International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395-0056
Volume: 04 Issue: 07 | July -2017
p-ISSN: 2395-0072
www.irjet.net
Turbulent Flow in Curved Square Duct: Prediction of Fluid flow and Heat transfer Characteristics R Girish Kumar1, Rajesh V Kale2 Student, RGIT, Andheri, Mumbai, India Dept of Mechanical Engineering, RGIT, Andheri, Mumbai, India ---------------------------------------------------------------------***--------------------------------------------------------------------2Professor,
1M.E
Abstract – Fully developed Turbulent flows in curved square duct with curvature of 30degree numerically and experimentally investigated. Turbulent flows in non circular duct leads to generate the secondary motions in crosswise direction. These secondary motions of second kind are generated due to the gradient of Reynolds Stresses in cross stream in straight duct. But these secondary motions are generated in curved square duct due to imbalance between centrifugal force and radial pressure gradients. This note aims to predict numerically these secondary motions and their effects on fluid flow and heat transfer characteristics in the curved square duct. SST K ω model has been used to simulate the flow. And these results are validated with experimental measurements. It has been observed that there is good agreement between the numerical and experimental results. Key Words: Turbulent flow, Secondary motions, Reynolds Stresses, Square Duct, Heat transfer
boundary conditions and geometries and has given the reason behind formation of secondary flows and relationships between duct geometry, aspect ratios and secondary flows [1, 6]. But there no exclusively devoted study of these secondary flows in curved duct in relationship with heat transfer. Present study focuses on presenting the relationship between heat transfer enhancement and Secondary motions or secondary flows. 2. GOVERNING EQUATIONS, METHODOLOGY AND TESTING DOMAIN The present case is of unsteady, three dimensional and turbulent in nature. Therefore an averaged continuity equation, Reynolds averaged Navier stokes equation and energy equations are solved. 1.
1.INTRODUCTION Prediction of Turbulent flow characteristics is of academic interest since few decades. In spite having numerous applications, there are only few exclusive studies which are focussed on secondary motions of turbulent flow. These secondary flows mean velocity will be up to 5-10% of mean velocity of primary flow. Experimental measurements of turbulent flow characteristics in 90˚ curved square duct have been studied by Humphery, White law and Yee [1]. These studies are done with the aid of non disturbing Laser Doppler Velocimetry and they have reported that stronger secondary motions and higher levels of turbulence is experienced near thicker boundary region. Numerous studies undertaken over the past few years done by Lesieur and Métais [2]; Moin [3]; Germano [4] demonstrate that LES is one of the most reliable approaches for the prediction of complex turbulent flows of practical relevance. Gavrilikas investigated the flow pattern inside the straight rectangular duct through numeric simulation and concluded that turbulent flow near the smooth corner is subjected to remarkable structural change, mean stream wise vortices attain their largest values in the region where the viscous effects are significant [5]. In few major applications the continuous change of fluid direction induces the centrifugal effects in fluid flow. Tilak T et al and Humphrey simulated the flow with various © 2017, IRJET
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2.
Continuity equation
ui 0 xi
(1)
Navier Stokes equation
(ui u j ) ui (ui u j ) 1 p ui ( ) t x j x j x j x j xi 1 1
3.
(2)
Energy Equation
T (uiT ) t x j x j
T ui1u1j x x j j
Where ‘u’ time averaged velocity and
(3)
ui1u1j is Reynolds
stress SST K-ω turbulence model is used in predicting the turbulent flow characteristics in the heated Curved squared duct. And this model is validated with DNS results of Gavrilakas(1992) for straight square duct at Reynolds number 4410 and they show good agreement in the results. Computational domain is as shown in figure.1 consists of 30˚ curvature and all other dimensions are in terms of hydraulic diameter of the duct Dh. It is square duct (Aspect Ratio=1) with 100mm side. Air has been used as working fluid with the properties of kinematic viscosity (ʋ) = 1.6x10-6 m2/s and Prandtle number (Pr) = 0.7. ISO 9001:2008 Certified Journal
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