The Transport of Vortices Through a Turbine Cascade (original) (raw)
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Encounters with Vortices in a Turbine Nozzle Passage
International Journal of Rotating Machinery, 2012
Experiments were conducted on the flow through a transonic turbine cascade. A wide range of vortices was encountered including horseshoe vortices, secondary flows, shock-induced passage vortices and streamwise vortices on the suction surface. In the separation region on the suction surface, a large roll-up of passage vorticity occurred. The blunt leading edge gave rise to strong horseshoe vortices and secondary flows. The suction surface had a strong convex curvature over the forward portion and was quite flat further downstream. Surface flow visualization was performed and this convex surface displayed coherent streamwise vorticity. At subsonic speeds strong von Kármán vortex shedding resulted in a substantial base pressure deficit. For these conditions time-resolved measurements were made of Eckert-Weise energy separation in the blade wake. At transonic speeds, exotic shedding modes were observed. These phenomena all occurred in experiments on the flow around one particular turbine nozzle vane in a linear cascade.
Blade-Vortex Interactions in High Pressure Steam Turbines
2000
i SUMMARY A detailed experimental and numerical investigation of the transport of streamwise (passage) vortices in high-pressure axial turbines and their interaction with the downstream blade rows was performed. The results indicate large variations in the downstream flow field, notably the development of the secondary flows. The mechanism of passage vortex transport was studied in two differently configured high-pressure turbine stages. In the first configuration, the blades are radially stacked while the second configuration features three-dimensionally stacked high-pressure steam turbine blading.
2000
An experimental study of the effect of wake disturbance frequency on the secondary flow vortices in a two-dimensional linear cascade is presented. The flow Reynolds numbers, based on exit velocity and suction side surface length were 25,000, 50,000 and 85,000. Secondary flow was visualized by injecting smoke into the boundary layer and illuminating it with a laser light sheet located at the exit of the cascade.
Development of Vortex Structures in a Turbine Stage Rotor Passage
2008
The article analyses the formation and development of horseshoe vortices in a highpressure turbine stage rotor passage. Two turbine stages are examined: a standard performance stage, revealing regular performance characteristics and distributions of flow parameters, and a lowefficiency stage in which a large separation zone is observed in rotor passages. In the latter stage the interaction of the hub horseshoe vortex with the separation structures has been found to take a highly unsteady and periodic course and be a source of remarkable flow fluctuations.
Organized Streamwise Vorticity on Convex Surfaces With Particular Reference to Turbine Blades
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010
Experiments were conducted on the flow through a transonic turbine cascade and at subsonic speeds past a circular cylinder in cross-flow. These followed extensive work on vortex shedding behind these bodies, displaying the phenomena of energy separation at subsonic speeds; the turbine blades also exhibited exotic vortex-shedding modes in transonic flow. Surface flow visualization was undertaken on the suction surface of the turbine blade and on the circular cylinder. This was effective in providing a time-average mapping of the vortical structures within the blade passage and around the cylinder. The usual phenomena of horseshoe vortices, secondary flows, passage vortices and wall and corner vortices were observed. In addition, and more surprisingly, organized systems of fine-scale streamwise vortices were observed for both cases. Under the influence of the strong favorable pressure gradients on the turbine blade suction surface, the vortices persisted to the trailing edge. For the circular cylinder work, undertaken at an inlet Mach number of 0.5, the streamwise vortices occupied the forward portion of the cylinder, almost to the 83 degree azimuth, and re-appeared after laminar separation. This streamwise vorticity had been predicted and observed previously for low speed flows, with attendant theories for wavelength. The present results have been compared with the predictions giving reasonable agreement.
Some Issues and Developments in Analytical and Experimental Work on Turbine Blade Flows
HAL (Le Centre pour la Communication Scientifique Directe), 2016
ISROMAC 2016 lntematJonal Symposium on Transport Phenomena and Dynamics of Areas where substantial research on planar turbine cascades is ongoing, or is still needed, are identified. Comp:ressibility effects are particularly important and are addressed in the three main sections. The modeling of the shock-boundary layer interaction is not yet reliable. For supersonic speeds the agreement is excellent apart from the crucial region downstream of the shocks. At subsonic speeds the vortices were shed in a classical von Karman vortex street. This resulted in strong base pressure deficits causing high wake losses and ene:rgy separation in the wake. The base pressure deficit and the measurements of wake ene:rgy separation coincide and it is concluded that the two phenomena are both manifestations of von Karman vortex shedding. At Mach numbers above unity the vortex shedding was found to be one of a number of transient shedding patterns.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2017
Hydro turbines operating at partial flow conditions usually have vortex ropes in the draft tube that generate large pressure fluctuations. This unsteady flow phenomenon is harmful to the safe operation of hydropower stations. This paper presents numerical simulations of the internal flow in the draft tube of a Francis turbine with particular emphasis on understanding the unsteady characteristics of the vortex rope structure and the underlying mechanisms for the interactions between the air and the vortices. The pressure fluctuations induced by the vortex rope are alleviated by air admission from the main shaft center, with the water-air two phase flow in the entire flow passage of a model turbine simulated based on the homogeneous flow assumption. The results show that aeration with suitable air flow rate can alleviate the pressure fluctuations in the draft tube, and the mechanism improving the flow stability in the draft tube is due to the change of vortex rope structure and distribution by aeration, i.e. a helical vortex rope at a small aeration volume while a cylindrical vortex rope with a large amount of aeration. The preferable vortex rope distribution can suppress the swirl at the smaller flow rates, and is helpful to alleviate the pressure fluctuation in the draft tube. The analysis based on the vorticity transport equation indicates that the vortex has strong stretching and dilation in the vortex rope evolution. The baroclinic torque term does not play a major role in the vortex evolution most of the time, but will much increase for some specific aeration volumes. The present study also depicts that vortex rope is mainly associated with a pair of spiral vortex stretching and dilation sources, and its swirling flow is alleviated little by the baroclinic torque term, whose effect region is only near the draft tube inlet.
Von Karman Vortices Formation at the Trailing Edge of a Turbine Blade
2008
The paper presents the results of an experimental investigation of the von Karman vortices formation at the blade trailing edge of a large scale turbine cascade. The mean and time varying characteristics of the flow in the trailing edge region were measured by means of a two-component fiber-optic laser Doppler velocimeter over an experimental grid very close to the blade
Study of Various Factors Affecting Secondary Loss Vortices Downstream a Straight Turbine Cascade
Volume 1: Turbomachinery, 1989
An experimental investigation is carried out to study the effect of inlet boundary layer thickness, aspect ratio and exit Mach number on the energy loss and on the behaviour of secondary vortices downstream of a straight turbine cascade of blades having 82°t urning angle. ITS Midspan values s Isentropic Superscripts-Pitch-averaged values = Pitch and span averaged values.