TJICF. The configuration of the TJICF consists of a pair of identical jet nozzles and jet-flow conditions at the nozzle exits. The twin jets are issuing normally into a crossflow. The mean-flow velocity vector and associated turbulence statistics of the TJICF are determined using the standard crossed hot-wire anemometry technique. In the present contribution two geometrically symmetric TJICF arrangements, namely tandem and side-by-side arrangements (both with a nozzle centre-to-centre separation of 5D). are examined, focusing upon the dominant vortical structure rather similar to that of the ell-known contrarotating vortex pair of the single JICF. The formation and decay of this dominant cortical structure is closely associated with the turbulent vorticity transport. The two TJICF arrangements under consideration have their own specific vorticity transport features which are. firstly, visualized and interpreted in terms of turbulent vorticity fluxes. Secondly, the vorticity transport analysis shows the vortex-strength decay (i.e. circulation decay) as described by the corresponding integral decay-rate formula. The similarities and differences between the vorticity (distribution and transport) features associated with the two different TJICF arrangements. tandem and side-by-side, and the single-jet case are examined and discussed. The TJICF flow phenomenon represents an interaction of two single JICF and the gross qualitative features of the vortex formation process of the resulting (mean-flow) dominant vortical structure are described. (C) 2003 Elsevier Science Inc. All rights reserved. [References: 24]
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Experiments were conducted to understand the effect of an axial jet on the merging process of a simulated flap-edge and wing-tip corotating vortex pair in the near wake. Cross-flow velocity measurements and flow visualization were...
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Experiments were conducted to understand the effect of an axial jet on the merging process of a simulated flap-edge and wing-tip corotating vortex pair in the near wake. Cross-flow velocity measurements and flow visualization were performed for the three realistic jet positions on both equal and unequal strength like-signed vortices for a range of momentum coefficients. The main finding was that the initial jet position has a vastly contrasting effect on the merging process. If the jet turbulence rapidly interacts with only one of the vortices, severe diffusion of that vortex occurs which ultimately wraps around and becomes consumed by the unaffected vortex structure. The jet causes a reduction in the vortex spacing and an increase in the rotation angle; hence, merging is promoted. If the jet turbulence does not directly interact with either vortex but instead interferes with the mechanism in the outer-recirculation region that advects vorticity to a larger radius, then merging can be retarded. In this case, an increase in vortex spacing and reduction in rotation angle were observed. Increasing the momentum coefficient, hence, introducing more turbulence into the flow, has a greater effect on the merging process. (C) 2008 American Institute of Physics.
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The evolution of vortex system in the wakes of the simplified large
civil aircraft afterbody is simulated with the improved delayed detached
eddy simulation (IDDES) method and adaptive mesh refinement technology.
First of all, ...
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The evolution of vortex system in the wakes of the simplified large
civil aircraft afterbody is simulated with the improved delayed detached
eddy simulation (IDDES) method and adaptive mesh refinement technology.
First of all, the physical characteristics of afterbody vortex system are
presented to perform qualitative analysis. Results based on two-dimensional
kinematic analysis demonstrate that three phases show up in vortical
interaction including formation, wake evolution and wake interaction.
Further, two patterns of vortical interaction are clearly identified as follows:
strong straining interaction (SSI) and strong rotating interaction (SRI).
Compared with SRI, SSI features considerable circulation decrease of 20%
in formation phase and interaction intensity reduction of up to 45% at
downstream wake location of eight-characteristic length. It is attributed to
that the circulation of afterbody primary vortex pair (APVP) has declined in
formation phase due to the remarkable stress deformation imposed by
horizontal tail root vortex pair (HRVP) in SSI, whereas the tip vortex pair
(HTVP) obtains a circulation augmentation for more dramatic convective
diffusion and fluid entrainment in SRI. Above all, the inner connection
between kinematic characteristics and vortex induced drag is revealed
quantitatively, which offers a novel perspective to reduce crusing resistance
of aircraft afterbody.
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摘要 :
The evolution of vortex system in the wakes of the simplified large civil aircraft afterbody is simulated with the improved delayed detached eddy simulation (IDDES) method and adaptive mesh refinement technology. First of all, the...
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The evolution of vortex system in the wakes of the simplified large civil aircraft afterbody is simulated with the improved delayed detached eddy simulation (IDDES) method and adaptive mesh refinement technology. First of all, the physical characteristics of afterbody vortex system are presented to perform qualitative analysis. Results based on two-dimensional kinematic analysis demonstrate that three phases show up in vortical interaction including formation, wake evolution and wake interaction. Further, two patterns of vortical interaction are clearly identified as follows: strong straining interaction (SSI) and strong rotating interaction (SRI). Compared with SRI, SSI features considerable circulation decrease of 20% in formation phase and interaction intensity reduction of up to 45% at downstream wake location of eight-characteristic length. It is attributed to that the circulation of afterbody primary vortex pair (APVP) has declined in formation phase due to the remarkable stress deformation imposed by horizontal tail root vortex pair (HRVP) in SSI, whereas the tip vortex pair (HTVP) obtains a circulation augmentation for more dramatic convective diffusion and fluid entrainment in SRI. Above all, the inner connection between kinematic characteristics and vortex induced drag is revealed quantitatively, which offers a novel perspective to reduce crusing resistance of aircraft afterbody.
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Wakes of upswept afterbodies are often characterized by counter-rotating streamwise vortex pairs which meander in space. One application concerns aft regions of cargo aircraft, which are characterized by a relatively flat upswept ...
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Wakes of upswept afterbodies are often characterized by counter-rotating streamwise vortex pairs which meander in space. One application concerns aft regions of cargo aircraft, which are characterized by a relatively flat upswept base. Here we consider a canonical configuration comprised of a cylinder with upswept basal surface. The resulting longitudinal vortices, which are much closer to each other than wing-tip vortices, can adversely influence paratrooper and cargo drop operations as well as trail-ing aircraft. The unsteady dynamics of these vortices are examined using spatio-temporally resolved Large-Eddy Simulations (LES) and stability considerations. Emphasis is placed on understanding the potential instability dynamics responsible for meandering, which was observed, characterized and quantified at a representative location downstream of the body. The dynamics is then successfully mapped to a matched Batchelor vortex pair, and spatial and temporal stability analyses are performed with both counter-rotating vortices in the computational domain. Both spatial and temporal analyses reveal dipole structures associated with |m| = 1 elliptic modes as dominant modes in afterbody vortices. A short-wave elliptic instability mode is found to dominate the meandering motion in the vortex pair; this mode was stable in the case of an isolated vortex. Further, the strain due to axial velocity plays a key role in the instability and therefore breakdown. The low frequency of the unstable mode (Strouhal number StD & SIME; 0.3 based on cylinder diameter) is consistent with the spectral analysis of meandering in the LES. Stability analyses at very low-wavenumber do not exhibit any unstable mode suggesting an absence of the Crow instability. (C) 2022 Elsevier Masson SAS. All rights reserved.
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An experimental study was performed to evaluate the effect of a cold jet on a single trailing vortex. Flow visualization and particle image velocimetry (PIV) measurements were conducted in wind and water tunnels. The main paramete...
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An experimental study was performed to evaluate the effect of a cold jet on a single trailing vortex. Flow visualization and particle image velocimetry (PIV) measurements were conducted in wind and water tunnels. The main parameters were the ratio of jet-to-vortex strength, the jet-to-vortex distance, the jet inclination angle and the Reynolds number. It was shown that the jet turbulence is wrapped around the vortex and ingested into it. This takes place faster with decreasing jet-to-vortex distance and increasing jet strength. Both time-averaged and instantaneous flow fields showed that the trailing vortex became diffused with its rotational velocity and vorticity levels reduced when the jet is located close to the vortex. The mechanism with which the jet interacts with the vortex is a combination of vortices shed by the jet and the turbulence. No noticeable differences were found within the Reynolds number range tested. The effect of jet on the vortex is delayed when the jet is blowing at an angle to the free stream and away from the vortex such as during take-off.
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The paper deals with intake swirling flow characterization in the cylinder of IC engine. The commonly used method based on the swirl resp. tumble number from angular momentum flux evaluation does not need to give the appropriate v...
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The paper deals with intake swirling flow characterization in the cylinder of IC engine. The commonly used method based on the swirl resp. tumble number from angular momentum flux evaluation does not need to give the appropriate values in some cases. Typically, in the case of two intake ports, a counter-rotating swirl vortex pair is presented. However their summary angular momentum flux is zero a thus corresponding swirl number is zero too. In order to correctly quantify these cases, it is proposed to evaluate so called vorticity numbers, i.e. dimensionless numbers based on vorticity evaluation. Concrete results are evaluated from data obtained using 3-D CFD simulation in AVL FIRE code. Comparison of variously defined vorticity numbers with each other and with the vortex numbers is performed. A practical way of calculating the vorticity numbers was also suggested with regard to possible adverse effects of the velocity gradients at the cylinder wall.
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The interaction of a short cylindrical vortex elongated along the transverse coordinate with a shear flow near a solid surface is considered. A cylindrical vortex with its ends lowered to the bottom of the channel is shown to turn...
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The interaction of a short cylindrical vortex elongated along the transverse coordinate with a shear flow near a solid surface is considered. A cylindrical vortex with its ends lowered to the bottom of the channel is shown to turn into a vortex ring. The obtained qualitative model is verified by experiment.
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In this paper, we present a numerical study on the transverse flow-induced vibration (FIV) of an elastically mounted sphere in the vicinity of a free surface at subcritical Reynolds numbers. We assess the interaction dynamics and ...
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In this paper, we present a numerical study on the transverse flow-induced vibration (FIV) of an elastically mounted sphere in the vicinity of a free surface at subcritical Reynolds numbers. We assess the interaction dynamics and the vibration characteristics of fully submerged and piercing spheres that are free to vibrate in the transverse direction. We employ the recently developed three-dimensional two-phase flow-structure interaction solver to investigate fully and partially submerged configurations of an elastically mounted sphere. To begin, we examine the vortex-induced vibration (VIV) phenomenon and the vortex-shedding modes of a fully-submerged sphere vibrating freely in all three spatial directions. We systematically verify and analyze the mode transitions and the motion trajectories in the three degrees-of-freedom (3-DOF) for the Reynolds number up to 30 000. We next simulate the transversely vibrating (1-DOF) full-submerged sphere over a wide range of reduced velocities 3 收起
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