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121.
《Applied Scientific Research》1996,57(3-4):279-290
This paper presents a new technique to produce controlled stretched vortices. Intense elliptical vortices are created by stretching
of an initial vorticity sheet. The initial vorticity comes from a laminar boundary layer flow and the stretching is parallel
to the vorticity vectors. This low velocity flow enables direct observation of the formation and destabilization of vortices.
Visualizations are combined with quasi-instantaneous measurements of a full velocity profile. The velocity profile is obtained
with an ultrasonic pulsed Doppler velocimeter. The evolution of the central diameter of the vortices is related to the stretching.
It is observed that destabilization occurs by pairing of two vortices, by hairpin deformation, and by breakdown of vortices
into a “coil shape”. 相似文献
122.
A. Yu. D’yachenko V. I. Terekhov N. I. Yarygina 《Journal of Applied Mechanics and Technical Physics》2006,47(5):671-678
The process of vortex formation in a cavity with inclined walls, which has a moderate aspect ratio, is experimentally studied,
and the distribution of pressure coefficients is measured. The angle of inclination of the side walls ϕ is varied from 30
to 90°. It is found that the flow in the cavity becomes unstable in the range of inclination angles ϕ = 60–70°. Flow reconstruction
occurs, which substantially alters the surface-temperature and static-pressure distributions. Large changes in these characteristics
and their nonuniform distributions for these angles are observed across the cavity on its frontal wall and on the bottom.
For small angles (ϕ = 30 and 45°), the pressure on the rear wall drastically increases, which leads to a small increase in
pressure averaged over the entire cavity surface.
__________
Translated from PrikladnayaMekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 5, pp. 68–76, September–October, 2006. 相似文献
123.
In the present work, a further numerical simulation of the starting flow around a flat plate normal to the direction of motion
in a uniform fluid has been made by means of the discrete vortex method. The secondary separation occurring at rear surface
of the plate is explored, and predicted approximately using Thwait's method. The calculated results show that in the early
stages of the flow secondary separation does occur. The evolution of flow field, the vortex growing process and the characteristics
of secondary vortices have been described. The time dependent drag coefficients, the vorticity shed from the edges and rear
surface, and the separation positions are calculated as well as the distributions of velocity and pressure on the plate. In
the case of flow normal to the plate, the calculated secondary vortices are weak. Their existence will change the local velocity
distributions and affect pressure distributions. However, the effect on drag coefficient is negligible. 相似文献
124.
Ling Guocan 《Acta Mechanica Sinica》1988,4(3):211-222
In the present paper the mechanism involved in vortex shedding flows is investigated in detail. In the early stage of the
unsteady separated flow the interaction between secondary vortices and primary vortices is quite strong. In the later stage
of the flow, corresponding to the vortex shedding the recirculating flow region on each side of the aft body goes through
such a cycle: growth-contraction-growth, the secondary separation occurs periodically rather than continuously. The reduction
of circulation is taken into account in three cases with different decay factors to study its influence on the prediction
of main flow characteristics. Results show that to simulate vortex shedding flow it is necessary to include the reduction
of circulation to bring the calculated results into good agreement with experiments. An improved discrete vortex model is
suggested in which both the secondary separation and the reduction are incorporated. The processes of vortex shedding, the
forces prediction and other flow characteristics are given and some discussions are made.
Porject is supported by National Natural Science Foundation of China. 相似文献
125.
Interaction of a supersonic streamwise vortex with an oblique shock wave is considered. A mathematical model of the streamwise vortex is constructed. Three interaction regimes (weak, moderate, and strong) are found. It is shown numerically that vortex breakdown is possible in the case of strong interaction. The influence of the governing parameters on the interaction type is studied. It is shown that the main effect on the interaction type is exerted by the streamwise velocity and angle of the wedge forming the shock wave. The effect of splitting of the primary vortex on the shock wave in the case of moderate and strong interaction regimes is found. 相似文献
126.
The 2D flow about a lentil-shaped body at high incidence in uniform stream is numerically simulated for high Reynolds numbers. The separation points are fixed on the body edges and the vorticity released through a Kutta-like condition is spatially discretized by point vortices. Their Lagrangianinviscid dynamics is described by using both aconformal mapping and aboundary elements method. The present results are in good agreement with previous calculations but still not satisfactory when compared with the experiments.The aim of the present work is to investigate the effect of different Kutta conditions and the effect of different amalgamation procedures in the far wake on global quantities such as theStrouhal number or the total shed circulation. Other remarkable effects induced either by the action of viscosity or by the rising of secondary 3D motion, may not be analyzed by the present simplified model.
Sommario Si studia il flusso attorno ad una lente ad elevata incidenza nelle ipotesi di elevato numero di Reynolds e flusso bidimensionale. I punti di separazione sono fissati sulle estremità della lente e la produzione di vorticità da questi è realizzata con opportune condizioni di Kutta. La dinamica dei vortici è descritta con un modello Lagrangiano non viscoso. I risultati, ottenuti sia con l'uso di una trasformazione conforme che con un metodo agli elementi di contorno, sono in ottimo accordo con i risultati di precedenti simulazioni numeriche, ma non sono ancora soddisfacenti se confrontati con gli esperimenti.Si analizza in termini di grandezze globali del flusso, quali il numero di Strouhal e la circolazione totale rilasciata, l'effetto di due diverse condizioni di Kutta e dell'uso di procedure di compattazione della scia lontana. Si conclude che l'uso di diverse condizioni di Kutta produce risultati pressoché identici mentre l'utilizzo di procedure di compattazione della scia può alterare in modo significativo il numero di Strouhal del flusso. Rimangono da analizzare altre possibili cause del disaccordo con le sperimentazioni quali la diffusione viscosa e la probabile presenza di moti tridimensionali.相似文献
127.
数值研究激波与旋涡的相互作用 总被引:4,自引:1,他引:4
从非定常形式的Euler方程出发,数值模拟了运动激波与旋涡相互作用的非定常流动过程。为保证激波具有较高的分辨率,采用对称型TVD格式进行了数值计算。结果表明。这样可以有效地模拟流场中一些复杂的流动现象,如激波变形、激波分叉和三波点的形成,以及旋涡结构的变化过程等,并与已有的实验流动显示相符良好。同时,也是对TVD格式求解这类问题的一次初步尝试。 相似文献
128.
129.
混合层强化混合的数值研究 总被引:2,自引:0,他引:2
受 Wang & Fiedler(1997)的实验的启发,采用高阶精度的差分格式,通过数值模拟的方法,研究了二维混合层及限于两平板间的二维混合层(二维受限混合层)入口处加振动对提高混合层混合效率的作用.计算结果表明:对二维混合层,振动的频率越低,在混合层中产生的大尺度涡结构的尺度越大,在频率很低时,涡具有相似性;对限于两平板间的二维混合层,在一定的振动频率下,混合层中产生的涡较大而且破碎得也较好,这将有利于混合.这一结论与 Wang & Fiedler(1997)的实验观测到的结果是一致的. 相似文献
130.
A. A. Shtarev 《Fluid Dynamics》2005,40(2):266-272
The variation of the flow-rate of a fluid flowing out of a prefilled cylindrical vessel through sinkholes with a diameter less than 0.1 of the vessel diameter has been studied experimentally. The study was carried out in both the presence and the absence of a vortex funnel around the sinkhole. In these experiments the vessel was filled in such a way that a funnel was formed only when a disk immersed in the fluid was rotated before the sinkhole was opened. The time dependence of the flow-rate is found for various initial heights and rates of artificial swirl. Four different outflow stages were detected. It is shown that for certain flow parameters there is a time interval on which the fluid flow-rate is independent of the column height. A critical rotation velocity W
0* below which (W
0 < W
0*) an intense funnel is not formed is found. A limiting curve approached by all the flow-rate curves in the final stage of outflow is obtained.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 113–121.Original Russian Text Copyright © 2005 by Shtarev. 相似文献