CFD Letters <p>CFD Letters publishes as rapidly as possible manuscripts of high quality which addresses eminent topics of computational fluid dynamics theory and applications. Being an international, peer-reviewed, online and open access journal, CFD Letters presents a world-wide forum for the dissemination of knowledge among engineers, scientists and mathematicians working in the field of computational fluid mechanics.</p> en-US (Nor Azwadi Che Sidik) (Wan Mohd. Arif Aziz Japar (Technical Editor)) Tue, 10 Aug 2021 00:00:00 +0000 OJS 60 Three Dimensional MHD Hybrid Nanofluid Flow with Rotating Stretching/Shrinking Sheet and Joule Heating <p>A three-dimensional hybrid nanofluid flow over a stretching/shrinking sheet is numerically studied. The hybrid nanofluid being considered in this study used water as the base fluid and mixed with two types of solid nanoparticles, namely alumina (Al<sub>2</sub>O<sub>3</sub>) and copper (Cu). The main focus of the current study is to examine the effect of magnetic field, Joule heating, and rotating sheet on the velocity, &nbsp;and temperature profiles. In addition, the impact of suction and stretching sheet on the variations of reduced skin friction, , and reduced heat transfer are studied as well. The fluid flow and heat transfer problem presented in this study is governed by a system of nonlinear partial differential equations (PDEs), which is then transformed into the corresponding system of high order nonlinear ordinary differential equations (ODEs) using similarity variables. The resulting system of higher order nonlinear ODEs is solved numerically using a boundary value solver known as bvp4c, which operates on the MATLAB computational platform. Results revealed that dual solutions exist for shrinking sheet while unique solutions are observed for stretching sheet with various values of Cu nanoparticles volume fraction and magnetic parameter. Dual solutions also exist for the value of the suction parameter greater than its critical point with various values of Cu nanoparticles volume fraction. Velocity profile of the hybrid nanofluid increases alongside with the value of magnetic parameter but declination was observed in the profile of &nbsp;and temperature, for both solutions as the value of Cu nanoparticles volume fraction increases. When the value of rotational parameter increases, both velocity and &nbsp;profiles increase for both solutions. This indicates that the momentum boundary layer thickness increases with increasing values of &nbsp;for both solutions, but thermal boundary layer thickness decreases for the first solution and increases for the second solution. Finally, an increment in the value of Eckert number causes the temperature of the hybrid nanofluid to rise as well for both first and second solutions.</p> Yuan Ying Teh, Adnan Ashgar Copyright (c) 2021 CFD Letters Tue, 10 Aug 2021 00:00:00 +0000 Numerical Studies on Thermo-Hydraulic Characteristics of Turbulent Flow in a Tube with a Regularly Spaced Dimple on Twisted Tape <p>Heat transfer augmentation is an important concern due to the increase in heat management problems in thermal systems. </p> Birlie Fekadu, Harish H.V, Manjunath. K Copyright (c) 2021 CFD Letters Tue, 10 Aug 2021 00:00:00 +0000 Thermal Radiation in Nanofluid Penetrable Flow Bounded with Partial Slip Condition <p>Thermal radiation enhances heat transfer, and it is used widely in manufacturing and materials processing applications. Thus, steady two-dimensional boundary layer flow over an exponentially porous shrinking sheet of nanofluids was considered in the influence of thermal radiation related to partial slip boundary conditions and suction. This paper aims to study the nanofluid penetrable flow over an exponentially shrinking sheet with thermal radiation and partial slip. The effects of silver (Ag) nanoparticles with two different types of base fluids named water and kerosene oil are investigated in this study. First, the governing equations and boundary conditions are transformed to a non-linear ordinary differential equation and then solved using bvp4c solver. Using Matlab software, it is found that the dual solution exists in some values from the suction parameter. Furthermore, we identified both nanoparticle volume fraction and suction parameter increase, leading to the rise in velocity profile. Moreover, the suction parameter increases both skin friction coefficient and Nusselt number increase.</p> Nadia Diana Mohd Rusdi, Siti Suzilliana Putri Mohamed Isa, Norihan Md. Arifin, Norfifah Bachok Copyright (c) 2021 CFD Letters Tue, 10 Aug 2021 00:00:00 +0000 Design Optimization of Diffuser Augmented Wind Turbine <p>The wind turbine power decreases at low wind speed. A flanged diffuser plays a role of a device for collecting and accelerating the approaching wind, and thus the optimization of the diffuser shape presents an important way to enhance the wind turbine power. In this work, a numerical parametric study was conducted on the diffuser to obtain the initial optimum form of flanged diffuser. Then, the Simplex algorithm is used to obtain the optimal diffuser shape starting from the obtained initial shape. Finally, the obtained optimum diffuser shape is used with conventional wind turbine blade. The diffuser shape is defined by four variables: open angle, flange height, centerbody length, and flange angle. The numerical simulation of flanged diffuser is carried out using the “CFDRC package. The results indicated that, the optimum diffuser shape can be obtained using simplex algorithm which maximizes the entrance average velocity to reach 1.77 times wind speed. The power augmented by a factor about 2.76:5.26 of a selected small wind turbine using the obtained diffuser shape compared to that without diffuser.</p> Ahmed M. Elsayed Copyright (c) 2021 CFD Letters Mon, 30 Aug 2021 00:00:00 +0000