Starting vortex

About: Starting vortex is a research topic. Over the lifetime, 4785 publications have been published within this topic receiving 100419 citations.

Phenomenology of Kármán vortex streets in oscillatory flow

Abstract: Vortex wakes of circular cylinders at low Reynolds numbers have been investigated Sound waves are superimposed on the flow in mean flow direction In this configuration the Karman vortices are shed at the sound frequency or at subharmonics of the sound frequency The Karman vortex street is treated as a nonlinear self-excited flow oscillator with forced oscillations Using a flow visualization technique a variety of wake structures has been identified as a function of sound frequency and sound amplitude, but independent of the Reynolds number The superimposed sound influences the distribution of circulation and accordingly the shedding mechanism Primary vortex and secondary vortex are shed simultaneously from one side of the cylinder The alternate vortex shedding is arranged spatially and temporally Structures along the vortex axes are revealed

Measurement of tonal-noise characteristics and periodic flow structure around NACA0018 airfoil

Abstract: The characteristics of tonal noise and the variations of flow structure around NACA0018 airfoil in a uniform flow are studied by means of simultaneous measurement of noise and velocity field by particle-image velocimetry to understand the generation mechanism of tonal noise. Measurements are made on the noise characteristics, the phase-averaged velocity field with respect to the noise signal, and the cross-correlation contour of velocity fluctuations and noise signal. These experimental results indicate that the tonal noise is generated from the periodic vortex structure on the pressure surface of the airfoil near the trailing edge of the airfoil. It is found that the vortex structure is highly correlated with the noise signal, which indicates the presence of noise-source distribution on the pressure surface. The vorticity distribution on the pressure surface breaks down near the trailing edge of the airfoil and forms a staggered vortex street in the wake of the airfoil.

Design optimization of the aerodynamic passive flow control on NACA 4415 airfoil using vortex generators

Abstract: The present paper provides an experimental optimization of a NACA 4415 airfoil equipped with vortex generators (VGs) to control its flow separation. To build this optimal configuration an experimental parametric study was conducted on five geometrical parameters: thickness and height of vortex generators, position, orientation angle with respect to the mean flow direction, spacing in the spanwise direction. Moreover, a new configuration that includes micro generators behind the conventional ones was also investigated as a potentially interesting solution. For all these cases wind tunnel tests were performed and compared for different angles of attack and various Reynolds numbers up to 2 10 5 . These experiments enabled us to highlight the main trends to get an optimal design, for which quantitative improvement can be achieved by passive means in terms of aerodynamic performances on NACA4415 airfoil. The results reveal that triangular shape vortex generators are best suited to control boundary layer separation. An optimum angle of VGs is obtained for 12°with a 3 mm distance between vortex generators located at 50% of the chord. It was found that micro vortex generators are very effective in controlling the flow with less parasite drag. The maximum lift coefficient for an airfoil with coupled vortex generators increases by 21% and a flow separation is delayed by 17°. However, this very good performance is counterbalanced by the appearance of parasitic drag. Indeed, it creates a counter-rotating array of vortices with the second raw of micro-vortex generators that reinforce the vortexes strength without any increase in device height.