Film Cooling Mass Flow Rate Influence on a Separation Shock in an Axisymmetric Nozzle

The ideal design of a turbine blade external film cooling system should contain a minimal uniform cooling film while simultaneously maximizing turbine efficiency. The current research reports on the tests on the pressure drop, hydraulic resistance, and mass flow rate of nine different nozzles. The effectiveness of the resulting film of cold air depends upon the mass flow rate and the shape, size, distribution and directional angles of these tiny nozzles. Of the orifices tested, the orifice shaped with the biggest spherical counter-sink inlet, allows the air to exit with the highest momentum. This shape produces the lowest hydraulic resistance and the highest blowing ratio.

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Investigation of Trailing Edge Cooling Concepts in a High Pressure Turbine Cascade: Analysis of the Adiabatic Film Cooling Effectiveness

Volume 3: Heat Transfer, Parts A and B ◽

10.1115/gt2009-59343 ◽

2009 ◽

Cited By ~ 8

Author(s):

Axel Dannhauer

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Film Cooling ◽

Pressure Side ◽

Cooling Efficiency ◽

Ir Thermography ◽

Trailing Edge ◽

Film Cooling Efficiency

Within a European research project experimental studies were performed concerning the determination of the film cooling efficiency on the pressure side of trailing edges of high pressure turbine blades. The experiments were carried out at the linear cascade wind tunnel (EGG) of the German Aerospace Center (DLR), Go¨ttingen. The thermodynamic investigations were performed using the same cascade geometries and trailing edge configurations as for the aerodynamic measurements. Two different trailing edge geometries with coolant ejection were investigated. The first configuration was equipped with a pressure side cutback while for the second configuration the pressure side film cooling was realized by a row of cylindrical holes. The determination of the surface temperatures was done by using a combination of IR-thermography and thermocouples. Preliminary studies showed the feasibility to use metallic surfaces of the suction side of the adjacent blade as a mirror for IR-thermography. Thus it is possible to observe the pressure side near the trailing edge of interest by means of an infrared camera. The camera was mounted outside of the cascade’s free stream ensuring no influence to the aerodynamic boundary conditions. Up to seven flush mounted thermocouples on each side of the trailing edge were used for an in-situ calibration of the infrared pictures and thermal loss calculations. The distributions and averaged values of the film cooling efficiency are in agreement with aerodynamic measurements [9]. The results for the cutback configuration with 0.5% mass flow rate ejected show an accumulation of coolant just behind the coolant slot which is caused by a vortex in the dead region of the cutback. In case of 1.0% mass flow rate a refilling of this region with coolant is indicated. For higher mass flow rates the distributions of the film cooling efficiency looses it’s homogeneity due to flow separations on some ribs of the pin fin array inside of the slot. For the configuration with pressure side bleeding the best coverage could be obtained applying 1.0% mass flow rate.

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A One-Dimensional Analytical Method for Turbine Blade Preliminary Cooling Design

Volume 2C: Turbomachinery ◽

10.1115/gt2016-56783 ◽

2016 ◽

Author(s):

Chen Li ◽

Jian-jun Liu

Keyword(s):

Mass Flow Rate ◽

Turbine Blade ◽

Mass Flow ◽

Flow Rate ◽

Film Cooling ◽

Three Dimensional ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness ◽

One Dimensional ◽

Cooling Design

The turbine blade cooling design is a complex procedure including one-dimensional preliminary cooling design, detailed two-dimensional design and fluid network analyses, and three-dimensional conjugate heat transfer and FEM predictions. Frequent alteration and modification of the cooling configurations make it unpractical to obtain all of three-dimensional design results quickly. Preliminary cooling design deals mainly with the coolant requirements and can be knitted into fluid network to look up the expected cooling structural style to promote three-dimensional geometry design. Previous methods to estimate the coolant requirements of the whole turbine blade in the preliminary cooling design were usually based on the semi-empirical air-cooled blade data. This paper combines turbine blade internal and external cooling, and presents a one-dimensional theoretical analytical method to investigate blade cooling performance, assuming that the coolant temperature increases along the blade span. Firstly, a function of non-dimensional cooling mass flow rate is derived to describe the new relationship between adiabatic film cooling effectiveness and overall cooling effectiveness. Secondly, a new variable related to film cooling is found to estimate the required adiabatic film cooling effectiveness without using the empirical correlations. Finally, a theoretical calculation about the relationship between non-dimensional cooling mass flow rate and overall cooling effectiveness well corresponds to semi-empirical air-cooled blade data within regular range of cooling efficiency. The currently proposed method is also a useful tool for the blade thermal analysis and the sensitivity analysis of coolant requirements to various design parameters. It not only can provide all the possible options at the given gas and coolant inlet temperatures to meet the design requirement, but also can give the third boundary conditions for calculating the blade temperature field. It’s convenient to use the heat transfer characteristic of internal cooling structures to estimate the coolant mass flow rate and the channel hydraulic diameter for both convection cooling and film cooling.

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Additively Manufactured Porous Geometries for Hybrid Turbine Cooling

10.1115/gt2021-58991 ◽

2021 ◽

Author(s):

Nathan D. Fier ◽

David G. Bogard

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Film Cooling ◽

Lattice Structure ◽

Low Velocity ◽

Fused Deposition ◽

Adiabatic Effectiveness ◽

Hybrid Configuration ◽

Film Cooling Holes

Abstract Discrete film cooling holes are limited by subtractive manufacturing techniques and experience depreciating performance when operating above critical velocity ratios. This study introduces an alternative method of bringing coolant to the surface of the blade via finite strips of porous material interlaced throughout the blade, made possible by advances in additive manufacturing (AM). Both experimental and computational studies were performed on the porous hybrid configuration to characterize downstream and off-wall performance, where experimental adiabatic effectiveness values were achieved using a plastic, fused deposition printed lattice structure. The method of bringing coolant onto the surface of the blade through an additively manufactured porous region experienced downstream adiabatic effectiveness values similar to slots while providing better structural stability. Additionally, the hybrid configuration outperformed shaped film cooling holes by injecting an ultra-thin layer of coolant that was evenly distributed span-wise across the blade. When operating at VRhybrid = 0.052 and L/d = 2 the hybrid configuration produced spatially averaged values 30% greater than the shaped holes while using equivalent coolant mass flow rate. Also, for an L/d = 10, the spatially averaged adiabatic effectiveness, for the hybrid configuration, is a factor of three greater than for shaped film cooling holes, while requiring a five times greater coolant mass flow rate. Finally, the RANS computational model accurately predicted downstream effectiveness values, at low velocity ratios, within experimental uncertainty but showed inaccuracies when predicting off wall effectiveness values and at higher velocity ratios.

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Cooling Optimization Theory—Part I: Optimum Wall Temperature, Coolant Exit Temperature, and the Effect of Wall/Film Properties on Performance

Journal of Turbomachinery ◽

10.1115/1.4032612 ◽

2016 ◽

Vol 138 (8) ◽

Cited By ~ 4

Author(s):

Benjamin Kirollos ◽

Thomas Povey

Keyword(s):

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Wall Temperature ◽

Film Cooling ◽

Cooling System ◽

Film Properties ◽

Uniform Wall Temperature ◽

Uniform Wall ◽

Exit Temperature

Gas turbine cooling system design is constrained by a maximum allowable wall temperature (dictated by the material and the life requirements of the component), minimum coolant mass flow rate (the requirement to minimize cycle-efficiency cost), and uniform wall temperature (to reduce thermal stresses). These three design requirements form the basis of an iterative design process. The relationship between the requirements has received little discussion in the literature, despite being of interest from both a theoretical and a practical viewpoint. In this paper, we consider the optimum cooling system for parts with both internal and film cooling. We show analytically that the coolant mass flow rate is minimized when the wall temperature is uniform and equal to the maximum allowable wall temperature. Thus, we show that achieving uniform wall temperature achieves minimum coolant flow rate, and vice versa. The purpose is to clarify the interplay between two design requirements that are often discussed separately in the literature. The penalty (in terms of coolant mass flow) associated with cooling nonisothermal components is quantified. We show that a typical high pressure nozzle guide vane (HPNGV) operating isothermally at the maximum allowable wall temperature requires two-thirds the coolant of a typical nonisothermal vane. The optimum coolant exit temperature is also considered. It is shown analytically that the optimum coolant exit temperature depends on the balance between the mean adiabatic film cooling effectiveness, the nondimensional mass flow rate, and the Biot number of the thermal barrier coating (TBC). For the large majority of gas turbine cooling systems (e.g., a typical HPNGV) it is shown that the optimum coolant exit temperature is equal to the local wall temperature at the point of injection. For a small minority of systems (e.g., long effusion cooling systems operating at low mass flow rates), it is shown that the coolant exit temperature should be minimized. An approximation relating the wall/film properties, the nondimensional mass flow, and the overall cooling effectiveness is derived. It is used to estimate the effect of Biot number (TBC and metal), heat transfer coefficient (HTC) ratio, and film properties on the performance of a typical HPNGV and effusion cooling system. In Part II, we show that designs which achieve uniform wall temperature have a particular corresponding internal HTC distribution.

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Fan-Shaped Hole Effects on the Aero-Thermal Performance of a Film-Cooled Endwall

Journal of Turbomachinery ◽

10.1115/1.2098788 ◽

2005 ◽

Vol 128 (1) ◽

pp. 43-52 ◽

Cited By ~ 29

Author(s):

Giovanna Barigozzi ◽

Giuseppe Benzoni ◽

Giuseppe Franchini ◽

Antonio Perdichizzi

Keyword(s):

Secondary Flow ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Thermal Performance ◽

Film Cooling ◽

Shaped Hole ◽

Adiabatic Effectiveness ◽

Endwall Cooling ◽

Injection Rates

The present paper investigates the effects of a fan-shaped hole endwall cooling geometry on the aero-thermal performance of a nozzle vane cascade. Two endwall cooling geometries with four rows of holes were tested, for different mass flow rate ratios: the first configuration is made of cylindrical holes, whereas the second one features conical expanded exits and a reduced number of holes. The experimental analysis is mainly focused on the variations of secondary flow phenomena related to different injection rates, as they have a strong relationship with the film cooling effectiveness. Secondary flow assessment was performed through downstream 3D aerodynamic measurements, by means of a miniaturized 5-hole probe. The results show that at high injection rates, the passage vortex and the 3D effects tend to become weaker, leading to a strong reduction of the endwall cross flow and to a more uniform flow in spanwise direction. This is of course obtained at the expense of a significant increase of losses. The thermal behavior was then investigated through the analysis of adiabatic effectiveness distributions on the two endwall configurations. The wide-banded thermochromic liquid crystals (TLC) technique was used to determine the adiabatic wall temperature. Using the measured distributions of film-cooling adiabatic effectiveness, the interaction between the secondary flow vortices and the cooling jets can be followed in good detail all over the endwall surface. Fan-shaped holes have been shown to perform better than cylindrical ones: at low injection rates, the cooling performance is increased only in the front part of the vane passage. A larger improvement of cooling coverage all over the endwall is attained with a larger mass flow rate, about 1.5% of core flow, without a substantial increase of the aerodynamic losses.

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Multi-Objective CFD Optimisation of Shaped Hole Film Cooling With Mesh Morphing

Volume 5B: Heat Transfer ◽

10.1115/gt2015-42249 ◽

2015 ◽

Cited By ~ 3

Author(s):

D. Proietti ◽

A. Pranzitelli ◽

G. E. Andrews ◽

M. E. Biancolini ◽

D. B. Ingham ◽

...

Keyword(s):

Design Of Experiments ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Film Cooling ◽

Maximum Deviation ◽

Geometrical Parameters ◽

Shape Parameters ◽

Cooling Effectiveness ◽

Adiabatic Cooling

A Computational Fluid Dynamics (CFD) optimisation of a single row of film cooling holes was performed. The aim was to achieve the highest adiabatic cooling effectiveness while minimising the coolant mass flow rate. The geometry investigated by Gritsch et al. [1] was the baseline model. It consisted of a row of cylindrical, 30° inclined holes, with a mainstream inlet Mach number of 0.6, a blowing ratio of 1 and a plenum for the upstream cooling air flow. The predictions agreed with the experimental data with a maximum deviation of 6%. The geometry was then optimised by varying three shape parameters: the injection angle, the lateral hole expansion angle and the downstream compound hole angle. A goal driven optimisation approach was based on a design of experiments table. The minimisation of the coolant mass flow together with the maximisation of the minimum and average cooling effectiveness were the optimisation objectives. The shape modifications were performed directly in the ANSYS Fluent CFD solver by using the software RBF Morph in the commercial software platform ANSYS Workbench. There was no need to generate a new geometry and a new computational mesh for each configuration investigated. The dependency of the average effectiveness along the plane centreline on the three geometrical parameters was investigated based on the metamodel generated from the design of experiments results. The goal driven optimisation led to the optimal combination of the three shape parameters to minimise the coolant flow without reducing the cooling effectiveness. The best results were obtained for a geometry with 20° hole angle and 7.5° compound angle injection, leading to a reduction of 15% in the coolant mass flow rate for an enhanced adiabatic cooling effectiveness. The results also showed the preponderance of the centreline angle over the other two parameters.

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Film Cooling Performance Improvement With Optimized Hole Arrangements on Pressure Side Surface of Nozzle Guide Vane: Part II — Experimental Validation

Volume 5C: Heat Transfer ◽

10.1115/gt2016-57978 ◽

2016 ◽

Cited By ~ 4

Author(s):

Dong-Ho Rhee ◽

Young Seok Kang ◽

Bong Jun Cha ◽

Jeong-Seek Kang ◽

Sanga Lee ◽

...

Keyword(s):

Mass Flow Rate ◽

Performance Improvement ◽

Mass Flow ◽

Flow Rate ◽

Film Cooling ◽

Side Surface ◽

Cooling Effectiveness ◽

Film Cooling Effectiveness ◽

Percentage Points ◽

Nozzle Guide

In the present study, the optimized configurations of film cooled turbine guide vanes proposed in Part I were validated experimentally and the effect of coolant mass flow rate on the performance was examined for those optimized configurations. A set of tests were conducted using an annular sector transonic turbine cascade test facility in Korea Aerospace Research Institute. The mainstream and the secondary air for cooling are supplied by 500 hp and 50 hp compressors, respectively, and the mainstream was heated approximately 20°C above the secondary flow by 300kW heater. To measure the film cooling effectiveness on the pressure side surface, the transient measurement method was used using a FLIR infrared camera system. The test section has five nozzle guide vanes with four passages. The three times scaled-up vane model is manufactured by a stereolithography method. The tests were conducted at mainstream exit Reynolds number based on the chord of 2.2×106 and the coolant mass flow rate ranging from 5 to 13% of the mainstream. The flow periodicity in the cascade passage was verified by surface static pressure measurements. The results showed that the optimized cases present better cooling effectiveness values in the overall region. The effect of coolant mass flow rate also presents the same trend. Comparison with the CFD results shows that the CFD results over-predict film cooling effectiveness by 10∼20 percentage points for baseline and 17∼23 percentage points for the optimized cases. This is probably partly due to the discrepancy of operating conditions such as inlet boundary condition and density ratio and partly due to the limitation of numerical method used in the optimization such as coarse grid near the surface. However, a quite good agreement is obtained qualitatively, which means the optimization process can be utilized as a reliable and efficient method for film cooling performance improvement.

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Fan-Shaped Hole Effects on the Aero-Thermal Performance of a Film Cooled Endwall

Volume 3: Turbo Expo 2005, Parts A and B ◽

10.1115/gt2005-68544 ◽

2005 ◽

Cited By ~ 19

Author(s):

Giovanna Barigozzi ◽

Giuseppe Benzoni ◽

Giuseppe Franchini ◽

Antonio Perdichizzi

Keyword(s):

Secondary Flow ◽

Mass Flow Rate ◽

Mass Flow ◽

Flow Rate ◽

Thermal Performance ◽

Film Cooling ◽

Shaped Hole ◽

Adiabatic Effectiveness ◽

Endwall Cooling ◽

Injection Rates

The present paper investigates the effects of a fan-shaped hole endwall cooling geometry on the aero-thermal performance of a nozzle vane cascade. Two endwall cooling geometries with four rows of holes were tested, for different mass flow rate ratios: the first configuration is made of cylindrical holes, whereas the second one features conical expanded exits and a reduced number of holes. The experimental analysis is mainly focused on the variations of secondary flow phenomena related to different injection rates, as they have a strong relationship with the film cooling effectiveness. Secondary flow assessment was performed through downstream 3D aerodynamic measurements, by means of a miniaturized 5-hole probe. The results show that at high injection rates, the passage vortex and the 3D effects tend to become weaker, leading to a strong reduction of the endwall cross flow and to a more uniform flow in spanwise direction. This is of course obtained at the expense of a significant increase of losses. The thermal behavior was then investigated through the analysis of adiabatic effectiveness distributions on the two endwall configurations. The wide banded TLC’s technique was used to determine the adiabatic wall temperature. Using the measured distributions of film cooling adiabatic effectiveness, the interaction between the secondary flow vortices and the cooling jets can be followed in good detail all over the endwall surface. Fan-shaped holes have been shown to perform better than cylindrical ones: at low injection rates, the cooling performance is increased only in the front part of the vane passage. A larger improvement of cooling coverage all over the endwall is attained with a larger mass flow rate, about 1.5% of core flow, without a substantial increase of the aerodynamic losses.

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