Sinusoidal Wavy Surface Research Articles

A Metasurface-Based LTC Polarization Converter with S-Shaped Split Ring Resonator Structure for Flexible Applications.

This paper presents a metasurface-based linear-to-circular polarization converter with a flexible structure for conformal and wearable applications. The converter consists of nested S- and C-shaped split ring resonators in the unit cell and can convert linearly polarized incident waves into left-handed circularly polarized ones at 12.4 GHz. Simulation results show that the proposed design has a high polarization conversion rate and efficiency at the operating frequency. Conformal tests are also conducted to evaluate the performance under curvature circumstances. A minor shift in the operating frequency is observed when the converter is applied on a sinusoidal wavy surface.

Nano-jet impingement cooling of a sinusoidal wavy hot surface by using an oriented L-shaped object under magnetic field with two phase mixture formulation

In this study, slot nano-jet impingement cooling of a wavy sinusoidal surface is analyzed by combined utilization of an oriented L-shaped object and magnetic field. A two phase mixture model of nanofluid is adopted. It is observed that the presence of the L-shaped object and its orientation are very influential on the local and average heat transfer performance. Magnetic field suppresses the vortices near the object and on the bottom all. The average Nusselt number (Nu) rises by 17.5% and 8.6% when its strength is varied for object orientations of te=−90 and te=90. When magnetic field inclination is concerned, the cooling performance improvements are in the range of 25.6%–53.9% depending upon the orientation of the object. The orientation of te=0 and te=45 are the most favorable cases in terms of thermal performance while significant variations in the average Nu are seen in the absence of magnetic field when varying the L-shaped object orientation. When compared to reference case of slot jet impingement (without magnetic field using pure fluid and without object), using nanofluid improves the cooling performance by about 8.4%. When object is installed at Ha=0, it rises by 27% at orientation of te=45. When magnetic field is used, additional rise of thermal performance with nanofluid is obtained up to 10% when compared to case by using only pure fluid.

Investigations of heat transfer and flow characteristics of wall-bounded jets on a sinusoidal wavy surface

Turbulent wall-bounded jets are used in various practical engineering and industrial applications, including cooing of electronics devices, heat exchange systems, and cooling of gas turbine blades. The aim of the present computational study is to investigate an enhancement in heat transfer using different wall-bounded jets. Detailed discussions on the effect of the amplitude of the wavy surface and offset ratio are provided. The offset ratio varies from 0 to 5.0, where the value of zero represents a turbulent wall jet. The amplitude of sinusoidal wall is ranging from 0.1 to 0.8. The computed results are validated with the reported experimental results. The validation shows that among four turbulence models used, namely, renormalization group k-ϵ (RNG), realizable k-ϵ, standard k-ω and shear-stress transport k-ω (SST), the latter provides a good agreement with the experimental results. The position of the offset ratio and amplitude of the wavy surface affect the heat transfer enhancement. An enhanced heat transfer of 29.46% for turbulent wall jet is achieved for the amplitude of 0.8. The thermal-hydraulic performance (THP) increases for the wall jet by approximately 15% for the maximum amplitude considered. The axial position of the reattachment length and primary vortex centre increase with amplitude. Correlations are developed for the average Nusselt number, vortex centre, reattachment point, and thermal-hydraulic performance parameter with the amplitude of the sinusoidal wall.

Performance Assessment of Different Turbulence Models for a Dual Jet Flowing Over a Heated Sinusoidal Wavy Surface

Abstract An enhancement in heat transfer is the key objective in any thermal system where an efficient cooling is needed. This requirement becomes more important for turbulent flow. A turbulent dual jet is associated with entrainment and mixing processes in several applications. This article aims at enhancing the heat transfer rate by utilizing the wavy surface of a heated plate. Heat transfer and flow characteristics are studied using five low Reynolds-Averaged Navier–Stokes (RANS) turbulence models, namely, Yang and Shih k − ɛ (YS), Launder and Sharma k − ɛ (LS), realizable k − ɛ, renormalization group k − ɛ (RNG), and shear-stress transport k − ω (SST) models. The amplitude of the wavy surface is varied from 0.1 to 0.8 for the number of cycles fixed to 7. The Reynolds number and offset ratio are set to 15,000 and 3, respectively. An isothermal wall condition is used at the wavy wall. An experimental validation has been performed. An enhancement of 55.94% in heat transfer is achieved by the RNG k − ɛ model. Furthermore, it is noticed that the YS model fails to predict the flow separation as the amplitude of the sinusoidal wavy surface increases. However, the SST model reveals that the flow separates when the amplitude increases beyond 0.6. The thermal hydraulic performance (THP) is found to increase for the RNG model by approximately 13.9% for the maximum amplitude considered. As the profiles of the bottom walls change, various turbulence models predict different fluid flow characteristics.

Direct numerical simulation of flow-induced vibrations of a wavy cable at a low Reynolds number

Previous studies have revealed that fluid induced forces and wake structure of a cylinder can be significantly modified by varying the cross-section size along its axis. However, the fluid dynamic characteristics behavior of a flexible cable with a sinusoidal wavy surface remains unclear. The current study endeavors to present a systematic investigation of flow-induced vibrations (FIV) of an infinitely long wavy cable with different wave amplitude (A=0.1D to 0.3D) and a constant spanwise wavelength λ=4π, by using a highly resolved direct numerical simulation employing a high-order spectral/hp element method at a Reynolds number of 100, corresponding to laminar flow state. A tensioned beam model with a tension value can trigger a single wave is selected to govern the dynamics of the wavy cables. In addition, the structural dynamics are initialized from a standing wave. The present study focuses on the effects of the wave amplitude on the cable wake and the structural dynamic response, including the transverse displacement, wake pattern, vortex formation length, energy transfer, vortex shedding frequency and flow separation angle. Two completely different vibration modes are identified from the numerical cases studied, and hence the wavy cable are divided into control failure (A<0.2D) and optimal wavy cable (0.2D⩽A⩽0.3D) classes, respectively. It is also revealed that the counter-rotating vortices observed in the optimal wavy cables play an important role in stabilizing the shear layer and elongating the vortex formation length. Furthermore, the three-dimensional wake patterns of the wavy cable are mainly caused by the variations of flow separation angle along its spanwise direction. For the optimal wavy cables, the separation point is almost fixed along its spanwise direction while is variable for the control failure cases.

Numerical analysis to study enhancement in heat transfer using wavy surface in turbulent dual jet

Enhancement in the heat transfer rate is an essential research area in the present time. Therefore, to achieve this goal in the present case, a sinusoidal wavy wall surface is used in a turbulent dual jet. The changes in amplitude (A) and number of cycle (N) of the sinusoidal wavy surface, not only affect the turbulent characteristics but also improve the heat transfer rate. In comparison to the plane wall surface in a dual jet, it is found that nearly 20.70% of improvement in heat transfer is achieved when N = 7 and A = 0.7. The A and N of the sinusoidal wavy surface are varied from 0.1 to 0.7 and 4 to 12 with an interval of 0.1 and 1, respectively. The Reynolds number (Re), offset ratio, and Prandtl number (Pr) are set to 15 × 103, 5 and 0.71, respectively, for all the computational simulations. The average Nusselt number (Nuavg) increases almost linearly when the amplitude changes from 0.1 − 0.7 up to N = 7. A new scaled self-similarity solution for the crest and trough positions is performed to neglect the effect of bottom wall variation. The similarity solution of the crest for various number of cycles in the combined region for different amplitudes suggests that when A ≥ 0.5, the profiles of all the number of cycles spread close to the wall region and in the outer region. Whereas, the self-similarity behaviour of trough shows that when A ≥ 0.3, the profiles of all the number of cycles spread only close to the wall region and almost coincide in the outer region and inflection point rises in the crosswise distance as amplitude increases. It is also noticed that the decay in bottom wall temperature increases with increasing A when N = 10, thereafter, the decrease in bottom wall temperature is nearly same beyond N > 9.

Viscous Dissipation Effect in the Free Convection of Non-Newtonian Fluid with Heat Generation or Absorption Effect on the Vertical Wavy Surface

The present article analyzes the effect of viscous dissipations on natural convection heat transfer. The power law model for non-Newtonian fluid with heat generation or absorption effect along a sinusoidal wavy surface with isothermal boundary condition is investigated. A simple coordinate transform is employed to map the wavy surface into a flat surface, and also, the fully implicit finite difference method is incorporated for the numerical solution. The findings of this study can help better understand the effect of parameters such as the Brinkman number, heat generation/absorption, wave amplitude magnitude, and generalized Prandtl number on convective heat transfer in dilatant and pseudoplastic non-Newtonian. Results show that as the Brinkman number increases, the amount of heat transfer decreases. This is physically justifiable considering that the fluid becomes warmer due to the viscous dissipation, decreasing its temperature difference with the constant temperature surface. Also, the effect of the power law viscosity index is surveyed. It is demonstrated that the magnitude of the local Nusselt number in the plane leading edge has the smallest quantity for pseudoplastic fluids compared to dilatant Newtonian fluids. Additionally, as the distance from the plane leading edge increases, the heat transfer declines.

Enhancing the Heat Transfer Rate Through Surface Manipulation

In the present paper, the flow characteristics and the heat transfer rate of turbulent dual jet impinging on a sinusoidal wavy surface are numerically studied. Finite-volume-based two-dimensional Reynolds-averaged Navier–Stokes equations are used to handle the complex behavior of the turbulent dual. The offset ratio is varied from 3 to 15 with an interval of 2. To evaluate the role of sinusoidal wavy surface on flow and heat transfer characteristics, the amplitude and number of cycle are varied from 0.1 to 0.7 m and from 4 to 12 with an interval of 0.1 m and 1, respectively. In the present numerical work, the Reynolds number and Prandtl number are set to 15,000 and 0.71, respectively. The bottom wall is maintained at a constant temperature. The results show that the sinusoidal wavy surface affects both the flow characteristics and heat transfer rate, and that it also enhances the heat transfer rate significantly. Approximately, a maximum of 23.27% enhancement in heat transfer rate is achieved with respect to the plane wall surface. It is also found that the average Nusselt number depends on both amplitude and number of cycle of the sinusoidal wavy surface.

Numerical investigation of MHD radiative heat and mass transfer of nanofluid flow towards a vertical wavy surface with viscous dissipation and Joule heating effects using Keller-box method

In this paper, the effect of viscous dissipation and Joule heating on magneto-hydrodynamic (MHD) nanofluid flow towards a vertical sinusoidal wavy surface has been investigated numerically. The wavy surface is considered to be heated with uniform flux. Effects of radiation and nanoparticle volume concentration are also considered. The fluid flow over the surface geometry is designed through the highly non-linear partial differential equations, and governing equations must be transformed into a dimensionless non-similar system of equations to get a better solution by applying the highly efficient well-known Keller-box scheme. In this regard, the numerical solutions are obtained for a concentration of mass fluid, velocity profile, temperature profile, local skin friction number coefficient, local Nusselt number, and Sherwood number shown graphically. Connected parameters involve in the modelled problem such as heat generation parameter, radiative conduction flow parameter, the amplitude of the waviness of the surface, Prandtl number, Brownian motion parameter, Buoyancy ratio, magnetic parameter, Thermophoresis parameter and the Lewis number for momentum, temperature profile, and concentration profile of the fluid through different graphs are explained. In this process, certain iterations were performed for different step sizes in the direction of η=0.01 and x=0.005, respectively. So, keeping this in view to get the more accurate results with all parameters considered, 0≤M≤1, 0≤Rd≤1,0≤Q≤1,0.01≤α≤0.04, 0≤Le≤40, 0.1≤Nb≤0.7,0.1≤Nt≤0.7,0.1≤Nr≤0.7,0.1≤Ec≤0.4,0.1≤J≤0.4,. The obtained results illustrate that Nusselt number, Sherwood number, and velocity profile decreases respectively with the increase of waviness amplitude, but skin friction changes its behaviour to wavier. Also, temperature and concentration profiles increase respectively with enhancing the value of the amplitude of waviness. Finally, it is noted that Nusselt number and Sherwood number decrease for higher values of the Brownian parameter. But after a specific value of x, the trend of Sherwood number increases. However, the behaviour of skin friction decreases, but in a precise manner, it remains almost unchanged.

Role of a Sinusoidal Wavy Surface in Enhancement of Heat Transfer Using Turbulent Dual Jet

Abstract In this paper, the role of sinusoidal wavy surface in enhancing the heat transfer is numerically studied. The heat transfer characteristics are studied for two thermal boundary conditions of the wavy wall. To assess the effect of wavy wall, the amplitude is varied between 0.1 and 0.7 and number of cycle from 4 to 12 at an interval of 0.1 and 1, respectively. In order to see the effect of offset ratio, it is varied between 3 and 15 at an interval of 2. The Reynolds number (Re) and Prandtl number (Pr) are set to 15, 000 and 0.71, respectively, for all the numerical simulations. It is found that the maximum average Nusselt number (Nuavg) depends not only on the amplitude and number of cycle but also on the offset ratio. Overall, 23.27% in maximum heat transfer enhancement is achieved with reference to the plane wall surface. An approximately linear decrement in maximum Nuavg is observed when offset ratio increases. The results indicate that Nuavg increases with an increase in the amplitude of sinusoidal wavy surface up to N = 8 and almost follows the linear trend up to N = 7. It is also found that Nux is always on the higher side as compared to the corresponding case of a plane wall surface when N = 4, irrespective of the offset ratio. With an increase in N, Nux fluctuates about the result of plane wall surface after the initial increase because of the obstruction. The amplitude of the fluctuation increases with an increase in the number of cycle N, which indicates that fluid accelerates and decelerates gradually owing to the presence of trough and crest. Also, it is worth noticing that for some cases, there is a decrease in the heat transfer rate as compared to the plane wall case. Therefore, it is concluded that the increase in the surface area does not necessarily result in an increase in the heat transfer rate.

A numerical-analytical approach to determining the real contact area of rough surface contact

ABSTRACT The objective of this study is to improve the accuracy of the real contact area calculated by the semi-analytical method (SAM). Two types of surface pairs are investigated: an analytically generated sinusoidal wavy surface against a rigid flat, and a pair of real rough surfaces. The results suggest that the real contact area calculated by the SAM is extremely sensitive to the resolution of input, i.e. the grid size. The SAM results of the real contact areas show poor convergence, especially in the case of the real rough surfaces. The main reason for this difference is the ‘over-covering’ effect when SAM calculates the real contact area. An exponential extrapolation technique is proposed to predict the real contact area values when further refinement of the grid resolution is unfeasible.

Numerical study to enhance the heat transfer using sinusoidal wavy surface for turbulent wall jet

To achieve higher heat transfer rate for cooling by air jet impingement is the most essential goal of the modern era. The aim of this article is to enhance the heat transfer rate significantly by using the sinusoidal wavy surface in a turbulent wall jet. A comprehensive numerical study is carried out to examine the complex behavior of turbulent wall jet flowing tangentially to the wavy surface. To explore all the possibilities associated with the wavy surface, the various number of cycles and amplitudes are considered; the number of cycle (n) is varied between 4 and 12 and the amplitude (A) is changed from 0.1 to 0.7. The results indicate that the local Nusselt number, local heat flux and Umax increase near the exit of the nozzle, while Pmin decreases when the amplitude of the wavy surface increases. Although these parameters increase near the jet exit; but the fate of these parameters are highly dependent on the number of cycle (n) and the amplitude of the wavy surface (A) in the downstream direction. Accordingly, a maximum increase of 14.43% of heat transfer rate is observed for n = 7 and A = 0.7. Also, the self-similar behavior shows different trends as compared to the plane wall case which is discussed in detail.

English

English

The influence of upstream wavy surface on the mixing zone of the transverse hydrogen jet at supersonic free stream

In this study, the computational fluid dynamic is applied to investigate the impact of the upstream wavy surface on the mixing rate of the hydrogen fuel jet. The flow feature analyses are also performed to disclose the man influence of the upstream wavy surface on the mixing zone and fuel penetration in the downstream of the jet. To simulate the jet interaction with supersonic free stream, Navier-Stokes equations are coupled with conservation equations of energy and species equation. Since the interaction of the transverse fuel jet with a supersonic mainstream is a complex, a three-dimensional model with high resolution is produced for our investigations. The impact of the supersonic Mach number on the efficiency of the fuel mixing in the presence of the sinusoidal wavy surface. Comprehensive parametric studies are done to reveal the influence of the jet pressure and wavy profile on the mixing performance in the downstream of the jet. According to obtained results, the mixing rate of the fuel in the downstream increases more than 35% when the free stream Mach number is increased from 2 to 4.

Thermo-hydraulic performance improvement, heat transfer, and pressure loss in a channel with sinusoidal-wavy surface

Thermal efficiency development in a square channel heat exchanger attached with sinusoidal wavy surface is presented numerically. The affectation of flow attack angles ( α = 30°, 45°, and 60°), flow directions or sinusoidal wavy surface arrangements (V-apex directing downstream named “V-Downstream” and V-apex indicating upstream named “V-Upstream”), and amplitude ratios (blockage ratios = 0.10, 0.15, 0.20, and 0.25) for heat transfer and flow structure are examined for laminar flow regime ( Re = 100–1000). The physical model for the present investigation is validated with the correlation data. The current problem is resolved with the finite volume approach (semi-implicit method for pressure-linked equations algorithm). The computational information is illustrated in forms of flow topology and heat transfer mechanism in the square channel heat exchanger. The understanding of flow topology and heat transfer mechanism in the square channel heat exchanger is important knowledge to develop the heat transfer coefficient in the heat exchanger. The present of the sinusoidal wavy surface in the square channel heat exchanger can expand the heat transfer coefficient greater than the plain channel in all examples ( Nu/ Nu0 &gt; 1). The maximal heat transfer rate is around 5.58 times above the plain square unit with the optimal performance around 1.98.

Statistical Structure and Deviations from Equilibrium in Wavy Channel Turbulence

The structure of turbulent flow over non-flat surfaces is a topic of major interest in practical applications in both engineering and geophysical settings. A lot of work has been done in the fully rough regime at high Reynolds numbers where the effect on the outer layer turbulence structure and the resulting friction drag is well documented. It turns out that surface topology plays a significant role on the flow drag especially in the transitional roughness regime and therefore, is hard to characterize. Survey of literature shows that roughness function depends on the interaction of roughness height, flow Reynolds number, and topology shape. In addition, if the surface topology contains large enough scales then it can impact the outer layer dynamics and in turn modulate the total frictional force. Therefore, it is important to understand the mechanisms underlying drag increase from systematically varied surface undulations in order to better interpret quantifications based on mean statistics such as roughness function. In this study, we explore the mechanisms that modulate the turbulence structure over a two-dimensional (2D) sinusoidal wavy surface with a fixed amplitude, but varying slopes that are sufficiently small to generate only intermittent flow separation. To accomplish this, we perform a set of highly resolved direct numerical simulations (DNS) to model the turbulent flow between two infinitely wide 2D wavy plates at a friction Reynolds number, R e τ = 180 , which represents modest scale separation. We pursue two different but related flavors of analysis. The first one adopts a roughness characterization flavor of such wavy surfaces. The second one focuses on understanding the nonequilibrium near-surface turbulence structure and their impact on roughness characterization. Analysis of the different statistical quantifications show strong dependence on wave slope for the roughness function indicating drag increase due to enhanced turbulent stresses resulting from increased production of vertical velocity variance from the surface undulations.

Development of Piezo-Actuated Two-Degree-of-Freedom Fast Tool Servo System.

Fast tool servo (FTS) machining technology is a promising method for freeform surfaces and machining micro-nanostructure surfaces. However, limited degrees of freedom (DOF) is an inherent drawback of existing FTS technologies. In this paper, a piezo-actuated serial structure FTS system is developed to obtain translational motions along with z and x-axis directions for ultra-precision machining. In addition, the principle of the developed 2-DOF FTS is introduced and explained. A high-rigidity four-bar (HRFB) mechanism is proposed to produce motion along the z-axis direction. Additionally, through a micro-rotation motion around flexible bearing hinges (FBHs), bi-directional motions along the x-axis direction can be produced. The kinematics of the mechanism are described using a matrix-based compliance modeling (MCM) method, and then the static analysis and dynamic analysis are performed using finite element analysis (FEA). Testing experiments were conducted to investigate the actual performance of the developed system. The results show that low coupling, proper travel, and high natural frequency are obtained. Finally, a sinusoidal wavy surface is uniformly generated by the mechanism developed to demonstrate the effectiveness of the FTS system.

Numerical Investigation on Convective Flow of Two-Phase MHD Dusty Nanofluids over a Wavy Surface with Brownian Motion and Thermophoresis Effects

The emergence of dusty nanofluids as a area of nanoscale heat transfer in fluids is directly correlated to miniaturization trends and nano technology. So, the prime focus of this analyzation is to describe the model of heat and mass transfer phenomenons of two-phase magnetohydrodynamic dusty nanofluids over a vertical sinusoidal wavy surface. The significances of Brownian motion and thermophoresis effects have been considered in the model. The three various nanofluids namely Aluminium oxide ( $$\hbox {Al}_2\hbox {O}_3$$ )-water, Copper (Cu)-water and Titanium oxide ( $$\hbox {TiO}_2$$ )-water immersed with conducting dust particles are taken into consideration for flow analysis. Novel governing equations involving conservation of momentum, mass and thermal energy are subjected to irregular region and converted into non-dimensional form. The resultant equations are numerically approached by developing a finite difference technique with Newton’s quasilinearization method using mathematical software MATLAB. Dynamic characteristics of the flow with the effect of physical parameters associated with velocity, temperature and concentration distributions are interpreted through graphs to get some physical view into the flow patterns. Also, skin-friction coefficient, heat and mass transfer rate are calculated at the boundaries and the outcomes obtained are compared with existing literature.

Numerical solutions of free convection flow of nanofluids along a radiating sinusoidal wavy surface

In this article, our interest is to investigate the free convection boundary-layer flow of a nanofluid past a sinusoidal semi-infinite vertical surface in the non-absorbing medium. The contribution of surface radiative heat flux is employed in the boundary conditions with the help of Stefan-Boltzmann law. Governing equations are transformed into a non-conserved dimensionless system and integrated numerically by means of an implicit finite difference scheme. The accuracy of numerical method is assessed by a comparison of the present results with the earlier published work and it is found that there exists a favorable agreement between the two. Our problem is subject to the influence of a set of parameters, which appear due to the presence of surface radiation, nanoparticles, and transverse curvature of vertical wall. It is noticed that radiative length parameter λ and surface radiation parameter R contribute in a reduction of local skin friction coefficient and local Nusselt number.

Effect of wavelength of sinusoidal wavy wall surface on drag and heat transfer at turbulent thermal boundary layer flow

Effect of wavelength of sinusoidal wavy wall surface on drag and heat transfer at turbulent thermal boundary layer flow