Numerical Analysis of the Multiple-Horseshoe-Vortex Effects on the Endwall Heat Transfer in the Leading-Edge Region of a Symmetric Bluff Body

2010 ◽  
Author(s):  
A. M. Levchenya ◽  
E. M. Smirnov
Keyword(s):  
Heat Transfer ◽  
Bluff Body ◽  
Stokes Equations ◽  
Correction Term ◽  
Low Frequency ◽  
Flow Simulation ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
The Body ◽  
Present Contribution

The present contribution covers results of a CFD analysis of the 3D flow and endwall heat transfer for a generic junction configuration with a wall-mounted symmetric bluff body experimentally investigated by Praisner and Smith [1, 2]. The computations based on the Reynolds-averaged Navier-Stokes equations (RANS) were performed using two codes of second order accuracy: the in-house code SINF and the commercial package ANSYS-CFX 12.0. For the turbulence closure problem, the Menter SST turbulence model with and without the streamline-curvature correction term was used. The grid sensitivity of solution was studied using a set of grids, the finest of which was of about five million cells. In accordance with the experiments, the computations with both the codes predict development of multiple horseshoe vortices and several bands of high values of the Stanton (St) number upstream of the body leading edge. The spatial relationships between the vorticity in individual planes and the associated endwall Stanton number are generally same in the measurements and in the computations. Some quantitative distinctions between the predictions and experimental data are attributed to the smoothing effect of the low-frequency unsteadiness of the horseshoe vortex system developing in the real flow. Simulation of this effect is outside of RANS-based formulations.

Boundary Layer Influence on the Unsteady Horseshoe Vortex Flow and Surface Heat Transfer

2007 ◽  
Author(s):  
D. R. Sabatino ◽  
C. R. Smith
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Bluff Body ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Surface Heat ◽  
Wall Region ◽  
Thermochromic Liquid Crystal ◽  
Surface Heat Transfer ◽  
End Wall

The spatial-temporal flow-field and associated surface heat transfer within the leading edge, end-wall region of a bluff body were examined using both particle image velocimetry and thermochromic liquid crystal temperature measurements. The horseshoe vortex system in the end-wall region is mechanistically linked to the upstream boundary layer unsteadiness. Hairpin vortex packets, associated with turbulent boundary layer bursting behavior, amalgamate with the horseshoe vortex resulting in unsteady strengthening and streamwise motion. The horseshoe vortex unsteadiness exhibits two different natural frequencies: one associated with the transient motion of the horseshoe vortex, and the other with the transient surface heat transfer. Comparable unsteadiness occurs in the end-wall region of the more complex airfoil geometry of a linear turbine cascade. To directly compare the horseshoe vortex behavior around a turning airfoil to that of a simple bluff body, a length scale based on the maximum airfoil thickness is proposed.

Boundary Layer Influence on the Unsteady Horseshoe Vortex Flow and Surface Heat Transfer

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
D. R. Sabatino ◽  
C. R. Smith
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Bluff Body ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Surface Heat ◽  
Wall Region ◽  
Thermochromic Liquid Crystal ◽  
Surface Heat Transfer ◽  
End Wall

The spatial-temporal flow field and associated surface heat transfer within the leading edge, end-wall region of a bluff body were examined using both particle image velocimetry and thermochromic liquid crystal temperature measurements. The horseshoe vortex system in the end-wall region is mechanistically linked to the upstream boundary layer unsteadiness. Hairpin vortex packets, associated with turbulent boundary layer bursting behavior, amalgamate with the horseshoe vortex resulting in unsteady strengthening and streamwise motion. The horseshoe vortex unsteadiness exhibits two different natural frequencies: one associated with the transient motion of the horseshoe vortex and the other with the transient surface heat transfer. Comparable unsteadiness occurs in the end-wall region of the more complex airfoil geometry of a linear turbine cascade. To directly compare the horseshoe vortex behavior around a turning airfoil to that of a simple bluff body, a length scale based on the maximum airfoil thickness is proposed.

Low-Frequency Fluctuations In The Flow Over Confined Cylinder In A Narrow Rectangular Duct At Re = 3 750

2017 ◽  
Vol 12 (1) ◽  
pp. 43-49
Author(s):  
Egor Palkin ◽  
Rustam Mullyadzhanov
Keyword(s):  
Stokes Equations ◽  
Low Frequency ◽  
Horseshoe Vortex ◽  
Navier Stokes ◽  
Infinite Cylinder ◽  
Rectangular Duct ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Frequency Modulations ◽  
Bounding Surfaces

Flows between two closely spaced bounding surfaces are frequently appear in engineering applications and natural flows. In current paper the flow over a cylinder in a narrow rectangular duct was investigated by numerical computations of Navier-Stokes equations using Large eddy simulations (LES) at ReD = 3 750 based on cylinder diameter and the bulk velocity at inflow boundary. The influence of the bounding walls was demonstrated by comparing mean flow streamlines with the flow over an infinite cylinder at close Reynolds numbers. A comparison between the time-averaged velocity field in front and past the cylinder with experimental from the literature data showed good agreement although the characteristic horseshoe vortex structures are highly sensitive to Reynolds number and turbulence level at inflow boundary. Most energetic modes in recirculating region were revealed by spectral analysis. These low-frequency modulations were characterized by the pair of dominating vortices which are expected to have high influence on the heat transfer in near wake of the cylinder.

Research on Heat-Transfer and Cooling Performance of Gas Turbine Endwall

2017 ◽  
Author(s):  
Kazuto Kakio ◽  
Y. Kawata
Keyword(s):  
Heat Transfer ◽  
Pressure Gradient ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Power Plants ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Combined Cycle ◽  
Inlet Temperature ◽  
Cooling Performance

Recently, the number of gas turbine combined cycle plants is rapidly increasing in substitution of nuclear power plants. The turbine inlet temperature (TIT) is being constantly increased in order to achieve higher efficiency. Therefore, the improvement of the cooling technology for high temperature gas turbine blades is one of the most important issue to be solved. In a gas turbine, the main flow impinging at the leading edge of the turbine blade generates a so called horseshoe vortex by the interaction of its boundary layer and generated pressure gradient at the leading edge. The pressure surface leg of this horseshoe vortex crosses the passage and reaches the blade suction surface, driven by the pressure gradient existing between two consecutive blades. In addition, this pressure gradient generates a crossflow along the endwall. This all results into a very complex flow field in proximity of the endwall. For this reason, burnouts tend to occur at a specific position in the vicinity of the leading edge. In this research, a methodology to cool the endwall of the turbine blade by means of film cooling jets from the blade surface is proposed. The cooling performance and heat transfer coefficient distribution is investigated using the transient thermography method. CFD analysis is also conducted to know the phenomena occurring at the end wall and calculate the heat transfer distribution.

Controlling Secondary-Flow Structure by Leading-Edge Airfoil Fillet and Inlet Swirl to Reduce Aerodynamic Loss and Surface Heat Transfer

2002 ◽  
Author(s):  
T. I.-P. Shih ◽  
Y.-L. Lin
Keyword(s):  
Heat Transfer ◽  
Stokes Equations ◽  
Leading Edge ◽  
Surface Heat ◽  
Secondary Flows ◽  
Maximum Height ◽  
Surface Heat Transfer ◽  
Aerodynamic Loss ◽  
Swirl Angle ◽  
Inlet Swirl

Computations, based on the ensemble-averaged compressible Navier-Stokes equations closed by the shear-stress transport (SST) turbulence model, were performed to investigate the effects of leading-edge airfoil fillet and inlet-swirl angle on the flow and heat transfer in a turbine-nozzle guide vane. Three fillet configurations were simulated: no fillet (baseline), a fillet whose thickness fades on the airfoil, and a fillet whose thickness fades on the endwall. For both fillets, the maximum height above the endwall is positioned along the stagnation zone/line on the airfoil under the condition of no swirl. For each configuration, three inlet swirls were investigated: no swirl (baseline) and two linearly varying swirl angle from one endwall to the other (+30° to −30° and −30° to +30°). Results obtained show that both leading-edge fillet and inlet swirl can reduce aerodynamic loss and surface heat transfer. For the conditions of this study, the difference in stagnation pressure from the nozzle’s inlet to its exit were reduced by more than 40% with swirl or with fillet without swirl. Surface heat transfer was reduced by more than 10% on the airfoil and by more than 30% on the endwalls. When there is swirl, leading-edge fillets became less effective in reducing aerodynamic loss and surface heat transfer, because the fillets were not optimized for swirl angles imposed. Since the intensity and size of the cross flow were found to increase instead of decrease by inlet swirl and by the type of fillet geometries investigated, the results of this study indicate that the mechanisms responsible for aerodynamic loss and surface heat transfer are more complex than just the intensity and the magnitude of the secondary flows. This study shows their location and interaction with the main flow to be more important, and this could be exploited for positive results.

On the Weis-Fogh mechanism of lift generation

1973 ◽  
Vol 60 (1) ◽  
pp. 1-17 ◽  
Author(s):  
M. J. Lighthill
Keyword(s):  
Stokes Equations ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Leading Edge ◽  
The Body ◽  
Navier Stokes ◽  
Encarsia Formosa ◽  
Concentrated Force ◽  
Stagnation Points ◽  
Wing Tips

Weis-Fogh (1973) proposed a new mechanism of lift generation of fundamental interest. Surprisingly, it could work even in inviscid two-dimensional motions starting from rest, when Kelvin's theorem states that the total circulation round a body must vanish, but does not exclude the possibility that if the body breaks into two pieces then there may be equal and opposite circulations round them, each suitable for generating the lift required in the pieces’ subsequent motions! The ‘fling’ of two insect wings of chord c (figure 1) turning with angular velocity Ω generates irrotational motions associated with the sucking of air into the opening gap which are calculated in § 2 as involving circulations −0·69Ωc2 and + 0.69Ωc2 around the wings when their trailing edges, which are stagnation points of those irrotational motions, break apart (position (f)). Viscous modifications to this irrotational flow pattern by shedding of vorticity at the boundary generate (§ 3) a leading-edge separation bubble, and tend to increase slightly the total bound vorticity. Its role in a three-dimensional picture of the Weis-Fogh mechanism of lift generation, involving formation of trailing vortices at the wing tips, and including the case of a hovering insect like Encarsia formosa moving those tips in circular paths, is investigated in § 4. The paper ends with the comment that the far flow field of such very small hovering insects should take the form of the exact solution (Landau 1944; Squire 1951) of the Navier-Stokes equations for the effect of a concentrated force (the weight mg of the animal) acting on a fluid of kinematic viscosity v and density p, whenever the ratio mg/pv2 is small enough for that jet-type induced motion to be stable.

Simulation of blunt-fin-induced shock-wave and turbulent boundary-layer interaction

1985 ◽  
Vol 154 ◽  
pp. 163-185 ◽  
Author(s):  
Ching-Mao Hung ◽  
Pieter G. Buning
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Flat Plate ◽  
High Speed ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Layer Interaction ◽  
Boundary Layer Interaction

The Reynolds-averaged Navier–Stokes equations are solved numerically for supersonic flow over a blunt fin mounted on a flat plate. The fin shock causes the boundary layer to separate, which results in a complicated, three-dimensional shock-wave and boundary-layer interaction. The computed results are in good agreement with the mean static pressure measured on the fin and the flat plate. The main features, such as peak pressure on the fin leading edge and a double peak on the plate, are predicted well. The role of the horseshoe vortex is discussed. This vortex leads to the development of high-speed flow and, hence, low-pressure regions on the fin and the plate. Different thicknesses of the incoming boundary layer have been studied. Varying the thicknesses by an order of magnitude shows that the size of the horseshoe vortex and, therefore, the spatial extent of the interaction are dominated by inviscid flow and only weakly dependent on the Reynolds number. Coloured graphics are used to show details of the interaction flow field.

Two-Dimensional Low Mach Number Heat Transfer Simulation of Turbine Blade Leading-Edge Model

2007 ◽  
Author(s):  
Jeff Litzler ◽  
Suman Mishra ◽  
Urmila Ghia ◽  
Karman Ghia ◽  
Shichuan Ou
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Bluff Body ◽  
Cross Flow ◽  
Leading Edge ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Grid Topology ◽  
Hybrid Grid ◽  
Blade Leading Edge

A subsonic, viscous, laminar flow and heat transfer is simulated in the present study over a two-dimensional, isothermal, bluff-body representing a turbine blade leading-edge. The purpose of this simulation is to predict local Frossling number; to determine the accuracy of the predictions as compared to experimental results, and to compare the results from two flow solvers, Fluent and Cobalt. The geometry consists of a half-cylinder of diameter 8.89 cm and a flat after-body, and represents to the model used in the corresponding experimental investigations. The simulations are performed on a multi-block, hybrid grid topology developed using GridGen as the grid generation software. Researchers have earlier investigated heat transfer over a similar model. Utilizing computational modeling techniques, a representative simulation of the physical flow mechanism enables further investigation into the characteristics of the flow. The boundary conditions for the problem are identified as no-slip and isothermal on the bluff body, and uniform velocity is assumed at the inlet. Results are presented in the form of the Frossling number, defined as the Nusselt number divided by the square root of Reynolds number. The results are compared with published experimental data for the experimental geometry described earlier, and the cross-flow-cylinder, to assess the validity of the numerical approaches.

Numerical Flow Simulation in the Induction System of an Internal Combustion Engine

1992 ◽  
Author(s):  
S. Y. Ho ◽  
A. J. Przekwas
Keyword(s):  
Internal Combustion Engine ◽  
Stokes Equations ◽  
Combustion Engine ◽  
Flow Simulation ◽  
Internal Combustion ◽  
Flow Fields ◽  
The Body ◽  
Design Parameters ◽  
Complex Flow ◽  
Induction System

Abstract An advanced computational fluid dynamics package, REFLEQS, has been adapted to calculate the flow in the induction system of an internal combustion engine. Results of complex flow fields in multi-valve engine intake/exhaust ports and cylinders, including moving valves and piston, are calculated. The body-fitted structured grids generated with partial differential equations method have been applied to represent complex engine components configuration such as engine intake/exhaust ports, ducts, valves and cylinders. An upwind scheme combined with SIMPLEC method is employed to solve the Navier-Stokes equations. Several 2D and 3D flows in engine ports/cylinders are simulated. Complex flow fields involve separated flows near the entry of cylinder head, vortices near the corner and behind the valves and the valve/stem generated swirling and tumbling flows. The present work aims at establishing a generalized computational environment for analyzing the physical mechanisms and design parameters controlling internal flows in automotive air/fuel induction systems.

Analysis of Flow and Heat Transfer in the End-Wall Region of a Turbine Blade Passage

2000 ◽  
Author(s):  
Yumin Xiao ◽  
R. S. Amano
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
High Heat ◽  
Wall Region ◽  
Trailing Edge ◽  
High Heat Transfer ◽  
Transfer Region ◽  
End Wall

A numerical study has been performed to predict a three-dimensional turbulent flow and end-wall heat transfer in a blade passage. The complex three-dimensional flow in the end-wall region has an important impact on the local heat transfer. The leading edge horseshoe vortex, the leading edge corner vortices, the passage vortex, and the trailing edge wake cause large variations in the entire end-wall region. The heat transfer distributions in the end-wall region are calculated and the mechanism for the high heat transfer region has been revealed. The calculations show that the algebraic turbulence model lacks the ability to predict the heat transfer in the transition region, but it is valid in other flow region. The local high heat transfer downstream of the trailing edge is enhanced by the wake downstream of the trailing edge. The horseshoe vortex results a high heat transfer region near the leading edge and induces the leading edge corner vortices which cause high heat transfer on the end-wall at both sides of blade end-wall corner.

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