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In this paper, thermal transfer with natural convection in a tilted annular cylinder with a Cu-water nanofluid has been numerically studied. The hot interior and cold exterior elliptical surfaces of the enclosure were maintained at constant temperatures Th and Tc , respectively. The governing equations were solved by the stream function-vorticity approach. The finite volume approach was utilized to discretise the controlling equations. The volume fraction range of the nanoparticles and the Rayleigh number was as follows: 0

The flow phenomena around a rotating elliptic cylinder placed in a narrow channel is studied numerically. The walls of the channel act as a confinement that limits the flow in the transverse direction. The confinement ratio (β) ⁠, nondimensional rotation rate (α) ⁠, and the Reynolds number (Re) span across multiple values. A parametric study is done to identify the variations in drag-coefficient (CD) ⁠, lift-coefficient (CL) ⁠, and moment coefficient (CM) with changes in β, α ⁠, and Re. Near-field and far-field vorticity contours are discussed in detail. fast Fourier transform (FFT) of the time-periodic lift signals are presented to understand the shedding-frequency characteristics. Furthermore, CM values are analyzed for possible cases of autorotation. It is observed that confinement acts to delay the shedding of vortices. However, a complete suppression is not obtained even for the maximum value of β ⁠. This is likely because of the sharp flow separation at the edges of the cylinder, which tends to promote the formation of a vortex. Hovering vortices are observed for α>1 ⁠, and a special case is identified for which the hovering vortex never dissipates. [ABSTRACT FROM AUTHOR]

In this paper, thermal transfer with natural convection in a tilted annular cylinder with a Cu-water nanofluid has been numerically studied. The hot interior and cold exterior elliptical surfaces of the enclosure were maintained at constant temperatures h T and c T, respectively. The governing equations were solved by the stream functionvorticity approach. The finite volume approach was utilized to discretise the controlling equations. The volume fraction range of the nanoparticles and the Rayleigh number was as follows: 0 < φ < 0.08 and 104 < Ra <106, respectively. The inclination angles were γ = 30°, 45° and 60°. Results were given as isotherm contours, streamlines, average and local Nusselt numbers. The results indicate that the thermal transfer ratio increases with an increase in the tilt angle, regardless of the nanoparticle size values. and the impact of the inclination angle on the heating transfer rate is more important the higher the Rayleigh number and the more convection there is. [ABSTRACT FROM AUTHOR]

An analysis of forces for flow around an elliptic cylinder at low Reynolds number has been presented in this work. The finite-volume based open source code OpenFOAM is used for the numerical simulations. pimpleFoam solver is used to solve Navier- Stokes equations for incompressible flow. The combined effects of aspect ratios (AR = 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0), domain sizes ( D s = 30 D h , 40 D h , 50 D h and 60 D h ) and Reynolds numbers (Re = 40, 100) on flow fields and various aerodynamic parameters are presented. Here, D h represents characteristic length, which is two times the semi-major axis. It is found that at R e = 40 , the value of C D , a v g decreases with the increase of aspect ratio. While, at R e = 100 , the value of C D , a v g first decreases up to A R = 0.5 and then increases for all domain sizes. The contribution of the pressure and viscous force in the flow is studied in detail for both the Reynolds number. The contribution of pressure in lift force at R e = 40 is found to be one to two times higher than that of viscous force. Whereas, at R e = 100 the contribution of viscous force in producing lift force is insignificant. The value of Strouhal number at R e = 100 is non-decreasing for increase in aspect ratio at a given value of domain size. [ABSTRACT FROM AUTHOR]

Undamped transverse-only flow-induced vibrations (FIV) of an elliptic cylinder of mass ratio, m ∗ = 10 at 45° incidence are investigated via two-dimensional computations at Reynolds numbers, R e = 100 and 200. Using quasi-steady theory, it is illustrated that the asymmetric oscillator does not gallop at R e = 100 and 200. Resolution of hysteresis-free solutions at R e = 100 is a novel finding. As compared to R e = 100 , response at R e = 200 is associated with additional branches: a lower branch, a terminal branch and a third regime of desynchronization. Assuming harmonic lift and response, mathematical expressions are obtained for modified dimensionless circular frequency, ω N ∗ 2 and modified damping. The variation of ω N ∗ 2 with reduced speed, U ∗ reveals excellent collapse with predicted dynamic response. For FIV at R e = 200 and not at R e = 100 , a second regime of significant vibrations develops in the neighbourhood of U ∗ = 8 in addition to the first one around U ∗ = 4. The period doubling bifurcation occurring around U ∗ = 8 is an 1:2 sub-harmonic synchronization; it halves the oscillation frequency that in turn closely approaches reduced natural frequency of the cylinder. In this regime, the wake mode is found to be 2(2S). Leontini et al. (2018) resolved periodic doubling bifurcation for FIV of an inclined elliptic cylinder using a low m ∗ of unity. The occurrences of second lock-in and period doubling therefore appear not to be a function of m ∗ ; they are rather Reynolds number phenomena. [ABSTRACT FROM AUTHOR]

The impacts of MHD and heat generation/absorption on lid‐driven convective fluid flow occasioned by a lid‐driven square enclosure housing an elliptic cylinder have been investigated numerically. The elliptic cylinder and the horizontal enclosure boundaries were insulated and the left vertical lid‐driven wall was experienced at a fixed hot temperature, and the right wall was exposed to a fixed cold temperature. COMSOL Multiphysics 5.6 software was used to resolve the nondimensional equations governing flow physics. A set of parameters, such as Hartmann number (0≤Ha≤50 $0\le {Ha}\le 50$), Reynolds number (102≤Re≤103 $1{0}^{2}\le {Re}\le 1{0}^{3}$), Grashof number (102≤Gr≤105 $1{0}^{2}\le {Gr}\le 1{0}^{5}$), heat generation‐absorption parameter (−3≤J≤3 $-3\le J\le 3$), and elliptical cylinder aspect ratio (AR) (1.0≤AR≤3.0 $1.0\le {AR}\le 3.0$) have been investigated. The current study discovered that for low Reynolds number, the adiabatic cylinder AR of 2.0 provided the optimum heat transfer enhancement for the model investigated, also the impact of cylinder size diminishes beyond Gr = 104. But for high Reynolds (Re = 1000), the size of the cylinder with AR = 3.0 offered the highest heat transfer augmentation. The clockwise flow circulation reduces because of an increase in AR, which hinders the flow circulation. In addition, heat absorption supports heat transfer augmentation while heat generation can suppress heat transfer improvement. [ABSTRACT FROM AUTHOR]

In this study, we focused on the photoacoustic wave production of a fluidic elliptic cylinder for modelling blood vessels, where the consideration of the elliptic cross section can be important for some diagnosis of vascular diseases. First, under the condition of optically-thin absorption, the analytic solution based on the photoacoustic Helmholtz equation in elliptic cylinder coordinates by using Mathieu functions was derived. Then, the finite element method (FEM) model was established to verify the analytic solution. In addition to photoacoustic waves and corresponding photoacoustic power spectra, both near- and far-field photoacoustic amplitude angular distributions were compared. The results revealed that the angular dependent photoacoustic power spectra are critical indicators of the ellipse shape variation. This finding can provide a considerable insight into the photoacoustic diagnosis of the blood vessel changes not only in terms of sizes but also shapes.

The influence of the body shape on gas cooling (decrease in the stagnation temperature) in regions of reduced total enthalpy in the wake is studied. The problem is simulated by numerically solving the Navier–Stokes equations for a two-dimensional viscous perfect gas flow around thermally insulated bodies at the Reynolds number and the Mach number . Elliptic-cross-section cylinders and a pair of side-by-side circular cylinders located across the flow are considered. The accuracy of the results of simplified models for describing the phenomenon based on the velocity field in the developed wake is discussed. Some examples that demonstrate that neglecting the total enthalpy redistribution during the vortex formation process in such models can lead to considerable deviations from the data of numerical calculations in vortex cores are given. [ABSTRACT FROM AUTHOR]

This work performed a direct simulation investigation on two-dimensional flow across two tandem elliptic cylinders at Re = 100. The cylinders are placed with a center-to-center distance D / d = 2-10 where d is the diameter, and the minor-to-major axis ratio, denoted as aspect ratio AR, varies as AR = 0.25-1.00. The objective of this study is to quantitatively identify the effect of surface curvature of the cylinders, as represented by AR, and the separating distance on the destabilization and unsteadiness of flow. Numerical results reveal that the local surface curvature at the ends of major axis of the cylinder has substantial influence on the separation and detachment of boundary layer flow on the leeward side of the upstream cylinder, determines the characteristics of gap flow, perturbs the flow around the downstream cylinder, and finally produces various patterns of wake flow. As AR increases, the gap flow tends to be stabilized for small separating distance and even quasi-steady flow for the AR = 0.75 and 1.00 cylinders at D / d = 2; the wake flow after the downstream cylinder also gets less unstable and only sheds in the far-wake region. The non-uniformity of time-averaged pressure coefficient around the downstream cylinder is reduced but the fluctuating amplitude increases, while the flow around the upstream cylinder is quite close to that of the single cylinder case. [ABSTRACT FROM AUTHOR]

The main focus of this article is to examine the effects of heat transfer for a compressible time-dependent laminar flow pass the two distinctly positioned elliptic cylinders. The Mac number is chosen below 0.3 to keep the flow laminar. The heat transfer feature has been added and coupled with the laminar flow. The heat transfer feature adjusted for constant pressure. The arising Naiver-Stokes equations have been addressed numerically. The mesh has also been created and its entities have been elaborated statistically. The outcomes of velocity distribution, pressure distribution, 2D temperature plots, isothermal contours, drag coefficient, streamlines, and surface volume of fluid are discussed. The BDF technique has been employed to tackle the problem numerically. It was observed that the velocity profile at the boundaries of the elliptic cylinder has a maximum value, 3.85 m/s. The pressure distribution is observed maximum around elliptic cylinders. The heat transfer coefficient has maximum values at the upper and lower boundaries, the maximum temperature value observed is 290K. The isothermal contours, streamlines, and velocity volume were also studied. The drag coefficient is observed increasing but the drag force is decreasing. The mathematical modeling of the current problem has been designed in COMSOL.

In this study the 2D laminar and steady water-based Al2O3 nanofluid flow over a cylinder with circular, horizontal and vertical elliptical cross section by constant surface temperature boundary condition has been studied. The main goal of this research is to investigate the effects of different natural and mixed convection heat transfer mechanisms on the convective heat transfer coefficient, and the entropy generation due to the thermal and frictional origination. Conservation equations of the mass, momentum and energy under the assumption of incompressible, Newtonian nanofluid, by using the homogeneous single phase method have been solved. The impact of considered parameters in this study (alteration in cross section, convective flow direction and volume fraction of nano particles) in enhancing the heat transfer rate is studied in association with the entropy generated value in each case. Based on the results, the vertical elliptical cross section, in comparison with others, shows the highest entropy generation value and the heat transfer coefficient in all considered mechanisms. Moreover, mixed convection heat transfer type 2, in which the force flow is perpendicular to the buoyant flow direction, has the highest entropy generation and heat transfer rate for all cross sections. In addition, in all cases in the presence of the nanoparticles, the heat transfer rate and entropy generation increases.

Mixed convective heat transfer from horizontal isothermal elliptic cylinder is experimentally studied. Three elliptic test cylinders with same perimeter and length are studied giving axis ratio (AR) equal 1, 0.709 and 0.496. The corresponding Gr for the three test sections is 9.8 × 105, 1.5 × 106, and 2.1 × 106, and Re varies from 111 to 1306. Consequently, the corresponding Ri is in range of 1 to 102. The angle of attack (ψ) is changed from 0° (assisting flow) to 180° (opposing flow) with an interval of 30°. New empirical correlation is obtained for the Nuavg as a function of the AR, Ri, and ψ. The experimental results are presented in the form of the average Nusselt number around the elliptic cylinder. It has been concluded that as the axis ratio decreases the averageNusselt number increases, in addition, increasing the angle of attack from 0° to 180° decreases the averageNusselt number considerably. New empirical correlations are obtained for the average Nusselt number as a function of the Richardson number and the attack angle. [ABSTRACT FROM AUTHOR]

Surface pressure characteristics of elliptic cylinders of various thicknesses and orientations are investigated in steady flow regime. A stabilized finite-element method has been used to discretize the conservation equations of incompressible fluid flow in two dimensions. The Reynolds number, Re, is based on the major axis of cylinder and free-stream speed. Results have been presented for R e ≤ 40 and 0 ∘ ≤ α ≤ 90 ∘ , where α is the angle of attack. Cylinder aspect ratios AR considered are 0.2 (thin), 0.5 and 0.8 (thick). It is found that a decrease in AR does not significantly alter the location of minimum surface pressure for α = 90 ∘ , but the value of minimum pressure decreases sharply, resulting in severe adverse pressure gradient. In contrast, for α = 0 ∘ , the location travels towards the base and the minimum pressure increases, leading to delayed flow separation. In general, the magnitude of forward stagnation pressure at low Re is smaller than the maximum pressure for A R ≤ 0.5 . The maximum pressure occurs at the forward stagnation point as the Re and AR increase. However, in most cases, the locations of forward stagnation and maximum pressure points differ even when the pressure coefficients are very close to each other. The forward stagnation and maximum pressure coefficients of an elliptic cylinder decrease monotonically with increasing α . The drag of a circular cylinder in most cases exceeds the ones obtained for elliptic cylinders. With increasing AR, the drag increases approximately linearly for small α , lift decreases approximately linearly and moment decreases non-linearly. For a thick cylinder, while the effect of Re on lift and moment is insignificant, the drag shows a strong dependence. Roughly α = 20 ∘ for R e = 40 flow represents a critical angle of attack below which a cylinder of A R ≤ 0.5 acts like a streamlined body and above, like a bluff body. [ABSTRACT FROM AUTHOR]

Two-dimensional space-time finite-element simulations are carried out to study the free vibrations of a rigid elliptic cylinder of aspect ratio 1.11 and low non-dimensional mass of unity. Undamped transverse-only as well as two-degrees-of-freedom oscillations are considered. The effect of damping is investigated on transverse-only motion. For all three cases, results for cylinder response are presented for 50≤Re≤180. In the absence of damping, transverse oscillations are mostly periodic except for a very narrow region near the end of lock-in. In contrast, a damping of 0.044 removes quasi-periodicity as well as secondary hysteresis from flow and body motion. For undamped motion, inclusion of in-line oscillations excites high amplitude oscillations, widens the range of synchronization and delays phase shift between lift and cross-stream response. In each case, synchronization between cylinder oscillations and vortex-shedding is 1:1. In addition, drag-lift phase plots are symmetric about mean lift (= 0) line. Thus, symmetrical shedding of two equally strong alternate vortices per oscillation cycle forms 2S, CNW(2S) or C(2S) modes. For each case, the lower branch initiates at Re = 65 where the oscillation or shedding frequency is found to be locally maximum.

In this work, a detailed numerical investigation has been carried out to study the forced convection heat transfer from an inclined elliptic cylinder of a fixed aspect ratio of 0.5 immersed in a streaming water-based Al2O3 nanofluid using the two-phase Buongiorno's model. In particular, this study presents extensive numerical results on how the cylinder inclination angle, nanoparticle volume fraction and its size are going to influence the local flow, temperature and nanoparticle concentration fields in the vicinity of the cylinder surface as well as the gross engineering parameters like the drag coefficient and Nusselt number over the following ranges of conditions as: Reynolds number, 0.01 ≤ R e ≤ 40 ; cylinder inclination angle, 0 ≤ λ ≤ 90 ; nanoparticle volume fraction, 0 ≤ ϕ ≤ 0.06 and two nanoparticle sizes (dnp), namely 30 nm and 60 nm. It has been found that both the Nusselt number and drag force increase with ϕ , but decrease with dnp under otherwise identical conditions. On the other hand, at a particular value of Re, ϕ and dnp, the value of the average Nusselt number increases with the increasing values of λ , whereas the value of the drag coefficient decreases. Finally, from an application standpoint, a simple analytical formula for the average Nusselt number is provided as a function of Re, ϕ and λ which will facilitate the interpolation of the present results for the intermediate values of these governing parameters. [ABSTRACT FROM AUTHOR]

An analytic solution is presented to the scattering of a left circularly polarized (LCP) plane wave from a chiral elliptic cylinder placed in another infinite chiral medium, using the method of separation of variables. The incident, scattered, as well as the transmitted electromagnetic fields are expressed using appropriate angular and radial Mathieu functions and expansion coefficients. The unknown scattered and transmitted field expansion coefficients are subsequently determined by imposing proper boundary conditions at the surface of the elliptic cylinder. Numerical results are presented graphically as normalized scattering widths for elliptic cylinders of different sizes and chiral materials, to show the effects of these on the scattering widths. [ABSTRACT FROM AUTHOR]

Longitudinal ultrasonic pulse propagation over the cross section of an elliptic cylinder is modeled for the case of transmission–reception of waves by a contactless electromagnetic acoustic transducer along the cylinder envelope. Modeling is based on ray approximation and finite-element method. Formation of series of multiple reflections within the cross section of an elliptic cylinder is studied both theoretically and experimentally. New informative parameters of determining the cylinder ellipticity by the mirror-shadow electromagnetic acoustic method of multiple reflections are justified: the modulation period of a series of multiple reflection pulses, the delay time of reflected pulses, and the probabilistic-statistical characteristics of the data array of multiple reflection series. [ABSTRACT FROM AUTHOR]

Abstract Two-degree-of-freedom (2-DOF) vortex-induced vibration (VIV) of an elliptic cylinder is numerically investigated at a Reynolds number R e = 150. The incompressible Navier–Stokes equations in arbitrary Lagrangian–Eulerian formulation are solved by a four-step fractional finite element method. The elliptic cylinder, with a variety of aspect ratios (AR = 1.0–2.5), is free to vibrate in both transverse and azimuthal directions. At each AR , the computations are conducted within a wide range of reduced velocities (2 ≤ U r ≤ 15). For comparison, the one-degree-of-freedom (1-DOF) responses of the cylinder vibrating only transversely are also provided. The results show that significant rotations occur under a condition of frequency synchronization similar to the lock-in condition of VIV in the transverse direction. Under the rotation effect, the transverse peak amplitude at AR = 1.0 reaches a higher value about 20% larger than its counterpart of 1-DOF VIV, whereas it fells by more than half at AR = 2.0 and 2.5, and the corresponding wake patterns present distinct characteristics. The typical phenomenon of phase switch can be captured successfully between the torque and rotation response, which occurs at the same reduced velocity to the phasing between the transverse force and motion. Our simulation results also elucidate that the free rotation may significantly affect the statistics of the drag, lift and moment coefficients. The most striking observation is that all of the force responses at AR = 2.0 and 2.5 collapse onto a very low level compared to those of the transverse-only VIV. This is consistent with the dramatic drop in the transverse vibration amplitude at the same AR. [ABSTRACT FROM AUTHOR]

Abstract A large eddy simulation based on the lattice Boltzmann method is used in this study to develop a computation program for fluid flow past an elliptic cylinder near a moving wall. The flow field around the elliptic cylinder as it approaches the moving wall is simulated for different axis ratios at Reynolds numbers of 200 and 400. The effects of the gap ratio, axis ratio, and Reynolds number on the flow field, force coefficient, and Strouhal number are investigated. The moving wall inhibits the normal velocity and stabilizes the flow, thereby suppressing vortex shedding. This study focuses on the mechanisms that various parameters influence the vortex shedding of flow past an elliptic cylinder near a moving wall. The calculation results show that decreasing the gap and axis ratios both suppress vortex shedding, while the increase in Reynolds number effectively alleviates the complete suppression of vortex shedding. A decreased axis ratio increases the gap ratio for vortex shedding suppression, and an increased Reynolds number significantly lowers the gap ratio for complete vortex shedding suppression. As the gap ratio decreases, owing to the interaction between the positive vortex separated from the lower side of the cylinder and the negative vortex separated from the moving wall, the strength of the positive vortex formed at the lower side of the cylinder gradually decreases downstream. This interaction is more prominent at small axis ratios. When the Reynolds number increases, the interaction between the positive vortex separated from the lower side of the cylinder and the negative vortex separated from the moving wall is noticeably weaker, and the positive vortex maintains its strength for a longer distance downstream. The computed results are in good agreement with the limited experimental data published in literature. Highlights • A MRT Lattice Boltzmann method based on large eddy simulation was applied. • The mechanisms of the vortex shedding from an elliptic cylinder near a moving wall was investigated. • A decrease in axis ratio increases the gap ratio for vortex shedding suppression. • An increase in Reynolds number effectively alleviates the complete suppression of vortex shedding. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to present a shape optimization method for the drag force reduction problem of an elliptic cylinder located in fluid flows. The fluid is assumed to be in an adiabatic state. The conservation equations of mass and momentum are used with the density and momentum employed as field variables. For the discretization, the finite element method is applied using SUPG stabilization based on a linear interpolation function is used. The performance function consists of the square sum of the drag forces, integrated between the starting and final times. The coordinates of the surface of the cylinder are updated to obtain the minimal performance function. For this minimization procedure, we employ the weighted gradient method using the solution of the adjoint equation. A numerical computation is executed to demonstrate that the proposed method is effective for the drag reduction problem.

Abstract Vortex-induced vibration (VIV) of an elliptic cylinder free to rotate about its center is numerical studied at Reynolds number 2580 ≤ Re ≤ 15490. The vibration and rotation responses occurring simultaneously are considered with normalized torsional friction varied from 3.34 × 10−4 to 1.17. A two-way fluid–structure interaction (FSI) approach is used to solve the incompressible flow equations and the structure motion including the vibration and rotation in two dimensions. The numerical results indicate that the torsional friction is a key factor, determining the rotation response and then affecting the vibration amplitude. When the torsional friction is too large or the reduced velocity is too small, the elliptic cylinder is unable to rotate, while too small friction leads to transverse galloping instead of the desynchronized region. For the elliptic cylinder with moderate frictions, the response occurs similar as the circular cylinder, but the amplitude in the desynchronized region is larger than the circular cylinder due to the hydrodynamic instability. The results show four kinds of rotation response, which are associated with the time-averaged torque and the flow field around the elliptic cylinder. Compared to the non-rotatable elliptic cylinder with 0° attack angle, the rotatable cylinder vibrates more vigorously. Highlights • The vibration and rotation of an elliptic cylinder are considered simultaneously. • Large torsional friction leads to no rotation while small friction results in galloping. • The elliptic cylinder undergoes unstable rotation at small reduced velocities. • The amplitude of rotatable cylinder is larger than that of non-rotatable one. • Rotation response is determined by friction, torque and flow field around the cylinder. [ABSTRACT FROM AUTHOR]

The problem of laminar mixed convective heat transfer from a horizontal isothermal elliptic cylinder has been experimentally and numerically investigated. The test elliptic cylinder has major and minor diameters of 70.3 mm and 34.9 mm respectively with an axis ratio of 0.496. The buoyancy due to the temperature difference between the cylinder surface and incoming air produces a Grashof number of 2.1 × 10 6 . Via the incoming cold air velocity, the generated Reynolds number varies from 145 to 1322.8. Hence, the corresponding Richardson number is in the range of 1.2–100. The combined effect of both upward natural convection and the forced convection has been executed for angle of attack from 0° (assisting flow) to 180° (opposing flow) with an interval of 30°. The numerical solution via the finite volume method (FVM) has been accomplished to validate the obtained experimental results. The numerical results are validated by previous experimental results which show good agreement. Results are presented in the form of average and local Nusselt number around the circumference of the elliptic cylinder. In addition, new empirical correlation is obtained for the average Nusselt number as a function of Richardson number and the attack angle. [ABSTRACT FROM AUTHOR]

In this paper, hot-wire anemometry (HWA) is used to experimentally investigate interactions between a fully developed turbulent boundary layer and wake of an elliptic cylinder where axis ratio (AR) of the cylinder is 2. The elliptic cylinder was located inside and outside a turbulent boundary layer with a thickness (δ) of 0.38B. Furthermore, experiments were conducted at different Reynolds numbers (13,250 and 26,500) based upon the smallest cylinder diameter (B). Mean velocity, turbulence intensity and higher-order central moments of velocity signals (i.e. skewness and flatness) measurements were performed using HWA upon wake-boundary layer interactions on a flat plate. Results showed that profiles of stream-wise mean velocity and turbulence intensity were greatly dependent on gap ratio (G/B) and Reynolds number (Re) in near-wake region. It was also observed that, except for G/B = 0.1, the wake-boundary layer interactions were faster at Reynolds number of 26,500 rather than 13,250. The interactions occurred earlier upon fluctuating the velocity rather than the case where a fixed mean velocity was considered. The results further show that an increase in the gap ratio increases Strouhal number almost independent of δ/B. Behind the cylinder, relatively smaller wake region was obtained at Re = 26,500 rather than Re = 13,250, where the velocity profiles quickly converged to the flat plate boundary layer velocity profiles. [ABSTRACT FROM AUTHOR]

Numerical experiments are performed at a Reynolds number, Re of 100 to explore in two-dimensions, the undamped, transverse-only vortex-induced vibrations of a rigid elliptic cylinder of aspect ratio 0.5. With major axis oriented parallel to the flow, the cylinder behaves as a streamlined object. The mass ratio of the oscillator is 10. Re is based on the length of the major axis. The reduced speed, U * is varied from 1 to 8. The lock-in initiates at U * = 3.5 and is soft in nature. The extent of lock-in gets severely truncated as compared to the one for a bluff oscillator; it spans just over an extremely narrow U * range of 3.5 to 4.2. The onset and closure of lock-in are marked with the oscillation frequency attaining its maximum and minimum, respectively. Streamlining of oscillator eliminates the whole of initial, quasi-periodic lower and desynchronization components of response. The response consists of a fragile periodic lower branch stretching over the range of lock-in and bracketed by a dominant pair of steady state regimes. The occurrence of peak response is noted at the onset of lock-in and the peak value is about 0.06 times the length of major axis. A closed standing wake characterizes the steady regimes while periodic vortex-shedding relates to the lower branch with weak vibrations. Interestingly, even in the steady regimes, the reduced speed is found to influence the surface pressure whereas global quantities like drag and lift forces remain invariant. In the lower branch, the mean surface pressure exhibits symmetry about base, thus mean lift disappears and wake mode is the basic anti-symmetric 2S. At the onset of lock-in, the instantaneous surface pressure is noticeably asymmetric along the upper and lower surfaces. Thus, vortex-shedding is strong and r.m.s. lift high. With rising U *, the strength of shedding decays, asymmetry of instantaneous pressure about the base weakens and consequently, r.m.s. lift falls. At U * = 4.3 , the free shear layers turn straight, shedding gets suppressed and the regime of steady state recovers. [ABSTRACT FROM AUTHOR]

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In this study the 2D laminar and steady water-based Al2O3 nanofluid flow over a cylinder with circular, horizontal and vertical elliptical cross section by constant surface temperature boundary condition has been studied. The main goal of this research is to investigate the effects of different natural and mixed convection heat transfer mechanisms on the convective heat transfer coefficient, and the entropy generation due to the thermal and frictional origination. Conservation equations of the mass, momentum and energy under the assumption of incompressible, Newtonian nanofluid, by using the homogeneous single phase method have been solved. The impact of considered parameters in this study (alteration in cross section, convective flow direction and volume fraction of nano particles) in enhancing the heat transfer rate is studied in association with the entropy generated value in each case. Based on the results, the vertical elliptical cross section, in comparison with others, shows the highest entropy generation value and the heat transfer coefficient in all considered mechanisms. Moreover, mixed convection heat transfer type 2, in which the force flow is perpendicular to the buoyant flow direction, has the highest entropy generation and heat transfer rate for all cross sections. In addition, in all cases in the presence of the nanoparticles, the heat transfer rate and entropy generation increases. [ABSTRACT FROM AUTHOR]

• We present a rigorous method to evaluate the scattering of a plane electromagnetic wave by a perfectly conducting elliptic cylinder parallel to a generally reflecting plane surface. • The solution is based on the Spectral Domain method and the plane-wave expansion of the elliptical cylindrical waves. • The surface is characterized by means of a reflection coefficient. • The analytical method is implemented in specific computational code to achieve a numerical solution. • Results are validated by means of a finite element method commercial software. Validation trials, show good agreement between the two independent computational methodologies. In this paper, we present a rigorous analytical and numerical method to evaluate the scattering of a plane electromagnetic wave by an infinite, perfectly conducting elliptic cylinder parallel to a non-perfectly reflecting plane surface. The analytical solution is based on the spectral domain method and the plane-wave expansion of the elliptic cylindrical waves and is applicable in a broad variety of cases in which the properties of the plane surface may be expressed by means of a reflection coefficient. The proposed approach is suitably implemented in a specific computational code to achieve a numerical solution. Results of validation trials, performed by using finite element method commercial software, are provided. [ABSTRACT FROM AUTHOR]

This paper presents an analytic solution to the scattering properties of chiral elliptic cylinder embedded in infinite chiral medium due to incident plane wave. The external electromagnetic fields as well as the internal electromagnetic fields are written in terms Mathieu functions and expansion coefficients. In order to obtain both the internal and external unknown field expansion coefficients, the boundary conditions are applied rigorously at the surface of different chiral/chiral material. Results are plotted graphically for the normalized scattering widths for elliptic cylinders of different sizes and chiral materials to show the effects of these parameters on scattering cross widths. It is shown numerically by adding the external chiral material to elliptic cylinder provides more parameters to control the RCS. [ABSTRACT FROM AUTHOR]

In this study, the effect of splitter plate on fluid flow characteristics past an elliptic cylinder of different axis ratios ( AR = 1.0 − 0.5 ) is numerically investigated for various Reynolds number ( Re = 50–200). The equations governing fluid flow are discretized using Streamline Upwind/Petrov-Galerkin (SUPG) based finite element method (FEM). The presence of a splitter plate alters the wake region where vortex shedding is suppressed. Depending on AR and Re two critical lengths of splitter plate are defined, one for suppression of vortex shedding and the other when shear layer interaction in the wake is inhibited. The correlations for the critical lengths of splitter plate as a function of AR and Re are derived using regression analysis. It is observed that, the variation of integral parameters like drag, lift and St are not monotonic with increasing plate length. From the results it is concluded that for a particular combination of Re and AR with suitable splitter plate length, the total drag is minimized approximately from 2% to 38%. Finally, C d _ avg is selected as an objective function and modelled using Response Surface Approximation (RSA). Furthermore, a single-objective Genetic algorithm has been implemented to obtain optimum configuration for minimum C d _ avg . [ABSTRACT FROM AUTHOR]

Two-dimensional space-time finite-element simulations are carried out to study the free vibrations of a rigid elliptic cylinder of aspect ratio 1.11 and low non-dimensional mass of unity. Undamped transverse-only as well as two-degrees-of-freedom oscillations are considered. The effect of damping is investigated on transverseonly motion. For all three cases, results for cylinder response are presented for 50⩽Re⩽180. In the absence of damping, transverse oscillations are mostly periodic except for a very narrow region near the end of lock-in. In contrast, a damping of 0.044 removes quasi-periodicity as well as secondary hysteresis from flow and body motion. For undamped motion, inclusion of in-line oscillations excites high amplitude oscillations, widens the range of synchronization and delays phase shift between lift and cross-stream response. In each case, synchronization between cylinder oscillations and vortex-shedding is 1:1. In addition, drag-lift phase plots are symmetric about mean lift (= 0) line. Thus, symmetrical shedding of two equally strong alternate vortices per oscillation cycle forms 2S, CNW(2S) or C(2S) modes. For each case, the lower branch initiates at Re = 65 where the oscillation or shedding frequency is found to be locally maximum. [ABSTRACT FROM AUTHOR]

Impact of Lorentz forces on CuO–water nanofluid flow in a permeable enclosure is presented by means of CVFEM. Darcy’s law is applied for porous media. In order to predict properties of nanofluid, KKL model has been utilized. Important parameters are inclination angle ( ξ = 0 ∘ to 90°), CuO–water volume fraction ( ϕ = 0 and 0.04), Hartmann ( Ha = 0 to 20) and Rayleigh ( Ra = 1 0 2 , 250 and 10 3 ) numbers for porous medium. A formula for Nu ave is provided. Results demonstrated that Nusselt number detracts with enhancement of ξ , Ha . Heat transfer augmentation detracts with rise of buoyancy forces but it enhances with rise of inclination angle and Hartmann number. [ABSTRACT FROM AUTHOR]

Influence of thermal radiation on nanofluid heat transfer in existence of Lorentz forces is investigated. Viscosity of Fe 3 O 4 ferrofluid is considered as a function of magnetic field. CVFEM is selected to solve this problem. Effects of radiation parameter ( Rd ) , inclination angle ( ξ ) , Fe 3 O 4 -water volume fraction ( ϕ ) , Hartmann ( Ha ) and Rayleigh ( Ra ) numbers are demonstrated graphically. A correlation for average Nusselt number is extracted. Results demonstrate that rate of heat transfer enhances with augment of inclination angle. Nusselt number augments with rise of buoyancy forces and radiation parameter but it reduces with rise of Hartmann number. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method of a thermoelastic problem for a medium with functionally graded material properties is developed in a theoretical manner for the elliptic-cylindrical coordinate system under the assumption that the material properties except for Poisson's ratio and density are assumed to vary arbitrarily with the exponential law in the radial direction. An attempt has been made to reconsider the fundamental system of equations for functionally graded solids in a two-dimensional state under thermal and mechanical loads. The general solution of displacement formulation is obtained by the introduction of appropriate transformation and carried out the analysis by taking into account the variation of inhomogeneity parameters. Furthermore, the aforementioned problem degenerated into the problem of the circular region by applying limiting conditions, and the results are validated. Numerical computations are carried out for ceramicmetal-based functionally graded material, in which zirconia is selected as ceramic and aluminium as metal and are represented graphically. [ABSTRACT FROM AUTHOR]

In this study, a detailed numerical investigation has been carried on the momentum and heat transfer phenomena from an elliptic cylinder, including the limiting cases of circular cylinder and flat plates, in streaming water based CuO nanofluids over the following ranges of conditions as: Reynolds number, 1 ≤ Re ≤ 40; nanoparticle volume fraction, 0 ≤ ϕ ≤ 0.06 and cylinder axis ratio, 0.1 ≤ AR ≤ 5.0 for two sizes of the nanoparticles, namely, 30 nm and 60 nm. The local flow field in the vicinity of the cylinder surface is visualized in terms of the streamline profiles, whereas the gross flow and heat transfer characteristics are presented in terms of the drag coefficient and Nusselt number respectively. All else being equal, the separation of the boundary layers is accelerated in 60 nm CuO nanofluids as compared to that seen in water, whereas it is decelerated in 30 nm CuO nanofluids. The total drag coefficient for an elliptic cylinder is always seen to be higher in nanofluids as compared to that seen in pure water. For 60 nm CuO nanofluids, the Nusselt number always increases with the increasing values of ϕ , whereas for 30 nm CuO nanofluids, it first increases and then decreases. Finally, simple analytical formulas for the total drag coefficient and average Nusselt number are provided which facilitate the interpolation of the present results for the intermediate values of Re , ϕ and AR . [ABSTRACT FROM AUTHOR]

CuO-water nanofluid MHD convective flow in a porous cavity is studied. Darcy and KKL models are considered for porous media and nanofluid, respectively. The solutions of final equations are obtained by CVFEM. Effective parameters are major axis of elliptic cylinder, CuO-water volume fraction, eccentricity, Hartmann and Rayleigh numbers for porous medium. A correlation for Nu ave is presented. Results depicted that heat transfer improvement enhances with rise of buoyancy forces and major axis of elliptic cylinder. Influence of adding nanoparticle augments with augment of Lorentz forces. Increasing eccentricity and Hartmann number leads to reduce Nusselt number. [ABSTRACT FROM AUTHOR]

In this attempt, influence of Lorentz forces on Fe 3 O 4 –water nanofluid is presented. Radiation source term is taken in to account in energy equation. Newly suggested model is imposed for viscosity of ferrofluid. Control Volume based Finite Element Method is selected to simulate this article. Graphs have been portrayed in order to explain the roles of Radiation parameter( Rd ), inclination angle( ξ ), Fe 3 O 4 -water volume fraction( ϕ ), Hartmann( Ha ) and Rayleigh ( Ra )numbers. Obtained findings indicate that Nusselt number enhances with augment of inclination angle. Rate of heat transfer augments with enhance of buoyancy forces, radiation parameter but it reduces with rise of Lorentz forces. [ABSTRACT FROM AUTHOR]

The effect of thermal radiation on unsteady mixed convection flow near a forward stagnation point over a cylinder of elliptic cross-section is investigated in this paper. The governing equations are transformed into dimensionless partial differential equations by using a suitable transformation and then solved numerically by using an implicit finite difference scheme known as Keller Box method. The accuracy of the results is verified by comparing the obtained results with the previous studies available in the literature. It is shown that the results are highly accurate and are in good agreement. The separation times for both blunt and slender orientations in the presence of thermal radiation are shown in tabular forms. Moreover, the effects of pertinent parameters including Prandtl number, mixed convection parameter, thermal radiation parameter, surface temperature parameter, and blunt/slender orientation parameter ω on the velocity profile, the temperature profile and the Nusselt number also are shown graphically. From the present study, it is observed that boundary layer separation occurs early due to thermal radiation and Nusselt number increases for both blunt and slender orientations [ABSTRACT FROM AUTHOR]