Separate and Combined Effects of Surface Roughness and Thermal Barrier Coating on Vane Cooling Performance

2020 ◽  
Vol 12 (5) ◽  
Author(s):  
Prasert Prapamonthon ◽  
Bo Yin ◽  
Guowei Yang ◽  
Mohan Zhang
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Suction Side ◽  
Local Heat ◽  
Roughness Height ◽  
Thermal Barrier ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Barrier Coating

Abstract This work investigates separate and combined effects of the vane surface roughness and thermal barrier coating (TBC) on the cooling performance of a film-cooled high-pressure turbine vane using computational fluid dynamics (CFD) with conjugate heat transfer (CHT) analysis. The cooling effectiveness and heat transfer coefficient, where are predicted within an investigated range of the roughness height from 5 to 20 µm, are compared with those of the smooth vane. Results show that the roughness height increases local heat transfer coefficients in general in the suction side (SS) and the rear-half portion of the pressure side (PS), thereby reducing the cooling effectiveness. The results are different from those in the suction-side vicinity of the leading edge (LE) to further downstream of the pressure side due to uncertain local heat transfer coefficients. In addition, thermal sensitivity to the roughness height and TBC is investigated based on the volume basis in the roughness height range which is extended to 120 µm. Results show that without TBC, a 120 µm increase in the roughness height causes 24 K and 20 K rises of the average and maximum vane temperatures, respectively. With TBC, the average and maximum vane temperatures are reduced as much as 18 K and 27.8 K, respectively.

Effect of Surface Roughness on Local Heat Transfer and Film Cooling Effectiveness

1995 ◽  
Author(s):  
Douglas N. Barlow ◽  
Yong W. Kim
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Smooth Surface ◽  
Rough Surfaces ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients

An experimental investigation of film cooling on rough surfaces has been accomplished at a Reynolds number and dimensionless boundary layer momentum thickness found in current high performance first stage turbine vanes. A transient experimental method using thermochromic liquid crystals is employed to determine both local heat transfer coefficients and film cooling effectiveness values on planar rough surfaces. Two surface roughness configurations are investigated with a single row of cooling holes spaced three diameters apart and inclined 30° to the mainstream flow. The mainstream turbulence level at the point of film injection is 8.5% and the density ratio considered is approximately 1.0. The influence of roughness on the centerline film cooling effectiveness, laterally averaged film cooling effectiveness, laterally averaged heat transfer coefficients, as well as area averaged values are presented. It is found that the presence of roughness causes a decrease in the film cooling effectiveness over that of the smooth surface for the range of experimental parameters considered in this study. In addition, significant lateral smoothing in film cooling effectiveness distribution is observed for the rougher surfaces. Measured heat transfer coefficients on rough surfaces show a trend of monotonic increase with blowing ratio. However, such increase is not as great as that for the case of smooth surface.

Film-Cooling Characteristics of Pressure-Side Discharge Slots in an Accelerating Mainstream Flow

2005 ◽  
Author(s):  
Yong W. Kim ◽  
Chad Coon ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Blowing Ratio ◽  
Mainstream Flow

Pressure-side discharge is commonly employed in turbine blades and nozzle guide vanes to keep the trailing edge metal temperatures within an allowable limit while minimizing aerodynamic penalties. Despite its widespread use, film-cooling data of the discharge slot are scarce in open literature. The objectives of the present experimental study were to measure detailed local heat transfer and film-cooling effectiveness from a 10x scale trailing-edge model of an industrial gas turbine airfoil in a low speed wind tunnel. To simulate the mainstream flow acceleration in vane and blade row passages, a linear velocity gradient was imposed using an adjustable top wall. The present work employed the composite slab quasi-steady liquid crystal method that allows measurements of local heat transfer coefficients and film-cooling effectiveness from two related tests. With this technique, the heat transfer measurement can be performed in a cold wind tunnel. The coolant-to-mainstream blowing ratio was varied between 0.25 and 1.0. The slot hydraulic diameter based Reynolds number ranged from 4,760 to 19,550. The coolant-to-mainstream density ratio was fixed at 0.95. Slot discharge coefficients were also measured with mainstream acceleration. Both local heat transfer coefficients and film-cooling effectiveness displayed a strong dependency on blowing ratio and mainstream acceleration. However, the discharge coefficients showed little dependency on the mainstream acceleration.

Heat Transfer Coefficients and Film Cooling Effectiveness of Transonic Turbine Vane Suction Surface Using TSP Technique

2016 ◽  
Author(s):  
Chao-Cheng Shiau ◽  
Nafiz H. K. Chowdhury ◽  
Shang-Feng Yang ◽  
Je-Chin Han ◽  
Alexander MirzaMoghadam ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Suction Surface ◽  
Cooling Effectiveness ◽  
Film Cooling Effectiveness ◽  
Heat Transfer Coefficients ◽  
Compound Angle

This paper experimentally studies the effect of transonic flow on local heat transfer coefficients and film cooling effectiveness distributions of a turbine vane’s suction surface with compound-angle shaped-hole configuration. A Temperature Sensitive Paint (TSP) method is used to determine the local heat transfer coefficients and film cooling effectiveness simultaneously. Tests were performed in a five-vane annular-sector cascade blow-down facility. The exit Mach numbers are controlled to be 0.7 and 0.9, from subsonic to transonic conditions. Compressed air is used as coolant with a coolant-to-mainstream density ratio 0.91 on film cooling and heat transfer study. Three averaged coolant-to-mainstream blowing ratios in the range, 0.7, 1.0, and 1.6 are investigated. The test vane features three rows of radial-angle cylindrical holes around the leading edge, and two rows of compound-angle shaped holes on the suction side. Effects of blowing ratio and exit Mach number on the vane suction surface heat transfer and film cooling effectiveness distributions are obtained, and the results are presented and explained in this investigation.

Latticework (Vortex) Cooling Effectiveness: Part 1 — Stationary Channel Experiments

2004 ◽  
Author(s):  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Suction Side ◽  
Local Heat ◽  
Test Methods ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios

The present investigation provides detailed information concerning the heat transfer coefficients and pressures in latticework (vortex) cooling channels. Two test methods are used to determine the local and overall heat transfer coefficients for a vortex channel with crossing angle of 45-degrees. Both liquid crystal and infrared thermography methods are used on acrylic and metallic models to discern the heat transfer coefficients without and with the effects of internal rib fin effectiveness. Tests with insulating ribs determine the heat transfer on the primary surfaces representing the pressure and suction side walls of an airfoil. Tests with integral metal ribs determine the additional impact of the fin effectiveness provided by the ribs. A simple radial vortex channel design is employed throughout with subchannel aspect ratios near unity, and Reynolds numbers from 20,000 to 100,000. Pressure loss variations through typical vortex channels are also measured. The objectives of this research are to show the detailed development of heat transfer in vortex channels leading to an understanding of the two main effects of turning and fin enhancements. Detailed primary surface heat transfer coefficients average about 1.5 over smooth duct behavior, but reach local values of about 3 immediately after each turn. Pressure distributions show high turning losses on the order of those associated with serpentine 180-degree turn circuits. Local heat transfer coefficient distributions are remarkably uniform throughout the channels excepting the turns themselves. Turn enhancements are retained for relatively long distances. Overall vortex channel heat transfer coefficient enhancement levels are shown to be 2.5 to 3. The effects of subchannel internal ribs, which act as fins, are shown to be very important in the overall thermal picture. Test results show that treatment of the ribs as simple fins is appropriate and that each rib surface has about the same heat transfer coefficient on average as that of the primary surface. This first detailed study shows that latticework channels have significant potential and should be further investigated.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

scholarly journals Heat Transfer Coefficient Determination in a Gravity Die Casting Process with Local Air Gap Formation and Contact Pressure Using Experimental Evaluation and Numerical Simulation

2021 ◽  
Author(s):  
T. Vossel ◽  
N. Wolff ◽  
B. Pustal ◽  
A. Bührig-Polaczek ◽  
M. Ahmadein
Keyword(s):  
Heat Transfer ◽  
Contact Pressure ◽  
Local Heat Transfer ◽  
Casting Process ◽  
Local Heat ◽  
Air Gap ◽  
Gap Formation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Die Casting Process

AbstractAnticipating the processes and parameters involved for accomplishing a sound metal casting requires an in-depth understanding of the underlying behaviors characterizing a liquid melt solidifying inside its mold. Heat balance represents a major factor in describing the thermal conditions in a casting process and one of its main influences is the heat transfer between the casting and its surroundings. Local heat transfer coefficients describe how well heat can be transferred from one body or material to another. This paper will discuss the estimation of these coefficients in a gravity die casting process with local air gap formation and heat shrinkage induced contact pressure. Both an experimental evaluation and a numerical modeling for a solidification simulation will be performed as two means of investigating the local heat transfer coefficients and their local differences for regions with air gap formation or contact pressure when casting A356 (AlSi7Mg0.3).

scholarly journals Condensation inside smooth horizontal tubes: Part 1. Survey of the methods of heat-exchange prediction

2015 ◽  
Vol 19 (5) ◽  
pp. 1769-1789 ◽  
Author(s):  
Volodymyr Rifert ◽  
Volodymyr Sereda
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Film Condensation ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

Survey of the works on condensation inside smooth horizontal tubes published from 1955 to 2013 has been performed. Theoretical and experimental investigations, as well as more than 25 methods and correlations for heat transfer prediction are considered. It is shown that accuracy of this prediction depends on the accuracy of volumetric vapor content and pressure drop at the interphase. The necessity of new studies concerning both local heat transfer coefficients and film condensation along tube perimeter and length under annular, stratified and intermediate regimes of phase flow was substantiated. These characteristics being defined will allow determining more precisely the boundaries of the flow regimes and the methods of heat transfer prediction.

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+), p/e, and e/D.

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