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

2003 ◽  
Vol 125 (1) ◽  
pp. 48-56 ◽  
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 deg and −30 to +30 deg). 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.

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.

Effects of Inlet Swirl Angle on Flow and Heat Transfer in Contoured Turbine Nozzle Guide Vanes

2001 ◽  
Author(s):  
Y.-L. Lin ◽  
H. J. Schock ◽  
T. I-P. Shih ◽  
R. S. Bunker
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Stokes Equations ◽  
Secondary Flows ◽  
Stagnation Zone ◽  
Transfer Coefficients ◽  
Pressure Surface ◽  
Flow And Heat Transfer ◽  
Swirl Angle ◽  
Inlet Swirl

Abstract Computations, based on the ensemble-averaged compressible Navier-Stokes equations closed by the shear-stress transport (SST) model of turbulence, were performed to investigate the effects of inlet swirl angle on the three-dimensional flow and heat transfer in two contoured endwall configurations. Swirl angles investigated include three constant angles (0°, 15°, 30°) and a linearly varying angle from +30° at one endwall to −30° at the other. For all swirl angles, the mass-flow rate through the nozzle was fixed so that the higher the swirl angle, the higher is the velocity magnitude. Of the two endwalls investigated, one has all of the contouring upstream of the airfoil (C1), and another has contouring that starts upstream of the airfoil and continues until the airfoil’s trailing edge (C2). Computed results show that at all swirl angles investigated, the C2 configuration was able to reduce significantly secondary flows on the contoured endwall. Results also show that with reduced secondary flows, the heat-transfer coefficients are also reduced on the suction surface next to the juncture, where the airfoil meets the contoured endwall. On aerodynamics, the C2 configuration was found to produce essentially the same lift as the C1 configuration, but does so with less loss in stagnation pressure. For the C1 configuration, secondary flows are quite pronounced, and they increase slightly in size and in magnitude when swirl angle is increased. However, aerodynamic loss and surface heat transfer were found to decrease with increase in swirl angle. One explanation is that increasing the swirl angle shifted the stagnation zone downstream on the pressure surface to a flatter portion of the airfoil, producing a thicker boundary layer at the stagnation zone, and this changed considerably the evolution of the turbulent boundary layer. When the swirl angle varied linearly from +30° to −30°, increasing the velocity component towards the pressure surface was found to enhance instead of suppress the formation of secondary flows.

Preventing Hot Gas Ingestion by Film-Cooling Jets via Flow-Aligned Blockers

2006 ◽  
Author(s):  
T. I.-P. Shih ◽  
S. Na ◽  
M. Chyu
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Pressure Loss ◽  
Stokes Equations ◽  
Leading Edge ◽  
Surface Heat ◽  
Surface Heat Transfer ◽  
Hot Gas ◽  
Cooling Hole ◽  
Adiabatic Effectiveness

Flow aligned blockers are proposed to minimize the entrainment of hot gases underneath film-cooling jets by the counter-rotating vortices within the jets. Computations, based on the ensemble-averaged Navier-Stokes equations closed by the realizable k-ε turbulence model, were used to assess the usefulness of rectangular prisms as blockers in increasing film-cooling adiabatic effectiveness without unduly increasing surface heat transfer and pressure loss. The Taguchi’s design of experiment method was used to investigate the effects of the height of the blocker (0.2D, 0.4D, 0.8D), the thickness of the blocker (D/20, D/10, D/5), and the spacing between the pair of blockers (0.8D, 1.0D, 1.2D), where D is the diameter of the film-cooling hole. The effects of blowing ratio (0.37, 0.5, 0.65) were also studied. Results obtained show that blockers can greatly increase film-cooling effectiveness. By using rectangular prisms as blockers, the laterally averaged adiabatic effectiveness at 15D downstream of the film-cooling hole is as high as that at 1D downstream. The surface heat transfer was found to increase slightly near the leading edge of the prisms, but reduced elsewhere from reduced temperature gradients that resulted from reduced hot gas entrainment. However, pressure loss was found to increase somewhat because of the flat rectangular leading edge, which can be made more streamlined.

The Effects of Localized Blade Endwall Suction on Secondary Flows and Heat Transfer

2010 ◽  
Author(s):  
Rebecca Hollis ◽  
Jeffrey P. Bons
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
High Surface ◽  
Surface Heat ◽  
Secondary Flows ◽  
Surface Shear Stress ◽  
Mean Velocity ◽  
Surface Shear ◽  
Surface Heat Transfer ◽  
High Heat Transfer

Two methods of flow control were designed to mitigate the effects of the horseshoe vortex structure (HV) at an airfoil/endwall junction. An experimental study was conducted to quantify the effects of localized boundary layer removal on surface heat transfer in a low-speed wind tunnel. A transient infrared technique was used to measure the convective heat transfer values along the surface surrounding the juncture. Particle image velocimetry was used to collect the time-mean velocity vectors of the flow field across three planes of interest. Boundary layer suction was applied through a thin slot cut into the leading edge of the airfoil at two locations. The first, referred to as Method 1, was directly along the endwall, the second, Method 2, was located at a height ∼1/3 of the approaching boundary layer height. Five suction rates were tested; 0%, 6.5%, 11%, 15% and 20% of the approaching boundary layer mass flow was removed at a constant rate. Both methods reduced the effects of the HV with increasing suction on the symmetry, 0.5-D and 1-D planes. Method 2 yielded a greater reduction in surface heat transfer but Method 1 outperformed Method 2 aerodynamically by completely removing the HV structure when 11% suction was applied. This method however produced other adverse effects such as high surface shear stress and localized areas of high heat transfer near the slot edges at high suction rates.

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.

Flowfield Measurements for a Highly Turbulent Flow in a Stator Vane Passage

1999 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Correlation Coefficients ◽  
Leading Edge ◽  
Surface Heat ◽  
Laser Doppler Velocimeter ◽  
Surface Heat Transfer ◽  
Turbine Vanes ◽  
Stator Vane

Turbine vanes experience high convective surface heat transfer as a consequence of the turbulent flow exiting the combustor. Before improvements to vane heat transfer predictions through boundary layer calculations can be made, we need to understand how the turbulent flow in the inviscid region of the passage reacts as it passes between two adjacent turbine vanes. In this study, a scaled-up turbine vane geometry was used in a low-speed wind tunnel simulation. The test section included a central airfoil with two adjacent vanes. To generate the 20% turbulence levels at the entrance to the cascade, which simulates levels exiting the combustor, an active grid was used. Three-component laser Doppler velocimeter measurements of the mean and fluctuating quantities were measured in a plane at the vane mid-span. Coincident velocity measurements were made to quantify Reynolds shear stress and correlation coefficients. The energy spectra and length scales were also measured to give a complete set of inlet boundary conditions that can be used for numerical simulations. The results show that the turbulent kinetic energy throughout the inviscid region remained relatively high. The surface heat transfer measurements indicated high augmentation near the leading edge as well as the pressure side of the vane as a result of the elevated turbulence levels.

Effect of Two-Scale Roughness on Boundary Layer Transition Over a Heated Flat Plate: Part 1—Surface Heat Transfer

1999 ◽  
Vol 122 (2) ◽  
pp. 301-307 ◽  
Author(s):  
Mark W. Pinson ◽  
Ting Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Leading Edge ◽  
Step Change ◽  
Surface Heat ◽  
Boundary Layer Transition ◽  
Test Surface ◽  
Layer Transition ◽  
Surface Heat Transfer ◽  
Scale Roughness

An experimental study was conducted to investigate surface heat transfer and boundary layer development associated with flow over a flat test surface covered with two roughness scales. Two-scale roughness was used because in-service aeroengines commonly display larger roughness concentrated at the leading edge with smaller roughness distributed downstream. The first scale, covering up to the first 5 cm of the test surface, was in the form of a sandpaper strip, an aluminum strip, or a cylinder. The second roughness scale covered the remainder of the test surface (2 m) in the form of sandpaper or a smooth surface. In Part 1, the surface heat transfer results are examined. Even though the roughness scales were hydraulically smooth, they induced significantly earlier transition onset, with the two-dimensional roughness causing earlier transition than three-dimensional roughness. All of the rough/smooth cases unexpectedly triggered earlier transition than rough/rough cases. This indicated that the scale of the step-change at the joint between two roughness scales was predominant over the downstream roughness on inducing early transition. Reducing the overall height of the step change was shown to have a greater effect on transition than the specific geometry of the roughness scale. [S0889-504X(00)00701-7]

Flowfield Measurements for a Highly Turbulent Flow in a Stator Vane Passage

1999 ◽  
Vol 122 (2) ◽  
pp. 255-262 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Reynolds Shear Stress ◽  
Correlation Coefficients ◽  
Leading Edge ◽  
Surface Heat ◽  
Laser Doppler Velocimeter ◽  
Surface Heat Transfer ◽  
Turbine Vanes ◽  
Stator Vane

Turbine vanes experience high convective surface heat transfer as a consequence of the turbulent flow exiting the combustor. Before improvements to vane heat transfer predictions through boundary layer calculations can be made, we need to understand how the turbulent flow in the inviscid region of the passage reacts as it passes between two adjacent turbine vanes. In this study, a scaled-up turbine vane geometry was used in a low-speed wind tunnel simulation. The test section included a central airfoil with two adjacent vanes. To generate the 20 percent turbulence levels at the entrance to the cascade, which simulates levels exiting the combustor, an active grid was used. Three-component laser-Doppler velocimeter measurements of the mean and fluctuating quantities were measured in a plane at the vane midspan. Coincident velocity measurements were made to quantify Reynolds shear stress and correlation coefficients. The energy spectra and length scales were also measured to give a complete set of inlet boundary conditions that can be used for numerical simulations. The results show that the turbulent kinetic energy throughout the inviscid region remained relatively high. The surface heat transfer measurements indicated high augmentation near the leading edge as well as the pressure side of the vane as a result of the elevated turbulence levels. [S0889-504X(00)02302-3]

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.

Flow Separation and Heat Transfer in Shear Flow Around a Wall-Mounted Obstacle

2002 ◽  
Author(s):  
S. Mahapatra ◽  
S. Bhattacharyya
Keyword(s):  
Heat Transfer ◽  
Flow Separation ◽  
Buoyancy Force ◽  
Stokes Equations ◽  
Plane Surface ◽  
Surface Heat ◽  
Staggered Grid ◽  
Grashof Number ◽  
Surface Heat Transfer ◽  
Uniform Shear

Flow structure and surface heat transfer around a single small obstacle of rectangular cross-section mounted on a smooth plane surface are investigated. The obstacle is considered to be submerged in the viscous layer so that the far field flow may be viewed as uniform shear. The obstacle is considered to be at a temperature higher than that of the surrounding fluid and the flat surface is insulated. The unsteady Navier-Stokes equations and heat transport equation are solved numerically through a finite volume method on a staggered grid system. Solutions are obtained over a range of Reynolds number Re, which is based on the obstacle height and the incident uniform shear and Grashof number Gr. An investigation of the influence of buoyancy on the upstream and downstream flow separation from the obstacle and the interaction of the separation with the thermal field is also made. Numerical results reveal that in absence of the buoyancy force, the recirculating eddy upstream of the obstacle elongates with increasing Re. It is found that the buoyancy effect reduces the size of the upstream eddy when Re ≤ 200 with Gr (which is a measure of buoyancy) equal to 100. At an increased value of buoyancy force, Gr = 104, the upstream separation zone shifts further close to the obstacle. It is also found that the downstream separation length (which increases with increasing Re) further increases with increasing Gr as long as Re ≤ 200. Buoyancy effects on the flow are not prominent when Re is above 200. The surface heat transfer is quite high at the protruding corners and it increases with increase in Re. Increase of Grashof number produces an increment on surface heat transfer.

Sign in / Sign up

Export Citation Format

Share Document