Experimental Evaluations of the Relative Contributions to Overall Effectiveness in Turbine Blade Leading Edge Cooling

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
Carol E. Bryant ◽  
Connor J. Wiese ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Biot Number ◽  
Film Cooling ◽  
Leading Edge ◽  
Internal Surface ◽  
Internal Cooling ◽  
Surface Cooling ◽  
External Cooling ◽  
Cooling Design ◽  
Computational Fluid Dynamics Cfd ◽  
Film Cooling Holes

Gas turbine components are protected through a combination of internal cooling and external film cooling. Efforts aimed at improving cooling are often focused on either the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. Measurements of overall cooling effectiveness, ϕ, using matched Biot number models allow evaluation of fully cooled components; however, the relative contributions of internal cooling, external cooling, and convection within the film cooling holes are not well understood. Matched Biot number experiments, complemented by computational fluid dynamics (CFD) simulations, were performed on a fully film cooled cylindrical leading edge model to quantify the effects of alterations in the cooling design. The relative influence of film cooling and cooling within the holes was evaluated by selectively disabling individual holes and quantifying how ϕ changed. Testing of several impingement cooling schemes revealed that impingement has a negligible influence on ϕ in the showerhead region. This indicates that the pressure drop penalties with impingement may not always be compensated by an increase in ϕ. Instead, internal cooling from convection within the holes and film cooling were shown to be the dominant contributors to ϕ. Indeed, the numerous holes within the showerhead region impede the ability of internal surface cooling schemes to influence the outside surface temperature. These results may allow improved focus of efforts on the forms of cooling with the greatest potential to improve performance.

Experimental Evaluations of the Relative Contributions to Overall Effectiveness in Turbine Blade Leading Edge Cooling

2018 ◽  
Author(s):  
Carol E. Bryant ◽  
Connor J. Wiese ◽  
James L. Rutledge ◽  
Marc D. Polanka
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Leading Edge ◽  
Internal Surface ◽  
Internal Cooling ◽  
Transfer Coefficients ◽  
Impingement Cooling ◽  
External Cooling ◽  
Turbine Component ◽  
Overall Effectiveness

Gas turbine hot gas path components are protected through a combination of internal cooling and external film cooling. The coolant typically travels through internal passageways, which may involve impingement on the internal surface of a turbine component, before being ejected as film cooling. Internal cooling effects have been studied in facilities that allow measurement of heat transfer coefficients within models of the internal cooling paths, with large heat transfer coefficients generally desirable. External film cooling is typically evaluated through measurements of the adiabatic effectiveness and its effect on the external heat transfer coefficient. Efforts aimed at improving cooling are often focused on either only the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. Recently, measurements of overall cooling effectiveness using matched Biot number turbine component models allow evaluation of the nondimensional wall temperature achieved for the fully cooled component. However, the relative contributions of internal cooling, external cooling, and convection within the film cooling holes is not well understood. Large scale, matched Biot number experiments, complemented by CFD simulations, were performed on a fully film cooled cylindrical leading edge model to evaluate the effects of various alterations in the cooling design on the overall effectiveness. The relative influence of film cooling and cooling within the holes was evaluated by selectively disabling individual holes and quantifying how the overall effectiveness changed. Several internal impingement cooling schemes in addition to a baseline case without impingement cooling were also tested. In general, impingement cooling is shown to have a negligible influence on the overall effectiveness in the showerhead region. This indicates that the cost and pressure drop penalties for implementing impingement cooling may not be compensated by an increase in thermal performance. Instead, the internal cooling provided by convection within the holes themselves was shown, along with external film cooling, to be a dominant contribution to the overall cooling effectiveness. Indeed, the numerous holes within the showerhead region impede the ability of internal surface cooling schemes to influence the outside surface temperature. The results of this research may allow improved focus of future efforts on the forms of cooling with the greatest potential to improve cooling performance.

A Computational Technique to Evaluate the Relative Influence of Internal and External Cooling on Overall Effectiveness

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Carol E. Bryant ◽  
James L. Rutledge
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Internal Surface ◽  
Coolant Flow ◽  
Relative Influence ◽  
Computational Technique ◽  
Internal Cooling ◽  
External Cooling ◽  
Film Cooling Holes ◽  
Overall Effectiveness

Abstract Gas turbine components are protected via a coolant that travels through internal passageways before being ejected as external film cooling. Modern computational approaches facilitate the simulation of the conjugate heat transfer that takes place within turbine components, allowing the prediction of the actual metal temperature, nondimensionalized as overall effectiveness. Efforts aimed at improving cooling are often focused on either the internal cooling or the film cooling; however, the common coolant flow means that the internal and external cooling schemes are linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. The relative influence of internal cooling, external cooling, and convection through the film cooling holes on overall effectiveness is not well understood. Computational fluid dynamics (CFD) simulations were performed to isolate each cooling mechanism, and thereby determine their relative contributions to overall effectiveness. The conjugate CFD model was a flat plate with five staggered rows of shaped film cooling holes. Unique boundary conditions were used to isolate the cooling mechanisms. The internal surface was modeled with and without heat transfer on the internal face in order to isolate the effects of plenum cooling. Convection through the coolant holes was isolated by making the inside of the film cooling holes adiabatic to evaluate the influence of the internal cooling provided by the cooling holes themselves. Finally, the effect of film cooling was removed through the novel use of an outlet boundary condition at the exit of each hole that allowed the internal coolant flow without external coolant ejection.

A Computational Technique to Evaluate the Relative Influence of Internal and External Cooling on Overall Effectiveness

2019 ◽  
Author(s):  
Carol E. Bryant ◽  
James L. Rutledge
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Internal Surface ◽  
Coolant Flow ◽  
Relative Influence ◽  
Computational Technique ◽  
Internal Cooling ◽  
External Cooling ◽  
Film Cooling Holes ◽  
Overall Effectiveness

Abstract Gas turbine hot gas path components are protected via coolant that travels through internal passageways before being ejected as external film cooling. Modern computational approaches facilitate simulation of the conjugate heat transfer that takes place within turbine components, allowing prediction of the actual metal temperature, usually nondimensionalized in the form of the overall effectiveness. Efforts aimed at improving cooling are often focused on either only the internal cooling or the film cooling; however, the common coolant flow means the internal and external cooling schemes are inextricably linked and the coolant holes themselves provide another convective path for heat transfer to the coolant. The relative influence of internal cooling, external cooling, and convection through the film cooling holes on overall effectiveness is not well understood. Computational fluid dynamics (CFD) simulations were performed in order to isolate each cooling mechanism, and thereby determine their relative contributions to overall effectiveness. The conjugate CFD model was a flat plate with five staggered rows of shaped film cooling holes. Unique boundary conditions were used to isolate the cooling mechanisms. The internal cooling was modeled with and without heat transfer on the internal surface in order to isolate the effects of plenum cooling. Convection through the coolant holes was isolated by making the inside of the film cooling holes adiabatic. This was done in order to evaluate the influence of the internal cooling provided by the cooling holes themselves. The effect of film cooling was removed through the novel use of an outlet boundary condition at the exit of each hole that allowed unaltered internal coolant flow without external coolant ejection.

Coolant Jets Blowing Across the Airfoil Stagnation Line to Enhance Film Effectiveness

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Nicholas E. Holgate ◽  
Peter T. Ireland ◽  
Eduardo Romero
Keyword(s):  
Film Cooling ◽  
Recent Literature ◽  
Leading Edge ◽  
The Other ◽  
Experimental Film ◽  
Stagnation Line ◽  
Mainstream Flow ◽  
Cooling Design ◽  
Film Cooling Holes ◽  
Effectiveness Data

Abstract A novel airfoil leading edge film cooling design has been investigated, and its performance over conventional alternatives quantified. In conventional designs, the region near the geometric stagnation line is typically between the two most upstream film hole rows, which each emit coolant in the downstream direction on their respective sides of the airfoil. This region is thus relatively starved of coolant flow and adequate cooling is achieved inefficiently with a high density of holes expelling a large amount of coolant in order to dilute the nearby mainstream flow. Drawing inspiration from recent literature on reverse-blowing film cooling holes, several film cooling geometries have been designed and tested with a view to improving upon this situation by blowing coolant from each side of the airfoil geometric stagnation line to the other in a criss-cross pattern. This is found to be capable of producing much higher film effectiveness near the stagnation line than a series of more conventional designs which were also tested, without decreasing downstream film effectiveness. A method is also described for using experimental film effectiveness data to estimate two novel measures of the efficiency of leading edge film coolant usage: the proportion of the mainstream which interacts with leading edge film coolant and the proportion of coolant from the two most upstream film hole rows which reaches the stagnation line.

Influence of Film-Hole Shape and Angle on Showerhead Film Cooling Using PSP Technique

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Zhihong Gao ◽  
Je-Chin Han
Keyword(s):  
Film Cooling ◽  
Leading Edge ◽  
Stagnation Line ◽  
Film Cooling Effectiveness ◽  
Blowing Ratio ◽  
Cooling Hole ◽  
Cooling Design ◽  
Cylindrical Holes ◽  
Film Cooling Holes ◽  
Compound Angle

The effect of film-hole geometry and angle on turbine blade leading edge film cooling has been experimentally studied using the pressure sensitive paint technique. The leading edge is modeled by a blunt body with a semicylinder and an after-body. Two film cooling designs are considered: a heavily film cooled leading edge featured with seven rows of film cooling holes and a moderately film cooled leading edge with three rows. For the seven-row design, the film holes are located at 0 deg (stagnation line), ±15 deg, ±30 deg, and ±45 deg on the model surface. For the three-row design, the film holes are located at 0 deg and ±30 deg. Four different film cooling hole configurations are applied to each design: radial angle cylindrical holes, compound angle cylindrical holes, radial angle shaped holes, and compound angle shaped holes. Testing was done in a low speed wind tunnel. The Reynolds number, based on mainstream velocity and diameter of the cylinder, is 100,900. The mainstream turbulence intensity is about 7% near of leading edge model and the turbulence integral length scale is about 1.5 cm. Five averaged blowing ratios are tested ranging from M=0.5 to M=2.0. The results show that the shaped holes provide higher film cooling effectiveness than the cylindrical holes, particularly at higher average blowing ratios. The radial angle holes give better effectiveness than the compound angle holes at M=1.0–2.0. The seven-row film cooling design results in much higher effectiveness on the leading edge region than the three-row design at the same average blowing ratio or same amount coolant flow.

Adiabatic and Overall Effectiveness for a Fully Cooled Turbine Vane

2013 ◽  
Author(s):  
Thomas E. Dyson ◽  
John W. McClintic ◽  
David G. Bogard ◽  
Sean D. Bradshaw
Keyword(s):  
Biot Number ◽  
Film Cooling ◽  
Large Scale ◽  
Internal Heat ◽  
Coolant Temperature ◽  
Internal Cooling ◽  
Impingement Cooling ◽  
Turbine Vane ◽  
Cooling Design ◽  
Overall Effectiveness

Adiabatic and overall effectiveness data were measured for a fully cooled, scaled up turbine vane model in a low speed linear cascade with a chord-exit Reynolds number of 700,000. The overall effectiveness is a measure of the external surface temperature relative to the mainstream temperature and the inlet coolant temperature, and consequently is a direct measure of how effectively the surface is cooled. This can be determined experimentally when the experimental model is constructed so that the Biot number of the model and the ratio of the external to internal heat transfer coefficient are chosen so that the model has a similar thermal behavior to that of an actual engine component. The model used in this study had a cooling design that consisted of 149 total coolant holes in 13 rows, including a showerhead containing five rows of holes. The model also incorporated an internal impingement cooling configuration. An identical model was also constructed out of low conductivity foam to measure adiabatic effectiveness. This is the first study to use a large scale, matched Biot number model to measure engine representative overall effectiveness for a vane employing full coverage film cooling. The focus of this research was to determine the relative contributions of the external and internal cooling, and to serve as a baseline for validation of computational simulations. Additionally, a simplified model using measurements of overall effectiveness with internal cooling alone was used to predict overall effectiveness downstream of the showerhead.

Numerical investigations of endwall film cooling design of a turbine vane using four-holes pattern

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Jian Liu ◽  
Xi Wenxiong ◽  
Mengyao Xu ◽  
Jiawen Song ◽  
Shibin Luo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Leading Edge ◽  
Full Scale ◽  
Junction Region ◽  
Content Type ◽  
Mesh Independence ◽  
Cooling Design ◽  
Endwall Film Cooling ◽  
Film Cooling Holes

Purpose Endwall film cooling protects vane endwall by coolant coverage, especially at the leading edge (LE) region and vane-pressure side (PS) junction region. Strong flow impingement and complex vortexaa structures on the vane endwall cause difficulties for coolant flows to cover properly. This work aims at a full-scale arrangement of film cooling holes on the endwall which improves coolant efficiency in the LE region and vane-PS junction region. Design/methodology/approach The endwall film holes are grouped in four-holes constructal patterns. Three ways of arranging the groups are studied: based on the pressure field, the streamlines or the heat transfer field. The computational analysis is done with the k-ω SST model after validating the turbulence model properly. Findings By clustering the film cooling holes in four-holes patterns, the ejection of the coolant flow is stronger. The four-holes constructal patterns also improve the local coolant coverage in the “tough” regions, such as the junction region of the PS and the endwall. The arrangement based on streamlines distribution can effectively improve the coolant coverage and the arrangement based on the heat transfer distribution (HTD) has benefits by reducing high-temperature regions on the endwall. Originality/value A full-scale endwall film cooling design is presented considering interactions of different film cooling holes. A comprehensive model validation and mesh independence study are provided. The cooling holes pattern on the endwall is designed as four-holes constructal patterns combined with several arrangement choices, i.e. by pressure, by heat transfer and by streamline distributions.

Exploitation of Acoustic Effects in Film Cooling

2015 ◽  
Vol 137 (10) ◽  
Author(s):  
Matthew Collins ◽  
Thomas Povey
Keyword(s):  
Film Cooling ◽  
Pressure Wave ◽  
Cooling System ◽  
Large Pressure ◽  
Cooling Hole ◽  
Cooling Design ◽  
Computational Fluid Dynamics Cfd ◽  
Rate Profile ◽  
Film Cooling Holes ◽  
First Time

There have been numerous studies of the behavior of shaped film cooling holes for turbine applications. It is known that the introduction of coolant is an unsteady process, and a handful of studies have described and characterized the unsteadiness. To the best of our knowledge, there are no studies in which unsteady acoustic effects have been actively exploited such that they have led to novel designs with improved cooling performance. This paper discusses the fundamental mechanism of pressure wave propagation through cooling holes and describes systems in which holes which have been acoustically shaped have led to a direct improvement in film cooling hole performance. The mechanism relies on sequential pressure wave reflection within an acoustically shaped hole and is therefore applicable in regions where the external surface is subject to large pressure wave fluctuations at high frequency. The principle is developed analytically, and then demonstrated with a number of computational fluid dynamics (CFD) simulations. We demonstrate that a desired temporal mass flow rate profile can be achieved by appropriate acoustic shaping of the cooling hole. The purpose of this paper is to describe the fundamental design considerations relevant to acoustic shaping. The discussion is developed with reference to a film cooling system for the over-tip region of an unshrouded rotor. The performance benefit of the system in terms of modulation of unsteady mass flux and ingestion characteristics is quantified. It is believed that this is the first time this significant effect has been exploited in film cooling design.

Unsteady simulations of migration and deposition of fly-ash particles in the first-stage turbine of an aero-engine

2021 ◽  
pp. 1-21
Author(s):  
Z. Hao ◽  
X. Yang ◽  
Z. Feng
Keyword(s):  
Fly Ash ◽  
Film Cooling ◽  
Particle Deposition ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Velocity Model ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Aero Engine

Abstract Particulate deposits in aero-engine turbines change the profile of blades, increase the blade surface roughness and block internal cooling channels and film cooling holes, which generally leads to the degradation of aerodynamic and cooling performance. To reveal particle deposition effects in the turbine, unsteady simulations were performed by investigating the migration patterns and deposition characteristics of the particle contaminant in a one-stage, high-pressure turbine of an aero-engine. Two typical operating conditions of the aero-engine, i.e. high-temperature take-off and economic cruise, were discussed, and the effects of particle size on the migration and deposition of fly-ash particles were demonstrated. A critical velocity model was applied to predict particle deposition. Comparisons between the stator and rotor were made by presenting the concentration and trajectory of the particles and the resulting deposition patterns on the aerofoil surfaces. Results show that the migration and deposition of the particles in the stator passage is dominated by the flow characteristics of fluid and the property of particles. In the subsequential rotor passage, in addition to these factors, particles are also affected by the stator–rotor interaction and the interference between rotors. With higher inlet temperature and larger diameter of the particle, the quantity of deposits increases and the deposition is distributed mainly on the Pressure Side (PS) and the Leading Edge (LE) of the aerofoil.

Influence of Anisotropic Thermal Conductivity on Overall Cooling Effectiveness on a Film Cooled Leading Edge

2021 ◽  
pp. 1-22
Author(s):  
Carol Bryant ◽  
James L. Rutledge
Keyword(s):  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Film Cooling ◽  
Leading Edge ◽  
Ceramic Matrix Composites ◽  
Internal Cooling ◽  
Matrix Composites ◽  
Edge Region ◽  
Turbine Engine ◽  
Anisotropic Thermal Conductivity

Abstract Increasing interest in the use of ceramic matrix composites (CMCs) for gas turbine engine hot gas path components requires a thorough examination of the thermal behavior one may expect of such components. Their highly anisotropic thermal conductivity is a substantial departure from traditional metallic components and can influence the temperature distribution in surprising ways. With the ultimate surface temperature dependent upon the internal cooling scheme, including cooling from within the film cooling holes themselves, as well as the external film cooling, the relative influence of these contributions to cooling can be affected by the directionality of the thermal conductivity. Conjugate heat transfer computational simulations were performed to evaluate the effect of anisotropy in the leading edge region of a turbine component. The leading edge region is modeled as a fully film-cooled half cylinder with a flat afterbody. The anisotropic directionality of the thermal conductivity is shown to have a significant effect on the temperature distribution over the surface of the leading edge. While structural considerations with CMC components are often paramount, designers should be aware of the thermal ramifications associated with the selection of the CMC layup.

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