Search results
1 – 10 of 429Krishna Anand Vasu Devan Nair Girija Kumari and Parammasivam Kanjikoil Mahali
This paper aims to investigate the film cooling effectiveness (FCE) and mixing flow characteristics of the flat surface ramp model integrated with a compound angled film cooling…
Abstract
Purpose
This paper aims to investigate the film cooling effectiveness (FCE) and mixing flow characteristics of the flat surface ramp model integrated with a compound angled film cooling jet.
Design/methodology/approach
Three-dimensional numerical simulation is performed on a flat surface ramp model with Reynolds Averaged Navier-Stokes approach using a finite volume solver. The tested model has a fixed ramp angle of 24° and a ramp width of two times the diameter of the film cooling hole. The coolant air is injected at 30° along the freestream direction. Three different film hole compound angles oriented to freestream direction at 0°, 90° and 180° were investigated for their performance on-ramp film cooling. The tested blowing ratios (BRs) are in the range of 0.9–2.0.
Findings
The film hole oriented at a compound angle of 180° has improved the area-averaged FCE on the ramp test surface by 86.74% at a mid-BR of 1.4% and 318.75% at higher BRs of 2.0. The 180° film hole compound angle has also produced higher local and spanwise averaged FCE on the ramp test surface.
Originality/value
According to the authors’ knowledge, this study is the first of its kind to investigate the ramp film cooling with a compound angle film cooling hole. The improved ramp model with a 180° film hole compound angle can be effectively applied for the end-wall surfaces of gas turbine film cooling.
Details
Keywords
X.‐Z. Zhang and I. Hassan
To develop a reliable methodology and procedure of simulating the jet‐in‐crossflow using the current turbulence models and numerically investigate the cooling performance of a new…
Abstract
Purpose
To develop a reliable methodology and procedure of simulating the jet‐in‐crossflow using the current turbulence models and numerically investigate the cooling performance of a new scheme for the engines of next generation.
Design/methodology/approach
A new advanced film cooling scheme is proposed based on the literature survey and a systematic methodology developed to successfully predict the right level of heat transfer in the CFD simulation of film cooling.
Findings
The proposed cooling scheme gives considerable lower heat transfer coefficient at the centerline in the near hole region than the traditional cylindrical hole, especially at a high blowing ratio when traditional cylindrical hole undergoes liftoff.
Research limitations/implications
The number of cooling holes in the computational domain is limited by the speed of the computers used.
Practical implications
The new methodology can be used to numerically test new cooling schemes in the design of turbine blades and to provide useful information/data under actual working conditions to design engineers.
Originality/value
This paper provides some useful information on the simulation of film cooling in terms of the performance of different turbulence models and wall treatments and also sends some valuable messages regarding the design of cooling scheme of turbine blades to the technical community.
Details
Keywords
Guohua Zhang, Gongnan Xie and Bengt Ake Sunden
In this study, numerical simulations are performed to compare the adiabatic film cooling effectiveness and reveal the difference of film cooling mechanisms of two models with the…
Abstract
Purpose
In this study, numerical simulations are performed to compare the adiabatic film cooling effectiveness and reveal the difference of film cooling mechanisms of two models with the same geometries and cross-section areas of film holes’ exits at three typical blowing ratios (M = 0.5, 1 and 1.5). The two models are an elliptical model and a cylindrical model with 90° compound angle, respectively.
Design/methodology/approach
Three different cases are considered in this work and the baseline is the model with a cylindrical film hole. The same boundary conditions and a validated turbulence model (realizable k-ε) are adopted for all cases.
Findings
The results show that both the elliptical and cylindrical models with 90° compound angle can enhance the film cooling effectiveness compared with the baseline. However, the elliptical model performs well at lower blowing ratios and in the near region at each blowing ratio because of the wider width of the film hole’s exit. The cylindrical model with 90° compound angle provides better film cooling effectiveness in the further downstream area of the film hole at higher blowing ratio because of the less lift-off and better coolant coverage in the larger x/D region along the mainstream direction.
Originality/value
Overall, it can be concluded that although the elliptical and cylindrical models with 90° compound angle have identical hole exits, the different inlet direction and cross-sectional geometry affect the flow structures when the coolant enters, moves through and exits the hole and finally different film cooling results appear.
Details
Keywords
Numerical simulations were carried out for two cooling schemes, a circular hole and a louver cooling scheme, at the leading edge of a rotor blade in a complete turbine stage.
Abstract
Purpose
Numerical simulations were carried out for two cooling schemes, a circular hole and a louver cooling scheme, at the leading edge of a rotor blade in a complete turbine stage.
Design/methodology/approach
Two holes were positioned at the leading edge of a rotating blade, one on the pressure side and the other on the suction side. The methodology was validated with a circular hole case. Numerical results of cooling effectiveness for three blowing ratios at three rotational speeds were successfully obtained. Both blowing ratio and rotating speed of the rotor affect the cooling effectiveness level.
Findings
It was shown that for the circular hole, the blowing ratio is the dominant factor at low blowing ratios and the rotational speed is the dominant factor at high blow ratios when jet is prone to lift off in determining the cooling effectiveness level. For the louver scheme, a higher rotational speed leads to a higher level of cooling effectiveness since jet liftoff is avoided.
Originality/value
There are only a few studies of film cooling on a rotational turbine blade and very few studies of film cooling at the leading edge of a rotating turbine blade in the open literature. The present work presents a challenging CFD case. The analysis of film cooling at the leading edge of an airfoil was presented, which sheds light on the physics of film cooling and should prove helpful to the cooling designs of turbine blades.
Details
Keywords
Ajay Kumar Jaiswal and Pallab Sinha Mahapatra
Maintaining the turbine blade’s temperature within the safety limit is challenging in high-pressure turbines. This paper aims to numerically present the conjugate heat transfer…
Abstract
Purpose
Maintaining the turbine blade’s temperature within the safety limit is challenging in high-pressure turbines. This paper aims to numerically present the conjugate heat transfer analysis of a novel approach to mini-channel embedded film-cooled flat plate.
Design/methodology/approach
Numerical simulations were performed at a steady state using SST k – ω turbulence model. Impingement and film cooling are classical approaches generally adopted for turbine blade analysis. The existing film cooling techniques were compared with the proposed design, where a mini-channel was constructed inside the solid plate. The impact of the blowing ratio (M), Biot number (Bi) and temperature ratio (TR) on overall cooling performance was also studied.
Findings
Overall cooling effectiveness was always shown to be higher for mini-channel embedded film-cooled plates. The effectiveness increases with increasing the blowing ratio from M = 0.3 to 0.7, then decreases with increasing blowing ratio (M = 1 and 1.4) due to lift-off conditions. The mini-channel embedded plate resulted in an approximately 21% increase in area-weighted average overall effectiveness at a blowing ratio of 0.7 and Bi = 1.605. The lower uniform temperature was also found for all blowing ratios at a low Biot number, where conduction heat transfer significantly impacts total cooling effectiveness.
Originality/value
To the best of the authors’ knowledge, this study presents a novel approach to improve the cooling performances of a film-cooled flat plate with better cooling uniformity by using embedded mini-channels. Despite the widespread application of microchannels and mini-channels in thermal and fluid flow analysis, the application of mini-channels for blade cooling is not explored in detail.
Details
Keywords
Jian Liu, Mengyao Xu, Wenxiong Xi, Jiawen Song, Shibin Luo and Bengt Ake Sunden
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…
Abstract
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.
Details
Keywords
The present study aims to conduct a numerical investigation of a novel film cooling scheme combining in‐hole impingement cooling and flow turbulators with traditional downstream…
Abstract
Purpose
The present study aims to conduct a numerical investigation of a novel film cooling scheme combining in‐hole impingement cooling and flow turbulators with traditional downstream film cooling, and was originally proposed by Pratt & Whitney Canada for high temperature gas turbine applications.
Design/methodology/approach
Steady‐state simulations were performed and the flow was considered incompressible and turbulent. The CFD package FLUENT 6.1 was used to solve the Navier‐Stokes equations numerically, and the preprocessor, Gambit, was used to generate the required grid.
Findings
It was determined that the proposed scheme geometry can prevent coolant lift‐off much better than standard round holes, since the cooling jet remains attached to the surface at much higher blowing rates, indicating a superior performance for the proposed scheme.
Research limitations/implications
The present study was concerned only with the downstream effectiveness aspect of performance. The performance related to the heat transfer coefficient is a prospective topic for future studies.
Practical implications
Advanced and innovative cooling techniques are essential in order to improve the efficiency and power output of gas turbines. This scheme combines in‐hole impingement cooling and flow turbulators with traditional downstream film cooling for improved cooling capabilities.
Originality/value
This new advanced cooling scheme both combines the advantages of traditional film cooling with those of impingement cooling, and provides greater airfoil protection than traditional film cooling. This study is of value for those interested in gas turbine cooling.
Details
Keywords
Rui Hou, Fengbo Wen, Tao Cui, Xiaolei Tang and Songtao Wang
This study aims to introduce a three-hole cooling unit to improve downstream cooling performance by jet interaction and coalescence at a lower manufacture cost.
Abstract
Purpose
This study aims to introduce a three-hole cooling unit to improve downstream cooling performance by jet interaction and coalescence at a lower manufacture cost.
Design/methodology/approach
A new three-hole cooling unit is proposed. Reynolds-averaged Navier–Stokes (RANS) simulation is performed in the present study. The CFD package ANSYS CFX is used to predict film-cooling effectiveness and flow fields.
Findings
The results show that, at pitch ratio P/D = 3, Case 4 configuration with a round hole upstream and two trenched holes downstream can obtain a high cooling performance at a lower manufacture cost, especially at the higher turbulence. Considering the effect of increased pitch ratio, Case 6 configurations of three staggered trenched holes show a superior downstream cooling performance than Case 4 configurations. Case 6 configurations have the potential of achieving a high cooling performance with a reduced number of holes and less coolant flow.
Research limitations/implications
The application of these cooling units in the turbine passage will be conducted in the future. The more detailed flow field will be simulated by large eddy simulation in the following research.
Practical implications
The round and trenched cooling holes have been proved to be achievable in the manufacture. This combined three-hole cooling unit will give the opportunity to increase turbine inlet temperature further.
Originality/value
Both cooling performance and practical manufacture are taken into account. This cooling scheme will give a superior surface protection on the hot components.
Details
Keywords
Jin Wang, Chunwei Gu and Bengt Ake Sunden
The purpose of this paper is to analyze the effect of thermal conductivity on gas turbine blades, and to investigate the contribution of different rib configurations to the heat…
Abstract
Purpose
The purpose of this paper is to analyze the effect of thermal conductivity on gas turbine blades, and to investigate the contribution of different rib configurations to the heat flux and the film cooling effectiveness.
Design/methodology/approach
The Renormalization Group (RNG) model with enhanced wall treatment was used for the turbulence modeling, and the SIMPLE algorithm was used to handle the pressure-velocity coupling.
Findings
A flame-shape distribution on the internal wall provides high heat flux compared to a hawk-shape distribution; the film cooling effectiveness on the external wall is enhanced for the lateral film cooling effectiveness by heat conduction and film cooling (convection); by comparing the square-rib and pin-rib configurations, the circular-rib configuration offers a higher film cooling effectiveness on the Aluminum wall.
Research limitations/implications
In the present research, the combination of internal cooling and external cooling is used to predict cooling effectiveness on film-cooled flat plate; two kinds of different plate materials are used to obtain the influence of the thermal conductivity. The successful computational method should give guidelines for potential CFD users in engineering sciences.
Practical implications
The results of the paper are of engineering interest where film cooling and ribbed surfaces are applied. The successful computational method will also serve as guidelines for potential users of CFD in design as well as research and development work.
Originality/value
In the present research, the combination of internal cooling and external cooling is used to predict cooling effectiveness on film-cooled flat plate; two kinds of different plate materials are used to obtain the influence of the thermal conductivity.
Details
Keywords
Guohua Zhang, Xueting Liu, Bengt Ake Sundén and Gongnan Xie
This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling…
Abstract
Purpose
This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling performance, three configurations are designed to observe the effects of the distance between the center of the ellipse and the side wall(Case 1, l = w/2, Case 2, l = w/3 and for Case 3, l = w/4).
Design/methodology/approach
Numerical simulations are conducted under two blowing ratios (i.e. 0.5 and 1) and a fixed cross-flow Reynolds number (Rec = 100,000) with a verified turbulence model.
Findings
It is shown that at low blowing ratio, reducing the distance increases the film cooling effectiveness but keeps the trend of the effectiveness unchanged, while at high blowing ratio, the characteristic is a little bit different in the range of 0 = x/D = 10.
Research limitations/implications
These features could be explained by the fact that shrinking the distance between the hole and side wall induces a much smaller reserved region and vortex downstream the ribs and a lower resistance for cooling air entering the film hole. Furthermore, the spiral flow inside the hole is impaired.
Originality/value
As a result, the kidney-shaped vortices originating from the jet flow are weakened, and the target surface can be well covered, resulting in an enhancement of the adiabatic film cooling performance.
Details