PİN FİN ŞEKLİ VE BÜYÜKLÜĞÜNÜN TÜRBİN KANADI FİRAR KENARINDAKİ AKIŞ VE ISI TRANSFERİNE ETKİLERİ

Year 2019, Volume: 39 Issue: 2, 191 - 207, 31.10.2019

Tuğba Tunçel Harika Kahveci

Abstract

Modern türbin kanatlarının firar kenarlarının soğutulmasında, adalarla desteklenen film soğutması oluklarının bulunduğu kesik basınç kenarları ve soğutma kanallarının içine yerleştirilen pin fin yapıları kullanılmaktadır. Bu soğutma konfigürasyonlarını termal açıdan inceleyen pek çok çalışma olmasına rağmen, aerodinamik açıdan inceleme yapan çalışmalar sınırlı sayıdadır. Bu çalışma bir film soğutması konfigürasyonunun, pin dizini şekil ve büyüklüğünün optimum kombinasyonunu belirlemek için yapılan detaylı bir hesaplamalı incelemesini sunmaktadır. Analizler, firar kenarındaki kesik bölgenin hem iç hem dış yüzeylerini kapsayacak şekilde yapılmış ve sonuçlar hem aerodinamik hem de termal açıdan değerlendirilmiştir. Çalışılan konfigürasyonun iç bölgesi, saptırılmış pin dizinleri ve kesik basınç kenarına açılan olukların önünde bulunan kanat şeklindeki tıkayıcılardan oluşmaktadır. Çalışmada, dairesel, eliptik ve bu tür konfigürasyonlarda nadir olarak çalışılmış olan kanat şekillerine sahip ve farklı büyüklüklerde olan pinler kullanılmış ve karşılaştırmalar için beş farklı model oluşturulmuştur. Firar kenarı yüzeylerinde, olukların civarında ve kesik dış yüzey bölgesindeki akış özellikleri, basınç kayıpları ve ısı transferi karakteristiği incelenmiştir. Elde edilen sonuçlar kanat şeklindeki pinlerin aynı büyüklükteki diğer şekilli pinlere göre, iç akışta basınç kayıplarını azalttığını göstermektedir. Bununla birlikte pin dizinleri, firar kenarı ayrışma bölgesindeki hız konturlarında küçük farklar oluşturmakta ve burada benzer basınç kayıplarına sebep olmaktadır. Küçük pinlerin, oluk çıkışlarındaki daha düşük sıcaklık seviyelerinden ötürü, firar kenarı ayrışma yüzeyinde biraz daha yüksek film soğutması verimliliği sağladığı görülmüştür. Sonuç olarak, kanat şeklindeki pinler kanat içindeki dizinde aerodinamik kayıpları azalttığı için, hedeflenen soğutma performansını elde etmek üzere bu pin şeklinin boyut optimizasyonunun yapılması tasarım aşamasında uygun bir yaklaşım olacaktır.

Keywords

Türbin, firar kenarı, film soğutması, basınç kaybı, ısı transferi katsayısı, film soğutması verimliliği

EFFECTS OF PIN FIN SHAPE AND SIZE ON TURBINE BLADE TRAILING EDGE FLOW AND HEAT TRANSFER

Abstract

In modern turbine blades, pressure-side cutbacks with film-cooling slots stiffened with lands and pin fins that are embedded in passages are used to cool trailing edges. There are many studies that have investigated these cooling configurations from a thermal perspective, while only a limited number have been concerned with the aerodynamic aspects. This study presents a thorough computational investigation of a film-cooling configuration to determine the optimum combination of shape and size of pin arrays. The analyses are performed to include both internal and external surfaces of the trailing-edge cutback region and the results are evaluated from both aerodynamics and thermal aspects. The internal structure of the configuration studied consists of staggered arrays of pins and airfoil-shaped blockages in front of the slot exits that open into a pressure-side cutback region. The pins used are of circular, elliptical, or airfoil shapes that are rarely studied in such configurations, and of different sizes, resulting in five different models for comparisons. The flow features, pressure losses and heat transfer characteristics inside of the trailing-edge surfaces and in the vicinity of the slots and on the external cutback region are examined. The airfoil-shaped pins are found to decrease the pressure losses in internal flow compared to the other pin shapes of similar size. However, the pin arrays produce minor differences in the velocity contours in the breakout region, resulting in similar pressure loss trends here. The small-sized pins are found to demonstrate slightly higher film-cooling effectiveness on the breakout surface due to lower temperatures at the slot exit. It can be inferred from the results that, since the airfoil-shaped pin reduces the aerodynamic penalty across the internal pin array, performing an optimization on the size of these pins to achieve the desired cooling performance could be a reasonable approach in the design process.

Keywords

Turbine, trailing edge, film cooling, pressure loss, heat transfer coefficient, film-cooling effectiveness

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