IJE TRANSACTIONS A: Basics Vol. 23, No. 2 (April 2010) 177-190   

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M. Kahrom, P. Haghparast and S. M. Javadi
( Received: October 02, 2009 – Accepted in Revised Form: May 20, 2010 )

Abstract    A quad inserted into a turbulent boundary layer of a flat plate and its effect on average heat transfer and the friction coefficient is studied. To optimize this effect, the edge sizes and distance of the quad from the flat plate are continually modified. In each case, simultaneously the heat transfer enhancement and reduction in skin friction are analyzed. For optimization, the genetic algorithm technique is employed and the results of each step of progress studied by following the Pareto curves. Physical domain is divided into control volumes, over which flow equations are discretized. To deal with the turbulence, several turbulence schemes are examined and appearance of flow features and stability in hard environments are monitored. The RNG k - ε turbulence model proved to give reliable solutions and stability to all the 1,600 cases under consideration. Based on the Pareto curve and with no single exceptions of the cases studied, results show that as the heat transfer coefficient rises, the skin friction falls simultaneously; in other words, there is an inverse relation between heat transfer enhancement and skin friction. Conclusion also made that the rate of heat transfer enhancement is more sensitive to modification on small area quads than those of large ones. Since the experimental validation of too many cases was impractical, random comparison between some numerical results and wind tunnel experiments is performed. The comparison showed that the numerical results are strongly in agreement with the experiments.


Keywords    Genetic Algorithm, Pareto Front, Heat Transfer Enhancement, Reynolds Analogy


چکیده    اثر ورود يك چهار گوش به داخل لايه مرزي توربولنت بر روي يك صفحه تخت بر افزايش ضريب انتقال حرارت بررسي مي شود. براي بهينه كردن ضريب انتقال حرارت، اندازه اضلاع چهارگوش و فاصله آن از سطح صفحه گرم مجاور آن، به دفعات تغيير داده شده و در هر حالت تغيير ضريب انتقال حرارت و ضريب اصطكاك تحليل شده است. براي بهينه كردن از روش الگوريتم ژنتيك استفاده مي شود كه در آن نتيجه هر مقايسه بر روي منحني هاي پَرِتو دنبال مي شود. ابتدا فضاي فيزيكي به حجم هاي كنترلي تقسيم و معادلات جريان بر روي اين حجم ها تفاضلي شده و مدل هاي مختلف توربولنسي مورد آزمون و انتخاب قرار گرفته است. ملاحظه شده است كه مدل RNG k - ε پاسخ هاي بهتري در 1600 مورد مطالعه به دست مي دهد. بر اساس منحني هاي پَرِتو و بدون استثنا ديده مي شود كه اولاً افزايش ضريب انتقال حرارت متوسط همواره با كاهش ضريب اصطكاك همراه است. يعني تغييرات اين دو مشخصه با يكديگر نسبت وارونه دارند. ثانياً افزايش ضريب انتقال حرارت براي سطح مقطع هاي كوچك چهار گوش حساس تر به تغيير اندازه مساحت بوده است. براي صحت سنجي نتايج عددي، گزينش تصادفي از حل هاي عددي انجام و با نتايج آزمايشگاهي مقايسه شده است. مقايسه انطباق خوبي را با نتايج آزمايشگاهي نشان مي دهند.


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