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Article
Numerical Study of Separated Flows in Backward Facing Step by Using Collocated Grid Arrangement
دراسة عددية للجريان المنفصل في درجة خلفية باستخدام ترتيب الشبكة المتحدة الموقع

Author: Dr. Ahmed Waheed Mustafa
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2011 Volume: 18 Issue: 4 Pages: 1-9
Publisher: Tikrit University جامعة تكريت

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Abstract

The effects of Reynolds number and the inlet height ratio on separated flow over backward facing step are investigated. The flow field is studied numerically with different inlet height ratio. The laminar flow field is analyzed numerically by solving the steady, two-dimensional incompressible Navier-Stokes equations. A collocated (non-staggered) grid is used in the momentum equations, which discretized by finite volume method, SIMPLE algorithm is used to adjust the velocity field to satisfy the conservation of mass. The range of Reynolds number is (Re = 100 - 800). The results show that at low height ratio (h/H = 0.25) and high Reynolds number the flow separated along the top wall of the channel. Good agreement with the experimental data is obtained.

تم دراسة تأثير رقم رينولد و نسبة ارتفاع الدخول على الجريان المنفصل في درجة خلفية. تمت دراسة حقل الجريان عدديا لنسب ارتفاع دخول مختلفة. حقل الجريان الطباقي تم تحليلية عدديا بحل معادلات نافير ستوك للجريان المستقر والثنائي البعد. تم استحدام شبكة متحدة الموقع لتقطيع معادلات الزخم باستخدام طريقة الحجم المحدد. خوازمية (SIMPLE) استخدمت لتصحيح حقل السرع لتحقيق حفظ الكتلة. مدى رقم رينولد هو (100-800) . بينت النتائج انه عند نسبة ارتفاع عند الدخول قليلة (h/H=0.25) ورقم رينولد عالي فأن الجريان ينفصل على السطح العلوي للقناة. توافق جيد بين نتائج البحث والنتائج العملية تم الحصول علية.


Article
Study of Turbulent Flow and Heat Transfer Over a Backward- Facing Step Under Impingement Cooling
دراسة الجريان الاضطرابي وانتقال الحرارة فوق عتبة داخل مجرى هوائي بوجود تبريد تصادمي

Author: Khudheyer S. Mushatet
Journal: University of Thi-Qar Journal for Engineering Sciences مجلة جامعة ذي قار للعلوم الهندسية ISSN: 26645564/26645572 Year: 2012 Volume: 3 Issue: 2 Pages: 1-21
Publisher: Thi-Qar University جامعة ذي قار

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Abstract

Computations are presented to study the turbulent flow and heat transfer over a channel backward-facing step under impingement cooling. The problem was simulated for different parameters, such as the number of impinging jets, contraction ratio, size of jets, and jet andchannel Reynolds numbers. The contraction ratio had the values 0.25, 0.35 and 0.5. The impinging jets were normal to the cross-channel flow. A control volume approach using staggered grid techniques was considered to integrate the continuity, fully elliptic Navier-Stockes and energy equations. A computer program was developed, and the SIMPLE algorithm was employed to determine the existence of coupling between the continuity and Navier-Stockes equations. The effect of turbulence was modelled using a k-ε model while the wall functions laws were used to treat the regions near the solid walls. The presented results show that the strength and size of recirculation regions near the reattachment region just after the backward-facing step increase as the contraction ratio increases. Also, the results show that the size of jets, number of jets, and jet and channel Reynolds numbers have a significant effect on the flow field, turbulent kinetic energy and variation of the Nusselt number.

في هذا البحث تم أجراء دراسة حسابية لدراسة خصائص الجريان الأضطرابي وانتقال الحرارة فوق عتبه داخل مجرى هوائي و بوجود التبريد التصادمي. تم نمذجة المسألة المدروسة بتأثير عدة عوامل مثل حجم وعدد المنافث،نسبة التحضر وأرقام رينولدز للمجرى الرئيسي والمنافث. نسب التخصر المدروسة كان لها قيم 0.25, 0.3،0.5 على التوالي والنفاثات التصادمية كانت عمودية على المجرى الرئيسي. أستخدمت طريقة الحجم المحدد مع تقنية الشبكة الزاحفة لتكامل معادلات الأستمرارية و ناقير-ستوكس والطاقة بينما طور برنامج حاسوب بلغة فورتران وبأعتماد خوارزمية الأجراء المبسط التي تحدد الأرتباط بين الأستمرارية ومعادلات نافير-ستوكس. أستخدم نموذج الأضطراب k-ε لنمذجة تأثير الأضطراب في الجريان. أوضحت النتائج التي تم الحصول عليها أن قوة وحجم مناطق إعادة التدوير وطول اعادة الأتصال خلف العتبة يزداد مع زيادة نسبة التخصر. أيضا بينت النتائج أن حجم وعدد المنافث وأرقام رينولدز للمجرى الرئيسي والمنافث لها تأثير واضح على مجال الجريان والطاقة الحركية للضطراب وعدد نسلت.


Article
Flow Separation Control of Backward-Facing Step Airfoil NACA0015 by Blowing Technique

Author: Khuder N. Abed
Journal: DIYALA JOURNAL OF ENGINEERING SCIENCES مجلة ديالى للعلوم الهندسية ISSN: 19998716/26166909 Year: 2019 Volume: 12 Issue: 1 Pages: 99-119
Publisher: Diyala University جامعة ديالى

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Abstract

The aim of this paper is to control the flow separation above backward-facing step (BFS) airfoil type NACA 0015 by blowing method. The flow field over airfoil has been studied both experimentally and computationally. The study was divided into two parts: a practical study through which NACA 0015 type with a backward -facing step (located at 44.4% c from leading edge) on the upper surface containing blowing holes parallel to the airfoil chord was used. The tests were done over two-dimensional airfoil in an open circuit suction subsonic wind tunnel with flow velocity 25m/s to obtain the pressure distribution coefficients. A numerical study was done by using ANSYS Fluent software version 16.0 on three models of NACA 0015, the first one has backward-facing step without blowing, the second with single blowing holes and the third have multi blowing holes technique. Both studies (experimental and numerical) were done at low Reynolds number (Re=4.4x105) and all models have chord length 0.27m.The experimental investigations and CFD simulations have been performed on the same geometry dimensions, it has been observed that the flow separation on the airfoil can be delayed by using velocity blowing (30m/s) on the upper surface. The multi blowing holes with velocity improved the aerodynamics properties.The multi blowing holes and single blowing hole thesame effect onpressure distribution coefficients.


Article
SIMULATION OF LAMINAR FORCED CONVECTION HEAT TRANSFER AND FLUID FLOW OVER A BACKWARD FACING STEP WITH OBSTACLE USING (SIO2) NANOPARTICLES

Authors: Mohammed Saad Kamel --- Ahmed Khafeef Obaid Albdoor
Journal: University of Thi-Qar Journal for Engineering Sciences مجلة جامعة ذي قار للعلوم الهندسية ISSN: 26645564/26645572 Year: 2015 Volume: 6 Issue: 2 Pages: 80-92
Publisher: Thi-Qar University جامعة ذي قار

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Abstract

Simulation of Heat transfer and laminar Sio2/water and Sio2/oil-engine flow over backward facing step with and without obstacle numerically studied in this paper. The finite volume method adopted to solve continuity, momentum and energy equations in two dimensions. The aspect ratio of triangular obstacle w/e = 0.5 presented. The step height and expansion ratio of channel were 4.8mm and 2 respectively, the range of Reynolds number varied from 100 to 250, constant heat flux subjected on downstream of wall was 2000W/m2.Two types of base fluid used in this simulation the water and oil-engine with constant properties at T = 300K°, The Sio2 nanoparticles used with nanoparticles diameter 30nm and volume friction 4%. The average nusselt number noticed increase with increase Reynolds number with obstacle for two basefluid and also noticed that the nanofluid of Sio2-oil engine has higher nusselt number compared with other nonofluid. The result shows increase of local nusselt number for backward facing step with obstacle in compared to those without obstacle. The maximum enhancement of heat transfer observed at obstacle due to increase recirculation flow after the obstacle. Streamline showing the increase of recirculation region with used obstacle in compared without obstacle and highest recirculation region observed at obstacle.

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