Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: www.elsevier.com/locate/ijts Mixed convection heat transfer from a triangular cylinder subjected to upward cross fow Zekeriya Altaç ∗ , Zerrin Sert, Necati Mahir, Çisil Timuralp Department of Mechanical Engineering, Eskişehir Osmangazi University, Eskisehir, Turkey ARTICLEINFO Keywords: Triangular cylinder Assisting fow Flow characteristics Mixed convection Nusselt correlations ABSTRACT Unsteady laminar mixed (forced and free) convection heat transfer and fuid fow over long horizontal equi- lateral triangular cylinder subjected to upward cross fow are investigated numerically. The computation model is a two-dimensional unconfned rectangular domain with an aspect ratio of 1.4. A second order upwind scheme was used for diferencing of the convection terms, and SIMPLE algorithm was adopted. The working fuids are air (Pr = 0.7) and water (Pr = 7). The equilateral isothermal triangular cylinder is placed in a uniform stream. The efect of buoyancy is incorporated into the Navier-Stokes (NS) equations using the Boussinesq approximation. This study is a case of “assisting fow” where the buoyancy-induced fow and fuid motions have the same upward direction. The basic dimensionless simulation variables, Reynolds and Richardson numbers, are varied in the range10≤Re≤200and0≤Ri≤10.Thefowcharacteristicssuchasthemeandrag,meanrmslift coefcients and the Strouhal number are computed for each simulation. The fow patterns and isotherms are generated to interpret and understand the underlying physical mechanism. The cylinder surface mean Nusselt number was computed for mixed as well as for forced and free convection conditions. The computational data were used to develop the several Nusselt number correlations for forced, free and mixed convection fow. 1. Introduction Flow around cylinders has been the topic of intense research for the last century due to its importance in engineering signifcance and ap- plications. Most published research is devoted to the fow character- istics (drag/lift coefcients and Strouhal number) of circular cylinders since these are commonly used as tubes or pipes in engineering designs. Only recently, attention has shifted to cylinders of diferent cross sec- tions (square, rectangular, semicircular, triangular etc.). The fow and heat transfer over bluf bodies, over the years, has received attention both numerically and experimentally as a result of increasing computational capabilities and in view of the advent of new experimental techniques. In spite of wide applications, very limited information is available in the literature on the mixed convection fow and heat transfer from noncircular cylinders. To the best of our knowledge, the fuid fow and heat transfer from a triangular cylinder in cross fow have received very little attention up until recently in both unbounded and bounded channels. Several studies involve only incompressible viscous fuid fow over triangular cylinders for which fow characteristics are explored. Two- dimensional numerical simulation of laminar fow past a triangular cylinder placed in free-stream was studied by De and Dalal [1] for 10 ≤ Re ≤ 250, by Shademani et al. [2] for a fxed blockage ratio (BR) of0.05and1.4≤Re≤38.Theefects on the wakes of unsteady fows past a cylinder having an equilateral triangular cross-section were in- vestigated numerically using a 2D analysis by Ng et al. [3]. Fluid fow over a triangular cylinder at an inclination producing a wake region whose stability characteristics are studied by Ng et al. [4] using a 3D numerical model for inclinations between 0 and 60°, and for Re = 100 and 150. Limited studies have involved forced convection heat transfer from horizontal triangular cylinders placed in a confned and/or unconfned channel. The fow and heat transfer in a 2D horizontal channel difer- entially heated triangular cylinder was numerically investigated by Abbasi et al. [5]forPr=0.71and20≤Re≤250.For80≤Re≤200, De and Dalal [6] numerically studied 2D fow and heat transfer past a triangular cylinder in horizontal channels of 1/12 ≤ BR ≤ 1/3. Using a 2D model, heat transfer in a channel in the presence of a triangular prism was numerically investigated in the turbulent fow regime up to Re = 40000 and for BR = 0.25 by Chattopadhyay [7]. Unsteady forced convection transfer characteristic of a heated equilateral triangular cylinder for Pr = 0.71 fuid was numerically investigated using a 2D https://doi.org/10.1016/j.ijthermalsci.2018.11.010 Received 17 March 2018; Received in revised form 7 November 2018; Accepted 10 November 2018 ∗ Corresponding author. Eskişehir Osmangazi University, School of Engineering and Architecture, Mechanical Engineering Department, Batı-Meşelik, 26480, Eskişehir, Turkey. E-mail addresses: zaltac@ogu.edu.tr (Z. Altaç), zbocu@ogu.edu.tr (Z. Sert), nmahir@ogu.edu.tr (N. Mahir), cisil@ogu.edu.tr (Ç. Timuralp). International Journal of Thermal Sciences 137 (2019) 75–85 1290-0729/ © 2018 Elsevier Masson SAS. All rights reserved. T