Effect Of Vortex Structures Research Articles

Effects of Vortex Structure on Hydraulic Loss in a Low Head Francis Turbine under Overall Operating Conditions Base on Entropy Production Method

Multi-energy complementary power generation mode has become the theme of modern power grid construction. In response to the requirements of the national multi-energy strategy, the operation mode of hydropower units will inevitably change frequently, resulting in unpredictable hydraulic unstable flow phenomena (such as the blade passage vortex, the vortex rope in the draft tube, etc.) which will reduce the hydraulic performance of units and may lead to strong vibration of units, and even threaten the safe operation of units and even power stations in severe cases. In order to study the effect of the blade passage vortex and the vortex rope in the draft tube on the hydraulic losses under the part load conditions, the sliding mesh method and SST k-ω turbulence model are adopted. The blade passage vortex and the vortex rope in the draft tube captured by the latest Liutex vortex identification method undergo a contrastive analysis with the hydraulic loss of internal flow based on the entropy production theory. The results indicate that compared with the results in the references, the results of the research are verified accurate; under different upstream flow conditions, the proportion of the hydraulic losses of the spiral casing is small and has no obvious changes; the shock and stall phenomena, the dynamic-static interference, the relatively high flow velocity gradient, and the streamwise vortices in the guide vane domain are the main factors that cause the increase of entropy production; a large number of the blade passage vortices, the fluid-impact blades, and the tip leakage vortices are the main causing factors of the hydraulic losses in the runner; and the various shapes of the vortex rope in the draft tube can lead to the dramatic increase of the hydraulic losses of the draft tube as the opening decreases, and the hydraulic losses of the draft tube account for the largest proportion, followed by that of the runner. At the designed flow rate, the hydraulic loss of draft tube is 0.58 m, accounting for 50% of the total channel hydraulic loss, and that of runner is 0.38 m, accounting for 32.6% of the total channel hydraulic loss. When the flow rate drops to 55% of the designed flow rate, the hydraulic loss of draft tube is 1.95 m, accounting for 68% of the whole channel, and that of runner is 0.70 m, accounting for 24.4% of the whole channel.

Modal analysis of trailing edge cutback film cooling

PurposeThe purpose of this paper devoted to the application of modal analysis to analyze the flow structure of trailing edge cutback film cooling and the effects of vortex structure on the film cooling effectiveness of the cutback surface.Design/methodology/approachLarge eddy simulation (LES) is used to simulate the trailing edge cutback film cooling. The results of LES are analyzed by proper orthogonal decomposition (POD) method and dynamic mode decomposition (DMD) method. The POD method is used to determine the dominated vortex structure and the energy level of these structures. The DMD method is used to analyze the relationship between vortex structures and wall temperature.FindingsThe POD method shows that the flow field consists of three main vortices – streamwise vortex, lip vortex and coolant vortex. The DMD results show that the lip vortex mainly acts on the middle section of the cutback surface, while the streamwise vortex mainly acts on the back section of the cutback surface.Research limitations/implicationsThe modal analysis is only based on numerical simulation but the modal analysis of experimental results will be further studied in the future.Practical implicationsThis paper presents the powerful ability of the modal analysis method to study complex flows in trailing edge cutback film cooling. Establishing the relationship between vortex and wall temperature by modal analysis method can provide a new idea for studying convective heat transfer problems.Originality/valueThe role of streamwise vortex in the flow of the trailing edge cutback cooling and its effect on the cooling effectiveness of the cutback surface is found.

Effects of vortex structure on performance characteristics of a multiblade fan with inclined tongue

The effects of complex vortex structure on the internal flow and performance of a centrifugal fan with inclining symmetrical volute tongue were investigated by numerical simulations. The comparison between experimental results and numerical results on performance of a centrifugal fan is presented. To provide a quantitative analysis on the vortex structure in the internal flow of fan, Q criterion as a rule of vortex decision is implemented. Effects on vortex structure and X-velocity of the volute outlet are analyzed by modifying clearance and radius. It is analyzed to provide insight into the performance of the centrifugal fan. Special attention is devoted to the influence of the static pressure and efficiency of the fan by increasing radius of the volute tongue, changing tongue clearance and inclining volute tongue in this paper. The results also show that the static pressure of model B rises as much as 10.59 Pa and the efficiency can be improved by more than 4% compared with the original configuration due to the reduction of flow loss. It is further found that the static pressure efficiency increases with decreasing Q value distribution in the internal flow of the fan.

The effect of vortex structures in the river bed on the concentration and size differentiation of the fish population

On the basis of recent hydroacoustic method with using “PanCor” computerized program-technological complex, research was conducted on the distribution of fish of different taxonomic groups in the water area of Irtysh, a large trans-border river on the bend (meander) with a vortex zone. A hydroacoustic complex allows one to conduct remote size-taxonomic identification of fish. It is demonstrated that on the examined area of the river, fish of different taxonomic groups and sizes concentrate in the zones of increased turbidity and intense whirlpools (vortices) which form as a result of opposite currents at the river meander. The largest concentrations of fish form in the deepest zone of the examined water area and in front of it – vortex zone. It was determined that in the zone of recorded vortices, the number of fish of different taxonomic groups (Cyprinidae, Percidae, Coregonus, Esocidae, Sturgeon, burbot) is on average 2.14–2.61 times reliably higher compared to the observations at the studied part of the river with no vortices at comparable parameters of depth. The size structure of the fish was dominated by small individuals (<10 cm) in the vortices, and large fish out of these zones, which can be an additional element of the survival strategy. The peculiarities of the studied area of the river with vortices, on one hand, are the factors of formation of fish concentrations, and on the other hand – factors of differentiation by taxonomical and size parameter, related to inability of certain groups of organisms to resist the hydrodynamic force of the vortex structure.

The effects of vortex structure and vortex translation on the tropical cyclone boundary layer wind field

AbstractThe effects of vortex translation and radial vortex structure in the distribution of boundary layer winds in the inner core of mature tropical cyclones are examined using a high‐resolution slab model and a multilevel model. It is shown that the structure and magnitude of the wind field (and the corresponding secondary circulation) depends sensitively on the radial gradient of the gradient wind field above the boundary layer. Furthermore, it is shown that vortex translation creates low wave number asymmetries in the wind field that rotate anticyclonically with height. A budget analysis of the steady state wind field for both models was also performed in this study. Although the agradient force drives the evolution of the boundary layer wind field for both models, it is shown that the manner in which the boundary layer flow responds to this force differs between the two model representations. In particular, the inner core boundary layer flow in the slab model is dominated by the effects of horizontal advection and horizontal diffusion, leading to the development of shock structures in the model. Conversely, the inner core boundary layer flow in the multilevel model is primarily influenced by the effects of vertical advection and vertical diffusion, which eliminates shock structures in this model. These results further indicate that special care is required to ensure that qualitative applications from slab models are not unduly affected by the neglect of vertical advection.

Stretched Lognormal Distribution and Extended Self-Similarity in 3D Turbulence

Using data of a direct numerical simulation (DNS) of 3D turbulence it is shown that the moments of order between 1 and 6 of both longitudinal and transverse components of velocity increment for forced as well as decay turbulence can be described by stretched lognormal distribution for all scales from the dissipation to the inertial ranges and for all values of Reynolds number investigated in this DNS (50< R λ <459). A new (local) version of extended self-similarity has been used for this purpose. Effects of vortex structure on increment of velocity field in forced and in decay turbulence are briefly discussed.

Effect of Vortex Structures on the Boundary Layer of External Flow Around Bodies

Numerical simulation of a slot-and-jet vortex generator and its effect on the wall boundary layer is considered. The existence of unsteady flow regime is shown, with initiation of unsteady votrices which separate from the jet and are carried by outer flow. When moving downstream, they deform the longitudinal velocity profile and reduce local skin friction. The considered slot-and-jet vortex generator is shown to be an effective way of overall friction reduction in its vicinity.

Large-scale vortex structures in shear flows

This article considers the developments of the Hamiltonian Approach to problems of fluid dynamics, and applies the general method to strongly non-linear large-scale vortex structures in shear flows. Such vortex structures can appear in shear flows like Poiseulle and Couette flows. The Hamiltonian version of contour dynamics for two-dimensional layer models in a constant-density ideal fluid has be developed. The Hamiltonian description is formulated in terms of the dynamic variables with KdV-type Poisson brackets. The use of the method of pseudo-differential operators permits the regular application of approximation methods. Thus, governing equations can be easily derived correctly in any order of perturbation theory. We discuss also the effect of vortex structures on the average velocity profile of the flows.

Experiments on particle dispersion in a plane wake

Detailed experimental results are presented concerning the effects of vortex structures on the solid particle dispersion process in a plane wake. Previous numerical results have indicated that vortex structures in plane wakes can disperse intermediate Stokes number particles into highly organized patterns. The cross stream spatial dispersion values associated with these particles were computed to be several times greater than that associated with fluid elements. The major objective of this study was to obtain direct experimental results concerning the time dependent particle dispersion process in a plane wake. The experimental approach used in this work primarily involves laser sheet pulsed imaging of glass bead particles in a wake downstream of a blunt trailing edge. Two sizes of glass beads with nominal diameters of 10 and 30 μm were used as particles in an air flow. The associated Stokes numbers of the particles were 0.15 and 1.4. Digital image analysis techniques were employed to identify and determine particle locations and velocities. The results demonstrate that particle dispersion in plane wakes can produce highly organized patterns of particle concentrations. The particles at intermediate Stokes number are focused into sheet-like regions near the boundaries of the large scale vortex structures. In addition the spatial dispersion of the intermediate Stokes number particles was much larger than the smaller Stokes number particles. These experimental results strongly support previous numerical simulation findings.