Optimal Turbulent Schmidt Number for RANS Modeling of Trailing Edge Slot Film Cooling

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Julia Ling ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Concentration Distribution ◽  
Schmidt Number ◽  
Imaging Techniques ◽  
Scalar Flux ◽  
Concentration Data ◽  
Trailing Edge ◽  
Turbulent Schmidt Number ◽  
Rans Simulations ◽  
Slot Film Cooling

It has been previously demonstrated that Reynolds-averaged Navier–Stokes (RANS) simulations do not accurately capture the mixing between the coolant flow and the main flow in trailing edge slot film cooling configurations. Most RANS simulations use a fixed turbulent Schmidt number of either 0.7 or 0.85 to determine the turbulent scalar flux, based on the values for canonical flows. This paper explores the extent to which RANS predictions can be improved by modifying the value of the turbulent Schmidt number. Experimental mean 3D velocity and coolant concentration data obtained using magnetic resonance imaging techniques are used to evaluate the accuracy of RANS simulations. A range of turbulent Schmidt numbers from 0.05 to 1.05 is evaluated and the optimal turbulent Schmidt number for each case is determined using an integral error metric which accounts for the difference between RANS and experiment throughout a three-dimensional region of interest (ROI). The resulting concentration distribution is compared in detail with the experimentally measured coolant concentration distribution to reveal where the fixed turbulent Schmidt number assumption fails. It is shown that the commonly used turbulent Schmidt number of 0.85 overpredicts the surface effectiveness in all cases, particularly when the k-omega shear stress transport (SST) model is employed, and that a lower value of the turbulent Schmidt number can improve predictions.

Optimal Turbulent Schmidt Number for RANS Modeling of Trailing Edge Slot Film Cooling

2014 ◽  
Author(s):  
Julia Ling ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Concentration Distribution ◽  
Schmidt Number ◽  
Imaging Techniques ◽  
Scalar Flux ◽  
Concentration Data ◽  
Trailing Edge ◽  
Turbulent Schmidt Number ◽  
Rans Simulations ◽  
Slot Film Cooling

It has been previously demonstrated that Reynolds Averaged Navier Stokes (RANS) simulations do not accurately capture the mixing between the coolant flow and the main flow in trailing edge slot film cooling configurations. Most RANS simulations use a fixed turbulent Schmidt number of either 0.7 or 0.85 to determine the turbulent scalar flux, based on the values for canonical flows. This paper explores the extent to which RANS predictions can be improved by modifying the value of the turbulent Schmidt number. Experimental mean 3D velocity and coolant concentration data obtained using Magnetic Resonance Imaging techniques are used to evaluate the accuracy of RANS simulations. A range of turbulent Schmidt numbers from 0.05 to 1.05 is evaluated and the optimal turbulent Schmidt number for each case is determined using an integral error metric which accounts for the difference between RANS and experiment throughout a 3-dimensional region of interest. The resulting concentration distribution is compared in detail with the experimentally measured coolant concentration distribution to reveal where the fixed turbulent Schmidt number assumption fails. It is shown that the commonly used turbulent Schmidt number of 0.85 over-predicts the surface effectiveness in all cases, particularly when the k-omega SST model is employed, and that a lower value of the turbulent Schmidt number can improve predictions.

The Effect of Land Taper Angle on Trailing Edge Slot Film Cooling

2014 ◽  
Author(s):  
Julia Ling ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Concentration Distribution ◽  
Imaging Techniques ◽  
Turbine Blades ◽  
Mean Flow ◽  
Trailing Edge ◽  
Taper Angle ◽  
The Mean ◽  
Slot Film Cooling ◽  
The Impact

Trailing edge slot film cooling is a widely used method of protecting the thin trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations which can be broadly classified as either “tapered” or “straight.” This paper examines the effect of the land taper angle on the mixing of the coolant flow with the main flow by comparing three configurations: a case with straight lands, a previously reported case with slightly tapered lands, and a case with strongly tapered lands. In each case, the slot width and the land width at the plane of the slot exit are kept constant. For each configuration, the mean volumetric coolant concentration distribution and 3-component velocity field were measured using Magnetic Resonance Imaging techniques. It is shown that the land taper angle has a strong effect on the mean flow features and coolant surface effectiveness. Furthermore, the impact of the lands configuration on the flow field and concentration distribution is seen not just in the cutback region, but also in the wake of the blade.

The Effect of Land Taper Angle on Trailing Edge Slot Film Cooling

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Julia Ling ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Concentration Distribution ◽  
Turbine Blades ◽  
Mean Flow ◽  
Trailing Edge ◽  
Taper Angle ◽  
Flow Features ◽  
The Mean ◽  
Slot Film Cooling ◽  
The Impact

Trailing edge slot film cooling is a widely used method of protecting the thin trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations which can be broadly classified as either “tapered” or “straight.” This paper examines the effect of the land taper angle on the mixing of the coolant flow with the main flow by comparing three configurations: a case with straight lands, a previously reported case with slightly tapered lands, and a case with strongly tapered lands. In each case, the slot width and the land width at the plane of the slot exit are kept constant. For each configuration, the mean volumetric coolant concentration distribution and three-component velocity field were measured using magnetic resonance imaging (MRI) techniques. It is shown that the land taper angle has a strong effect on the mean flow features and coolant surface effectiveness. Furthermore, the impact of the lands configuration on the flow field and concentration distribution is seen not just in the cutback region, but also in the wake of the blade.

Investigation on the Effect of Different Lands on Trailing Edge Slot Film Cooling

2018 ◽  
Vol 0 (0) ◽  
Author(s):  
Yang Xu ◽  
Hui-ren Zhu ◽  
Wei-jiang Xu ◽  
Jian-sheng Wei
Keyword(s):  
Nusselt Number ◽  
Film Cooling ◽  
Turbine Blades ◽  
Experimental Studies ◽  
Navier Stokes ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Wall Functions ◽  
Film Cooling Effectiveness ◽  
Slot Film Cooling

Abstract Trailing edge slot film cooling is a widely used method for protecting the trailing edge of turbine blades from hot gas impingement. The structures that separate the slots, known as “lands,” come in a variety of configurations. This paper presents the effects of the trailing edge with different lands on the film cooling performance. Experimental studies are conducted on the film cooling effectiveness and Nusselt number with different lands. Four trailing edge configurations, including the straight lands, the beveling lands, the fillet lands and the tapered lands are considered under four blowing ratios (0.5, 0.7, 1.0 and 1.5). The Reynolds numbers of mainstream is fixed as 375,000. Film cooling effectiveness and Nusselt number performances are measured by transient liquid crystal measurement technique. Reynolds-averaged Navier-Stokes (RANS) simulation with realizable k-ε turbulence model and enhanced wall functions are performed using a commercial code Fluent. In each case, the slot height is kept constant. It is shown that the beveling lands, the fillet lands and the tapered lands have higher cooling effectiveness and lower Nusselt number compared with the straight lands. Under higher blowing ratios, the trailing edges of all four lands have higher cooling effectiveness and higher Nusselt number.

Measurements of a Trailing Edge Slot Film Cooling Geometry Designed for Reduced Coolant Flowrate and High Surface Effectiveness

2013 ◽  
Author(s):  
Julia Ling ◽  
Christopher J. Elkins ◽  
Michael J. Benson ◽  
Sayuri D. Yapa ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
High Surface ◽  
Trailing Edge ◽  
Mean Fields ◽  
The Mean ◽  
Magnetic Resonance Imaging Mri ◽  
Slot Film Cooling ◽  
Spatially Varying ◽  
Enhanced Surface ◽  
Insight Into

A trailing edge slot film cooling configuration designed for enhanced surface effectiveness at a decreased coolant flowrate is proposed. Magnetic resonance imaging (MRI) techniques were used to obtain measurements of the mean 3D velocity and concentration fields. These measurements are compared to previously reported results on two other trailing edge configurations. The surface effectiveness of the proposed slot film cooling configuration is higher than that of the baseline configuration, even at a 25% lower coolant flowrate. The mean fields are used to calculate an isotropic, spatially-varying turbulent diffusivity for each of these trailing edge configurations. These diffusivities are compared to offer insight into the effect of land shape on turbulence properties.

Near Wall Modeling for Trailing Edge Slot Film Cooling

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Julia Ling ◽  
Riccardo Rossi ◽  
John K. Eaton
Keyword(s):  
Boundary Layer ◽  
Film Cooling ◽  
Scale Model ◽  
Wall Region ◽  
Turbulent Diffusivity ◽  
Trailing Edge ◽  
Reynolds Analogy ◽  
Rans Models ◽  
Slot Film Cooling ◽  
Near Wall

Trailing edge slot film cooling is a widely used active cooling scheme for turbine blade trailing edges. Current Reynolds-Averaged Navier–Stokes (RANS) models are known to significantly overpredict the adiabatic effectiveness of these configurations. It is shown that this overprediction is due in part to the breakdown of the Reynolds analogy between turbulent shear stress and scalar transport in the near wall region. By examining previously reported direct numerical simulation (DNS) results for a wall-mounted cube in cross flow, it is seen that in a flow with a significantly perturbed outer boundary layer, the turbulent diffusivity is not as strongly damped as the turbulent viscosity in the viscous sublayer and buffer layer of the boundary layer. By removing the Van Driest damping function from the length scale model for the turbulent diffusivity, more accurate turbulent diffusivity predictions are possible. This near wall correction is applied to trailing edge slot film cooling flows and it is demonstrated that the predictive accuracy of the RANS models is significantly enhanced. Detailed comparisons between RANS results and experimental datasets for 15 different cases demonstrate that this correction gives significant improvement to the accuracy of the RANS predictions across a broad range of trailing edge slot film cooling configurations.

Three-Dimensional Velocity and Scalar Field Measurements of an Airfoil Trailing Edge With Slot Film Cooling: The Effect of an Internal Structure in the Slot

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Julia Ling ◽  
Sayuri D. Yapa ◽  
Michael J. Benson ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Three Dimensional ◽  
Field Measurements ◽  
Resonance Imaging ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Horseshoe Vortices ◽  
Edge Span ◽  
Slot Film Cooling

Measurements of the 3D velocity and concentration fields were obtained using magnetic resonance imaging for a pressure-side cutback film cooling experiment. The cutback geometry consisted of rectangular slots separated by straight lands; inside each of the slots was an airfoil-shaped blockage. The results from this trailing edge configuration, the “island airfoil,” are compared to the results obtained with the “generic airfoil,” a geometry with narrower slots, wider, tapered lands, and no blockages. The objective was to determine how the narrower lands and internal blockages affected the average film cooling effectiveness and the spanwise uniformity. Velocimetry data revealed that strong horseshoe vortices formed around the blockages in the slots, which resulted in greater coolant nonuniformity on the airfoil breakout surface and in the wake. The thinner lands of the island airfoil allowed the coolant to cover a larger fraction of the trailing edge span, giving a much higher spanwise-averaged surface effectiveness, especially near the slot exit where the generic airfoil lands are widest.

3D Velocity and Scalar Field Measurements of an Airfoil Trailing Edge With Slot Film Cooling: The Effect of an Internal Structure in the Slot

2012 ◽  
Author(s):  
Julia Ling ◽  
Sayuri D. Yapa ◽  
Michael J. Benson ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Field Measurements ◽  
Pressure Side ◽  
Resonance Imaging ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Horseshoe Vortices ◽  
Edge Span ◽  
Slot Film Cooling

Measurements of the 3D velocity and concentration fields were obtained using magnetic resonance imaging for a pressure side cutback film cooling experiment. The cutback geometry consisted of rectangular slots separated by straight lands; inside each of the slots was an airfoil-shaped blockage. The results from this trailing edge configuration, the “island airfoil,” are compared to the results obtained with the “generic airfoil,” a geometry with narrower slots, wider, tapered lands, and no blockages. The objective was to determine how the narrower lands and internal blockages affected the average film cooling effectiveness and the spanwise uniformity. Velocimetry data revealed that strong horseshoe vortices formed around the blockages in the slots, which resulted in greater coolant non-uniformity on the airfoil breakout surface and in the wake. The thinner lands of the island airfoil allowed the coolant to cover a larger fraction of the trailing edge span, giving a much higher spanwise-averaged surface effectiveness, especially near the slot exit where the generic airfoil lands are widest.

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