Experimental-Based Redesigns for Trailing Edge Film Cooling of Gas Turbine Blades

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Michael Benson ◽  
Sayuri D. Yapa ◽  
Chris Elkins ◽  
John K. Eaton
Keyword(s):  
Magnetic Resonance ◽  
Film Cooling ◽  
Large Scale ◽  
Thermal Stresses ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Structures ◽  
Mean Flow ◽  
Trailing Edge ◽  
Mean Velocity

Magnetic resonance imaging experiments have provided the three-dimensional mean concentration and three component mean velocity field for a typical trailing edge film-cooling cutback geometry built into a conventional uncambered airfoil. This geometry is typical of modern aircraft engines and includes three dimensional slot jets separated by tapered lands. Previous analysis of these data identified the critical mean flow structures that contribute to rapid mixing and low effectiveness in the fully turbulent flow. Three new trailing edge geometries were designed to modify the large scale mean flow structures responsible for surface effectiveness degradation. One modification called the Dolphin Nose attempted to weaken strong vortex flows by reducing three dimensionality near the slot breakout. This design changed the flow structure but resulted in minimal improvement in the surface effectiveness. Two other designs called the Shield and Rounded Shield changed the land planform and added an overhanging land edge while maintaining the same breakout surface. These designs substantially modified the vortex structure and improved the surface effectiveness by as much as 30%. Improvements included superior coolant uniformity on the breakout surface which reduces potential thermal stresses. The utilization of the time averaged data from combined magnetic resonance velocimetry (MRV) and concentration (MRC) experiments for designing improved trailing edge breakout film cooling is demonstrated.

Experimental-Based Redesigns for Trailing Edge Film Cooling of Gas Turbine Blades

2012 ◽  
Author(s):  
Michael Benson ◽  
Sayuri Yapa ◽  
Chris Elkins ◽  
John K. Eaton
Keyword(s):  
Magnetic Resonance ◽  
Film Cooling ◽  
Large Scale ◽  
Thermal Stresses ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Flow Structures ◽  
Mean Flow ◽  
Trailing Edge ◽  
Mean Velocity

Magnetic resonance imaging experiments have provided the three-dimensional mean concentration and three component mean velocity field for a typical trailing edge film-cooling cutback geometry built into a conventional uncambered airfoil. This geometry is typical of modern aircraft engines and includes three dimensional slot jets separated by tapered lands. Previous analysis of these data identified the critical mean flow structures that contribute to rapid mixing and low effectiveness in the fully turbulent flow. Three new trailing edge geometries were designed to modify the large scale mean flow structures responsible for surface effectiveness degradation. One modification called the Dolphin Nose attempted to weaken strong vortex flows by reducing three dimensionality near the slot breakout. This design changed the flow structure but resulted in minimal improvement in the surface effectiveness. Two other designs called the Shield and Rounded Shield changed the land planform and added an overhanging land edge while maintaining the same breakout surface. These designs substantially modified the vortex structure and improved the surface effectiveness by as much as 30%. Improvements included superior coolant uniformity on the breakout surface which reduces potential thermal stresses. The utilization of the time averaged data from combined magnetic resonance velocimetry (MRV) and concentration (MRC) experiments for designing improved trailing edge breakout film cooling is demonstrated.

Film-Cooled Trailing Edge Measurements: 3D Velocity and Scalar Field

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
Michael Benson ◽  
Gregory Laskowski ◽  
Chris Elkins ◽  
John K. Eaton
Keyword(s):  
Magnetic Resonance ◽  
Film Cooling ◽  
Three Dimensional ◽  
Turbulent Regime ◽  
Velocity Measurements ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Longitudinal Vortices

Aircraft turbine blade trailing edges commonly are cooled by blowing air through pressure-side cutback slots. The surface effectiveness is governed by the rate of mixing of the coolant with the mainstream, which is typically much faster than predicted by CFD models. Three-dimensional velocity and coolant concentration fields were measured in and around a cutback slot using a simple uncambered airfoil with a realistic trailing edge cooling geometry at a Reynolds number of 110,000 based on airfoil chord length, which is lower than practical engines but still in the turbulent regime. The results were obtained using magnetic resonance imaging (MRI) techniques in a water flow apparatus. Magnetic resonance concentration (MRC) scans measured the concentration distribution with a spatial resolution of 0.5 mm3 (compared to a slot height of 5 mm) and an uncertainty near 5%. Magnetic resonance velocimetry (MRV) was used to acquire 3D, three-component mean velocity measurements with a resolution of 1.0 mm3. Coupled concentration and velocity measurements were used to identify flow structures contributing to the rapid mixing, including longitudinal vortices and separation bubbles. Velocity measurements at several locations were compared with an unsteady RANS model. Concentration measurements extrapolated to the surface provided film cooling effectiveness and showed that the longitudinal vortices decreased effectiveness near the lands and reduced the average film cooling effectiveness.

Film-Cooled Trailing Edge Measurements: 3D Velocity and Scalar Field

2011 ◽  
Author(s):  
Michael Benson ◽  
Gregory Laskowski ◽  
Chris Elkins ◽  
John K. Eaton
Keyword(s):  
Magnetic Resonance ◽  
Film Cooling ◽  
Turbulent Regime ◽  
Velocity Measurements ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Longitudinal Vortices ◽  
Magnetic Resonance Velocimetry

Aircraft turbine blade trailing edges commonly are cooled by blowing air through pressure-side cutback slots. The surface effectiveness is governed by the rate of mixing of the coolant with the mainstream, which is typically much faster than predicted by CFD models. 3D velocity and coolant concentration fields were measured in and around a cutback slot using a simple uncambered airfoil with a realistic trailing edge cooling geometry at a Reynolds number of 110,000 based on airfoil chord length, which is lower than practical engines but still in the turbulent regime. The results were obtained using magnetic resonance imaging (MRI) techniques in a water flow apparatus. Magnetic resonance concentration (MRC) scans measured the concentration distribution with a spatial resolution of 0.5 mm3 (compared to a slot height of 5 mm) and an uncertainty near 5%. Magnetic resonance velocimetry (MRV) was used to acquire 3D, three-component mean velocity measurements with a resolution of 1.0 mm3. Coupled concentration and velocity measurements were used to identify flow structures contributing to the rapid mixing, including longitudinal vortices and separation bubbles. Velocity measurements at several locations were compared with an unsteady RANS model. Concentration measurements extrapolated to the surface provided film cooling effectiveness and showed that the longitudinal vortices decreased effectiveness near the lands and reduced the average film cooling effectiveness.

Quantitative MRI Measurements of Hot Streak Development in a Turbine Vane Cascade

2015 ◽  
Author(s):  
Sayuri D. Yapa ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Film Cooling ◽  
Thermal Stresses ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Turbine Rotor ◽  
Quantitative Mri ◽  
Inlet Temperature ◽  
Cooling Design ◽  
Pass Through ◽  
Hot Streak

Hot streaks from the combustor and cool streaks from nozzle vane film cooling impose strong inlet temperature variations on high pressure turbine blades, which can lead to local hot or cold spots, high thermal stresses, and fatigue failures. Furthermore, the complex three dimensional flows around the vane may act to concentrate cool or hot fluid exiting the vane row. In order to optimize the cooling design of the turbine blades, the designer must be able to predict the temperature distribution entering the turbine rotor. Therefore, it is important to understand and predict how combustor hot streaks are dispersed as they pass through the vane row. The goal of the present work is to provide detailed three dimensional velocity and temperature data for simulated combustor hot streaks developing through a film cooled vane cascade using the Magnetic Resonance Velocity/Concentration experimental technique. The measurements show that the hot streaks are thinned by acceleration through the vane cascade and diffused by turbulence. The turbulent diffusivity is suppressed by acceleration and leaves significant temperature nonuniformity in the vane wake.

Transport of Microparticles in a Turbulated Serpentine Passage

2017 ◽  
Author(s):  
Daniel D. Borup ◽  
Christopher J. Elkins ◽  
John K. Eaton
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Turbulent Dispersion ◽  
Channel Height ◽  
Mean Flow ◽  
High Concentration ◽  
Concentration Data ◽  
Mean Velocity ◽  
Data Set ◽  
Improved Design

Quantitative, fully three-dimensional particle concentration data were obtained for a streak of ∼30 micron titanium micro-spheres injected isokinetically into the center of flow at Re = 20,000 through a ribbed serpentine passage. The rib height to channel height ratio was 10% and the pitch was 60% channel height. The ribs were oriented at 45° to the flow and staggered on opposite walls. Each passage was 10 ribs long. Concentration measurements were made using a newly developed Magnetic Resonance Imaging (MRI) based technique with an uncertainty of ±0.018% particles by volume. Three-component mean velocity data were also obtained using an existing MRI technique. The concentration data are in good agreement with the expected large-scale particle transport based on the mean flow field. Quantitative analysis is performed in the high-concentration portion of the streak where turbulent dispersion plays a significant role. Particles also tend to concentrate just upstream of the angled ribs, forming rivulets that persist as the flow returns to the channel center. These results suggest the potential for improved design of dust-resistant cooling systems based on experimental data. It is also concluded that the data set comprises a suitable validation case for Computational Fluid Dynamics (CFD) simulations.

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.

On Coupling of RANS and LES for Integrated Computations of Jet Engines

2007 ◽  
Author(s):  
Gorazd Medic ◽  
Donghyun You ◽  
Georgi Kalitzin
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Operating Conditions ◽  
Jet Engines ◽  
Mean Flow ◽  
Mean Velocity ◽  
Novel Approach ◽  
The Mean ◽  
Flow Variables

Large scale integrated computations of jet engines can be performed by using the unsteady RANS framework to compute the flow in turbomachinery components while using the LES framework to compute the flow in the combustor. This requires a proper coupling of the flow variables at the interfaces between the RANS and LES solvers. In this paper, a novel approach to turbulence coupling is proposed. It is based on the observation that in full operating conditions the mean flow at the interfaces is highly non-uniform and local turbulence production dominates convection effects in regions of large velocity gradients. This observation has lead to the concept of using auxilliary ducts to compute turbulence based on the mean velocity at the interface. In the case of the RANS/LES interface, turbulent fluctuations are reconstructed from an LES computation in an auxiliary three-dimensional duct using a recycling technique. For the LES/RANS interface, the turbulence variables for the RANS model are computed from an auxilliary solution of the RANS turbulence model in a quasi-2D duct. We have demonstrated the feasibility of this approach for the integrated flow simulation of a 20° sector of an entire jet engine.

Numerical Predictions of Three-Dimensional Unsteady Turbulent Film-Cooling for Trailing Edge of Gas-Turbine Blade Using Large Eddy Simulation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Ahmed Khalil ◽  
Hatem Kayed ◽  
Abdallah Hanafi ◽  
Medhat Nemitallah ◽  
Mohamed Habib
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Trailing Edge ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Gas Turbine Blades ◽  
Blowing Ratio ◽  
Eddy Simulation

This work investigates the performance of film-cooling on trailing edge of gas turbine blades using unsteady three-dimensional numerical model adopting large eddy simulation (LES) turbulence scheme in a low Mach number flow regime. This study is concerned with the scaling parameters affecting effectiveness and heat transfer performance on the trailing edge, as a critical design parameter, of gas turbine blades. Simulations were performed using ANSYS-fluentworkbench 17.2. High quality mesh was adapted, whereas the size of cells adjacent to the wall was optimized carefully to sufficiently resolve the boundary layer to obtain insight predictions of the film-cooling effectiveness on a flat plate downstream the slot opening. Blowing ratio, density ratio, Reynolds number, and the turbulence intensity of the mainstream and coolant flow are optimally examined against the film-cooling effectiveness. The predicted results showed a great agreement when compared with the experiments. The results show a distinctive behavior of the cooling effectiveness with blowing ratio variation as it has a dip in vicinity of unity which is explained by the behavior of the vortex entrainment and momentum of coolant flow. The negative effect of the turbulence intensity on the cooling effectiveness is demonstrated as well.

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.

Characterization of Vortex Dynamics in the Near Wake of an Oscillating Flexible Foil

2016 ◽  
Author(s):  
Firas F. Siala ◽  
Alexander D. Totpal ◽  
James A. Liburdy
Keyword(s):  
Large Scale ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Mean Flow ◽  
Near Wake ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
The Mean

An experimental study was conducted to explore the effect of surface flexibility at the leading and trailing edges on the near-wake flow dynamics of a sinusoidal heaving foil. Mid-span particle image velocimetry measurements were taken in a closed loop wind tunnel at a Reynolds number of 25,000 and at a range of reduced frequencies (k = fc/U) from 0.09–0.20. Time resolved and phase locked measurements were used to describe the mean flow characteristics and phase averaged vortex structures and their evolution throughout the oscillation cycle. Large eddy scale decomposition and swirl strength analysis were used to quantify the effect of flexibility on the vortical structures. The results demonstrate that flexibility at the trailing edge has a minimal influence on the mean flow characteristics when compared to the purely rigid foil. The mean velocity deficit for the flexible trailing edge and rigid foils is shown to remain constant for all reduced frequencies tested. However, the trailing edge flexibility increases the swirl strength of the small scale structures, which results in enhanced cross stream dispersion of the mean velocity profile. Flexibility at the leading edge is shown to generate a large scale leading edge vortex for k ≥ 0.18. This results in a reduction in the swirl strength due to the complex vortex interactions when compared to the flexible trailing edge and rigid foils. Furthermore, it is shown that the large scale leading edge vortex is responsible for extracting a significant portion of the energy from the mean flow, resulting in a substantial reduction of mean flow momentum in the wake. The kinetic energy loss in the wake is shown to scale well with the energy content of the leading edge vortex.

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