Arrangement effects of inclined teardrop-shaped dimples on film cooling performance of dimpled cutback surface at airfoil trailing edge

Abstract:The decrease in the performance of centrifugal compressors operating at low Reynolds numbers (e.g., unmanned aerial vehicles at high altitudes or small turbomachines) can reach 10% due to increased friction. The purposes of this review are to represent the state-of-the-art of the active and passive flow control methods used to improve performance and/or widen the operating range in numerous engineering applications, and to investigate their applicability in low-Reynolds-number centrifugal compressors. The applicable method should increase performance by reducing drag, increasing blade loading, or reducing tip leakage. Based on the aerodynamic and structural demands, passive methods like riblets, squealers, winglets and grooves could be beneficial; however, the drawbacks of these approaches are that their performance depends on the operating conditions and the effect might be negative at higher Reynolds numbers. The flow control method, which would reduce the boundary layer thickness and reduce wake, could have a beneficial impact on the performance of a low-Reynolds-number compressor in the entire operating range, but none of the methods represented in this review fully fulfil this objective.

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“…+ 10 • . Heat transfer augmentation by the dimples [157][158][159][160] has been investigated more than their aerodynamic performance.…”

Section: Turbulence and Vortex Generators (Classification: Passive Gmentioning

confidence: 99%

Flow Control Methods and Their Applicability in Low-Reynolds-Number Centrifugal Compressors—A Review

Tiainen

Grönman

Jaatinen-Värri

et al. 2017

IJTPP

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“…Lands are usually designed to divide the entire slot to form a series of discrete-slots, which can enhance effectively the lateral and span-wise coolant coverages 7 Figure 1(b) illustrates the thermal protection mechanism of slotoutflow at cutback surface. It can be clearly found that the cooling air ejected from TE slots can shield the cutback surface from the impingement of hot mainstream at cutback, at the same time, act as a convective heat sink for the heat load to the blade suction side 8,9 Consequently, to enhance the overall cooling performances at the entire cutback surface, it is an important task to improve the film cooling effectiveness in near-slot region and the wall heat transfer coefficient at entire surface. Rough surfaces are widely proposed to acquire the higher wall heat transfer, for example, dimpled cutback surface by Murata et al 9 In present work, special attention is paid to the film cooling effectiveness in near-slot region at cutback surface.…”

Section: Introductionmentioning

confidence: 99%

“…It can be clearly found that the cooling air ejected from TE slots can shield the cutback surface from the impingement of hot mainstream at cutback, at the same time, act as a convective heat sink for the heat load to the blade suction side 8,9 Consequently, to enhance the overall cooling performances at the entire cutback surface, it is an important task to improve the film cooling effectiveness in near-slot region and the wall heat transfer coefficient at entire surface. Rough surfaces are widely proposed to acquire the higher wall heat transfer, for example, dimpled cutback surface by Murata et al 9 In present work, special attention is paid to the film cooling effectiveness in near-slot region at cutback surface. Previously, many great efforts have been devoted to the effects of slot geometries and internal cooling schemes on the film cooling effectiveness.…”

Section: Introductionmentioning

confidence: 99%

Exit-shape effect of film holes at pressure side on trailing edge cutback film cooling characteristics

Wang

Song

et al. 2021

Proceedings of the Institution of Mechanical Engineers, Part A:

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Pressure side (PS) cutback structure has been widely employed in modern turbine blade trailing edge (TE) cooling design. However, hot gas flows around lip of TE slot to generate an impingement to cutback, resulting in a rapid decay of film cooling effectiveness and hence thermal damage of entire TE. Proper angled-ejections upstream of TE can suppress the downstream effectiveness-decay. Therefore, in present work, five types of film-holes were designed to discuss the effect of exit-shape of film-hole on TE film cooling characteristics, inlet boundary layer profile, fluid-interactions, discharge behaviors and total pressure losses. The studied models included cylindrical-hole, common and laidback fan-shaped film-holes, and converging slot-holes with two different exit-to-inlet area ratios ( ARs). The solo cutback cooling was chosen as a reference. Thermal tests were conducted in a hot wind tunnel featuring a simplified TE test section by infrared thermal technique. Engine-similar mainstream-to-coolant temperature ratio of 2.0 was controlled. Comparisons of experimental results revealed that the converging slot-holes can obtain the highest film cooling effectiveness at TE region and overall cooling effectiveness at PS film-plate, but the slightest increase of total pressure losses. Flow measurements using Particle Image Velocimetry technique indicated the converging slot-holes can modify the inlet boundary layer profile, suppress effectively the impingement of mainstream and change the flow separation features at cutback. In addition, applying shaped-holes can effectively suppress the flow ingestion under low coolant amounts. However, relative to the exit-shape effect, the coolant amount plays a more important role on the aerodynamic and thermal characteristics of TE cooling.

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“…The design of an efficient cooling system for either a trailing-edge (TE) cutback or a breakout turbine blade remains a challenging problem because of its thin thickness, aerodynamic shape, the high thermal loads encountered, narrow passage geometry, combined with the need for material and structure integrity for safety and long-life operation [2]. Advanced cooling technology [3] and durable thermal barrier coatings [4] [5] have played important roles for the development of advanced gas turbines with high thermal performance.…”

Section: Introductionmentioning

confidence: 99%

Detached eddy simulation of blade trailing-edge cutback cooling performance at various ejection slot angles

Effendy

Yao

et al. 2019

International Journal of Heat and Fluid Flow

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Detached eddy simulation (DES) has been carried out to study a three-dimensional trailing-edge (TE) cutback turbine blade model with five rows of staggered circular pin-fin arrays inside the cooling passage, in order to evaluate the cooling performance in relation to coolant ejection slot angle. Simulations were performed by adopting a shear-stress transport k-ω turbulence model, and the effects of three different ejection slot angles 5°, 10° and 15° were investigated in terms of the characteristics of adiabatic film-cooling effectiveness, coefficient of discharge, and vortex shedding frequencies, respectively. The results obtained have shown that the TE cutback blade cooling with a 5° coolant ejection slot angle produced a better heat transfer coefficient than the other two ejection slot angles tested. The distributions of adiabatic film-cooling effectiveness along the cutback walls were found to be sensitive to the coolant ejection slot angle, e.g. the increase of ejection slot angle to 15 o yielded near unity of cooling effectiveness along the entire breakout walls, whereas the decrease of ejection slot angle caused a drastic decay of cooling effectiveness after the maximum effectiveness has been reached. Of the three angles studied, a TE cutback blade model with a 15° ejection slot angle produced an optimum film-cooling effectiveness. In the breakout region, vortex shedding was observed along the shear layer between the hot gas and the coolant airflow. The shedding frequencies were evaluated to be 2.93, 2.21, and 2.18 kHz for the ejection slot angles of 5°, 10° and 15°, respectively. The findings from this study

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Arrangement effects of inclined teardrop-shaped dimples on film cooling performance of dimpled cutback surface at airfoil trailing edge

Cited by 37 publications

References 10 publications

Flow Control Methods and Their Applicability in Low-Reynolds-Number Centrifugal Compressors—A Review

Flow Control Methods and Their Applicability in Low-Reynolds-Number Centrifugal Compressors—A Review

Exit-shape effect of film holes at pressure side on trailing edge cutback film cooling characteristics

Detached eddy simulation of blade trailing-edge cutback cooling performance at various ejection slot angles

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