Wall Gradient Research Articles

Mechanical property enhancement in additively manufactured NiTi double-asymmetric honeycombs with bioinspired graded design

ABSTRACT The cuttlebone is known for its ability to possess high specific stiffness, progressive failure and lightweight from the porous chambered structure. Inspired by the microstructural characteristics of cuttlebone and incorporating the wall gradient design, a series of double-asymmetric honeycombs were designed and processed by LPBF. Results indicated that bionic structural units with the junction design can maintain the integrity of the residual parts after local buckling and failure, improving the load-bearing capacity. The double-asymmetric honeycomb with gradation parameter α = 2/3 achieved a maximum specific compressive strength of 70.64 MPa cm3/g. As α decreases, there is an increase in specific energy absorption and a narrowing of the hysteresis loop. The as-build honeycomb had undergone stress-induced martensite transformation during compression. The dissipated mechanical energy (ME) decreased with the increasing cycle number and the decreasing α. The results provide design guidelines and process strategies for developing high-performance honeycombs.

Mechanical factors influence β-catenin localization and barrier properties.

Mechanical forces are of major importance in regulating vascular homeostasis by influencing endothelial cell behavior and functions. Adherens junctions are critical sites for mechanotransduction in endothelial cells. β-catenin, a component of adherens junctions and the canonical Wnt signaling pathway, plays a role in mechanoactivation. Evidence suggests that β-catenin is involved in flow sensing and responds to tensional forces, impacting junction dynamics. The mechanoregulation of β-catenin signaling is context-dependent, influenced by the type and duration of mechanical loads. In endothelial cells, β-catenin's nuclear translocation and signaling are influenced by shear stress and strain, affecting endothelial permeability. The study investigates how shear stress, strain, and surface topography impact adherens junction dynamics, regulate β-catenin localization, and influence endothelial barrier properties. Insight box Mechanical loads are potent regulators of endothelial functions through not completely elucidated mechanisms. Surface topography, wall shear stress and cyclic wall deformation contribute overlapping mechanical stimuli to which endothelial monolayer respond to adapt and maintain barrier functions. The use of custom developed flow chamber and bioreactor allows quantifying the response of mature human endothelial to well-defined wall shear stress and gradients of strain. Here, the mechanoregulation of β-catenin by substrate topography, wall shear stress, and cyclic stretch is analyzed and linked to the monolayer control of endothelial permeability.

Biomimetic Study of a Honeycomb Energy Absorption Structure Based on Straw Micro-Porous Structure.

In this paper, sorghum and reed, which possess light stem structures in nature, were selected as biomimetic prototypes. Based on their mechanical stability characteristics-the porous structure at the node feature and the porous feature in the outer skin- biomimetic optimization design, simulation, and experimental research on both the traditional hexagonal structure and a hexagonal honeycomb structure were carried out. According to the two types of straw microcell and chamber structure characteristics, as well as the cellular energy absorption structure for the bionic optimization design, 22 honeycomb structures in 6 categories were considered, including a corrugated cell wall bionic design, a modular cell design, a reinforcement plate structure, and a self-similar structure, as well as a porous cell wall structure and gradient structures of variable wall thickness. Among them, HTPC-3 (a combined honeycomb structure), HSHT (a self-similar honeycomb structure), and HBCT-257 (a radial gradient variable wall thickness honeycomb structure) had the best performance: their energy absorption was 41.06%, 17.84%, and 83.59% higher than that of HHT (the traditional hexagonal honeycomb decoupling unit), respectively. Compared with HHT (a traditional hexagon honeycomb decoupling unit), the specific energy absorption was increased by 39.98%, 17.24%, and 26.61%, respectively. Verification test analysis revealed that the combined honeycomb structure performed the best and that its specific energy absorption was 22.82% higher than that of the traditional hexagonal structure.

Accurate solution of unsteadiness natural convective Maxwell nanofluid based-mineral oil flow via oscillation vertical surface: Thermic case specification

Due to its wide range of uses in numerous manufacturing, technological, and industrial processes, mineral oil (MO) is extremely significant. Mineral oil (MO) is used in the manufacture of PVC, polystyrene, as a lubricant and cutting fluid, thermoplastic rubber, glossing products, wood products, cleaning products, lamp oil, glues, toys, veterinary, cosmetic, food preparation, and other things. Due to the above applications, this article deals with the exact solution of unsteadiness naturally convective flowing of Maxwell nanofluid with radiation and uniform heat flux. Al2O3 nanoparticles are suspended in so-called mineral oil to make a homogeneous solution of nanofluid. The problem is demonstrated regarding coupled PDEs with initial and boundary conditions. Certain dimensionless factors are utilized to make the governing equation into a dimensionless structure. The solution for energy and momentum profiles is captured through the Laplace transform method. To predict heat transport and shear stress at the wall, the temperature and velocity gradient is also calculated. In the lack of the radiation factor, the relevant heat equation is simplified to the well-known solution in the literature. These solutions are greatly affected by the variety of different dimensionless variables like the thermal radiation parameter, volume fraction, and Grashof number. In a specific situation, the solutions relating to Newtonian fluids are retrieved, and a graphic juxtaposition of Newtonian and Maxwell fluids is displayed. Finally, the impact of pertinent parameters is shown by plotting graphs. The range of the pertinent parameters is 0.1≤λ≤0.4, Gr=5×K(K=1,2,3,4), 0.01≤χ≤0.04, Nr=5×K(K=1,2,3,4), t=1,3,5,7 while Pr=158 is fixed for mineral oil. The volume fraction declines the nanofluid's temperature while accelerating the velocity. The amplification in the Grashof number and radiation parameter improves the velocity. The increasing Maxwell fluid factor enhances the nanofluid's velocity. A decrease in the nanofluid's shear stress occurs, but after certain estimations of y, the nanofluid's shear stress goes up against the Maxwell fluid factor.

Construction relationship between a functionally graded structure of bamboo and its strength and toughness: Underlying mechanisms

The special functional gradient structure of bamboo determines its excellent properties of strength and toughness, which make it an excellent candidate for biomimicking purposes in advanced material design. However, the construction relationship and underlying mechanism of the functionally graded structure in the direction of the bamboo wall and its excellent strength and toughness have not been elucidated. Accordingly, this study first conducts a quantitative analysis of the relationship between the directional gradient structure of the bamboo wall layer and its chemical composition and physical and mechanical properties. To this end, in situ scanning electron microscopy (in situ SEM) was used to investigate the mechanical behavior and failure mode of the bamboo wall layer under the effect of external loads, and to investigate the structure–activity relationship between the gradient structure of the bamboo wall layer and its strength and toughness, as well as the potential mechanism of action. From the perspective of structural mechanics, the mechanical model of the bamboo wall direction under the applied load was analyzed, and the mechanism by which the bamboo wall gradient structure improves the strength and toughness of bamboo was further elucidated. The results showed that the uniform gradient distribution of the vascular bundles and their interfaces in the direction of the bamboo wall determines the gradient distribution of its chemical components and physical and mechanical properties. Together, the uneven deformation of parenchyma cells and fibers, multi-path propagation of cracks, fiber bridging, pull-out and fracture constitute the mechanism by which the bamboo gradient structure contributes to its strength and toughness. This study provides a theoretical basis and innovative ideas for the design of biomimetic advanced materials based on the bamboo wall gradient structure by revealing the potential close relationship between the excellent mechanical properties of bamboo of high strength and toughness and its functional gradient structure.

Features of left ventricle longitudinal strain in children from one to five years old, born with low, very low, and extremely low body weight

Purpose. The study assessed left ventricle longitudinal strain of the endocardial, middle, and epicardial layers in children from one to five years old, born with low, very low, and extremely low body weight.Material and methods. The study was performed in 204 children aged from one to five years; of these, 53 children were prematurely born late in pregnancy, 103 children were born very preterm, and 48 children were born healthy and full-term. The left ventricle longitudinal strain of the endocardial, middle, and epicardial layers was assessed off-line using the Speckle Tracking Imaging-2D Strain technology.Results. Disturbance of the transmural gradient strain of left ventricle wall were detected in 11.32% of prematurely born late in pregnancy children and in 16.5% of very preterm children. A decrease of left ventricle segments strain was registered in 33.96% of children prematurely born late in pregnancy and in 18.44% very preterm children. In children of the same age, born healthy and full-term, transmural wall gradient disturbances and decrease of strain in left ventricle segments were not observed. In children prematurely born late in pregnancy, the disturbance of the transmural strain gradient of left ventricle and the decrease of strain in left ventricle segments are not associated with left ventricle remodeling.Conclusion. The development of the cardiovascular system in children of early and preschool age, born prematurely with low, very low, and extremely low body weight, is characterized by disturbances in the transmural strain gradient of left ventricle wall, due to the processes of postnatal growth and development of the child’s heart, which requires monitoring on an outpatient basis in polyclinic in childhood — by a pediatric cardiologist and a pediatrician, and in adulthood — by a cardiologist and therapist.

Crashworthiness Study of 3D Printed Lattice Reinforced Thin-Walled Tube Hybrid Structures

Based on the advantages of thin-walled tubes and lattice structures in energy absorption and improved crashworthiness, a hybrid structure of lattice-reinforced thin-walled tubes with different cross-sectional cell numbers and gradient densities was constructed, and a high crashworthiness absorber with adjustable energy absorption was proposed. The experimental and finite element characterization of the impact resistance of uniform density and gradient density hybrid tubes with different lattice arrangements to withstand axial compression was carried out to investigate the interaction mechanism between the lattice packing and the metal shell, and the energy absorption of the hybrid structure was increased by 43.40% relative to the sum of its individual components. The effect of transverse cell number configuration and gradient configuration on the impact resistance of the hybrid structure was investigated, and the results showed that the hybrid structure showed higher energy absorption than the empty tube, and the best specific energy absorption was increased by 83.02%; the transverse cell number configuration had a greater effect on the specific energy absorption of the hybrid structure with uniform density, and the maximum specific energy absorption of the hybrid structure with different configurations was increased by 48.21%. The gradient density configuration had a significant effect on the peak crushing force of the gradient structure. In addition, the effects of wall thickness, density and gradient configuration on energy absorption were quantitatively analyzed. This study provides a new idea to optimize the impact resistance of lattice-structure-filled thin-walled square tube hybrid structures under compressive loading through a combination of experiments and numerical simulations.

Study on the effect of the size irregularity gradient of metal foams on macroscopic compressive properties

Size irregularity gradient and cell wall gradient, combined as the density gradient in previous studies, affect the macroscopic mechanical properties of the gradient metal foam. More and more complex mesostructures are designed and applied in metal foams, and the density gradient becomes insufficient to describe the difference in mesostructures. To explore the effect of mesostructures carefully, this study focuses on the effect of the size irregularity gradient on the macroscopic compressive properties of metal foams. A series of metal foam models were developed using the 3D Voronoi technique. These models have the same average relative densities, the same average diameters and different size irregularity gradients. Simulation results indicated that the macroscopic mechanical properties of cell wall gradient metal foams are significantly different from those of size irregularity gradient metal foams, though these models have the same relative density gradient. To explore the effect of size irregularity gradient, a theoretical model was developed to characterize the compression process from the first cell-collapse to full condensation. Theoretical results showed a linear relationship between the nominal stress and the current relative density. These findings can provide efficient guidance for the design and applications of gradient metal foams.

Quadratic mixed convective nanofluid flow past a moving yawed cylinder in the presence of thermal radiation and diffusive liquids

AbstractThe fluid flow around a yawed cylinder helps to understand the practical implications for undersea applications, such as managing transference, separating the boundary layer above submerged blocks, and suppressing recirculating bubbles. As many authors such as Roy, Chiu and Lienhard, Roy and Saikrishnan, and Revathi et al. have analyzed a boundary layer flow over a yawed cylinder, and their work sticks to only forced convection, we are interested to work on mixed convection flow. Therefore, the work of these researchers has stimulated us to work on the present article. As a result, we have examined the work on triple diffusion quadratic mixed convective nanofluid flow over a moving yawed cylinder. The impact of yaw angle, which exists due to the inclination of a vertically moving cylinder away from the origin, is mathematically investigated in the present paper by converting the governing equations into a compatible form using appropriate nonsimilar transformations and the quasilinearization technique. Nanofluids have crucial usages in science and technology, marine engineering, and applications in industries such as plastic, polymer industries, cancer home therapy, and building sciences. Many processes in new engineering areas occur at high temperatures, and knowledge of radiation heat transfer becomes very important for designing the pertinent equipment. Nuclear power plants, gas turbines, and the various propulsion devices for aircraft, missiles, satellites, and space vehicles are examples of such engineering areas. The finite difference approximation is employed to solve the resulting equations. Enhancing the magnitude of thermal radiation enhances the temperature of the liquid and the energy transport strength. However, liquid hydrogen and liquid oxygen species concentration patterns are reduced in nanofluid compared to traditional liquids. At the same time, the outcomes behave conversely in the case of their wall gradients. Furthermore, the temperature of the liquid enhances the enhancing values of Brownian motion and thermophoresis characteristics. Moreover, nanoparticle mass transport augments with enhancing yaw angle and Lewis number values. Both species' concentration profiles decrease for increasing values of yaw angle. The velocity profiles increase for increasing values of velocity ratio parameter in the spanwise and chordwise directions.

Generalized differential quadrature analysis of MHD mixed convective motion of Casson fluids past an isothermal irregular slender geometry via Cattaneo–Christov's approach

AbstractClassical Fourier's theory is well‐known in continuum physics and thermal sciences. However, the primary drawback of this law is that it contradicts the principle of causality. To explore the thermal relaxation time characteristic, Cattaneo–Christov's theory is adopted thermally. In this regard, the features of magnetohydrodynamic (MHD) mixed convective flows of Casson fluids over an impermeable irregular sheet are revealed numerically. In addition, the resulting system of partial differential equations is altered via practical transformations into nonlinear ordinary differential equations. An advanced numerical algorithm is developed in this respect to get higher approximations for temperature and velocity fields, as well as their corresponding wall gradients. For validating our numerical code, the current outcomes are compared with the available literature results. Moreover, it is revealed that the velocity field is more prominent in the suction flow situation as compared with the injection flow case. It is also found that the Casson fluid is hastened in the case of lower yield stress. Larger values of thermal relaxation parameters create a lessening trend in the temperature distribution and its related boundary layer breadth.

Role of concentration gradient in the re-initiation of H2/O2 detonation in a 90° bifurcated channel

This paper numerically investigates the effect of concentration gradient on the re-initiation process of H2/O2 detonation propagating from a vertical channel to a horizontal channel. Two different types of concentration gradient distribution are considered in this study: from fuel-rich near the upper wall to fuel-lean near the lower wall (gradient > 0), from fuel-rich near the lower wall to fuel-lean near the upper wall (gradient < 0). The results show that the detonation can be re-initiated successfully for the two different types of concentration gradient, but the formation modes of the transverse waves in the re-initiation process are different. When the gradient > 0, the transverse waves are mainly formed after the 2nd reflection. When the gradient < 0, the transverse waves are mainly formed after the 1st reflection. However, whether the concentration gradient > 0 or < 0, the transverse waves are mainly formed on the fuel-lean side. The earlier transverse waves are mainly originated from the transverse waves of the transverse detonation. The detonation speed under fuel-rich condition is much higher as predicted by 1D simulation in the current study, and a local reactant distribution from fuel-lean to fuel-rich is formed by the leading shock in the horizontal direction. Thus, the transverse waves of the transverse detonation on the fuel-lean side can overtake the Mach detonation. Furthermore, the number of the transverse waves decreases with steeper concentration gradient, leading to the cell structure more irregular and the detonation transition from multi-head mode to single-head mode.

Numerical study of axisymmetric magneto-gyrotactic bioconvection in non-Fourier tangent hyperbolic nano-functional reactive coating flow of a cylindrical body in porous media

Modern functional nanomaterials coating processes feature an increasing range of intelligent properties including rheology, biological (bio-inspired) modifications, elaborate thermophysical behaviour and complex chemical reactions which are needed for the precise synthesis of bespoke designs. Such manufacturing flow processes are extremely complex and involve both heat and multiple mass transfer (species diffusion) phenomena. Intelligent nano-coatings are particularly attractive since they exploit magnetic nanoparticles which can be manipulated by external magnetic fields. Recently, Boeing Aerospace have explored the use of micro-organisms for intelligent aircraft coatings. Mathematical models provide an excellent analysis for elucidating the response characteristics of such coating dynamics processes. With this motivation, the present analysis is indented to develop a new mathematical model to examine the axisymmetric, magnetohydrodynamic, chemically reactive, gyrotactic bioconvection flow of a tangent hyperbolic nanofluid past a cylinder saturated with Darcy porous medium, as a model of smart-coating enrobing flow. The influence of Cattaneo–Christov heat flux (non-Fourier thermal relaxation parameter), thermophoresis and Brownian motion are taken into consideration. The steady-state, boundary layer, partial differential conservation equations are rendered dimensionless via appropriate transformations, and the subsequent nonlinear, coupled, system of governing equations is numerically solved by employing implicit Keller box method. The impact of various factors such as Hartmann magnetic number, Weissenberg viscoelastic parameter, Prandtl number, non-Fourier thermal relaxation parameter, thermophoresis, Brownian motion, micro-organisms concentration difference variable, chemical reaction, bioconvection Peclet number, Schmidt number and bio-convection Schmidt number on the flow, heat transfer, mass transfer, motile density, local friction factor, local heat transfer rate, local mass transfer rate and local microorganism density number wall gradient is visualized graphically. Validation with earlier studies is included. Further validation with a finite element method (FEM) code (SMART-FEM) is presented. Results reveal that the heat transfer upsurges for amplifying the Weissenberg number and Hartmann magnetic number. Microorganism concentration distribution of the non-Newtonian nanofluid coating diminishes for amplifying the bioconvection Schmidt number and Peclet number. Magnifying the power law index parameter reduces the momentum boundary layer thickness of tangent hyperbolic nanofluid, while there is an acceleration in the fluid flow near the surface of the cylinder. Local Sherwood number rises with higher values of homogenous destructive chemical reaction parameter. The computations provide a solid benchmark for further CFD modelling.

Impacts of Thermal Conductivity and Variable Viscosity on the Dissipative Heat and Species Transport of MHD Flow in Porous Media

The investigation of dissipative heat and species diffusion of a conducting liquid under the combined influence of buoyancy forces in a moving plate is examined in the existence of magnetic field. The flowing liquid heat conductivity and viscosity are taken to be linearly varied as a temperature function. The governing derivative equations of the problem are changed to anon-linear coupled ordinary derivative equations by applying similarity quantities. The dimensionless model is solved using shooting technique along with the Runge-Kutta method. The outcomes for the flow wall friction, heat gradient and species wall gradient are offered in table and qualitatively explained. The study revealed that the Newtonian fluid viscosity can be enhanced by increasing the fluid flow medium porosity and the magnetic field strength. Hence, the study will improve the industrial usage of Newtonian working fluid.

Modelling Three Dimensional Unsteady Turbulent HVAC Induced Flow

A three-dimensional numerical model for HVAC induced flow is presented. The nonlinear set of buoyancy driven incompressible flow equations, augmented with those of energy and turbulence model is solved. Various relevant are discussed. These challenges include avoiding expensive commercial packages, modeling complex boundaries, and capturing near wall gradients. Adaptive time stepping is employed to optimize computational effort. Three-dimensional simulation requirements are addressed using parallel computations. Two-dimensional and three-dimensional results are presented to clarify the model significance. Validation is done using full scale measurements. Good agreement with velocity and temperature profiles are illustrated.

A discontinuous Galerkin method for wall-modeled large-eddy simulations

We develop an augmented discontinuous Galerkin method for wall-modeled large-eddy simulations. This method is motivated by the enrichment method that has been formulated for finite-element method, by statistically augmenting the variational solution of the near-wall element with a simple wall function to model the effects of the unresolved momentum-carrying near-wall eddies on the resolved scales. An explicit model is employed to model the subgrid-scale stresses. It is shown that this approach improves the solution accuracy on significantly underresolved grids and reduces spurious oscillations that occur in the presence of strong wall gradients on coarse grids with high-order DG methods. The proposed method is applied in low-Mach-number plane channel flows over a range of Reynolds numbers to examine effects of mesh resolution, polynomial order, solution-augmentation, and the SGS closure on the model performance. The results show that the proposed approach reproduces the log-law profile for different flow conditions, even at extreme Reynolds numbers, and yields improved predictions with increasing polynomial order. In addition, the capability of the present DG-based WMLES framework for computations of complex flows is demonstrated in LES of a shock-induced boundary-layer separation for the transonic bump experiment by Bachalo & Johnson (AIAA J., 24, 1986).

Energy conservation of nanofluids from a biomagnetic needle in the presence of Stefan blowing: Lie symmetry and numerical simulation

Thermal energy management associated with the transmission of heat is one of the main problems in many industrial setups (e.g. pharmaceutical, chemical and food) and bio-engineering devices (e.g. hospital ventilation, heating, cooling devices, heat exchanger and drying food, etc). The current study aims to examine thermo-bioconvection of oxytactic microorganisms taking place in a nanofluid-saturated needle with the magnetic field. Stefan-blowing is applied. The leading equations of continuity, momentum and energy, species transport equations for oxygen concentration and population density of microorganisms are reduced dimensionless and Lie symmetry group transformations are used to generate appropriate invariant transformations. The resulting similarity boundary value problem (in which the blowing parameter is coupled with concentration) have been simulated using MATLAB (2015a) bvp5c built in function. The impact of the emerging factors on the nondimensional velocity, temperature, nanoparticle concentration and motile microorganism density functions and their slopes at the wall, are pictured and tabulated. Justification with published results are included. It is found that all physical quantities decrease with Stefan blowing and increase with power law index parameter. With elevation in magnetic field parameter i.e., Lorentzian drag force, the friction factor reduces while the local Nusselt number, local Sherwood number, and the local motile microorganism density wall gradient increase. Present study could be used in food and pharmaceutical industries, chemical processing equipment, fuel cell technology, enhanced oil recovery, etc.

Hydromagnetic Flow of Prandtl Nanofluid Past Cylindrical Surface with Chemical Reaction and Convective Heat Transfer Aspects

Thermodynamical attributes of non-Newtonian fluids over stretched surfaces have gained pervasive essence due to extensive utilization in extruding plastic sheet procedures, liquid film condensation, glass blowing, paper production, biopolymer cylinder coatings, and so forth. So, currently communication is aimed to candidly explicate flow characteristic of Prandtl fluid generated by axial stretching of cylindrical surface. Mathematical modelling by using conservation laws of momentum, energy and concentration fields containing the aspects of magnetic field, convective heating, and chemical reaction are presented initially in the form of partial differential expressions. Later on, these attained PDEs are transmuted into nonlinear ordinary differential equations with implementation of similarity variables. Numerical approach renowned as shooting technique with improved coefficient of the Runge–Kutta (R–K) method by Cash and Karp is used to access accurate solution. Linear curved fitting analysis is also performed to analyze results. Influence of flow-controlling parameters on associated profiles is revealed through graphical visualization. Stream line plots representing flow behavior of Prandtl fluid versus different magnitudes of the curvature parameter are adorned. Variation in friction drag force at wall, heat flux, and concentration gradient are evaluated through numerical data and with interpolation of linear curved fittings. It is deduced from results that increasing curvature parameter momentum and temperature distributions enriches whereas skin-friction coefficient depicts reverse pattern. It is also inferred that temperature shows incrementing deviation in the absence of chemical reaction whereas concentration profiles exhibit reduction with consideration of influence of chemical reaction parameter. Magnetic field tends to reduce the velocity and create thinness of boundary layer thickness.

Nonlinear mixed convective nanofluid flow about a rough sphere with the diffusion of liquid hydrogen

In this paper, a study of steady nonlinear mixed convective nanoliquid flow about a rough sphere with the diffusion of liquid hydrogen is considered. The governing equations are first modelled from the current physical problem, and then, suitable non-similar transformations are applied to non-dimensionalize the model equations. The resultant nonlinear dimensionless equations are linearized by using the Quasilinearization technique. The resulting linear system of differential equations are approximated by finite differences to obtain numerical solutions. The impacts of different physical parameters involved in the problem, such as the distribution of velocity, temperature, nanoparticle volume fraction and species concentration are studied. The analysis of wall gradients is carried out, which discusses the skin friction, heat and mass transfer rates defined at the surface of the sphere. The graphs of numerical results are plotted, which reveal that the flow velocity is increased, while the fluid temperature is reduced, for increasing values of the roughness parameter. The presence of mixed convection parameter delays the occurrence of separation in the boundary layer in both the cases of an ordinary fluid and a nanofluid. For increasing values of the Schmidt number, the species concentration decreases, while the rate of mass transfer increases. Moreover, the thermophoresis parameter of the nanofluid increases the fluid's temperature, while it decreases the heat transfer rate. The fluid's temperature reduces for larger values of nonlinear convection parameter. Also, the flow velocity increases for the diffusion of liquid hydrogen.

An instability mechanism for channel flows in the presence of wall roughness

Abstract

Inviscid, Incompressible, Axisymmetric, Annular Jet Impingement

Abstract An analytical Bessel-sine series solution is presented for inviscid, incompressible, axisymmetric, annular impinging jets. The inflow velocity profile is relatable to an aircraft engine thrust reverser, and has a velocity deficit as well as nonzero vorticity function at the inner radius. As a consequence, inviscid recirculation appears at the impingement corner, the strength of which is made determinate by assuming a local patch of constant vorticity function. Results are first compared against prior round jet solutions, with rigorous convergence and accuracy assessment, before extension to annular impinging jets. Finally, while the Bessel-sine series are consistent with the governing equations and boundary conditions, computational issues arise with steep near wall gradients of a composite parameter that is inherent to the methodology, necessitating extremely fine mesh resolution. A hybrid of finite differences and Bessel series is proposed to address these numerical issues.