bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved Power for Wind Farm Savonius Rotors: Effect of Blade Shape and Rotors Position
Authors: Filali Abdelkader , Khezzar Lyes , Semmari Hamza
Published: October 2020

In the present study the effect of distance between five vertical Savonius rotors « Gap » on the total performance of the wind farm rotors is investigated. Numerical computations are conducted for a single Savonius turbine, and for the five clustered turbines aligned in perpendicular direction with respect to the upstream wind velocity. The study is carried out using ANSYS FLUENT commercial code and the moving mesh approach for the rotating zones is used. The turbulence model adopted in this work is the k-ω shear stress transport (SST) model. Numerical approach was first validated with previously published experimental and numerical data for a single rotating Savonius rotor case with semi-circular blades. Then, an improvement process based on the modification of the blades profiles to an elliptical shape was adopted. Subsequently, the change in distance between the five vertical Savonius rotors « Gap » has been considered with values of 0.25, 1 and 1.4 times the rotor radius (R). Results show that the Gap = 1R provides the optimum power coefficient for the wind farm rotors. However, the generated wake zone behind the five aligned rotors for this value is more important in particular for the 90 ° angle of the advanced and returned rotor blades. The field efficiency defined by the total power ratio of the five isolated rotors to the total power of the wind farm with five Savonius rotors is around 67%. All these geometrical considerations and propositions made it possible to define an optimal wind farm rotors arrangement.
Numerical Performance Predictions of Artificial Intelligence-Driven Centrifugal Compressor Designs
Authors: Fritsche Manuel , Epple Philipp , Kubrak Boris , Gast Stefan , Delgado Antonio , Barannik Valentyn
Published: October 2020

This paper demonstrates the application of artificial intelligence-driven turbomachinery design, its numerical performance predictions and their numerical validation. A common problem in the industrial application of turbomachinery is that readily available turbomachines are not necessarily matching the desired performance targets (performance characteristics) required for a specific application. Many machines operate under off-design conditions and hence are not operating at maximum efficiency. Traditional numerical analysis and response-driven optimization methods are ineffective and still too time-consuming and are particularly sensitive to changing performance targets. Most commercially available optimization algorithms are based on maximizing or minimizing a response function, for instance the standard error from a desired target performance characteristic of a turbomachine, by changing design variables.

This work uses a newly developed artificial intelligence-based approach that is not dependent on the specific design target using the turbomachinery design software AxSTREAM from SoftInWay. Here a neural network was trained within a constraint design space by many samples of design variables and their respective numerical performance predictions. For the numerical verification of the designs the solver Simcenter STAR-CCM+ from Siemens was used. Subsequently the trained neural network was applied to generate a set of design parameters that satisfied the physically feasible desired target performance characteristics very fast. This trained neural network enabled an effective reversal of the traditional iterative design process where now the desired target performance characteristics became the input and the geometry became the output, turning it into a generative inverse design process. This method was applied to generate a centrifugal compressor design within a given geometrically and physically constraint design space. A specific desired target performance characteristic was chosen. The generated designs and results are presented in detail.
Evaluation of Frictional Pressure Drop Correlations During Flow Boiling of Refrigerants in Micro-Fin Tubes
Authors: Tang Weiyu , Li Wei , Zhou Jianxin
Published: October 2020

Due to the widely commercial application of micro-fin tube and eco-friendly refrigerants, more general frictional pressure drop correlations is demanded for better prediction, and this study is aimed at compared existing correlations and provide guides for the furthermore improvement. Experimental data points for frictional pressure drop during flow boiling of refrigerants in horizontal micro-fin tubes were extracted from literature and our previous experimental work to evaluate numerous existing frictional pressure drop correlations and specify their applicability to meet the urgent demand of extensive application of eco-friendly refrigerants. The database consists of 949 data points covering eleven refrigerants (R1233zd(Z), R410A, R1234ze(E), R410A, R22, R32, R1234ze(Z), R22, R134a, R245fa and R1234yf included), and the involved operation conditions are as follows: mass velocity 94–888 kg m−2s−1, vapor quality 0.04–0.99, heat flux 3.9–85.2 kW m−2, and equivalent diameter 2.12–11.84mm. Eight existing general frictional pressure drop correlation including Cavallini et al., Kuo and Wang, Wongsangam et al. and Rollman and Spindler correlation were evaluated against the present database. In addition, the Churchill et al. model was employed in several correlation to improve their performance. It was found that none of these correlations was capable of providing a satisfactory prediction for a general operation condition. A detailed predictive ability of these correlation against specific work fluids were given for reference, and their individual parametric-trend predictive ability were also compared under varied operating conditions using several datasets.
Performance Assessment of a NACA-2412 Surrogate Model Using Non-Intrusive Polynomial Chaos Method
Authors: El Dine Matbouli Houssam , Fayssal Iyad
Published: October 2020

Computational Fluid Dynamics (CFD) models have been regarded as inevitable tools in the design of various aerodynamics applications like formula 1 cars, wind turbines, airfoil design, and many others. Such models rely on applying advanced numerical methods to solve the set of Navier-Stokes equations and other auxiliary models to quantify the aerodynamics performance, such as lift and drag in airfoil applications. However, currently adopted advanced mathematical models that are used to predict airfoil performance, though are essential tools in the advancement of aviation industry, incur large computational costs. As a primary step, an approximate model of an airfoil is built for the sake of reducing computational cost while preserving accuracy. The approximate model is based on creating a simplified algebraic model which is suitable then to perform aerodynamic design optimization rather than solving the highly non-linear set of continuity and momentum equations. In this work, the non-intrusive polynomial chaos expansion (NIPC) technique is employed on a NACA-2412 airfoil. The main objective of this research is to investigate the performance of the NIPC model with different orders on solution accuracy. A methodology is designed by first developing a full CFD model of the NACA-2412 airfoil. An experimental setup of the airfoil was then prepared with the variations of lift and drag coefficients under different operative conditions were reported. The experimental data were used to validate the numerical results generated by the CFD simulations. The surrogate model was then constructed via the NIPC technique. The performance of the surrogate model was then benchmarked with CFD results under different flow and operating conditions. Analysis was also performed to investigate the effect of polynomial order on the solution accuracy. Results showed that for a given data set size, increasing the order of the polynomial would deteriorate the solution accuracy. At a certain order k, the analytical solution starts diverging especially for values of angle of attack close to −60 and 60°.
Novel Propulsion System for VTOL Aircraft Based on Cycloidal Rotors Coupled With Wings
Authors: Rodrigues F. F. , Habibnia M. , Pascoa J.
Published: October 2020

Aircraft being capable of Vertical Take-off and Landing (VTOL) and hover are increasingly emerging in various critical and routine applications. Rescue missions in roads and environmental disasters, observance and monitoring-based carriers, surveillance and payload carriage in environments that require high maneuverability and controllability are just a few examples in which this type of aircraft is essential. Helicopters are the most typical aircraft in this kind, but concerning the thrusting mechanism, several alternatives are yet in hand. The tendency to equip aircraft with cycloidal rotors (shortly say, cyclorotors) as means of Vertical Take-Off and Landing thrusters has increased in recent years. These devices present several advantages such as considerably lower noise production and more stable hover and vertical displacements in comparison with conventional screw propellers as used in helicopters. In the present work a novel concept of propulsion system combining two cycloidal rotors with a pair-wing system is presented. A double wing assembly is designed to place in between the two cyclorotors on each side of the aircraft. The bottom wing is intended to divide the flow in two separate portions through the downwash region of the front cycloidal rotor. To improve the efficiency of this propulsion system, the implementation of plasma actuators in the pair-wing system will be experimentally studied. The concept behind this novel propulsion system is explained and numerical and experimental results, that support its operation concept, are presented.
Numerical Simulation of Non-Stationary Turbulent Flows Using Double Exponential Dynamic Time Filtering Technique
Authors: Jamal Tausif , Bhushan Shanti , Walters D. Keith
Published: October 2020

Temporally varying turbulent flows are of considerable interest in complex engineering problems such as combustion, hydrodynamics, and hemodynamics. These types of flows are often associated with complex flow physics such as varying mean pressure gradients, interactions of different scales of motion, and complex boundary layer separations. Hybrid Reynolds-averaged Navier-Stokes (RANS)/Large-Eddy Simulation (LES) methods have recently shown promise for accurate and computationally efficient simulation of these flows. One such method is the dyanamic hybrid RANS-LES (DHRL) model which has been demonstrated for numerous statistically stationary turbulent flows. More recently, it has been shown that Exponential Time-Averaging (ETA) and Dynamic Time Filtering (DTF) methods for obtaining resolved flow statistics have significantly improved the predictive capabilities of the Dynamic Hybrid RANS-LES (DHRL) model performance for a non-stationary turbulent flows with periodically time-varying statistics. However, for non-periodic temporally evolving flows with monotonically varying statistics, a more suitable alternative is desired. In this study, the performance of the Dynamic Hybrid RANS-LES (DHRL) model with a double exponential dynamic time filtering (DDTF) methodology is evaluated against a Reynolds-Averaged Navier-Stokes (RANS) model, a conventional Hybrid RANS-LES (HRL) model, implicit LES, and the DHRL model with DTF for a pulsating channel and a temporally-varying turbulent mixing layer. Model performance is evaluated based on comparisons to existing experimental and Direct Numerical Simulation (DNS) results. A comprehensive analysis of the results highlights key similarities and differences between the models and indicates that the use of a double exponential DTF technique improves the accuracy of the baseline DHRL model. It is concluded that the DDTF is a useful alternative to simulate unsteady non-periodic temporally evolving turbulent flows.
Order of Accuracy and Sensitivity to Freestream Conditions of a Modified k-ω Turbulence Model for High-Order Finite Element Methods
Authors: Bagheri-Sadeghi Nojan , Helenbrook Brian T. , Visser Kenneth D.
Published: October 2020

Using turbulence models with finite element methods (FEM) can be challenging as the turbulence variables can assume negative non-physical values and hinder solution convergence. A modified k–ω model was recently proposed by Stefanski et al. (2018) to be used with finite element solvers of compressible flows. The model overcomes this issue by replacing k and ω with working variables that ensure positivity and smoothness of k and ω. In this work the applicability of this model for high-order FEM simulations of incompressible flows was examined. The model was implemented for incompressible flow in an hp-FEM solver using streamline Petrov-Galerkin discretization and was validated and verified using a fully-developed channel flow and a boundary layer flow over a flat plate. Several aspects of the turbulence model behavior were studied. These included the possibilitty of getting orders of accuracy higher than 2, and the model’s sensitivity to freestream values of k and ω. The results suggested that higher orders of accuracy are possible when quadratic and quartic basis functions are used. However, this depended on the way the boundary condition for ω was defined. The commonly used boundary condition for ω, which depends on the wall-distance of the first grid point resulted in poor orders of accuracy compared to the so-called slightly-rough-surface boundary condition which is independent of the wall distance of the first grid point. Additionally, results indicated that increasing the nondimensional wall distance of the first gridpoint makes it more sensitive to the value of ω on the wall. Adding a cross-diffusion term to the transport equation for ω is known to significantly improve the accuracy of turbulence model prediction for certain flows and reduce the sensitivity of the original k–ω model to freestream values of turbulence variables. Following a more recent version of k–ω model, this term was added to the turbulence model and some other modifications including a different production term with a stress-limiter were applied. The drag coefficient of the flat plate from the new turbulence model showed similar sensitivity to the freestream values of turbulence variables as the model of Stefanski et al. (2018).
A Correction to the Barotropic Model of Gaseous Cavitation in Choked Converging-Diverging Nozzle Flows
Authors: Waldrop Michael , Thomas Flint
Published: October 2020

The Barotropic Cavitation Model describes the behavior of a homogeneous mixture of liquid and gas bubbles (gaseous cavitation) as it traverses a converging-diverging (CD) nozzle. Its normal shock formulation makes reliable and accurate predictions of streamwise static pressure distribution from the nozzle inlet to just downstream of the throat and in the diverging section as the flow approaches the nozzle outlet. It fails in the intermediate portion of the divergence with maximum pressure prediction errors (as a fraction of nozzle inlet pressure) roughly equivalent to the back pressure ratio (as high as 0.46). A correction to the streamwise static pressure distributions predicted by the normal shock solution of the Barotropic Cavitation Model is proposed, applied and compared to experiments with aerated and non-aerated cavitation in several fluids. When used to simulate aerated cavitation of dodecane in a CD nozzle it predicts the location of first disagreement between the normal shock solution and experimental static pressure measurements within 4% of nozzle length. A polynomial curve fit between this predicted point (xcorr) and the normal shock location (xshock) then reduces maximum prediction error for static pressure in the correction region to no more than 0.11 (as a fraction of inlet pressure) for the aerated dodecane cases examined. For non-aerated gaseous cavitation in dodecane, water or JP8 jet fuel this error ratio does not exceed 0.13 and typical values are less than 0.07.
Large Eddy Simulation of Slurry Erosion in Submerged Impinging Jets
Authors: Wang Qiuchen , Huang Qiyu , Sun Xu , Zhang Jun , Karimi Soroor , Shirazi Siamack A.
Published: October 2020

Submerged impingement jets are widely used in erosion/corrosion investigation as it is easy to control standoff distance as well as jet angle and flow velocities in experiments. In addition to experiments, typically Computational Fluid Dynamics (CFD) technique has been used to simulate slurry flow in this geometry to investigate erosion process and develop and verify erosion equations. This is done by solving Reynolds Averaged Navier-Stokes (RANS) equations with turbulence models, time-averaged fluid flow is revealed, and thus time-averaged erosion rate can be obtained by tracking particles in the fluid flow field. The current work shows that this seemingly simple flow displays unsteady flow structures in the stagnation zone of the flow field and its effects on erosion process was unclear. In this study, Large Eddy Simulation (LES) is used to simulate unsteady fluid flow in different impingement jets in Eulerian scheme. Then particles are injected randomly in the surface and tracked transiently to simulate unsteady erosion process in Lagrangian scheme. Finally, an erosion equation is used to calculate solid particle erosion rates. The LES Eulerian-Lagrangian erosion modeling are further validated by experimental fluid velocities and erosion profile measured before. It was found the accuracy of erosion prediction of small particles can be improved and unsteady properties can be well resolved by using this method.
Lattice Boltzmann Method Based on Large-Eddy Simulation (LES) Used to Investigate the Unsteady Turbulent Flow on Series of Cavities
Authors: Mehrez Insaf , Gheith Ramla , Aloui Fethi
Published: October 2020

A numerical study is proposed to analyze the turbulent flow structures. This paper aims to determine the effect of the series of the cavities. The configuration is similar to that represented by two walls with infinite width, one of which is mobile and the other is fixed. The series of cavity are placed on the fixed wall. The objectives are to study the aero acoustic capabilities of LBM and to build and to assess the efficiency of the Lattice Boltzmann Equation (LBE) as a new computational tool to perform the Large-Eddy Simulations (LES) for turbulent flows. In the first part, the background of LBM is presented and the construction of Navier-Stokes equations from Boltzmann equation is discussed. The LBM-LES model for solving transition is developed and turbulence modeling is implemented. In the second part, the dynamics of the flows in the vicinity of cavities with symmetric or asymmetric edges are considered, to then discuss the oscillation phenomenon. The effect of the geometric of the cavity and the Reynolds numbers were studied to investigate the fluid flow dynamics. We were focusing on the dynamics of asymmetric deep cavity flows, to put forward the topology of the cavity flow and to highlight the effects of dissymmetry and aspect ratio.
Optimal Design of Thermally Stressed Turbocharger Blade Using Response Surface Method
Authors: Jung Kuk Jin , Lee Jin-Woo , Kim Youn-Jea
Published: October 2020

RI turbine is a device that rotates the shaft by the working fluid enters the radial direction and exit in the axial direction. It is mainly used in automobile turbochargers and helicopters. Turbocharger is an important part of reducing fuel use as part of the vehicle’s power source. It is largely divided into compressor part and turbine part, and rotates the compressor by the power received from the turbine part. The gas emitted after combustion in the engine is the working fluid and the driving force for rotating the turbine. In this process the turbine is directly exposed to hot combustion gases. There is an intermediate cooling process, but the trend is to reduce and simplify it. Therefore, thermal stress analysis and optimal design process for the blades of the turbocharger turbine is required. In this study, the optimal design of turbine blade was carried out to alleviate thermally vulnerable areas without compromising efficiency through CFD (computational fluid dynamics) and RSM (response surface method). After preliminary design, numerical analysis was used to identify thermal weakness, and the optimal design was carried out with vulnerable area and efficiency as output parameters. As a result, a blade design that can lower the temperature from the weakness was derived, and a thermal optimization design process of the RI turbine was presented.
Fabrication of a Microchannel Device With a Three-Dimensional Pore Network Using a Sacrificial Sugar Template
Authors: Zhang Haipeng , Palmon Tomer , Kim Seunghee , Ryu Sangjin
Published: October 2020

Porous media compressed air energy storage (PM-CAES) is an emerging technology that stores compressed air in an underground aquifer during the off-peak periods, to mitigate the mismatch between energy supplies and demands. Thus, PM-CAES involves repeated two-phase fluid flow in porous media, and ensuring the success of PM-CAES requires a better understanding of repetitive two-phase fluid flow through porous media. For this purpose, we previously developed microfluidic channels that retain a two-dimensional (2D) pore network. Because it was found that the geometry of the pore structure significantly affects the patterns and occupational efficiencies of a non-wetting fluid during the drainage-imbibition cycles, a more realistic microfluidic model is needed to reflect the three-dimensional (3D) nature of pore structures in the underground geologic formation.

In this study, we developed an easy-to-adopt method to fabricate a microfluidic device with a 3D random pore network using a sacrificial sugar template. Instead of using a master mold made in photolithography, a sacrificial mold was made using sugar grains so that the mold could be washed away after PDMS curing. First, we made sugar templates with different levels of compaction load, and found that the thickness of the templates decreased as the compaction load increased, which suggests more packing of sugar grains and thus lower porosity in the template. Second, we fabricated PDMS porous media using the sugar template as a mold, and imaged their pore structure using micro computed tomography (micro-CT). Pores within PDSM samples appeared more tightly packed as the compacting force increased. Last, we fabricated a prototype PDMS channel device with a 3D pore network using a sugar template, and visualized flow through the pore network using colored water. The flow visualization result shows that the water was guided by the random pores and that the resultant flow pattern was three dimensional.
Wake Properties of an Oscillating Airfoil Undergoing Small Amplitude Asymmetric Oscillation
Authors: Stutz Colin , Bohl Douglas , Green Melissa
Published: October 2020

The flow around, and in the wake of, pitching airfoils has received renewed interest due to its potential for thrust production at low Reynolds numbers. Past work has centered on the flow fields generated by symmetric pitching of the airfoil. Studies investigating the effects of asymmetric motion are more limited. This work focuses on the wake patterns developed due to asymmetric pitching. Particle Image Velocimetry (PIV) is used to quantify the flow field around a NACA0012 airfoil undergoing small amplitude, high frequency asymmetric pitching. The airfoil is pitched about the quarter chord point with an amplitude of ±4° at reduced frequencies of k = 2.6–5.8 at a Rec = 12000. Pitching symmetries of 50/50, 40/60 and 30/70 are studied, where the symmetry is defined by the fraction of the cycle spent in the pitch down versus pitch up motion. The data show that for the 50/50 (symmetric) motions two alternating sign vortices, with equivalent strength, are formed as expected. The asymmetric cases show that a single vortex is formed during the “fast” portion of the pitching motion. Multiple vortices are formed during the “slow” portion of the pitching motion. The number of secondary vortices and the downstream evolution of the vortices depends on the symmetry value. In some cases they remain isolated but orbit other vortical structures, while in other cases they pair with other vortical structures, and finally when the reduced frequency and asymmetry values are high enough the vortex array shows interaction between cycles.
Effect of Head Posture on Airflow and Pressure Behavior of Human Upper Airway During Snoring
Authors: Wang Junshi , Han Pan , Tang Ruixuan , Tang Hong , Kwon Younghoon , Xi Jinxiang , Dong Haibo
Published: October 2020

Snoring is a common breathing disorder during sleep. It is hypothesized that head posture during sleep could change the bending angle and the cross-sectional area of the airway, which could cause changes in airflow and aerodynamic pressure during sleep. In this work, an experiment-driven computational study was conducted to examine the aerodynamics and pressure behavior in human upper airway during snoring. An anatomically accurate human upper airway model associated with a dynamic uvula was reconstructed from human magnetic resonance image (MRI) and high-speed photography. The airway bending at different head posture and the corresponding change in airway cross-sectional area are modeled based on measurements from literature. An immersed-boundary-method (IBM)-based direct numerical simulation (DNS) flow solver was adopted to simulate the corresponding unsteady flows of the bent airway model in all their complexity. Analyses were performed on vortex dynamics and pressure fluctuations in the pharyngeal airway. It was found that the vortex formation and aerodynamic pressure were significantly affected by the airway bending. A head-neck junction extension posture tends to facilitate the airflow through the upper human airway. Fast Fourier transformation (FFT) analysis of the pressure time history revealed the existence of higher order harmonics of base frequency with significant pressure amplitudes and energy intensities. The results of this study help better understand the pathology of snoring under the influence of head posture from an aerodynamic perspective.
On the Application of the Full Reynolds Stress Model for Unsteady CFD in Hydraulic Turbomachines
Authors: Casartelli Ernesto , Mangani Luca , Roos David , Del Rio Armando
Published: October 2020

The computation of the characteristic of hydraulic machines, both in pump and turbine mode, needs, when performed over a wide operating range, to take into account turbulence anisotropy. This because highly separated flows largely deviate from isotropic turbulence structures as assumed in RANS eddy viscosity models with the Boussinesq approximation. In this paper CFD computations were performed with anisotropic turbulence models in order to capture the characteristic and investigate flow structures phenomena. Experimental results are compared against the CFD simulations in order to validate the results. Specific occurring phenomena are highlighted and more complex flow structures are evident compared to those computed with standard eddy viscosity models. A in-house pressure based coupled solver was used for the CFD simulations. The code is a finite volume polyhedral CFD solver implemented in a C++ framework with the possibility to implement implicit and coupled algorithms. Second moment closure turbulence model have been successfully implemented with a standard and novel fully coupled algorithm. In the paper the advantage of the novel algorithm is presented for industrial applications. The fully coupled approach for the Reynolds Stress model allows stable simulations of transient and steady state hydraulic machines at any operating point, opening also new opportunities in obtaining high accurate results for anisotropic turbulent flows without the usage of hybrid LES/RANS models and without the model limitation of standard eddy viscosity models.
Modeling Microbubble Microvessel Interaction for Sonoporation Application
Authors: Gnanaskandan Aswin , Deng Xiaolong , Hsiao Chao-Tsung , Chahine Georges
Published: October 2020

Modeling the dynamics of microbubbles inside confined spaces has many potential applications in biomedicine, sonoporation being one classic example. Sonoporation is the permeabilization of a blood vessel’s endothelial cell membrane by acoustic waves in order to non-invasively deliver large-sized drug molecules into cells for therapeutic applications. By controlled activation of ultrasound contrast agents (UCA) in a microvessel, one can achieve better permeabilization without causing permanent damage associated with high intensity ultrasound. This paper considers numerically, the fluid-structure interactions (FSI) of UCA microbubbles with a microvessel accounting for large deformations. The modeling approach is based on a multi-material compressible flow solver that uses a Lagrangian treatment for numerical discretization of cells containing an interface between two phases and an Eulerian treatment for cells away from material interfaces. A re-mapping procedure is employed to map the Lagrangian solution back to the Eulerian grid. The model is first validated by simulating a microbubble oscillating due to an imposed ultrasound inside a microvessel and good agreement with experiments is obtained for both the bubble and vessel dynamics. The effect of vessel elasticity is then studied and it is shown that increasing the vessel elasticity damps the bubble oscillations. Then the effect of placing the bubble away from the axis of vessel is studied and it is shown that bubbles closer the vessel wall are capable of creating maximum deformation on the wall compared to those away from the wall.
Two-Dimensional CFD Study on the Enhancement of Tube Bank Configuration Heat Exchanger
Authors: Elmekawy Ahmed M. Nagib , Shahin Abdalrahman M. , Ibrahim Alaa A. , Al-Ali Sara
Published: October 2020

Two-dimensional simulations are carried out for a heat exchanger to study the cross-flow behavior in a circular tube bank in a staggered configuration in case of bare cylinders and cylinders with splitter plate attachment. A considerable performance evaluation of the heat exchanger with splitter plate can be achieved by studying the heat transfer and the pressure drop of the flow. Numerical simulation results carried out from this study are compared to experimental results. The numerical investigation has been established to study the effect of splitter plate on the heat exchanger thermal performance as there were no previous studies performed on the optimization of the splitter thickness. The study also illustrates the effect of splitter plate thickness variation on pressure drop and heat transfer for different Reynolds number.
Passive Bristling of Shark Skin Scales at the Micro-Level: A Fundamental Viscous Flow Study to Understand the Separation Control Mechanism
Authors: Prichard Reid , Strasser Wayne , Cherok Chad , Kacinski Robert , Lang Amy
Published: October 2020

In this paper, we use a CFD analysis of a simplified, 2D geometry to study the ability of mako shark denticles to mitigate flow separation. We represent the viscous sublayer below a turbulent boundary layer streak as a Couette flow. Incipient separation is simulated by balancing upper wall velocity and adverse pressure gradient to achieve zero net mass flow, and we add various denticle geometries to study their effects. Each modeled denticle protrudes at an angle from 15° to 85° and sublayer blockage ratio from 0.05 to 0.85. Through variation of fluid properties and boundary conditions, we show that the anti-flow-reversal abilities of a single, bristled shark denticle are independent of Reynolds number, and we investigate the effect of the denticle at cases other than zero net mass flux. Based on these results, we create a new relationship to predict separation inhibition. These conclusions are highly generalizable and represent previously undiscovered universal behavior.
Effect of Heat Flux on Bubble Coalescence Phenomena and Sound Signatures During Pool Boiling
Authors: Negi Akshat , Rishi Aniket M. , Kandlikar Satish G.
Published: October 2020

Boiling heat transfer is extensively used in various industrial applications to efficiently dissipate a large amount of heat by maintaining lower surface temperatures. The maximum heat flux dissipated during boiling is limited by the critical heat flux (CHF) and limited visualization of the boiling surface limits the identification of the impending CHF condition to rely on temperature monitoring alone. The study presented here focuses on developing a method for analyzing and identifying acoustic signatures throughout the nucleate boiling regimes that are indicative of the boiling state of the heater surface. The bubble nucleation and coalescence along with bubble collapse at the liquid-vapor interface leads to variation in acoustic emission patterns during boiling. These sound waves are studied and acoustic signatures that are representative of the impending CHF are identified over plain and enhanced copper substrates with water as the working fluid. During pool boiling study, it was observed that sound was dominant in two frequency regions (400–500 Hz dominant throughout nucleate boiling and 100–200 Hz dominant at heat fluxes > 100 W/cm2). However, just before CHF, a sudden drop in amplitude was observed in the high frequency region (400–500 Hz), while the amplitude in low frequency region (100–200 Hz) continued to rise. It was concluded that this acoustic study can be used as a tool to predict the approaching CHF condition.
An Experimental Study of R134a Condensation Heat Transfer in Horizontal Smooth and Enhanced Tubes
Authors: Guo Yu , Gu Zong-bao , Ayub Zahid , Li Wei , Ma Xiang , He Yan , Kukulka David J.
Published: October 2020

In this paper, the condensation heat transfer characteristics of R134a inside enhanced tubes using two type of surface structures with different materials was investigated, which were then compared with plain tubes under the same test conditions. The enhanced tubes were: 1EHTa tube with dimpled and petal arrays structure and 1EHTb tube with protrusion and similar petal arrays structure. The experiment was conducted for a mass flux ranging from 100 to 200 kg m−2 s−1 with saturation temperature of 318 K. The inlet and outlet vapor qualities were fixed at 0.8 and 0.2, respectively. The test tubes had the same outer diameter of 12.7 mm. Results showed that the dimpled and protruded surface tubes enhanced the convection condensation heat transfer and the heat transfer coefficient was 1.4 to 1.6 times higher than that of the smooth tube. Heat transfer enhancement of the 1EHTa and 1EHTb tube was mainly due to the complex roughness surface structures that created swirling and increased the interface turbulence. Enhanced tubes exhibited higher performance factors compared to the smooth tube. The average performance factor was 1.3–1.5. As the flow rate increases, there is no significant increase in the condensation heat transfer coefficient. The pressure drop penalty increased with mass flux. Compared with smooth tube, the pressure drop penalty of enhanced tube was larger.
Slip in the Presence of Semi-Circular Menisci Between Parallel Ridges
Authors: Steigerwalt Lam Lisa , Muzychka Yuri
Published: October 2020

Surfaces which are structured on the micro- and nanoscale to resist wetting are being considered for internal flows due to their drag reducing properties in applications such as electronics cooling and lab-on-chip. Here, an expression is developed to characterize the hydrodynamic slip in a laminar flow which occurs near the surface for the case when positive meniscus curvature is present. The surfaces considered are composed of ridges oriented parallel to the flow. Curvature of the meniscus, which resides between the liquid in the Cassie state and the gas trapped in cavities between the ridges, results from the pressure difference between the liquid and the gas. The meniscus is considered shear free. The no slip condition exists at the tips of the ridges. Conformal maps from the literature are used to derive an expression which is a function of cavity fraction of the surface. The positive protrusion angle is 90 degrees. Cavity fractions range from 0 to 75%.
A Comparative Analysis of the Tumor Pathology and the Metabolic Heat Generation of Growing Malignant Tumors
Authors: Owens Alyssa , Godbole Manasi , Dabydeen Donnette , Medeiros Lori , Phatak Pradyumna , Kandlikar Satish
Published: October 2020

Cancer is one of the most debilitating diseases in the world, affecting over 9.6 million people worldwide every year. Breast cancer remains the second largest cause of death in women. Despite major advances in treatment, over 40,920 women died of breast cancer in 2018 in the United States alone. Early detection of abnormal masses can be crucial for diagnosis and dramatically increase survival. Current screening techniques have varying accuracy and perform poorly when used on heterogeneously and extremely dense breast tissue. Infrared imaging has the potential to detect growing tumors within the breast based on thermal signatures on the breast surface by imaging temperature gradients induced by blood perfusion and tumor metabolic activity. Using clinical patient images, previous methods to estimate tumor properties involve an iterative algorithm to estimate the tumor position and diameter. The details from the MRI are used in estimating the volumetric heat generation rate. This is compared with the published values and the reasons for differences are investigated. The tumor pathology is used in estimating the expected growth rate and compared with the predicted values. The correlation between the tumor characteristics and heat generation rate is fundamental information that is needed in accurately predicting the tumor size and location.
Caloric restriction extends lifespan of mothers at the expense of offspring survival in a predatory mite (Neoseiulus cucumeris)

Authors: Lee Ming Hui , Fan Qing-Hai , Yu Lichen , Zhang Zhi-Qiang
Published: October 2020

The extension of lifespan by means of calorie restriction (CR) is one of the most replicable mechanisms across a range of different taxa. However, the effects of this on the next generation are less studied due to the complexities associated with such an experiment. In this study, the effects of CR and ad libitum (AL) feeding on lifespan, duration of ovipositional stages, and fecundity of a predatory mite, Neoseiulus cucumeris were investigated. The egg volume, sex ratio, and survival rate of the offspring were then compared across the different treatments. The three treatments were: (1) 40 prey Tyrophagus putrescentiae eggs per day representing the AL treatment; (2) 10 eggs per day representing medium CR; and (3) 5 eggs per day being high CR. To assess for transgenerational effects, the eggs produced under the three different treatments were fed AL and reared until adulthood or death. Mothers under the medium CR treatment had a lifespan that almost doubled the lifespan of mothers fed AL. Contrastingly, a higher reproductive rate was seen in mothers under AL, which also had a significantly higher total fecundity when compared with both CR treatments. The AL mothers had a shorter gestational period and produced larger eggs. There was no difference between the sex ratio of offspring for the medium CR and AL treatments. These results indicate the different effects of the two levels of CR and highlight the trade-offs that are accompanied with a longer lifespan due to caloric restriction.
Evaluating Multiple Domains of Health in High School Athletes With Sport-Related Concussion
Authors: Williams Richelle M. , Johnson Rachel S. , Snyder Valier Alison R. , Curtis Bay R. , Valovich McLeod Tamara C.
Published: October 2020

Context: Concussions are shown to hinder multiple health dimensions, including health-related quality of life (HRQOL), suggesting a need for a whole-person approach to assessment and treatment. Patient-reported outcome measures are one method to gather the patient’s perspective regarding their HRQOL. Objective: To evaluate perceived HRQOL using the Patient-Reported Outcomes Measurement Information System Pediatric-25 subscale in patients throughout concussion recovery. Design: Prospective cohort, descriptive survey. Setting: There were 9 high school athletic training facilities. Participants: A total of 70 patients with diagnosed concussions (51 males, 7 females, 12 unreported; age = 15.7 [0.9] y, height = 174.6 [8.4] cm, mass = 72.8 [14.8] kg, grade = 10.0 [0.9] level). Interventions: Patient-Reported Outcomes Measurement Information System Pediatric-25 was administered at 3 days, 10 days postconcussion, and return to play (RTP). Main Outcome Measures: Patient-Reported Outcomes Measurement Information System Pediatric-25 subscale T scores and self-reported concussion history (yes/no). Results: A total of 70 patients completed the study. For the Pediatric-25 subscales, the severity of problems associated with Physical Function Mobility, Anxiety, Depression, Fatigue, and Pain Interference were highest 3 days postconcussion, decreasing at 10 days and RTP (all p < .05). No differences were found between days 3 and 10 for Peer Relationship scores, but improvements were identified at RTP (p < .05). Pediatric-25 subscale scores at the 3 measurements were not statistically associated with concussion history (all p > .05). Ceiling and floor effects were present in all subscales throughout each timepoint, except for Physical Function Mobility (14.7%), and pain interference (11.8%) at day 3 postinjury. Conclusions: Patients who had suffered a concussion improved from day 3 through RTP on multiple health domains as demonstrated through the Pediatric-25 subscales. These findings highlight the need for health care professionals to serially monitor HRQOL and social factors that may affect the patient postconcussion as part of a multifactorial assessment. Ceiling effects in high functioning adolescent athletes were present; thus, efforts should be made to identify appropriate scales for use in managing recovery in athletic populations.
Targeting Methionine Synthase in a Fungal Pathogen Causes a Metabolic Imbalance That Impacts Cell Energetics, Growth, and Virulence
Authors: Scott Jennifer , Sueiro-Olivares Monica , Thornton Benjamin P. , Owens Rebecca A. , Muhamadali Howbeer , Fortune-Grant Rachael , Thomson Darren , Thomas Riba , Hollywood Katherine , Doyle Sean , Goodacre Royston , Tabernero Lydia , Bignell Elaine , Amich Jorge
Published: October 2020

Fungal pathogens are responsible for millions of life-threatening infections on an annual basis worldwide. The current repertoire of antifungal drugs is very limited and, worryingly, resistance has emerged and already become a serious threat to our capacity to treat fungal diseases. The first step to develop new drugs is often to identify molecular targets in the pathogen whose inhibition during infection can prevent its growth. However, the current models are not suitable to validate targets in established infections. Here, we have characterized the promising antifungal target methionine synthase in great detail, using the prominent fungal pathogenAspergillus fumigatusas a model. We have uncovered the underlying reason for its essentiality and confirmed its druggability. Furthermore, we have optimized the use of a genetic system to show a beneficial effect of targeting methionine synthase in established infections. Therefore, we believe that antifungal drugs to target methionine synthase should be pursued and additionally, we provide a model that permits gaining information about the validity of antifungal targets in established infections.
Metatranscriptomics by
In Situ
RNA Stabilization Directly and Comprehensively Revealed Episymbiotic Microbial Communities of Deep-Sea Squat Lobsters
Authors: Motoki Kaori , Watsuji Tomo-o , Takaki Yoshihiro , Takai Ken , Iwasaki Wataru
Published: October 2020

Deep-sea hydrothermal vent ecosystems remain mysterious. To depict in detail the enigmatic life of chemosynthetic microbes, which are key primary producers in these ecosystems, metatranscriptomic analysis is expected to be a promising approach. However, this has been hindered by substantial perturbation (e.g., RNA degradation) during time-consuming retrieval from the deep sea. In this study, we conducted direct metatranscriptome analysis of microbial episymbionts of deep-sea squat lobsters (
Shinkaia crosnieri
) by applying
in situ
RNA stabilization equipment. Compared to conventional metatranscriptomics (i.e., RNA stabilization after retrieval), our method provided substantially different RNA expression profiles. Moreover, we discovered that
S. crosnieri
and its episymbiotic microbes constitute complex and resilient ecosystems, where closely related but various episymbionts are stably maintained by horizontal exchange and partly by their sulfur storage ability for survival even when sulfur compounds are not usable, likely also in a detached and free-living state.
Fragmentation of South China from greater India during the Rodinia-Gondwana transition
Authors: Wang Wei , Cawood Peter A. , Pandit Manoj K. , Xia Xiaoping , Raveggi Massimo , Zhao Junhong , Zheng Jianping , Qi Liang
Published: October 2020

Late Tonian to Cambrian sedimentary sequences in northwestern India and South China provide vital evidence for modeling their paleogeographic linkage, including their juxtaposition and subsequent separation during the transition from the Rodinia to the Gondwana supercontinents. Similarities in lithostratigraphy and detrital zircon U-Pb-Hf-O isotopic characteristics in the late Tonian sedimentary units from both regions underline a common provenance. A substantial decrease in zircon δ18O values from super- to sub-mantle compositions and simultaneous increase in the zircon εHf(t) values in South China and northwestern India for the 800–700 Ma time window suggest a common Neoproterozoic extensional magmatic event, corresponding with the Rodinia breakup. A distinct change in sedimentary provenance is noted during the Cryogenian period. Sedimentation along the northwestern margin of India for the remainder of the Neoproterozoic encompasses large volumes of clastic detritus dominated by old zircon ages, derived inboard from the Indian craton. In contrast, contemporaneous sedimentary units in the Yangtze region of South China are dominated by Neoproterozoic zircons. The detrital zircon age data underline a close paleogeographic linkage between northwestern India and South China (Yangtze and Cathaysia regions) in the Rodinia supercontinent configuration and argue for their separation through continental rifting during the Cryogenian. Northwestern India developed into a passive margin, whereas the South China block partially rifted, rotated, and migrated dextrally along the Gondwana margin toward northeastern India and Western Australia, such that the Cathaysia block continued to receive detritus from Gondwana continental regions.
Discharge planning considerations for the neonatal intensive care unit
Authors: Smith Vincent C
Published: October 2020

Neonatal intensive care unit (NICU) discharge readiness is the primary caregivers’ masterful attainment of technical care skills and knowledge, emotional comfort and confidence with infant care by the time of discharge. NICU discharge preparation is the process of facilitating discharge readiness. Discharge preparation is the process with discharge readiness as the goal. Our previous work described the importance of NICU discharge readiness and strategies for discharge preparation from an American medical system perspective. NICU discharge planning is, however, of international relevance as challenges in relation to hospital discharge are a recurring global theme. In this manuscript, we conceptualise NICU discharge preparation with international perspective.