hittite j sci eng Hittite Journal of Science and Engineering 2148-4171 Hitit University 10.17350/HJSE19030000369 Mechanical Engineering (Other) Makine Mühendisliği (Diğer) Enhancing Heat Transfer in Turbulent Channel Flows: A Numerical Study on the Geometric and Orientational Effects of Delta, Trapezoidal, and Rectangular Winglet Vortex Generators Türbülanslı Kanal Akışlarında Isı Transferinin İyileştirilmesi: Delta, Trapez ve Dikdörtgen Kanatçık Tipi Vorteks Üreteçlerinin Geometrik ve Yönlenme Etkilerine İlişkin Sayısal Bir İnceleme https://orcid.org/0000-0001-9679-4623 İğci Atila Abir BOZOK ÜNİVERSİTESİ, MÜHENDİSLİK-MİMARLIK FAKÜLTESİ, MAKİNE MÜHENDİSLİĞİ BÖLÜMÜ 03 31 2026 13 1 11 28 10 12 2025 12 12 2025 Copyright © 2014, Hittite Journal of Science and Engineering 2014 Hittite Journal of Science and Engineering

This paper presents a numerical study on the enhancement of heat transfer in a solar air heater (SAH) duct using winglet-type longitudinal vortex generators (WLVGs). Delta (DW), trapezoidal (TW1, TW2), and rectangular (RW) winglets are examined in pointing-up (PU) and pointing-down (PD) orientations, with the span-wise spacing ratio (S/H) varied to determine the optimal layout (S/H = 1.43, b/H = 0.50). Computational Fluid Dynamics (CFD) simulations using the GEKO turbulence model in ANSYS Fluent are performed for Reynolds numbers (Re) ranging from 5,000 to 22,500. Flow structures are analysed via Q-criterion isosurfaces, Nusselt number distributions, and streamwise vorticity contours. Results show that PU orientations generally outperform PD due to closer vortex–wall interaction. The RW configuration exhibits the highest Nusselt number, achieving a maximum Nusselt number of 114.37 at Re = 22,500, primarily attributed to the persistence of its generated vortices. However, it also results in the greatest frictional penalty, with a maximum friction factor of 0.1562 at Re = 5,000 and a corresponding normalized value of 𝑓/𝑓₀ = 5.21 at Re = 22,500. Consequently, the RW configuration yields the lowest thermal enhancement factor (TEF) at high Reynolds numbers, reaching a minimum value of 1.050 at Re = 22,500, despite its strong heat transfer rate. In contrast, the highest TEF is achieved with the PU TW1 configuration (TEF = 1.473 at Re = 5,000), which offers the most favourable balance between enhanced heat transfer and acceptable frictional losses. These results provide design-oriented implications for solar air heater (SAH) systems, identifying PU TW1 as the most energy-efficient configuration, whereas RW may be more suitable for applications where maximizing heat transfer rate is prioritised over minimising frictional losses.

Bu çalışma, kanatçık tipli boyuna girdap üreticileri (WLVG) kullanılarak bir güneş hava ısıtıcısı (SAH) kanalında ısı transferinin iyileştirilmesine yönelik sayısal bir araştırmayı sunmaktadır. Delta (DW), trapezoidal (TW1, TW2) ve dikdörtgen (RW) kanatçıklar, akış-yukarı yönelimli (PU) ve akış-aşağı yönelimli (PD) konumlarda incelenmiş, en uygun yerleşimi belirlemek amacıyla kanatçıklar arası yatay aralık oranı (S/H) değiştirilmiştir (S/H = 1.43, b/H = 0.50). Sayısal akışkanlar dinamiği (CFD) simülasyonları, ANSYS Fluent yazılımında GEKO türbülans modeli kullanılarak, Reynolds sayısı (Re) 5.000 ile 22.500 aralığında gerçekleştirilmiştir. Akış yapıları, Q-kriteri eşyüzeyleri, Nusselt sayısı dağılımları ve akış yönündeki vortisite konturları aracılığıyla analiz edilmiştir. Sonuçlar, PU konumlarının, vortekslerin ısıtılan duvara daha yakın seyretmesi nedeniyle PD konumlarına kıyasla genellikle daha iyi performans gösterdiğini ortaya koymaktadır. RW konfigürasyonu, üretilen vortekslerin uzun süreli kararlılığı sayesinde en yüksek Nusselt sayısını sağlamış (Re = 22.500’de Nu = 114.37) ancak aynı zamanda en yüksek sürtünme kaybına da yol açmıştır (Re = 5.000’de 𝑓 = 0.1562 ve Re = 22.500’de normalize değer 𝑓/𝑓₀ = 5.21). Bu nedenle, RW konfigürasyonu güçlü ısı transfer oranına rağmen yüksek Reynolds sayılarında en düşük termal iyileştirme faktörünü (TEF) vermektedir (Re = 22.500’de TEF = 1.050). Buna karşılık, en yüksek TEF değeri PU TW1 konfigürasyonunda elde edilmiştir (Re = 5.000’de TEF = 1.473), bu yapı artan ısı transferi ile kabul edilebilir sürtünme kayıpları arasında en uygun dengeyi sağlamaktadır. Bu bulgular, güneş hava ısıtıcısı (SAH) sistemleri için tasarım odaklı çıkarımlar sunmakta; PU TW1 konfigürasyonunun enerji açısından en verimli düzenleme olduğunu, RW konfigürasyonunun ise minimum sürtünme kaybından ziyade maksimum ısı transferinin önceliklendirildiği uygulamalarda daha uygun olabileceğini göstermektedir.

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