Duct Of Cross-section Research Articles

Dynamics of an oblate spheroidal particle in a square duct filled with viscoelastic fluids

Herein, we used the fictitious domain method to numerically investigate the lateral migration and rotation of an oblate spheroidal particle in a square duct filled with Oldroyd-B fluids. We adopted Reynolds numbers ranging from 25 to 100 and Weissenberg numbers from 0.01 to 0.50. At low to moderate Weissenberg numbers (Wi ≤ 0.50), viscous forces remain dominant in particle motion. Additionally, we considered the effects of initial lateral position, orientation, and blocking ratio on particle dynamics. The results indicate that for flow in square channels with finite fluid inertia, as Wi increases, the elastic effects gradually strengthen, causing the equilibrium position of the particles to shift from near the centerline of the channel toward the diagonal. Notably, under significant fluid elasticity conditions, additional equilibrium positions emerge in the corners of the channel. When released with their x0–y0 plane (containing the two longest axes of the oblate spheroid) parallel to the x–y plane (duct cross section) of the flow field, particles exhibited three distinct motion modes: tumbling, rolling, and kayaking. Tumbling was influenced by fluid inertia and corner attraction, which exhibited transitions to rolling or kayaking. The study also emphasized that the initial orientation of the particles impacted their sustained tumbling under low inertial flows. In addition, the blockage ratio (the ratio of the equivalent diameter of the particle to the duct height) mainly affected the equilibrium positions, and particles with a blockage ratio β ≤ 0.125 were readily attracted to the corners.

Multi-Objective Numerical Analysis of Horizontal Rectilinear Earth–Air Heat Exchangers with Elliptical Cross Section Using Constructal Design and TOPSIS

This study presents a numerical evaluation of a Horizontal Rectilinear Earth–air Heat Exchanger (EAHE), considering the climatic and soil conditions of Viamão, Brazil, a subtropical region. The Constructal Design method, combined with the Exhaustive Search, was utilized to define the system constraints, degree of freedom, and performance indicators. The degree of freedom was characterized by the aspect ratio between the vertical and horizontal lengths of the elliptical cross-section duct (H/L). The performance indicators for the EAHE configurations were assessed based on thermal potential (TP) and pressure drop (PD). The Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) was applied for multi-objective evaluation, and a methodology for EAHE is proposed. The problem was solved using FLUENT software (version 2024 R2), which employs the Finite Volume Method to solve the conservation equations for mass, momentum, and energy. The (H/L)T,o = 6.0 configuration showed a 16.4% increase in thermal performance for heating and 15.9% for cooling compared to the conventional circular duct. Conversely, the (H/L)F,o = 1.0 configuration reduced pressure loss by 65.33%. The integration of Constructal Design with TOPSIS facilitated the identification of optimized geometries that achieve a balance between performance indicators and those that specifically prioritize thermal or fluid dynamic aspects, being this approach an original scientific contribution of the present work.

Localization of acoustical sources rotating in the cylindrical duct using a sparse nonuniform microphone array

The Doppler effect caused by the rotation of turbine fans brings significant challenges to the identification of fan noise sources inside the nacelle. Current methods of rotating source localization inside the cylindrical duct are executed with tough requirements for the microphone array mounted on the duct wall, which includes a fair enough number of microphones and equal-space distribution of each microphone in the azimuthal direction. A methodology based on nonuniform measurements and duct spin modes superposition (NMDMS) is proposed to identify rotating sources with high spatial resolution and few side lobes even near cut-on frequencies, which requires much fewer microphones and no uniform distribution of each microphone in the circumference. The sparsity in the azimuthal domain of the duct field generated by multiple rotating sources is verified theoretically, after which the azimuthal mode in each duct cross-section is reconstructed by the inhomogeneous measurements through the orthogonal matching pursuit (OMP) method. Followed by the identification of mode amplitude in the rotation frame, the sound pressure distribution as well as the axial acoustic velocity distribution on the source plane is reconstructed through duct modes summation. Numerical simulations and experiments are implemented to validate the method. Localization results indicate that rotating sources identification using the proposed method could not only save more than half the microphones without requirements of equal-space distribution but obtain good accuracy of localization and remarkably fewer side lobes.

Interaction of inertia and magnetic force in the liquid metal flow past a magnetic obstacle

In this paper, we present a numerical study of the three-dimensional behavior of a liquid metal flow in an insulating rectangular duct of narrow cross section past a localized magnetic field (i.e., a magnetic obstacle) produced by two parallel square magnets arranged externally on the walls of the duct. A series of simulations are conducted focused mainly on describing the interplay between inertial and magnetic forces in a wide range of interaction parameters (1.8<N<48) by varying the Reynolds number while the Hartmann number is kept fixed (Ha = 75). The analyzed configuration coincides with that studied experimentally by Domínguez et al. [“Experimental and theoretical study of the dynamics of wakes generated by magnetic obstacles,” Magnetohydrodynamics 51(2), 215–224 (2015)] and, as a first step, experimental data from local variables (streamwise velocity component) and global parameters (oscillation frequency and kinetic energy of the wake) are consistently replicated by the numerical model. Furthermore, to complement the flow phenomenology, the transition to different flow structures as the interaction parameter varies is explored. It is found that when the magnetic forces predominate over inertia, stationary vortex patterns with two, four, and six vortices appear while, unlike the hydrodynamic flow past a bluff body, the increase in inertial effects leads to a reduction in the number of vortices and eventually to their disappearance, reaching a state in which the magnetic obstacle becomes imperceptible to the flow. The existence of a critical value of the interaction parameter that maximizes the kinetic energy of the wake is confirmed numerically and corroborated from the experimental data.

Inertial particle focusing in fluid flow through spiral ducts: dynamics, tipping phenomena and particle separation

Small finite-size particles suspended in fluid flow through an enclosed curved duct can focus to points or periodic orbits in the two-dimensional duct cross-section. This particle focusing is due to a balance between inertial lift forces arising from axial flow and drag forces arising from cross-sectional vortices. The inertial particle focusing phenomenon has been exploited in various industrial and medical applications to passively separate particles by size using purely hydrodynamic effects. A fixed size particle in a circular duct with a uniform rectangular cross-section can have a variety of particle attractors, such as stable nodes/spirals or limit cycles, depending on the radius of curvature of the duct. Bifurcations occur at different radii of curvature, such as pitchfork, saddle-node and saddle-node infinite period (SNIPER), which result in variations in the location, number and nature of these particle attractors. By using a quasi-steady approximation, we extend the theoretical model of Harding et al. (J. Fluid Mech., vol. 875, 2019, pp. 1–43) developed for the particle dynamics in circular ducts to spiral duct geometries with slowly varying curvature, and numerically explore the particle dynamics within. Bifurcations of particle attractors with respect to radius of curvature can be traversed within spiral ducts and give rise to a rich nonlinear particle dynamics and various types of tipping phenomena, such as bifurcation-induced tipping (B-tipping), rate-induced tipping (R-tipping) and a combination of both, which we explore in detail. We discuss implications of these unsteady dynamical behaviours for particle separation and propose novel mechanisms to separate particles by size in a non-equilibrium manner.

Computation of three-dimensional incompressible flows using high-order weighted essentially non-oscillatory finite-difference lattice Boltzmann method

In the present work, an accurate and robust solution methodology based on the high-order weighted essentially non-oscillatory (WENO) finite-difference lattice Boltzmann method (LBM) in the three-dimensional generalized curvilinear coordinates is presented and applied for simulating the three-dimensional incompressible flows over complicated configurations with curved boundaries. Here, the incompressible form of the lattice Boltzmann equation in three dimensions is considered and the discretization of the spatial derivative terms is performed with the fifth-order WENO finite-difference method and the temporal derivative term is discretized with the fourth-order Runge–Kutta scheme to ensure the accuracy and stability of the solution method for both the steady and unsteady problems. The three-dimensional lattice Boltzmann equation applied here is based on a nineteen discrete velocity model for transforming the microscopic properties to the macroscopic ones. To assess the accuracy and robustness of the present three-dimensional high-order finite-difference LBM solver, different incompressible flow benchmarks and practical test cases are studied that are the cavity flow, the Beltrami flow, the flow in the curved ducts of rectangular cross sections, and the flow over a sphere for different flow conditions. The decay of the homogeneous isotropic turbulence is also computed to examine the suitability of the present solution method to be applied as the direct numerical simulation of turbulent flows. It is demonstrated that the solution methodology presented based on the high-order WENO finite-difference LBM in the three-dimensional generalized curvilinear coordinate can be used for accurately and effectively computing the three-dimensional practical incompressible flow problems.

Limits of Riemann Solutions for Isentropic MHD in a Variable Cross-Section Duct as Magnetic Field Vanishes

Limits of Riemann Solutions for Isentropic MHD in a Variable Cross-Section Duct as Magnetic Field Vanishes

Retraction notice: Numerical investigation on turbulent convective heat transfer of nanofluid flow in a square cross-sectioned duct

Retraction notice: Numerical investigation on turbulent convective heat transfer of nanofluid flow in a square cross-sectioned duct

Time-resolved measurement of acoustic density fluctuations using a phase-shifting Mach-Zehnder interferometer.

Phase-shifting interferometry is one of the optical measurement techniques that improves accuracy and resolution by incorporating a controlled phase shift into conventional optical interferometry. In this study, a four-step phase-shifting interferometer is developed to measure the spatiotemporal distribution of acoustic density oscillations of the gas next to a rigid plate. The experimental apparatus consists of a polarizing Mach-Zehnder interferometer with a polarization camera capable of capturing four polarization directions in one shot image and it is used to measure the magnitude and the phase of density fluctuations through a duct of rectangular cross section connected to a loudspeaker. The results are compared with the well-established thermoacoustic theory describing the thermal coupling between acoustic oscillations and rigid boundaries, and the results show a very good agreement for various ratios of the (frequency-dependent) thermal boundary layer thickness to the plate spacing. This measurement technique could be advantageously employed to analyze more complex heat transfer processes involving the coupling of acoustic oscillations with rigid boundaries.

Thermo-hydraulic and entropy generation analysis of nanofluid flow with variable properties in various duct cross sections: a 3-D two-phase approach

A three-dimensional computational fluid dynamics (CFD) study is carried out to explore the effect of duct cross section on the thermo-hydraulic performance of various ducts. A finite volume-based scheme with an SST k-omega model and mixture model (two-phase model) was used to obtain more realistic results. A two-phase mixture model was used to consider the movement between base fluid and nanoparticles. Al2O3 nanoparticle having a volume fraction of 0.01% and 42 nm as particle size, the heat transfer and friction factor characteristic are studied for turbulent flow regime (3000 < Re < 9000) with variable thermo-physical properties. A maximum enhancement of 86% in heat transfer rate is obtained for the serpentine duct compared to the conventional circular duct at Re = 4500. Owing to a significantly lower increase in pressure drop, the elliptical duct has the highest thermo-hydraulic performance parameter of 1.54 relative to the circular duct. Further, to analyze the heat transfer quality, the entropy generation rate is studied, and it is observed that the square duct reported the highest with an increase of 60% and the elliptical duct the lowest with a reduction of 54% relative to the circular duct. This study can aid in choosing the duct geometry to enhance the heat transfer rate with nanofluid for applications such as solar-thermal, heat exchangers, etc.

Particle transport in turbulent square duct flows with a free surface

Direct numerical simulation combined with a one-way coupled Lagrangian particle tracking technique is employed to investigate dilute particle-laden turbulent flows in open square ducts with a free surface. The focus is on examining the influence of the mean cross-stream secondary flow on particle transport near the wall, free surface, and across the duct cross section. Based on the duct half-width and mean friction velocity, a shear Reynolds number of Reτ = 300 is considered, with the corresponding particle Stokes numbers ranging from St+ = 0.31 to 260. The results reveal that particle concentration near the sidewalls is lower than that near the bottom wall, and the minimum particle concentration is observed at the free surface. Along the bottom wall centerline orientated upward, particle concentration gradually decreases. An exception to this is in the vicinity of the free surface where a slight increase is observed for the heavier particles (St+ ≥ 25), and the amplitude of this increase gradually declines as the Stokes number increases. In the streamwise direction near the free surface, heavier particles tend to preferentially concentrate in regions where the instantaneous transverse secondary flow velocity is negative. As the Stokes number increases, the position of the maximum streamwise velocity for heavier particles is closer to the free surface, and the rotation centers of inner and outer secondary particle motions gradually disappear. The streamwise root mean square velocity for the lightest St+ = 0.31 particles is higher than that for particles with higher inertia in the middle region of the free surface.

Novel Cooling Strategy for a Hybrid Photovoltaic/Parabolic Dish Concentrator

In this paper, the thermo-optical performance using novel cooling strategy improvements for a hybrid photovoltaic/parabolic dish concentrator with a conical thermal receiver using a beam splitter filter (PV/PDC-CTR-BSF) is investigated. The study’s main goal is to improve the cooling effectiveness of the serpentine-shaped cooling duct by investigating the effect of the cross-section shape and positioning of the cooling duct under the PV panel. Typical cooling pipes have either a rectangular or circular cross-section and are usually attached to the back sheet of the PV panel using off-the-shelf adhesives that have very low thermal conductivity. With the advent of 3D printing technology, the back sheets could be 3D-printed with integral cooling ducts of different cross-sections at different locations and orientations within the back sheet that allow for increased heat transfer from the back sheet and thus improve PV/PDC-CTR-BSF’s thermos-optical performance. For this purpose, the study investigates and compares the thermal performance of four different cooling duct cross-sections that include: rectangular, semi-circular, semi-elliptical and triangular. For each of the cooling duct cross-sections, several positions and orientations, which include flush below the back sheet layer and embedded inside the back sheet but positioned at the bottom, middle and top of the back sheet, are examined. Numerical simulations using the commercial software ANSYS FLUENT(R2019) are performed to assess the performance of the cooling ducts and, in turn, the thermo-optical performance of the PV/PDC-CTR-BSF system. The semi-elliptical cross-section duct embedded in the middle of the back sheet was found to yield the best cooling performance since its rate of heat removal from the PV back sheet was found to be the highest.

Analysis of the Impact of Structural Parameter Changes on the Overall Aerodynamic Characteristics of Ducted UAVs

Ducted UAVs have attracted much attention because the duct structure can reduce the propeller tip vortices and thus increase the effective lift area of the lower propeller. This paper investigates the effects of parameters on the aerodynamic characteristics of ducted UAVs, such as co-axial twin propeller configuration and duct structure. The aerodynamic characteristics of the UAV were analyzed using CFD methods, while the impact sensitivity analysis of the simulation data was sorted using the orthogonal test method. The results indicate that, while maintaining overall strength, increasing the propeller spacing by about 0.055 times the duct chord length can increase the lift of the upper propeller by approximately 1.3% faster. Reducing the distance between the propeller and the top surface of the duct by about 0.5 times the duct chord length can increase the lift of the lower propeller by approximately 7.7%. Increasing the chord length of the duct cross-section by about 35.3% can simultaneously make the structure of the duct and the total lift of the drone faster by approximately 150.6% and 15.7%, respectively. This research provides valuable guidance and reference for the subsequent overall design of ducted UAVs.

Advancing flow-duct noise control: Examples of innovative silencers

Two examples of innovative silencers for advanced duct noise control are presented. The first example is related to using metamaterials and the so-called ‘slow sound' to create a compact virtual Herschel-Quincke tube [1]. The second example revolves around a concept called the ‘modal filter' [2], which is designed to selectively damp a single propagating mode. For plane waves, optimal propagational damping is achieved by a wall impedance equal to the Cremer impedance. We will demonstrate how to compute the Cremer impedance, even for low frequencies, at which the classical solution is invalid [3]. Such an arrangement efficiently dampens both the plane (0,0) and the first radial mode (0,1). To further dampen the first two circumferential modes (1,0) and (2,0), a section with the Cremer impedance can be combined with a modal filter made of micro-perforated plates. These plates are inserted parallel to the flow direction and positioned at modal velocity maxima in the duct cross-section. We anticipate that both examples can be useful in industries requiring compact noise mitigation solutions in flow ducts. [1] https://doi.org/10.1016/j.jsv.2019.115045. [2] https://doi.org/10.1121/2.0000473. [3] https://doi.org/10.1121/1.5136952

NUMERICAL ANALYSIS OF THE HEAT TRANSFER AND THE ENTROPY GENERATION FOR A CuO-Al2O3-WATER HYBRID NANOFLUID FLOW THROUGH AN EXTENDED CURVED DUCT

The present paper focus on the theoretical analysis of the convective heat transfer and the irreversibility state of a laminar flow of a hybrid nanofluid inside a extended curved duct of circular cross section. This nanofluid is obtained from the suspension of the Al2O3 and CuO nanoparticles in the pure water. The flow of the nanofluid start from a narrowed part of a curved duct of a semi-circular shape, its enlarged part is subjected to a uniform hot temperature. The present analysis deals with highlighting the impact of some parameters namely: Dean number (13.83 ⩽ De ⩽ 55.33), Richardson number (0 ⩽ Ri ⩽ 0.1) as well as the effect of the hybrid nanoparticles on the heat transfer rate and the generated entropy. The resolution of the governing equations that include mass, momentum and energy has been performed by the use of the finite element method. The results have shown that the rate of the heat exchange rise according to the augmentation of the Dean number and the hybrid nanofluid volume fraction. However, the flow system irreversibility is more important in the case of the highest Dean number and volume fraction. Moreover, a comparison between different simple and hybrid nanofluids has demonstrated that the latter is more efficient especially for technological and economic reasons

Gall bladder diseases: a study of histopathological spectrum of cholecystectomy specimens from rural tertiary hospital in Telangana state during COVID pandemic

Background: The debate of “is it worth spending the busy pathologist’s time on gall bladder specimens” has been there for decades. The selective approach may result in missing discrete pathologies such as premalignant lesions. We are presenting an interesting series of gall bladder histopathology diagnosed at our institute in the past two years. Methods: This is a retrospective study done at Bhaskar Medical College between 2020-2022 (specifically chosen as this is the period of COVID pandemic). This study included 43 patients who underwent cholecystectomy. All confirmed cases of acute abdomen operated for other reasons and trauma were excluded. Sections were taken from neck, fundus, body and cross section of cystic duct of each cholecystectomy specimen. The whole gallbladder was submitted and screened for the invasion in ICPN case. These sections were processed through routine paraffin embedding, microtome cutting and H&amp;E staining for evaluation of spectrum of various gallbladder lesions. Results: In our study, 25 cases showed lymphoplasmacytic infiltration with fibrosis, 9 cases showed ulceration, congested blood vessels and neutrophilic infiltration. We encountered few rare cases like eosinophilic cholecystitis, xanthogranulomatous cholecystitis, and Intracholecystic papillary neoplasm (ICPN)”. Pyloric metaplasia was seen in 27.9% cases, which is also higher Conclusions: Our study emphasizes the need for the routine examination of these specimens, to have a detailed understanding of the etiology to prevent/predict the other associated medical conditions. We also could find 2% of the cases having pre-malignant lesions and 28% having metaplasia, which if missed shall progress to malignant conditions.

A study on microchip cooling performance increment by using air jet impingement with one and double rows

The impinging jet technique is a high-performance cooling technology for microchips which are basic elements of computer systems and have high heat generation rates in small volumes. In this study, the improvement of heat transfer of the desktop microchips used in all technological products today by air-impinging jet flow was examined. For this purpose, numerical research was carried out on the cooling of copper plate surfaces with two different patterns, concave and roof shaped having 1000 W/m2 constant heat flux in rectangular cross-sectional ducts by one and double air jets with distances of Dh and 2 Dh between them. Numerical analysis was performed steady and in three dimensions with the k– ε turbulence model by the Ansys–Fluent program. The obtained results were compared with the numerical and experimental results of the study in the literature and it was seen that they are determined to be compatible. The results were presented as the mean Nu number for each of both patterned surfaces and the mean outlet temperature of the jet flow ( Tmoj) and the mean Nu number ( Num) of all patterned surfaces in single and double jet channels with different distances. Besides, pressure drop (Δ P), friction factor ( f), thermal resistance ( Rt) and thermo-hydraulic performance (THP) of concave and roof-patterned surfaces in the channels with different jet setup configurations were analyzed. Streamline and temperature contour distributions of the jet flow along the channel for different H/ Dh ratios and jet numbers were evaluated for both patterned surfaces. In H/ Dh = 4 and at Re = 7000, the average Nu number for roof-patterned surfaces was found to be 30.52% higher than concave patterned surfaces in the case of double jets with a distance of Dh. Rt reduction values of the roof and concave pattern surfaces with a double jet arrangement having 2 Dh distance at Re = 5000 and H/ Dh = 8 are 163.7% and 36.23% when compared to single jet, respectively.

Spectral analysis of acoustic plane waves in ductworks with uniform and varying cross-section waveguides

The problem of low-frequency sound propagation in ducts involving varying cross-sections is analyzed. Spectral finite element formulations for the dynamic analysis of varying cross-section ducts are presented as tapered spectral elements. These elements can be used in connected waveguides through dynamic stiffness relations. Linear and polynomial duct types are considered. The elements’ shape functions are established as well as the dynamic stiffness matrices describing the spectral relation between the acoustic pressure and the volume velocity. The presented spectral approach describes the acoustic wave motion at any position along arbitrary multiply connected duct waveguides within the one-dimensional plane-wave assumption. The derived expressions are verified experimentally, and by comparison with 3-D finite element solutions. The modeling of varying cross-section duct waveguides can play an important role in the design of acoustic excitation devices and horn-type loudspeakers. The advantage of the presented formulations lies in the low computational cost when compared to the finite element approach.

Non-unique solutions for flow depth and velocity estimations in free-surface annular-channel for single-phase viscous flows

Flow depth and mean velocity estimations for partially filled annular ducts are performed using a one-dimensional free-surface flow formulation. The formulation considers a Newtonian fluid flowing in a closed channel with a circular annular cross-section, in steady-state and uniform regimes. The Darcy–Weisbach friction factor, combined with the Churchill equation and hydraulic-diameter approach, is used. Expressions for the flow cross-section area and the wetted perimeter of the partially full annular channel flow, both terms of hydraulic-diameter definition, are derived from trigonometric rules as a function of the flow depth. In contrast to partially filled pipe flow where a bi-univocal and monotonic trend solution between flow depth and flow rate occurs, for annular-channel, multiple values for the flow depth satisfy the formulation for a single flow rate value. Multiple solutions existence is accounted for the abrupt changes in the flow geometry, mainly related to the wetted perimeter, when (i) the flow height enters in contact with the internal duct, (ii) the internal duct becomes completely submerged, and (iii) the flow completely fills the duct cross-section. Calculations for a broad range of geometries and flow conditions (inclination angles: 15°–85°, viscosity: 0.001–0.576 Pa s., and Reynolds numbers: 101–8×105) show errors up to 47% can be reached for flow velocity and flow depth estimations. Specifically, for turbulent flows, discrepancies are lower, being less than 10%. Thus, the higher the inclination angle and viscosity, the more significant errors. The paper outlines the implication of the flow depth and velocity estimations using a well-accepted formulation that impacts on industrial systems’ design and operation stages. We draw attention to the existence of non-unique solutions for free-surface flows in annulus and the need for experiments to elucidate which of these solutions is physically possible and consequently improve predictions for the flow depth and mean velocity in this kind of flow.

Smoothed Particle Hydrodynamics-Based Study of 3D Confined Microflows

In this study, we investigate the performance of the smoothed particle hydrodynamics (SPH) method regarding the computation of confined flows in microchannels. Modeling and numerical simulation with SPH involve the representation of flowing matter as distinct mass points, leading to particle discretization of the Navier–Stokes equations. The computational methodology exhibits similarities with other well-established particle methods, such as molecular dynamics (MD), dissipative particle dynamics (DPD), and smooth dissipative particle dynamics (SDPD). SPH has been extensively tested in the simulation of free-surface flows. However, studies on the performance of the method in internal flow computations are limited. In this work, we study flows in microchannels of variable cross-sections with a weakly compressible SPH formulation. After preliminary studies of flows in straight constant cross-section ducts, we focus on channels with sudden expansion and/or contraction. Flow models based on periodic or various inlet/outlet boundary conditions and their implementations are discussed in the context of 2D and 3D simulations. Numerical experiments are conducted to evaluate the accuracy of the method in terms of flowrate, velocity profiles, and wall shear stress. The relation between f and Re for constant cross-section channels is computed with excellent accuracy. SPH captured the flow characteristics and achieved very good accuracy. Compressibility effects due to the weakly compressible smoothed particle hydrodynamics (WCSPH) formulation are negligible for the flows considered. Several typical difficulties and pitfalls in the application of the SPH method in closed conduits are highlighted as well as some of the immediate needs for the method’s improvement.