Optimization of contraction cone length in an open-circuit wind tunnel

Year 2024, Volume: 26 Issue: 2, 431 - 440, 15.07.2024

Seyhun Durmuş

https://doi.org/10.25092/baunfbed.1339334

Abstract

The studies in the literature mostly focus on the curvature of the contraction cone, while research regarding the impact of contraction length on flow characteristics is limited. This study aims to determine the optimal length of the contraction cone, which ensures uniform flow at the outlet section, considering the wall shear factor. Four contraction cones of varying lengths were designed based on the hydraulic radius of the inlet. Numerical analysis was conducted to obtain static pressure and velocity distributions for the designed geometries. It was observed that wind tunnels designed with contraction cone lengths 2, 3, and 3.5 times the inlet hydraulic radius exhibited similar flow patterns. However, a longer contraction curve minimizes flow disturbances and turbulence, thereby enhancing flow uniformity and steadiness, while thicker boundary layers result from increased wall shears due to boundary layer growth. Consequently, it was concluded that a wind tunnel configured with a contraction cone length of 2 times the inlet hydraulic radius (square contraction cone) is the optimal choice, considering the combined effects of wall shear and flow uniformity.

Keywords

Contraction cone length, wind tunnel, nozzle design, flow uniformity, CFD.

Açık devre rüzgar tünelinde daralma konisi uzunluğunun optimizasyonu

Abstract

Bu çalışmada Literatürdeki çalışmalar çoğunlukla daralma konisinin eğriliğine odaklanırken, daralma uzunluğunun akış özellikleri üzerindeki etkisine ilişkin çalışmalar azdır. Çalışma, duvar kesme gerilme faktörünü birlikte dikkate alarak daralma konisinin çıkış bölümünde düzgün akış sağlayan daralma konisinin optimum uzunluğunu ortaya çıkarmayı amaçlamaktadır. Giriş hidrolik yarıçapının uzunluğuna bağlı olarak, farklı uzunlukta dört daralma konisi tasarlanmıştır. Tasarlanan geometriler için sayısal analiz yapılarak statik basınç ve hız dağılımları elde edilmiştir. Giriş hidrolik yarıçapının 2, 3 ve 3,5 katı daralma konisi uzunluğu ile tasarlanan rüzgar tünelinde de benzer bir akış patterni elde edildiği bulunmuştur. Bununla birlikte, daha uzun bir daralma eğrisi, akış bozukluklarını ve türbülansı en aza indirir ve bu, akış düzgünlüğüne yardımcı olur, oysa sınır tabakası büyümesi nedeniyle duvardaki kesme gerilmesi daha kalın sınır tabakası ile sonuçlanır. Bu nedenle, duvar kesme ve akış homojenliğinin birlikte etkisi göz önüne alındığında giriş hidrolik yarıçapının (kare daralma konisi) 2 katı daralma konisi uzunluğu ile yapılandırılmış rüzgar tünelinin en iyi seçim olduğu sonucuna varılmıştır.

Keywords

Daralma konisi uzunluğu, rüzgar tüneli, nozul tasarımı, düzün akış, HAD.

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