Numerical Study on Analogy Principle of Overall Cooling Effectiveness in Engine and Laboratory Condition

2018 ◽  
Author(s):  
Gang Xie ◽  
Cun-liang Liu ◽  
Lin Ye ◽  
Rui Wang
Keyword(s):  
Heat Transfer ◽  
Laboratory Condition ◽  
Biot Number ◽  
Gas Turbines ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Temperature Ratio ◽  
Cooling Effectiveness ◽  
Momentum Flux Ratio ◽  
Engine Condition

The overall cooling effectiveness, which represents the distribution of dimensionless temperature on gas turbines surface, is an important parameter for conjugate heat transfer analysis of gas turbines. Generally, it is difficult to measure the overall cooling effectiveness in engine condition. However, the overall cooling effectiveness can be measured in the laboratory by matching the appropriate parameters to those of the actual turbine blade. Thus, it is important to evaluate the key parameters of matching methods. In this paper, the effects of adiabatic film effectiveness and Biot number on the overall cooling effectiveness were investigated with an impingement/effusion model by numerical simulation, in which 3-D steady RANS approach with the k–ω SST turbulence model were used. The tested plate had 8 cylinder hole rows of 30 degree inclined angle, and the internal cooling employed staggered array jet impingements. The matching performance was evaluated by comparing the results in both typical engine condition and laboratory condition. The analogy principles were discussed in detail, the results showed that the overall cooling effectiveness can be matched by using different matching principles in different lab condition. The theoretical analysis was verified by numerical results. The distribution and values of overall cooling effectiveness can be matched well between engine condition and lab condition by matching both temperature ratio, mainstream side Biot number and blowing ratio. If the temperature ratio is mismatched, the momentum flux ratio will be an important parameter for overall cooling effectiveness. Matching momentum flux ratio will reduce the difference of the adiabatic cooling effectiveness and heat transfer ratio between engine condition and laboratory condition.

scholarly journals Theory of Non-Dimensional Groups in Film Effectiveness Studies

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Francesco Ornano ◽  
Thomas Povey
Keyword(s):  
Heat Capacity ◽  
Physical Interpretation ◽  
Film Cooling ◽  
Gas Turbines ◽  
Momentum Flux ◽  
Density Ratio ◽  
Flux Ratio ◽  
Cooling Performance ◽  
Momentum Flux Ratio ◽  
Blowing Ratio

Abstract The desire to improve gas turbines has led to a significant body of research concerning film cooling optimization. The open literature contains many studies considering the impact on film cooling performance of both geometrical factors (hole shape, hole separation, hole inclination, row separation, etc.) and physical influences (effect of density ratio (DR), momentum flux ratio, etc.). Film cooling performance (typically film effectiveness, under either adiabatic or diabatic conditions) is almost universally presented as a function of one or more of three commonly used non-dimensional groups: blowing—or local mass flux—ratio, density ratio, and momentum flux ratio. Despite the abundance of papers in this field, there is some confusion in the literature about the best way of presenting such data. Indeed, the very existence of a discussion on this topic points to lack of clarity. In fact, the three non-dimensional groups in common use (blowing ratio (BR), density ratio, and momentum flux ratio) are not entirely independent of each other making aspects of this discussion rather meaningless, and there is at least one further independent group of significance that is rarely discussed in the literature (specific heat capacity flux ratio). The purpose of this paper is to bring clarity to this issue of correct scaling of film cooling data. We show that the film effectiveness is a function of 11 (additional) non-dimensional groups. Of these, seven can be regarded as boundary conditions for the main flow path and should be matched where complete similarity is required. The remaining four non-dimensional groups relate specifically to the introduction of film cooling. These can be cast in numerous ways, but we show that the following forms allow clear physical interpretation: the momentum flux ratio, the blowing ratio, the temperature ratio (TR), and the heat capacity flux ratio. Two of these parameters are in common use, a third is rarely discussed, and the fourth is not discussed in the literature. To understand the physical mechanisms that lead to each of these groups being independently important for scaling, we isolate the contribution of each to the overall thermal field with a parametric numerical study using 3D Reynolds-averaged Navier–Stokes (RANS) and large eddy simulations (LES). The results and physical interpretation are discussed.

Prediction of Film Cooling Effectiveness and Heat Transfer due to Streamwise and Compound Angle Injection on Flat Surfaces

1995 ◽  
Author(s):  
S. Neelakantan ◽  
M. E. Crawford
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Equation Model ◽  
Transfer Coefficients ◽  
Film Cooling Effectiveness ◽  
Flat Surfaces ◽  
Momentum Flux Ratio ◽  
Density Ratios

The distributed Yavuzkurt injection model is extended to predict the effectiveness and heat transfer coefficients for film cooling injection from a single row of holes, aligned both along the direction of the freestream and at an angle with it. The injection angles were 24° and 35°. The compound angles considered were 50.5° and 60°. The Yavuzkurt film cooling model is used in conjunction with a one-equation model to yield the effectiveness and heat transfer predictions. The density ratios considered were 1.6 and 0.95 for the effectiveness predictions and 1.0 and 0.95 for the heat transfer predictions. For the effectiveness predictions, the blowing ratios range from 0.5 to 2.5, and the momentum flux ratios from 0.16 until 3.9. The hole spacings were 3, 6, and 7.8 hole diameters. The Yavuzkurt model constants are seen to be definitely correlated with the momentum flux ratio. Correlations for the model constants are obtained in terms of the momentum flux ratio. For the heat transfer predictions, the blowing ratios ranged from 0.4 to 2.0, and the momentum flux ratios from 0.16 to 3.9. The spacing between the holes was 3, 6, and 7.8 hole diameters. The matching between the effectiveness correlations and the heat transfer predictions is done on the basis of the momentum flux ratio. Results indicate that the Yavuzkurt model predictions are best for the in-line round holes. Heat transfer predictions are close to the experimental results for lower blowing ratios, until the ratio exceeds 1. For higher blowing ratios, the predictions, though less accurate, follow the experimental trends.

scholarly journals Numerical Investigation Into the Impact of Injector Geometrical Design Parameters on Hydrogen Micromix Combustion Characteristics

2020 ◽  
Author(s):  
Xiaoxiao Sun ◽  
Parash Agarwal ◽  
Francesco Carbonara ◽  
David Abbott ◽  
Pierre Gauthier ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Momentum Flux ◽  
Flux Ratio ◽  
Injection System ◽  
Design Parameters ◽  
Gas Temperature ◽  
Geometrical Design ◽  
Momentum Flux Ratio ◽  
Mixing Characteristics ◽  
The Impact

Abstract Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. As a part of the ENABLEH2 project, the current study focuses on the influence of design parameters on the micromix hydrogen combustion injectors. This study provides deeper insights into the design space of a hydrogen micromix injection system via numerical simulations. The key geometrical design parameters of the micromix combustion system are the sizing of the air gates and the hydrogen injector orifices together with the offset distance between air gate and hydrogen injection, the mixing distance and the injector to injector spacing. This paper first presents results of the numerical simulation of four designs, down selected from a series of combinations of the key design parameters, including cases with low and high momentum flux ratio, weak and strong flame-flame interaction. It was discovered that the hydrogen/air mixing characteristics, and flame to flame interactions, are the main factors influencing the combustor gas temperature distributions, flame lengths and the corresponding NOx production. The current study then focused on the effect of air gate geometry on the mixing characteristics, flame shape and temperature distribution. The momentum flux ratio was kept constant throughout this investigation by keeping the air gate area constant. Variations of the original baseline air gate design were studied, followed by a study of various novel air gate geometries, including circular, semi-circular and elliptical shapes. It is concluded that NOx production is influenced by a number of factors including jet penetration flame interactions and air gate shape and that there is a “Sweet Spot” that results in the lowest practicable NOx production. Flatter and wider air gate shapes tend to yield the lowest temperature and consequently the lowest NOx. Reduced interaction between flames also tends to reduce NOx and by manipulating hydrogen penetration, there is the potential to further reduce the NOx production.

Heat Transfer and Friction Augmentation in High Aspect Ratio, Ribbed Channels With Dissimilar Inlet Conditions

2010 ◽  
Author(s):  
Carson D. Slabaugh ◽  
Lucky V. Tran ◽  
J. S. Kapat ◽  
Bobby A. Warren
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Momentum Flux ◽  
Rectangular Channel ◽  
Cross Flow ◽  
Flux Ratio ◽  
Momentum Flux Ratio ◽  
The Cross ◽  
Inlet Conditions ◽  
Channel Configuration

This work is an investigation of the heat transfer and pressure-loss characteristics in a rectangular channel with ribs oriented perpendicular to the flow. The novelty of this study lies in the immoderate parameters of the channel geometry and transport enhancing features. Specifically, the aspect ratio (AR) of the rectangular channel is considerably high, varying from fifteen to thirty for the cases reported. Also varied is the rib-pitch to rib-height (p/e), studied at two values; 18.8 and 37.3. Rib-pitch to rib-width (p/w) is held to a value of two for all configurations. Channel Reynolds number is varied between approximately 3,000 and 27,000 for four different tests of each channel configuration. Each channel configuration is studied with two different inlet conditions. The baseline condition consists of a long entrance section leading to the entrance of the channel to provide a hydrodynamically-developed flow at the inlet. The second inlet condition studied consists of a cross-flow supply in a direction perpendicular to the channel axis, oriented in the direction of the channel width (the longer channel dimension). In the second case, the flow rate of the cross-flow supply is varied to understand the effects of a varying momentum flux ratio on the heat transfer and pressure-loss characteristics of the channel. Numerical simulations revealed a strong dependence of the local flow physics on the momentum flux ratio. The turning effect of the flow entering the channel from the cross-flow channel is strongly affected by the pressure gradient across the channel. Strong pressure fields have the ability to propagate farther into the cross-flow channel to ‘pull’ the flow, partially redirecting it before entering the channel and reducing the impingement effect of the flow on the back wall of the channel. Experimental result shows a maximum value of Nusselt number augmentation to be found in the 30:1 AR channel with the aggressive augmenter (p/e = 37.3) and a high momentum flux ratio: Nu/Nuo = 3.15. This design also yielded the friction with f/f0 = 2.6.

Film-Cooling Effectiveness Downstream of a Single Row of Holes With Variable Density Ratio

1991 ◽  
Vol 113 (3) ◽  
pp. 442-449 ◽  
Author(s):  
A. K. Sinha ◽  
D. G. Bogard ◽  
M. E. Crawford
Keyword(s):  
Mass Flux ◽  
Film Cooling ◽  
Momentum Flux ◽  
Velocity Ratio ◽  
Density Ratio ◽  
Flux Ratio ◽  
General Distribution ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Momentum Flux Ratio

Film-cooling effectiveness was studied using a row of inclined holes that injected cryogenically cooled air across a flat, adiabatic test plate. The density ratio of the coolant to mainstream varied from 1.2 to 2.0. Surface temperatures were measured using a unique surface thermocouple arrangement free of conduction errors. Temperatures were obtained along the jet centerline and across a number of lateral locations. By independently varying density ratio and blowing rate, scaling of adiabatic effectiveness with mass flux ratio, velocity ratio, and momentum ratio was determined. Depending on the momentum flux ratio, the jet either remains attached to the surface, detaches and then reattaches, or is fully detached. For attached jets, the centerline effectiveness scaled with the mass flux ratio. However, for detached-reattached jets, a consistent scaling was not found although the general distribution of the centerline effectiveness scaled with momentum flux ratio. Laterally averaged effectiveness was found to be dependent on density ratio and momentum flux ratio. Decreases in density ratio and increases in momentum flux ratio were found to reduce the spreading of the film cooling jet significantly and thereby reduce laterally averaged effectiveness.

Heat Transfer and Friction Augmentation in High Aspect Ratio, Ribbed Channels With Dissimilar Inlet Conditions

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Carson D. Slabaugh ◽  
Lucky V. Tran ◽  
J. S. Kapat ◽  
Bobby A. Warren
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Momentum Flux ◽  
Rectangular Channel ◽  
Cross Flow ◽  
Flux Ratio ◽  
Momentum Flux Ratio ◽  
The Cross ◽  
Inlet Conditions ◽  
Channel Configuration

This work is an investigation of the heat transfer and pressure-loss characteristics in a rectangular channel with ribs oriented perpendicular to the flow. The novelty of this study lies in the immoderate parameters of the channel geometry and transport enhancing features. Specifically, the aspect ratio (AR) of the rectangular channel is considerably high, varying from 15 to 30 for the cases reported. Also varied is the rib-pitch to rib-height (p/e), studied at two values, 18.8 and 37.3. Rib-pitch to rib-width (p/w) is held to a value of two for all configurations. Channel Reynolds number is varied between approximately 3000 and 27,000 for four different tests of each channel configuration. Each channel configuration is studied with two different inlet conditions. The baseline condition consists of a long entrance section leading to the entrance of the channel to provide a hydrodynamically developed flow at the inlet. The second inlet condition studied consists of a cross-flow supply in a direction perpendicular to the channel axis, oriented in the direction of the channel width (the longer channel dimension). In the second case, the flow rate of the cross-flow supply is varied to understand the effects of a varying momentum flux ratio on the heat transfer and pressure-loss characteristics of the channel. Numerical simulations revealed a strong dependence of the local flow physics on the momentum flux ratio. The turning effect of the flow entering the channel from the cross-flow channel is strongly affected by the pressure gradient across the channel. Strong pressure fields have the ability to propagate farther into the cross-flow channel to “pull” the flow, partially redirecting it before entering the channel and reducing the impingement effect of the flow on the back wall of the channel. Experimental results show a maximum value of Nusselt number augmentation to be found in the 30:1 AR channel with the aggressive augmenter (p/e = 37.3) and a high momentum flux ratio: Nu/Nuo = 3.15. This design also yielded the friction with f/f0 = 2.6.

Cooling Effectiveness Measurements With Thermal Radiometry in a Turbine Cascade

2000 ◽  
Author(s):  
H. K. Moon ◽  
R. Jaiswal
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Real Time ◽  
Background Radiation ◽  
Temperature Measurements ◽  
Coolant Temperature ◽  
Turbine Cascade ◽  
Temperature Ratio ◽  
Cooling Effectiveness ◽  
Engine Condition

Airfoil temperature measurements in a hot cascade were traditionally conducted with thermocouples in spite of their limitations. In the present work, a real-time full imaging of the airfoil temperature distribution is demonstrated in a turbine cascade using a thermal radiometry system. Two synthetic sapphire windows provided infrared (IR)-viewing access from the outside. The apparent emissivity of the test airfoil was calibrated with thermocouples buried flush into the wall. The turbine cascade, fabricated with actual engine hardware, provided heat transfer similarity by matching Re, Ma, and Tu. The effect of gas to coolant temperature ratio (Tg/Tc) on the cooling effectiveness was investigated. Heating (“reverse” cooling) of the test airfoil in a relatively cold mainstream air resulted in a much more detailed temperature image than the normal (forward) cooling case, as it significantly reduced the background radiation. A methodology to correct the cooling effectiveness obtained at different gas to coolant temperature ratios than the engine condition was developed and has been experimentally validated.

Conjugate Heat Transfer and Film Cooling of a Multi-Stage Cooling Scheme

2008 ◽  
Author(s):  
M. Ghorab ◽  
S. I. Kim ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Gas Turbines ◽  
Conjugate Heat Transfer ◽  
Density Ratio ◽  
Design Parameters ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Multi Stage ◽  
Internal Gap

Cooling techniques play a key role in improving efficiency and power output of modern gas turbines. The conjugate technique of film and impingement cooling schemes is considered in this study. The Multi-Stage Cooling Scheme (MSCS) involves coolant passing from inside to outside turbine blade through two stages. The first stage; the coolant passes through first hole to internal gap where the impinging jet cools the external layer of the blade. Finally, the coolant passes through the internal gap to the second hole which has specific designed geometry for external film cooling. The effect of design parameters, such as, offset distance between two-stage holes, gap height, and inclination angle of the first hole, on upstream conjugate heat transfer rate and downstream film cooling effectiveness performance are investigated computationally. An Inconel 617 alloy with variable properties is selected for the solid material. The conjugate heat transfer and film cooling characteristics of MSCS are analyzed across blowing ratios of Br = 1 and 2 for density ratio, 2. This study presents upstream wall temperature distributions due to conjugate heat transfer for different gap design parameters. The maximum film cooling effectiveness with upstream conjugate heat transfer is less than adiabatic film cooling effectiveness by 24–34%. However, the full coverage of cooling effectiveness in spanwise direction can be obtained using internal cooling with conjugate heat transfer, whereas adiabatic film cooling effectiveness has narrow distribution.

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