ORIGINAL Turbulent forced convection of nanofluids downstream an abrupt expansion Abdelali Kimouche 1 & Amina Mataoui 1 Received: 5 March 2016 /Accepted: 6 September 2017 # Springer-Verlag GmbH Germany 2017 Abstract Turbulent forced convection of Nanofluids through an axisymmetric abrupt expansion is investigated numerically in the present study. The governing equations are solved by ANYS 14.0 CFD code based on the finite volume method by implementing the thermo-physical properties of each nanofluid. All results are analyzed through the evolutions of skin friction coefficient and Nusselt number. For each nanofluid, the effect of both volume fraction and Reynolds number on this type of flow configuration, are examined. An increase on average Nusselt number with the volume fraction and Reynolds number, are highlighted and correlated. Two relationships are proposed. The first one, determines the aver- age Nusselt number versus Reynolds number, volume fraction and the ratio of densities of the solid particles to that of the base fluid ( Nu ¼ f Re; ϕ; ρ s ρ f   ). The second one varies ac- cording Reynolds number, volume fraction and the conduc- tivities ratio of solid particle to that of the base fluid ( Nu ¼ f Re; ϕ; k s k f   ). Keywords Abrupt expansion . Forced convection . Nanofluids . Turbulent flow . Turbulence modeling 1 Introduction The use of nanofluid may be efficient in several applications of forced convection. Since the last decade, transport and the properties of nanofluids, were extensively studied for different applications of heat transfer enhancement. Flows through abrupt expansion geometries are of interest from the point of view of academic problem of fluid mechanics, knowing that the flow through an axisymmetric abrupt expansion is charac- terized by the complexities of internally separating and reattaching flows. The turbulent fluid flows through abrupt expansion duct are common in several engineering applica- tions such as heat exchanger, pipe line, dump combustor and nuclear reactor. So, many experimental and numerical studies were devoted on performance of heat transfer for separated and reattached flows. Drust et al. [1] performed an experimen- tal study of flow downstream a symmetric expansion in a duct. They found that the flow depends mainly on Reynolds num- ber and they have highlighted three eddies of different size behind each step. Afshin and Peter [2] studied experimentally laminar flow of water through a confined annular channel with abrupt expansion, using Particle Image Velocimetry (PIV) and Refractive Index Matching (RIM). They have found that the separation zones augment with increasing Reynolds number. Oliverira and Pinho [3], have studied numerically pressure drop coefficient of laminar Newtonian flow through an abrupt expansion. Their results evidence an increase of Nusselt num- ber leading to a decrease of local loss friction coefficient. Miranda et al. [4] have found the same results for inelastic laminar fluids flowing in an axisymmetric abrupt expansion. Chiang et al. [5] have performed 2D and 3D simulations ex- amining the effect of the sidewall, on flow structure of a lam- inar incompressible fluid, through a symmetrical abrupt ex- pansion. They have checked 14 aspect ratios ranging from 3 to 48. A good agreement with experimental data of Fean et al. [6] * Amina Mataoui mataoui_amina@yahoo.fr; amataoui@usthb.dz 1 Theoretical and Applied Laboratory of Fluid Mechanics, Faculty of Physics, University of Science and Technology Houari Boumedienne – USTHB, Algiers, Algeria Heat Mass Transfer DOI 10.1007/s00231-017-2161-x