Starting vortex

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

Controlled leading-edge suction for management of unsteady separation over pitching airfoils

Abstract: The effect on the unsteady surface pressures of controlled suction from a spanwise slot, located at 2% chord in the suction surface of a two-dimensional NACA 0012 airfoil model, was examined in detail for a wide range of pitch rates with a constant velocity ramp motion. The experiments were conducted in the Andrew Fejer Wind Tunnel at the Illinois Institute of Technology's Fluid Dynamics Research Center. The optimum suction required to meet three different control objectives, suppression of the dynamic-stall vortex, delaying detachment of the vortex from the airfoil surface, and maximizing the unsteady lift, was determined for different pitch rates and angles of attack. The pressure data were used to develop specifications for the flow state over the airfoil surface that would meet these objectives. Such specifications are necessary for the development of on-line flow management systems. A procedure was also developed to account for variations in suction and motion history.

The Coherent Structure of Turbulent Mixing Layers. I. Similarity of the Primary Vortex Structure. II. Secondary Streamwise Vortex Structure

Abstract: The primary spanwise organized vortex structure and the secondary streamwise vortex structure of turbulent mixing layers have been investigated Flow visualization motion pictures of a constant density mixing layer were used to measure the properties of the large scale vortices It was found that after an initial transition region mean properties of the large scale vortices reach the expected linear growth with downstream distance required by similarity In the self-similar region, the vortex core area and visual thickness increase continuously during its life-span A theoretical model of probability distribution function for the large-scale vortex circulation was developed This distribution is found to be lognormal and to have a standard deviation, normalized with the mean of 028 From this model the mean life-span of the vortices could also be obtained and was found to be 067 times the mean life-span position The streamwise streak pattern observed by Konrad (1976) and Breidenthal (1978) in plan-view pictures of the mixing layer was investigated, using flow visualization and spanwise concentration measurements It was confirmed that this pattern is the result of a secondary vortex structure dominated by streamwise, counterrotating vortices A detailed description of its spatial relation to the primary, spanwise vortex structure is presented From time average flow pictures, the onset position and initial scale of the secondary structures were determined From concentration measurements, spanwise variations in mean properties, resulting from the secondary structure, were found This also showed an increase of the spanwise scale with downstream distance and the existence of the streamwise vortices in the fully developed turbulent region In this region the mean spacing is found approximately equal to the vorticity thickness

Interaction of Vortex Streets

Abstract: Vortex street eddies shed from multiple cylinders located one behind the other in the plane of flow were observed to interact in a very complex fashion. Contraction, expansion, cancellation, and coalescence of vortices occurred for different values of cylinder separation and Reynolds number. The results appear to have important implications both for turbulence promotion during heat or mass transfer and for theoretical interpretation of vortex street phenomena.

CFD prediction and model experiment on suction vortices in pump sump

Abstract: The sump size is being reduced in order to lower the construction costs of urban drainage pump stations in Japan. As a result of such size reductions, undesirable vortices such as air-entrained and submerged vortices are apt to appear in sumps because of the higher flow velocities. The Turbomachinery Society of Japan (TSJ) Standard S002:2005 states that the appearance of such visible vortices is not permissible for conventional sumps, and experiments with scale models usually have been done to assess the performance of sumps. Such tests, however, are expensive and time-consuming, and therefore, alternative computational fluid dynamics (CFD) methods for evaluating sump performance are desirable. The Research Committee on Pump Sump Model Testing, which is an organization in the TSJ, carried out a benchmark for flows in model sumps. They contributed commercial CFD codes such as “Virtual Fluid System 3D”, “Star-CD 3.22”, “Star-CD 3.26”, and “ANSYS CFX 10.0”. Some of the benchmark results were reported by Matsui, J. at the 23 rd IAHR Symposium in Yokohama, Oct 2006. The remaining results comprise this second paper. The calculated results were compared with experimental ones for flow patterns, locations of vortices, and their vorticity. In the experiments, the critical submergences for flow rates were minutely examined through visual observation with a video camera. The locations of the vortices were obtained by using the laser light sheet visualization method. The velocity and vorticity distribution in the sump were measured by using a PIV method. The following results were obtained. 1) The critical submergence for the air-entrained vortex is almost proportional to the flow rate in the sump. The vortex behavior is unsteady and the duration of the vortex varies greatly. 2) The submerged vortex appears accompanying the air-entrained vortex in the region of low submergences and high flow rates. The critical submergence for the submerged vortex is also proportional to the flow rate. 3) Some CFD codes can predict the visible vortex occurrence and its location for submergence and flow rate conditions with enough accuracy for industrial use. 4) The calculated velocity distribution at the bell entrance qualitatively agrees with the experimental results. However, the agreement is poor in terms of the magnitude and distribution patterns of the vorticity. This difference is caused by the lack of accuracy of the experiment and CFD computation. 5) Predicting the critical submergence for the visible vortices was not imposed in the benchmark. The calculated stream lines and vortex core lines are not able to be used to predict the visible vortices with much accuracy. An additional post-processing such as obtaining the vortex core static pressure and comparing it with ambient pressure for an air-entrained vortex or with the saturated vapor pressure of the water for a submerged vortex would be necessary to predict the visible vortices.