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.

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]

scholarly journals Effects of High Freestream Turbulence Levels and Length Scales on Stator Vane Heat Transfer

1998 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Laser Doppler Velocimeter ◽  
Freestream Turbulence ◽  
Length Scales ◽  
Surface Heat Transfer ◽  
Stator Vane

Gaining a good understanding of how high freestream turbulence augments heat transfer is important for predicting thermal loadings for turbine blades and vanes. This study was aimed at documenting the surface heat transfer and the highly turbulent flowfield around a stator vane. The effects of turbulence levels between 11% and 24% were studied. At the highest turbulence level, two different Reynolds numbers (Reex = 6 × 105 and 1.2 × 106) and two different length scales were also studied. Three-component laser Doppler velocimeter measurements of the velocity fluctuations indicated that downstream of the active grid there was an initial decay of the turbulent kinetic energy which then leveled off at about one leading edge radius upstream of the vane. Inside the vane passage the turbulent kinetic energy increased slightly and then decayed through the passage. The surface heat transfer showed the largest augmentations on the pressure side of the vane with higher augmentations at higher turbulence levels, smaller length scales, and higher Reynolds numbers.

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.

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.

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]

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.

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.

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

1999 ◽  
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.

High Freestream Turbulence Effects on Endwall Heat Transfer for a Gas Turbine Stator Vane

2000 ◽  
Author(s):  
R. W. Radomsky ◽  
K. A. Thole
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Convective Heat ◽  
Leading Edge ◽  
Secondary Flows ◽  
Laser Doppler Velocimeter ◽  
Freestream Turbulence ◽  
Stator Vane ◽  
The Mean

High freestream turbulence along a gas turbine airfoil and strong secondary flows along the endwall have both been reported to significantly increase convective heat transfer. This study superimposes high freestream turbulence on the naturally occurring secondary flow vortices to determine the effects on the flowfield and the endwall convective heat transfer. Measured flowfield and heat transfer data were compared between low freestream turbulence levels (0.6%) and combustor simulated turbulence levels (19.5%) that were generated using an active grid. These experiments were conducted using a scaled-up, first stage stator vane geometry. Infrared thermography was used to measure surface temperatures on a constant heat flux plate placed on the endwall surface. Laser Doppler velocimeter (LDV) measurements were performed of all three components of the mean and fluctuating velocities of the leading edge horse-shoe vortex. The results indicate that the mean flowfields for the leading edge horseshoe vortex were similar between the low and high freestream turbulence cases. High turbulence levels in the leading edge-endwall juncture were attributed to a vortex unsteadiness for both the low and high freestream tubulence cases. While, in general, the high freestream turbulence increased the endwall heat transfer, low augmentations were found to coincide with the regions having the most intense vortex motions.

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.

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