Mesoscale interactions during the genesis and intensification of October 1999 Orissa super cyclone

lkj & ;g loZfofnr rF; gS fd iw.kZ fodflr m".kdfVca/kh; pØokr esa izk;% v{klekuqikfrd lajpuk ikbZ tkrh gS tcfd pØokr ds cuus dh voLFkk esa vR;kf/kd vlaxfr fn[kkbZ nsrh gSA iz’kkar egklkxj esa gky gh esa fd, x, v/;;uksa vkSj izs{k.kksa ls ;g irk pyk gS fd m".kdfVca/kh; pØokrksa dh mRifRr dk irk yxkkus esa eslksLdsy dh ijLij fØ;k,sa egRoiw.kZ Hkwfedk fuHkk ldrh gSaA m".kdfVca/kh; pØokr dh mRifRr ds vk/kqfud fl)kar Hkh mi;qZDr iwoZdfFkr rF; ij vk/kkfjr gSaA bl 'kks/k&Ik= esa vkbZ- vkj- mixzg ls izkIr foEckoyh vkSj cM+s iSekus ij Hkzfeyrk ds {ks=ksa dk fo’ys"k.k izLrqr fd;k x;k gSA ftuesa ;g ns[kk x;k gS fd 1999 esa mM+hlk esa vk, egkpØokr dh Hkh izkjfEHkd voLFkkvksa esa eslksLdsy ls pØokr ds coaMj dh ijLij fØ;kvksa dk irk yxk gSA It is well known that a mature tropical cyclone is known to have a nearly axisymmetric structure but that the formation stage exhibits considerable asymmetry. Recent studies and observations in the Pacific indicate that mesoscale interactions could play an important role in the genesis of tropical cyclones. Modern theories of tropical cyclone genesis are also based on this premise. In this paper, an analysis of the IR satellite imagery and large scale vorticity fields is presented, which shows that mesoscale vortex interactions occur in the early stages of the 1999 Orissa super cyclone also.

Experimental investigation of a rotor blade tip vortex pair

This paper presents the results of an experimental study of two closely spaced vortices generated by a rotating blade with a modified tip geometry. The experiments are carried out in two water channel facilities and involve a generic one-bladed rotor operating in a regime near hover. It is equipped with a parametric fin placed perpendicular to the pressure surface near the tip, which generates a co-rotating vortex pair having a helical geometry. Based on previous results obtained with a fixed wing, a series of small-scale experiments is first carried out, to validate the method of vortex pair generation also for a rotating blade, and to obtain a qualitative overview of its evolution going downstream. A more detailed quantitative study is then performed in a larger facility at three times the initial scale. By varying the fin parameters, it was possible to obtain a configuration in which the two vortices have almost the same circulation. In both experiments, the vortex pair is found to merge into a single helical wake vortex within one blade rotation. Particle image velocimetry measurements show that the resulting vortex has a significantly larger core radius than the single tip vortex from a blade without fin. This finding may have relevance in the context of blade–vortex interactions, where noise generation and fatigue from fluid–structure interactions depend strongly on the vortex core size.

Effects of Wavy Leading-Edge Protuberance on Hydrofoil Performance and Its Flow Mechanism

This paper examines the effects on a Clark-y three-dimensional hydrofoil of wavy leading-edge protuberances in a quantitative and qualitative way. The simulation is accompanied by a hybrid RANS-LES model in conjunction with Zwart-Gerber–Belamri model. Detailed discussions of the stable no-cavitating, unsteady cavitating flow fields and the control mechanics are involved. The force characteristics, complicated flow behaviors, cavitation–streamwise vortex interactions, and the cavitating flow instability are all presented. The results demonstrate that protuberances acting as vortex generators produce a continuous influx of boundary-layer vorticity, significantly enhancing the momentum transfer of streamwise vortices and therefore improving the hydrodynamics of the hydrofoil. Significant interactions are described, including the encouragement impact of cavitation evolution on the fragmentation of streamwise vorticities as well as the compartmentation effect of streamwise vorticities binding the cavitation inception inside the troughs. The variations in cavitation pressure are mainly due to the acceleration in steam volume. In summary, it is vital for new hydrofoils or propeller designs to understand in depth the effects of leading-edge protuberances on flow control.

Experiments in Shock-Vortex Interactions

Studies of shock-vortex interactions in the past have predominantly been numerical, with a number of idealizations such as assuming an isolated vortex and a plane shock wave. In the present case the vortex is generated from flow separation at a corner. A shear layer results which wraps up into a spiral vortex. The flow is impulsively initiated by the diffraction of a shock wave over the edge. The strength of the shock determines the nature of the flow at the corner and that induced behind the diffracted wave. A wide variety of cases are considered using different experimental arrangements such as having two independent shock waves arriving at the corner at different times, to reflecting the diffracting wave off different surfaces back into the vortex, and to examining the flow around bends where the reflection off the far wall reflects back onto the vortex. The majority of studies have shown that the vortex normally retains its integrity after shock transit. Some studies with curved shock waves and numerous traverses have shown evidence of vortex breakup and the development of turbulent patches in the flow, as well as significant vortex stretching. Depending on the direction of approach of the shock wave it refracts through the shear layer thereby changing the strength and direction of both. Of particular note is that the two diffracted waves which emerge from the vortex as the incident wave passes through interact with each other resulting in a pressure spike of considerable magnitude. An additional spike is also identified.