Highest-Efficient Film Cooling by Improved NEKOMIMI Film Cooling Holes: Part 2 — Hot Gas Flow Conditions

2013 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Azadeh Kasiri ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Gas Flow ◽  
Flow Conditions ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Hot Gas ◽  
High Efficient ◽  
Cooling Technology ◽  
Cooling Air

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is common knowledge today that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-counter-rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for fabrication by advanced machining processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under hot gas flow conditions. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. The best configuration outperforms the basic configuration by more than 20% regarding the overall averaged adiabatic film cooling effectiveness.

Highest-Efficient Film Cooling by Improved NEKOMIMI Film Cooling Holes: Part 1 — Ambient Air Flow Conditions

2013 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Frederieke Reiners ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Air Flow ◽  
Ambient Air ◽  
Flow Conditions ◽  
Test Rig ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Technology ◽  
Cooling Air

In modern gas turbines, the film cooling technology is essential for the protection of the hot parts, in particular of the first stage vanes and blades of the turbine, against the hot gases from the combustion process in order to reach an acceptable life span of the components. As the cooling air is usually extracted from the compressor, the reduction of the cooling effort would directly result to an increased thermal efficiency of the gas turbine. Understanding of the fundamental physics of film cooling is necessary for the improvement of the state-of-the-art. Thus, huge research efforts by industry as well as research organizations have been undertaken to establish high efficient film cooling technologies. It is a today common knowledge that film cooling effectiveness degradation is caused by secondary flows inside the cooling jets, i.e. the Counter-Rotating Vortices (CRV) or sometimes also mentioned as kidney-vortices, which induce a lift-off of the jet. Further understanding of the secondary flow development inside the jet and how this could be influenced, has led to hole configurations, which can induce Anti-Counter-Rotating Vortices (ACRV) in the cooling jets. As a result, the cooling air remains close to the wall and is additionally distributed flatly along the surface. Beside different other technologies, the NEKOMIMI cooling technology is a promising approach to establish the desired ACRV. It consists of a combination of two holes in just one configuration so that the air is distributed mainly on two cooling air streaks following the special shape of the generated geometry. The original configuration was found to be difficult for manufacturing even by advanced manufacturing processes. Thus, the improvement of this configuration has been reached by a set of geometry parameters, which lead to configurations much easier to be manufactured but preserving the principle of the NEKOMIMI technology. Within a numerical parametric study several advanced configurations have been obtained and investigated under ambient air flow conditions similar to conditions for a wind tunnel test rig. By systematic variation of the parameters a further optimization with respect to highest film cooling effectiveness has been performed. A set of most promising configurations has been also investigated experimentally in the test rig. The best configuration outperforms the basic configuration by 17% regarding the overall averaged adiabatic film cooling effectiveness under the experimental conditions.

The NEKOMIMI Cooling Technology: Cooling Holes With Ears for High-Efficient Film Cooling

2011 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Experimental Investigations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
High Efficient ◽  
Cylindrical Holes ◽  
Cooling Technology ◽  
Lift Off ◽  
Cooling Air

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness, so that the available cooling air fulfils the cooling task even if the amount has been reduced. Due to experimental and numerical efforts, it is well understood today that aerodynamic mixing processes are enhanced by counter-rotating vortices (CRV) in the cooling jets and lead to jet lift-off effects. Thus, the film-cooling effectiveness is reduced soon behind the cooling air ejection through the holes. Due to that basic understanding, different technologies for improving film cooling have been developed. Some of them focus on establishing anti-counter-rotating vortices (ACRV) inside the cooling jet that prevent the hot gas from flowing underneath the jet and, thus, avoid the lift-off effect. One of these technologies is the double-jet film cooling (DJFC), invented by the authors, where the special arrangement of two cylindrical holes lead to a cooling jet with such an anti-vortex system. However, beside the advantage that the holes are simple cylindrical holes, one disadvantage is that appropriate supply with cooling air for both holes is sometimes difficult to be established in real configurations. Thus, the authors have followed the idea to transfer the original double-jet film cooling principle to a special configuration with merged holes. Thus, in that case only one air supply is necessary but the anti-vortex effect has been preserved. The derived cooling technology has been named NEKOMIMI technology. The paper explains the principle of that technology. Results from experimental investigations including film cooling effectiveness measurements for the new technology are presented. The results are compared to conventional cooling hole configurations showing the tremendous positive effect in reaching highest film cooling effectiveness for the new configuration at M = 1.5 and partly for M = 1. Numerical investigations for the M = 1.5 case indicate that the existence of the ACRV is the likely reason for the enhanced cooling performance of the new configuration.

Double-Jet Ejection of Cooling Air for Improved Film-Cooling

2006 ◽  
Author(s):  
Karsten Kusterer ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Gas Flow ◽  
Operating Conditions ◽  
Cooling Effectiveness ◽  
Equal Distribution ◽  
Cooling Fluid ◽  
Film Cooling Effectiveness ◽  
Conventional Film ◽  
Cooling Technology

Film-cooling in gas turbines leads to aerodynamic mixing losses and reduced temperatures of the gas flow. Improvements of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount and by establishing a more equal distribution of the cooling fluid along the surface. It is well known that vortex systems in the cooling jets are the origin of reduced film-cooling effectiveness. For the streamwise ejection case, kidney-vortices result in a lift-off of the cooling jets; for the lateral ejection case, usually only one dominating vortex remains, leading to hot gas flow underneath the jet from one side. Based on the results of numerical analyses, a new cooling technology has been introduced by the authors, which reaches high film-cooling effectiveness as a result of a well-designed cooling hole arrangement for interaction of two neighbouring cooling jets (Double-jet Film-cooling DJFC). The results show that configurations exist, where an improved film-cooling effectiveness can be reached because an anti-kidney vortex pair is established in the double-jet. The paper aims on following major contributions: • to introduce the Double-jet Film-cooling (DJFC) as an alternative film-cooling technology to conventional film-cooling design. • to explain the major phenomena, which lead to the improvement of the film-cooling effectiveness by application of the DJFC. • to prove basic applicability of the DJFC to a realistic blade cooling configuration and present first test results under machine operating conditions.

Experimental and Numerical Investigations of the NEKOMIMI Film Cooling Technology

2012 ◽  
Author(s):  
Karsten Kusterer ◽  
Nurettin Tekin ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Thermal Efficiency ◽  
Film Cooling ◽  
Gas Turbines ◽  
Mixing Processes ◽  
Cooling Effectiveness ◽  
Numerical Investigations ◽  
Hot Gas ◽  
Cooling Technology ◽  
Lift Off ◽  
Cooling Air

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the required cooling air amount. Therefore, it is necessary to increase the cooling effectiveness, so that the available cooling air fulfils the cooling task even if the amount has been reduced. Due to experimental and numerical efforts, it is well understood today that aerodynamic mixing processes are enhanced by counter rotating vortices (CRV) in the cooling jets and lead to jet liftoff effects. Novel film cooling technologies focus on establishing anti-counter-rotating-vortices (ACRV) inside the cooling jet that prevent the hot gas from flowing underneath the jet and, thus, avoid the lift-off effect. One of these technologies is the NEKOMIMI film cooling, which is derived from the original double-jet film cooling (DJFC).

A Parametric Study on the Influence of the Lateral Ejection Angle of Double-Jet Holes on the Film Cooling Effectiveness for High Blowing Ratios

2009 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Parametric Study ◽  
Film Cooling ◽  
Gas Turbines ◽  
Lateral Spreading ◽  
Experimental Investigations ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Ejection Angle ◽  
Cooling Technology ◽  
Cooling Air

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the required cooling air amount. The reduction of the cooling air claims for an improved cooling technology, which assures the protection of the vane and blade airfoil from the hot mainstream flow. Consequently, it is required to increase the cooling efficiency of applied cooling technologies. Streamwise ejection from a cylindrical hole causes kidney vortices, which transport hot gas underneath the cooling jet and leads the cooling jet to lift off the surface. The double-jet film cooling technology represents a solution to establish an anti-kidney vortex, which prevents the double jet from lifting off the surface and raises the lateral spreading of the cooling air. This is achieved by a particular arrangement of simple cylindrical holes to each other. Additionally, the design of double-jet holes reduces significantly the effort of hole manufacturing compared to the effort of manufacturing a shaped hole design. Numerical investigations for blowing ratios from M = 0.5 up to M = 2 and experimental investigations in a test rig prove the proper film cooling ability of the double-jet film cooling technology. Furthermore, this paper presents a numerical parametric study of the double jet film cooling technology. The influence of the lateral ejection angle on the distribution of the cooling film is calculated and analyzed for the blowing ratios of M = 1, M = 1.5 and M = 2. It can be shown that an even higher film cooling effectiveness is reached with the use of the double-jet film cooling technology by an improvement of the hole positions and hole angles than in previous investigations.

Double-Jet Ejection of Cooling Air for Improved Film Cooling

2006 ◽  
Vol 129 (4) ◽  
pp. 809-815 ◽  
Author(s):  
Karsten Kusterer ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Gas Flow ◽  
Operating Conditions ◽  
Cooling Effectiveness ◽  
Equal Distribution ◽  
Cooling Fluid ◽  
Film Cooling Effectiveness ◽  
Conventional Film ◽  
Cooling Technology

Film cooling in gas turbines leads to aerodynamic mixing losses and reduced temperatures of the gas flow. Improvements of the gas turbine thermal efficiency can be achieved by reducing the cooling fluid amount and by establishing a more equal distribution of the cooling fluid along the surface. It is well known that vortex systems in the cooling jets are the origin of reduced film-cooling effectiveness. For the streamwise ejection case, kidney vortices result in a liftoff of the cooling jets; for the lateral ejection case, usually only one dominating vortex remains, leading to hot gas flow underneath the jet from one side. Based on the results of numerical analyses, a new cooling technology has been introduced by the authors, which reaches high film-cooling effectiveness as a result of a well-designed cooling hole arrangement for interaction of two neighboring cooling jets (double-jet film cooling (DJFC)). The results show that configurations exist, where an improved film-cooling effectiveness can be reached because an anti-kidney vortex pair is established in the double-jet. The paper aims at the following major contributions: (1) to introduce the DJFC as an alternative film-cooling technology to conventional film-cooling design; (2) to explain the major phenomena, which leads to the improvement of the film-cooling effectiveness by application of the DJFC; and (3) to prove basic applicability of the DJFC to a realistic blade cooling configuration and present the first test results under machine operating conditions.

Performance of Public Film Cooling Geometries Produced Through Additive Manufacturing

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Jacob C. Snyder ◽  
Karen A. Thole
Keyword(s):  
Additive Manufacturing ◽  
Film Cooling ◽  
Gas Turbines ◽  
Nickel Alloys ◽  
Cooling Effectiveness ◽  
Powder Bed ◽  
The Public ◽  
Hot Gas ◽  
Cooling Hole ◽  
Cooling Technology

Abstract Film cooling is an essential cooling technology to allow modern gas turbines to operate at high temperatures. For years, researchers in this community have worked to improve the effectiveness of film cooling configurations by maximizing the coolant coverage and minimizing the heat flux from the hot gas into the part. Working toward this goal has generated many promising film cooling concepts with unique shapes and configurations. However, until recently, many of these designs were challenging to manufacture in actual turbine hardware due to limitations with legacy manufacturing methods. Now, with the advances in additive manufacturing, it is possible to create turbine parts using high-temperature nickel alloys that feature detailed and unique geometry features. Armed with this new manufacturing power, this study aims to build and test the promising designs from the public literature that were previously difficult or impossible to implement. In this study, different cooling hole designs were manufactured in test coupons using a laser powder bed fusion process. Each nickel alloy coupon featured a single row of engine scale cooling holes, fed by a microchannel. To evaluate performance, the overall cooling effectiveness of each coupon was measured using a matched Biot test at engine relevant conditions. The results showed that certain hole shapes are better suited for additive manufacturing than others and that the manufacturing process can cause significant deviations from the performance reported in the literature.

Effect of Internal Coolant Crossflow on the Effectiveness of Shaped Film-Cooling Holes

2003 ◽  
Vol 125 (3) ◽  
pp. 547-554 ◽  
Author(s):  
Michael Gritsch ◽  
Achmed Schulz ◽  
Sigmar Wittig
Keyword(s):  
Film Cooling ◽  
Gas Flow ◽  
Flow Direction ◽  
Turbine Blades ◽  
Density Ratio ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Film Cooling Effectiveness ◽  
Hot Gas ◽  
Wide Range

Film-cooling was the subject of numerous studies during the past decades. However, the effect of flow conditions on the entry side of the film-cooling hole on film-cooling performance has surprisingly not received much attention. A stagnant plenum which is widely used in experimental and numerical studies to feed the holes is not necessarily a right means to re-present real engine conditions. For this reason, the present paper reports on an experimental study investigating the effect of a coolant crossflow feeding the holes that is oriented perpendicular to the hot gas flow direction to model a flow situation that is, for instance, of common use in modern turbine blades’ cooling schemes. A comprehensive set of experiments was performed to evaluate the effect of perpendicular coolant supply direction on film-cooling effectiveness over a wide range of blowing ratios (M=0.5…2.0) and coolant crossflow Mach numbers Mac=0…0.6. The coolant-to-hot gas density ratio, however, was kept constant at 1.85 which can be assumed to be representative for typical gas turbine applications. Three different hole geometries, including a cylindrical hole as well as two holes with expanded exits, were considered. Particularly, two-dimensional distributions of local film-cooling effectiveness acquired by means of an infrared camera system were used to give detailed insight into the governing flow phenomena. The results of the present investigation show that there is a profound effect of how the coolant is supplied to the hole on the film-cooling performance in the near hole region. Therefore, crossflow at the hole entry side has be taken into account when modeling film-cooling schemes of turbine bladings.

Double-Jet Film-Cooling for Highly Efficient Film-Cooling With Low Blowing Ratios

2008 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka
Keyword(s):  
Gas Turbine ◽  
Film Cooling ◽  
Gas Turbines ◽  
Original Design ◽  
Long Distance ◽  
Mixing Processes ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Cooling Air ◽  
Very High

Further improvement of the thermal efficiency of modern gas turbines can be achieved by a further reduction of the cooling air amount. Therefore, it is necessary to increase the cooling effectiveness so that the available cooling air fulfils the cooling task even if the amount has been reduced. In particular, the cooling effort for the vanes and blades of the first stage in a modern gas turbine is very high. The task of the film-cooling is to protect the blade material from the hot gas attack to the surface. Unfortunately, aerodynamic mixing processes are enhanced by secondary vortices in the cooling jets and, thus, the film-cooling effectiveness is reduced shortly behind the cooling air ejection through the holes. By improvement of the hole positioning the negative interaction effects can be reduced. The Double-jet Film-cooling (DJFC) Technology invented by the authors is one method to reach a significant increase in film-cooling effectiveness by establishing an anti-kidney vortex pair in a combined jet from the two jets starting from cylindrical ejection holes. This has been shown by numerical investigations and application to an industrial gas turbine as reported in recent publications. Whereas the original design application has been for moderate and high blowing ratios, the present numerical investigation shows that the DJFC is also applicable for lower blowing ratios (0.5<M<1.0) with only slight modification of the geometry of the configuration. The anti-kidney vortex concept can also be established for the lower blowing ratios and, as a result, a very high film-cooling effectiveness is reached not only behind the ejection holes but also for a very long distance downstream (> 30 hole diameters).

Film Cooling Effectiveness Comparison Between Shaped- and Double Jet Film Cooling Holes in a Row Arrangement

2010 ◽  
Author(s):  
Karsten Kusterer ◽  
Anas Elyas ◽  
Dieter Bohn ◽  
Takao Sugimoto ◽  
Ryozo Tanaka ◽  
...  
Keyword(s):  
Film Cooling ◽  
Gas Turbines ◽  
Experimental Comparison ◽  
Comparison Study ◽  
Surface Cooling ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Shaped Hole ◽  
Cooling Air ◽  
Cooling Technique

The improvement of the thermal efficiency of modern gas turbines can be achieved by reducing the needed cooling air amount. Consequently it is required to increase the cooling efficiency of applied cooling technologies. Streamwise ejection from a cylindrical hole causes kidney vortices which transport hot gas underneath the cooling jet and leads the cooling jet to lift off from the surface. Cooling performance is highly increased by using the shaped hole technique, which weakens the kidney vortex structure. However the formation of secondary flows can not completely be avoided by using shaped holes instead of cylindrical holes. Another promising film cooling technology is the double-jet film cooling, which prevents the cooling jet from lifting off the surface and raises the lateral spreading of the cooling air by generating an anti kidney vortex. This paper presents a comparison of the film cooling effectiveness between the shaped film cooling technique and the novel double jet film cooling technique for the high blowing ratios M = 1, M = 1.5 and M = 2. Various geometries of fan-shaped holes with lateral expansion angles of 10°, 14° and 18° are used for the comparison study. It can be shown that the shaped hole row arrangement provides higher cooling values in a slight region near to the hole exits, while the double jet film cooling technique shows a obvious cooling advantage in the further downstream area for high blowing ratios. Furthermore recent results of an on-going experimental comparison study between the double jet, trench and cylindrical technique are presented, which proves the advantage capability of the double jet film cooling.

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