Cylinder Configuration Research Articles

Acoustic metamaterial design using Conditional Wasserstein Generative Adversarial Networks

This talk presents a method for generating planar configurations of scatterers with a reduced total scattering cross section (TSCS) by means of generative modeling and deep learning. The TSCS minimization via repeated forward modeling techniques, trial-error methods, and traditional optimization methods requires considerable computer resources and time. However, similar or better results can be achieved more efficiently by training a deep learning model to generate such optimized configurations producing low scattering effect. In this work, the Conditional Wasserstein Generative Adversarial Networks (cWGAN) is combined with Convolutional Neural Networks (CNN) to create the generative modeling architecture [1]. The generative model is implemented with a conditional proponent to allow the TSCS targeted design generation and is enhanced with the coordinate convolution (CordConv) layer to improve the model’s spatial recognition of cylinder configurations. The cWGAN model [1] is capable of generating images of 2D configurations of scatterers that exhibit low scattering. The method is demonstrated by giving examples of generating 2-cylinder and 4-cylinder planar configurations with minimal TSCS. [1]. P. Lai, F. Amirkulova, and P. Gerstoft. “Conditional Wasserstein generative adversarial networks applied to acoustic metamaterial design,” J. Acoust. Soc. Am. 150(6), 4362–4374 (2021).

Experimental Investigation of Flow and Noise Control by Porous Coated Tandem Cylinder Configurations

The aerodynamic noise generated by aircraft landing gear components is often studied using a so-called tandem cylinder configuration, consisting of two circular cylinders arranged in a streamwise row and separated by a certain distance. The subject of the present study is the experimental investigation of the effect of porous coatings on the noise generated by such a tandem cylinder configuration. This was done by performing acoustic and flow measurements in a small aeroacoustic wind tunnel at Reynolds numbers (based on cylinder diameter) between 30,000 and 130,000. It is found that the porous coatings lead to a decrease of both the tonal noise and the broadband noise and to a notable shift of the resulting tonal noise peak toward lower frequencies. The noise reduction is mainly caused by the stabilizing effect of the coating of the upstream cylinder on the wake flow and the absorption of turbulence by the coating of the downstream cylinder. The observed shift of the frequency is most likely due to the mean velocity reduction in the wake of the porous coated upstream cylinder and the interaction of the turbulent flow with the porous coating of the downstream cylinder.

Nanofluid Flow of Alumina–Copper/Water Through Isotropic Porous Arrays of Periodic Square Cylinders: Mixed Convection and Competent Array Shape

Abstract The flow of hybrid alumina–copper/water nanofluid with mixed convection heat transfer from multiple square cylinders arranged in three different types of arrays, namely equilateral triangle (ET), rotated square (RS), and rotated rhombus (RR) in a heat exchanger, has never been studied before the present study. Navier–Stokes and energy equations with a periodic boundary condition in the transverse direction for all three array types having the same porosity are solved with the finite volume methodology. The combined effect of aiding buoyancy (Richardson number 0–2), the configuration of square cylinders, and hybrid nanoparticle volume fraction (0-0.06) on the flow dynamics and their impact on the overall heat transfer phenomenon through three different array configurations is thoroughly elucidated. The arrays’ overall drag and friction coefficient increases with an increase in the strength of aiding buoyancy and nanoparticle volume fraction. An increment in Richardson number, and nanoparticle volume fraction, causes thermal boundary layer thinning and results in higher heat transfer rates across all three arrays. With an increase in Ri from 0 to 2 at a nanoparticle volume fraction of 0.06, the mean Nusselt number of ET, RS, and RR arrays is increased by 161%, 5%, and 32%, respectively. While, with an increase in nanoparticle volume fraction from 0 to 0.06 at Ri = 2, the mean Nusselt number of ET, RS, and RR arrays is augmented by 17%, 6%, and 9%, respectively. Finally, the efficient array configuration in terms of fluid-thermal behavior is proposed to design various heat-exchange systems under differing operating conditions.

Effect of Inner Cylinder Configuration on Liquid Droplet Dispersion and Size Distributions in a Taylor-Couette Reactor

Effect of Inner Cylinder Configuration on Liquid Droplet Dispersion and Size Distributions in a Taylor-Couette Reactor

Conditional Wasserstein generative adversarial networks applied to acoustic metamaterial design.

This work presents a method for the reduction of the total scattering cross section (TSCS) for a planar configuration of cylinders by means of generative modeling and deep learning. Currently, the minimization of TSCS requires repeated forward modelling at considerable computer resources, whereas deep learning can do this more efficiently. The conditional Wasserstein generative adversarial networks (cWGANs) model is proposed for minimization of TSCS in two dimensions by combining Wasserstein generative adversarial networks with convolutional neural networks to simulate TSCS of configuration of rigid scatterers. The proposed cWGAN model is enhanced by adding to it a coordinate convolution (CoordConv) layer. For a given number of cylinders, the cWGAN model generates images of 2D configurations of cylinders that minimize the TSCS. The proposed generative model is illustrated with examples for planar uniform configurations of rigid cylinders.

Sound Localization through Multi-Scattering and Gradient-Based Optimization

A gradient-based optimization (GBO) method is presented for acoustic lens design and sound localization. GBO uses a semi-analytical optimization combined with the principle of acoustic reciprocity. The idea differs from earlier inverse designs that use topology optimization tools and generic algorithms. We first derive a formula for the gradients of the pressure at the focal point with respect to positions of a set of cylindrical scatterers. The analytic form of the gradients enhances modeling capability when combined with optimization algorithms and parallel computing. The GBO algorithm maximizes the sound amplification at the focal point and enhances the sound localization by evaluating pressure derivatives with respect to the cylinder positions and then perturbatively optimizing the position of each cylinder in the lens while incorporating multiple scattering between the cylindrical scatterers. The results of the GBO of the uni- and multi-directional broadband acoustic lens designs are presented including several performance measures for the frequency dependence and the incidence angle. A multi-directional broadband acoustic lens is designed to localize the sound and to focus acoustic incident waves received from multiple directions onto a predetermined localization region or focal point. The method is illustrated for configurations of sound hard and sound soft cylinders as well as clusters of elastic thin shells in water.

Noise reduction of sinusoidal wavy cylinder in subcritical flow regime

The sinusoidal wavy cylinder of circular cross section is able to substantially reduce the fluid forces by effectively stabilizing the near wake in the subcritical flow regime. Based on the anechoic wind tunnel measurements and large eddy simulations (LESs), we investigate the capability of the sinusoidal wavy cylinder to reduce aeroacoustic noise as well as underlying flow physics. The wavy cylinder studied in this work covers a range of spanwise wavelength λz = 1.8–6.0Dm and a range of wave amplitude a = 0.15–0.25Dm, where Dm is the mean diameter of the wavy cylinder. The wind tunnel measurements are conducted at Reynolds number ReDm = 2.9–8.0 × 104, while LESs are conducted at ReDm = 3.0 × 104. It is observed that the wavy cylinder's configuration, determined by λz and a, has a profound impact on the far-field sound pressure level (SPL) of both tonal and broadband noise. Compared with the baseline smooth cylinder, the wavy cylinder with λz = 1.8Dm and a = 0.25Dm can reduce the peak value of SPL at the tonal frequency by up to 36.7 dB. The reductions in the overall SPL of the tonal and broadband noise are also tremendous, by up to 31.0 and 7.5 dB, respectively, by the wavy cylinder with the optimum wavelength. Consistent with observations on noise reduction are the significantly weakened near-wake structures and largely attenuated spanwise coherence, as well as substantially suppressed pressure fluctuations in the near wake and over the cylinder surface, based on the LES results. Dependence of the noise reduction on Reynolds number is discussed as well.

Numerical simulations of flow-induced vibrations of two rigidly coupled cylinders with uneven diameters in the upper transition Reynolds number regime

Two degree-of-freedom (2-DoF) flow-induced vibrations (FIV) of two rigidly coupled cylinders are numerically investigated at the Reynolds number of 3.6×106. Two-dimensional (2D) Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations are performed combined with the k−ω SST turbulence model. A low mass-damping system is considered with a mass ratio of 2 and a damping ratio of zero. The diameter ratio is set to 0.25. The influence of the reduced velocity (Ur), the position angle (α) of the small cylinder relative to the large cylinder and the gap ratio (G/D) between the cylinders on the FIV response of the system are analyzed. The simulations are performed for 2≤Ur≤12. To analyze the effect of α, three values are considered, [α=0°, 90°, 180°] with a constant value of G/D=0.1. The effect of G/D is studied for the α=90° configuration in which the G/D=0.25 and G/D=0.5 configurations are analyzed in addition to the G/D=0.1 configuration. It is found that the lock-in regime extends beyond Ur=12 for the α=0°, 180° and α=90° at G/D=0.1 and 0.25 configurations compared with the single cylinder configuration. Extended lock-in range is observed when the small cylinder is placed at α=90°, with G/D=0.1, and at α=180°. In addition, for the α=90° configuration, the results obtained for C¯D, C¯L and Ay,max/D converge to those of the single cylinder with the increase of G/D. A 2T shedding mode is observed for the single cylinder at 6.5≤Ur≤10 and for the α=0° configuration when Ur≥8. For the α=90° and 180° configurations, the wake patterns are irregular. With the increase of G/D, a longer vortex street behind the small cylinder is observed, which creates many vortical structures in the wake of the cylinders.

Efficiency of Mixed-Element USM3D for Benchmark Three-Dimensional Flows

The unstructured mixed-element cell-centered finite volume flow solver USM3D is enhanced with new capabilities such as line generation for general unstructured grids and optimization of the iterative solver. The efficiency of the new developments is assessed in a massively parallel environment. The assessments are conducted using a baseline method and the recent hierarchical adaptive nonlinear iteration method framework. Three benchmark turbulent flows (namely, a subsonic separated flow around a three-dimensional hemisphere–cylinder configuration, a transonic flow around the ONERA M6 wing, and a supersonic flow through a square duct) are considered.

A study on the working characteristics of free piston linear generator with dual cylinder configuration by different secondary injection strategies

Aiming at the dead center change of free piston linear generator with dual-cylinder configuration(FPLGDC), this paper proposes stratified combustion technology and studies the influence of secondary injection timing and injection ratio on the formation and combustion characteristics of stratified mixture. The results show as the secondary injection timing was advanced from 16oCABTDC to 36oCABTDC, local over-concentrated mixture in-cylinder was diluted, and the overall uniformity of the mixture was improved. Further, the overall evaporation increased from 89% to 97%. More, as secondary injection ratio decreased from 20% to 10%, the fuel evaporation ratio increased from 14% to 16%, and the stratification of the in-cylinder mixture at the ignition time was more obvious. Therefore, advancing the time of secondary injection and reducing secondary injection ratio can make the mixture more properly stratified, shorten the rapid combustion period, and improve combustion quality. Further, compared with the secondary injection ratio was 20% for secondary injection time at 16oCABTDC, the peak pressure in the cylinder increased by 14%, and the peak pressure position increased by about 2oCA when the secondary injection ratio was 10% at a secondary injection time of 36oCABTDC. Thus, reasonable control the injection strategy can significantly improve the dynamic performance of FPLGDC.

Effects of stagnating and thermal shielding of an upstream promoter on forced convection of flow past a square cylinder in a channel

This work performs a direct simulation on forced convection heat transfer of flow past a square cylinder in a channel with an upstream promoter. The promoter is small in size that the incoming flow is stagnated and heated, thus the flow in the gap between the promoter and main cylinder keeps steady and the heating by the main cylinder gets weak as it develops downstream. The objective of the present study is to explore the effects of two parameters, i.e., Reynolds number and gap ratio, on the thermal and flow characteristics for Re = 70-140 and GR = 2-8. The effects of the two parameters are presented and analyzed by the thermal and flow fields, variations of global characteristics quantities, local heat transfer characteristics, patterns of flow in the gap and near-wake region, and temperature on the channel walls. We emphasize both time-averaged and fluctuating quantities to reflect the mean and pulsating characteristics of the flow. Numerical results reveal that although the promoter produces a steady flow in the gap, it alters the velocity profile of the gap flow and consequently changes the shearing properties, thus influences the flow around and even in the wake downstream of the main cylinder. In general, the small promoter partially stabilizes the wake flow and reduces the amplitude of fluctuating forces acting on the main cylinder compared with the single cylinder configuration, and the stabilization is more remarkable for small gap ratios. However, the fluctuation of heat transfer rate on the surface of main cylinder may increase. A further analysis indicates that as the promoter is placed close to the main cylinder, the recovery rate of deficit wake flow is slower and the fluctuating amplitude of velocity and temperature is relatively smaller due to the stabilized flow.

Experimentally-Benchmarked kinetic simulations of heat transfer through rarefied gas with constant heat flux at the boundary

In many applications, the heat flux at the surface is known instead of the surface temperature. In addition, in some applications, like vacuum drying or high altitude flights, the pressure is below atmospheric pressure, so the rarefaction effects become important, and therefore, the Navier-Stokes-Fourier equations fail to predict gas thermal behavior. In this paper, a constant heat flux boundary condition is developed and implemented in the frame of the Shakhov model kinetic equation, with the possibility to simulate the diffuse-specular reflexion of the molecules from the surface. The developed technique is implemented for the simulation of gas heat transfer in a two concentric cylinders configuration, similar to vacuum drying of used nuclear fuel canisters. The numerical results obtained using developed approach are compared with experimental data of heat transfer through rarefied gas between two concentric cylinders.

Computational aeroacoustic modeling using hybrid Reynolds averaged Navier–Stokes/large‐eddy simulations methods with modified acoustic analogies

AbstractThis study employs a numerical approach to investigate noise mechanisms in tandem cylinders. The tandem cylinder configuration is an excellent model for aircraft landing gear. The study is therefore primarily motivated by the need to understand the aircraft landing gear as a primary contributor to airframe noise during approach and landing. Fluctuations in the flow properties induced by turbulent flow around the tandem cylinders are computed and analyzed. A hybrid improved delayed detached eddy simulation turbulence model is employed to compute the boundary layer flow as well as to compute the fluctuations in the flow properties. The numerical methodologies for the turbulent flow computations are implemented on the OpenFOAM software platform. The study also considers the impact of neglecting the volume sources and employs two modified versions of Curle's and Ffowcs‐Williams and Hawkings analogies. The results are in good agreement with published numerical and experimental data in the existing literature.

Wave transmission and drag coefficients through dense cylinder arrays: Implications for designing structures for mangrove restoration

Mangrove vegetation constitutes a natural coastal defence against waves and erosion. Despite their protective role, mangrove ecosystems have experienced continuous degradation over the last decades due to human causes. At retreating mangrove coastlines, bamboo structures are built to create new habitat for mangrove colonization. Existing structures have experienced mixed rates of success due to the lack of a scientific basis in their design. Optimizing future structure designs requires investigating the effect of the bamboo poles on waves. We consequently conducted laboratory experiments to measure wave transformation, hydrodynamic forces, and flow velocities inside cylinder arrays, mimicking bamboo poles, with varying cylinder configurations and orientations. The experiments provided relationships for wave transmission, wave reflection, and the drag coefficients for configurations with volumetric porosities between n = 0.64 − 0.9. Configurations with a small lateral spacing (causing higher blockage) and a relatively longer streamwise spacing (causing less sheltering) exhibit larger forces and dissipation per element. Such arrangements enable optimizing wave dissipation at locations where the wave direction has low variability over the year. Placing the poles horizontally instead of vertically increases the forces and wave dissipation per element in relatively deeper water. Based on the experiments, we developed a conceptual analytical model that predicts wave reflection and dissipation through cylinder arrays, including blockage and sheltering. The model can reproduce the influence of cylinder arrangement on wave transformation, and it suggests that accurate predictions of sheltering and wave reflection are important to find optimal designs. Overall, these results provide useful insights on how to model and optimize the design of structures for mangrove restoration.

Broadband optimization of volumetric sound metadiffusers

Broadband volumetric sound metadiffusers are designed by using gradient-based optimization and by means of multiple scattering theory (MST) employed to evaluate the scattered pressure field by a uniform planar configuration of cylindrical scatterers. The method is illustrated by giving numerical examples for planar configurations of rigid cylinders and thin elastic cylindrical shells situated in the air medium. By rearranging the position of each cylinder, a metadiffuser is optimized to have a high diffusion coefficient. Multiple scenarios are evaluated considering a single frequency and broadband optimization. Single frequency optimization is performed to optimize a configuration of cylinders at a specific wavenumber. Broadband optimization is used to optimize a cylinder configuration for a range of wavenumbers by optimizing the root mean square of diffusion coefficient evaluated at discreet values of normalized wavenumber. MATLAB MultiStart solver combined with parallel computing along with global optimization toolboxes is used to enhance the modeling for optimizing for both scenarios due to its ability to evaluate multiple starting points in parallel, hence being able to find the global optimum. A wide array of metadiffusers is optimized using MATLAB MultiStart and fmincon solvers with the sequential quadratic programming and genetic algorithm for a comparison of performance of these algorithms.

Scattering from an inhomogeneous dielectric cylinder partially buried in a dielectric half-space

A hybrid method is presented for computing the TM polarized plane wave scattered by an inhomogeneous penetrable cylinder embedded in the planar interface between two dielectric half-spaces. In this method, the infinite interface is represented by an unknown equivalent magnetic current, which is expressed in terms of the difference between the current with the cylinder present and the current of the known physical optics (PO) solution of the unperturbed (without cylinder) problem. Coupled integral equations for the equivalent surface electric and magnetic currents on the cylinder surface and the perturbed equivalent magnetic current on the finite section of the interface are obtained and solved by the Method of Moments (MoM). The half-space and the inhomogeneous cylinder configuration in this paper can be used in a wide range of settings.

A Symmetric Multichamber Hydraulic Cylinder With Variable Piston Area: An Approach to Compact and Efficient Electrohydrostatic Actuation

Abstract This paper presents an approach for designing symmetric (effective cylinder area during extension is the same as that during retraction) multichamber cylinders with discretely variable piston area. The design methodology is presented in a generalizable manner and is demonstrated on an example five-chamber cylinder design. A method for finding symmetric multichamber cylinder configurations from a given cylinder topology is presented, and subsequently, a method for discretely varying the effective piston area is developed, subject to a cylinder symmetry constraint. Furthermore, an algorithm is presented to optimally switch the effective cylinder area of an electrohydrostatic actuation system either to minimize the magnitude of motor torque or to minimize resistive power losses in the system. Additionally, a method for optimizing standard (constant area) hydraulic cylinders to minimize motor torque magnitude or resistive power losses is presented. These methods are then demonstrated on an example electrohydrostatic actuation system via simulation. Results indicate that this multichamber cylinder approach with discretely variable piston area may allow for the design of compact and efficient actuators relative to standard methods.

Comparative evaluation of different heat transfer correlations on a single curved-cylinder spark ignition crank-rocker engine

Crank-rocker (CR) engine is a new kind of combustion engine that has a curved-cylinder combustion chamber. To enhance CR engine development and performance, high accuracy modeling which accurately predicts combustion characteristics is required. Due to the difference in cylinder configurations, the first empirical-model used to predict the combustion characteristics of a conventional engine may not be applicable. Currently, only a single correlation model has been proposed for CR engine. The main aims of this study are to improve the existing developed CR engine model and to investigate the impact of various heat transfer correlations in predicting combustion characteristics using single-zone combustion modeling. The model has been improved by including a sub-model of the specific heat ratio which varies with temperatures. Four cases of models incorporating various heat transfer correlations namely Woschni, Sitkei, Hohenberg, and Annand have been simulated. Then, the results were analyzed and compared with experimental data. Further simulations have been carried out to predict maximum pressures, temperatures, heat transfer coefficients, etc. under various loads. Annand’s model was found to yield the best prediction for the combustion characteristics and it is considered the best choice concerning the accuracy and other criteria such as time and ease of usage.

Analysis and optimization of triple tube phase change material based energy storage system

We present an analysis and optimization of triple tube phase change material (PCM) based energy storage system. The study considers a triple tube energy storage system with PCM stored in the inner cylinder and outer annular region while heated water is passed through the inner annular region. Simulations are performed to analyze the effect of inner cylinder diameter on the total time required for complete melting of PCM while keeping the volume of PCM constant. Results show that the triple cylinder configuration leads to considerably faster melting as compared to the double cylinder system for the same mass flow rate of water and same quantity of PCM. It is found that the inner diameter, inlet temperature and mass flow rate of heat transfer fluid have considerable effect on the melting time while the effect of cylinder length is negligible. The main outcome of the study is that it shows that there exists an optimum diameter of the inner cylinder for which the melting rate is highest and considerably faster than that for the maximum and minimum diameter. Subsequent studies for different mass flow rates of water show that the optimum diameter does not vary significantly with change in mass flow rate.

Effect of sedimentation on the rheological properties of cement pastes

Rheology has been widely used to describe the flow properties of fresh cement-based suspensions. Nevertheless, the characterization and understanding of the rheological behavior of cement-based materials have become essential with the recent introduction of novel applications like digital construction in the field of civil engineering, among others. It has been well documented that concrete and mortar may suffer stability problems (i.e. the ability of the mixture to maintain homogeneous). At the scale of cement paste, this phenomenon can still arise and affect the rheological properties of the measured paste. Therefore, inaccuracies during the measurements and incorrect interpretation may occur, resulting in erroneous conclusions. This study explores the impact of sedimentation of cement particles when characterizing the rheological properties of cement paste. The w/c employed in the pastes were 0.45 and 0.35 with the addition of superplasticizer to obtain a dispersed system. The rheological properties were measured using a coaxial cylinder configuration and followed up to 180 min after the contact between cement and water. Repeated measurements were executed with and without a homogenization procedure after each application of a measuring procedure. Comparing the results shows a clear influence of sedimentation on the evolution of rheological properties with time, and the effect is more pronounced for the mixtures with high w/c and for the procedure with the larger shear rate. Therefore, it is strongly recommended to keep a measuring procedure sufficiently short in duration.