A numerical study of forced convection from an isothermal cylinder performing rotational oscillations in a uniform stream
TL;DR: In this paper, a heated rotationally oscillating circular cylinder placed in a uniform cross flow of constant properties fluid is investigated and the two-dimensional governing equations of flow motion and energy are solved numerically on non-uniform polar grids using a higher order compact (HOC) formulation.
About: This article is published in International Journal of Heat and Mass Transfer.The article was published on 2018-12-01. It has received 25 citations till now. The article focuses on the topics: Forced convection & Heat transfer coefficient.
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TL;DR: In this paper, the duality of solutions and the flow and heat transfer of the hybrid nanofluid past a shrinking cylinder in the appearance of Joule heating were observed.
Abstract: The objectives of the present study are (i) to observe the duality of solutions, and (ii) to investigate the flow and heat transfer of the hybrid nanofluid past a shrinking cylinder in the appearance of Joule heating. The single phase nanofluid model with modified thermophysical properties are used for the mathematical model. The similarity transformation simplifies the model (PDEs) into similarity (ordinary) differential equations. bvp4c solver is used to compute the reduced equations. For the validation part, the analytical solution is developed using an exact analytical method and compared with the numerical values for several cases. First and second solutions are observable for the shrinking cylinder case only if suction parameter is applied. Meanwhile, only the first solution is found to be stable from the stability analysis. The application of high suction strength make the reduced heat transfer rate is lower for hybrid nanofluid (Cu-Al2O3/water) than alumina-water nanofluid but, opposite result is found for the skin friction coefficient. The addition of curvature parameter (flat plate to cylinder) can quicken the separation process of boundary layer. This results are conclusive to the pair of alumina and copper only.
88 citations
TL;DR: In this article, a comparison between the magnetohydrodynamic (MHD) flow and heat transfer of non-Newtonian (Sodium Alginate) base fluid with three ferroparticles, that is Cobalt ferrite (C o F e 2 O 4 ), Manganese-Zinc ferrite(M n − Z n F e 4 ) and Nickel -Zinc-ferrite (N i − Z N F e 6 O 4 ), over an unsteady contracting cylinder was performed.
36 citations
TL;DR: In this paper, the effect of 2DOF flow-induced vibration on the characteristics of forced convective heat transfer from an isothermal circular cylinder is numerically simulated by commercial software-FLUENT in combination with the user defined function.
28 citations
Book Chapter•
01 Nov 2011TL;DR: This chapter discusses the appearance of viscoelastic instabilities, which are seen to occur even under creeping flow conditions, and the governing equations for Newtonian and nonNewtonian fluid flow, including the constitutive equations that describe the rheology of the fluids.
Abstract: In this chapter we provide an overview of viscoelastic fluid flow at the microscale. We briefly review the rheology of these nonlinear fluids and assess its implications on the flow behavior. In particular, we discuss the appearance of viscoelastic instabilities, which are seen to occur even under creeping flow conditions. The first type of instability changes the flow type from symmetric to asymmetric, while the flow remains steady. The second (andmore frequent) type of instability, which sets in when elastic effects are enhanced, causes theflow to becomeunsteady varying in time periodically. This unsteadiness results in a nearly chaotic flow, bringing about a significant improvement in mixing performance. After a brief introduction to the theme of microfluidics, its basic principles, relevance and applications, this chapter is organized in five additional sections. Section 6.2 provides an overviewof the problemofmixing at themicroscale and of the current methods used to tackle this problem. Section 6.3 presents an introduction to non-Newtonian viscoelastic fluids describing their most relevant rheological properties. Section 6.4 presents the governing equations for Newtonian and nonNewtonian fluid flow, including the constitutive equations that describe the rheology of thefluids. Section 6.5 dealswith passivemixingmethods in viscoelasticfluidflows, whereas in Section 6.6 other forcing methods for promoting viscoelastic fluid flow at the microscale are briefly described.
17 citations
TL;DR: In this paper, the motion of a two-degree-of-freedom non-linear dynamical system represented by a spring pendulum in which its suspension point moves in an elliptic trajectory is investigated.
Abstract: This article investigates the motion of two degrees of freedom non-linear dynamical system represented by a spring pendulum in which its suspension point moves in an elliptic trajectory. Lagrange's equations are utilized to derive the governing equations of motion in light of the generalized coordinates of this system. The asymptotic solutions for the governing equations of motion up to the third approximation are obtained using the multiple scales technique. The different resonance cases are classified according to the modulation equations. The steady-state solutions are verified in the presence of the solvability conditions. The time histories of the considered motion, the resonance curves, and steady-state solutions are presented graphically. In addition to the simulations of the non-linear equations of the system's evolution, the stability criteria are carried out. The stability and instability regions are investigated, in which it is found the behaviour of the system is stable for a large number of the system’s parameters. In various engineering applications, a better understanding of the vibrational motion near resonance is critical, in which it can be avoided continued exposure to events that can cause severe damage.
15 citations
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TL;DR: In this paper, a global numerical stability analysis of the periodic wake of a circular cylinder for Reynolds numbers between 140 and 300 is presented, showing that the two-dimensional wake becomes (absolutely) linearly unstable to three-dimensional perturbations at a critical Reynolds number of 1885±10.
Abstract: Results are reported from a highly accurate, global numerical stability analysis of the periodic wake of a circular cylinder for Reynolds numbers between 140 and 300 The analysis shows that the two-dimensional wake becomes (absolutely) linearly unstable to three-dimensional perturbations at a critical Reynolds number of 1885±10 The critical spanwise wavelength is 396 ± 002 diameters and the critical Floquet mode corresponds to a ‘Mode A’ instability At Reynolds number 259 the two-dimensional wake becomes linearly unstable to a second branch of modes with wavelength 0822 diameters at onset Stability spectra and corresponding neutral stability curves are presented for Reynolds numbers up to 300
792 citations
TL;DR: In this paper, it is suggested that two modes of vortex shedding alternate in time, i.e., between Reynolds numbers (Re) of 170 to 180 and between Re=230 to 260, correspond with a change to a finer-scale streamwise vortex structure.
Abstract: The transition to three‐dimensionality in the near wake of a circular cylinder involves two successive transitions, each of which corresponds with a discontinuity in the Strouhal–Reynolds number relationship. The first discontinuity [between Reynolds numbers (Re) of 170 to 180] is associated with the inception of vortex loops, and it is hysteretic. The second discontinuity (between Re=230 to 260) corresponds with a change to a finer‐scale streamwise vortex structure. At this discontinuity there is no hysteresis, and it is suggested that two modes of vortex shedding alternate in time.
499 citations
TL;DR: In this article, a large increase or decrease in the resulting displacement thickness, estimated cylinder drag, and associated mixing with the free stream can be achieved, depending on the frequency and amplitude of oscillation.
Abstract: Exploratory experiments have been performed on circular cylinders executing forced rotary oscillations in a steady uniform flow. Flow visualization and wake profile measurements at moderate Reynolds numbers have shown that a considerable amount of control can be exerted over the structure of the wake by such means. In particular, a large increase, or decrease, in the resulting displacement thickness, estimated cylinder drag, and associated mixing with the free stream can be achieved, depending on the frequency and amplitude of oscillation.
394 citations
TL;DR: In this article, the authors measured the pressure fluctuations acting on a stationary square-section cylinder, with the front face normal to the flow, and one forced to oscillate, transverse to a flow, at amplitudes up to 25% of the length of a side.
Abstract: Measurements are presented of the pressure fluctuations acting on a stationary squaresection cylinder, with the front face normal to the flow, and one forced to oscillate, transverse to a flow, at amplitudes up to 25% of the length of a side. The range of reduced velocities investigated, 4–13, includes the vortex lock-in regime. At lock-in the amplification of the coefficient of fluctuating lift is found to be much less than that found for a circular cylinder. The variation of the phase angle, between lift and displacement, is also different from that measured on a circular cylinder, and vortex-induced oscillations are possible only at the high-reduced-velocity end of the lock-in range. At reduced velocities sufficiently far below lock-in the natural vortex-shedding mode is suppressed and vortices are found to form over the side faces at the body frequency. Intermittent reattachment occurs over the side faces and, for an amplitude of oscillation equal to 10% of the length of a side face, the time-mean drag coefficient can be reduced to 60% of its fixed-cylinder value.
365 citations
TL;DR: In this article, a simulation of the transition from two-dimensional to three-dimensional states due to secondary instability in the wake of a circular cylinder is presented. And the authors quantify the nonlinear response of the system to threedimensional perturbations near threshold for the two separate linear instabilities of the wake: mode A and mode B.
Abstract: Results are reported on direct numerical simulations of transition from two-dimensional to three-dimensional states due to secondary instability in the wake of a circular cylinder. These calculations quantify the nonlinear response of the system to three-dimensional perturbations near threshold for the two separate linear instabilities of the wake: mode A and mode B. The objectives are to classify the nonlinear form of the bifurcation to mode A and mode B and to identify the conditions under which the wake evolves to periodic, quasi-periodic, or chaotic states with respect to changes in spanwise dimension and Reynolds number. The onset of mode A is shown to occur through a subcritical bifurcation that causes a reduction in the primary oscillation frequency of the wake at saturation. In contrast, the onset of mode B occurs through a supercritical bifurcation with no frequency shift near threshold. Simulations of the three-dimensional wake for fixed Reynolds number and increasing spanwise dimension show that large systems evolve to a state of spatiotemporal chaos, and suggest that three-dimensionality in the wake leads to irregular states and fast transition to turbulence at Reynolds numbers just beyond the onset of the secondary instability. A key feature of these ‘turbulent’ states is the competition between self-excited, three-dimensional instability modes (global modes) in the mode A wavenumber band. These instability modes produce irregular spatiotemporal patterns and large-scale ‘spot-like’ disturbances in the wake during the breakdown of the regular mode A pattern. Simulations at higher Reynolds number show that long-wavelength interactions modulate fluctuating forces and cause variations in phase along the span of the cylinder that reduce the fluctuating amplitude of lift and drag. Results of both two-dimensional and three-dimensional simulations are presented for a range of Reynolds number from about 10 up to 1000.
349 citations