Flow Domain
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Author(s):  
Md Mizanur Rahman ◽  
Khalid Hasan ◽  
Wenchang Liu ◽  
Xinming Li

A new zero-equation model (ZEM) is devised with an eddy-viscosity formulation using a stress length variable which the structural ensemble dynamics (SED) theory predicts. The ZEM is distinguished by obvious physical parameters, quantifying the underlying flow domain with a universal multi-layer structure. The SED theory is also utilized to formulate an anisotropic Bradshaw stress-intensity factor, parameterized with an eddy-to-laminar viscosity ratio. Bradshaw’s structure function is employed to evaluate the kinetic energy of turbulence k and turbulent dissipation rate epsilon  . The proposed ZEM is intrinsically plausible, having a dramatic impact on the prediction of wall-bounded turbulence. 


Coatings ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 16
Author(s):  
Sardar Bilal ◽  
Noor Zeb Khan ◽  
Imtiaz Ali Shah ◽  
Jan Awrejcewicz ◽  
Ali Akgül ◽  
...  

A study on strategies regarding advancement in heat transfer characteristics in two-dimensional closed domains by placing cold cylinders is conducted. This effort is undertaken due to the fact that active and passive control in heat transmission is connected with provision of temperature differences at different locations of enclosures. Based on the experiments, researchers have concluded that placement of cold cylinder in non-uniformly distributed heat in a cavity is the most effective technique to enrich heat transfer rate, along with reducing the the waste of extra heat generation in processes such as polymer and aero dynamical extrusion, glass cooling, refrigeration, heating and cooling systems. Thus, the prime goal of this work is to outline heat and flow characteristics of non-linear fluid occupied in a square enclosure with adjustment of the cold cylinder. Heat transfer attributes are incorporated by accounting buoyancy forces and forming coupling of molecular diffusion of fluid within the flow domain. Formulation of the problem in dimensionless form is attained by encapsulating the aspects of natural convection in view of principal partial differential equations. Parametric study for governing expressions is computed numerically with the finite element method based on COMSOL Multiphysics version 5.6. Quadric interpolating functions are used to obtain information about velocity and temperature on nodes in elements. Hybrid meshing is manifested for discretization of the domain into rectangular and triangular elements. For the optimized variation in flow structures, prospective parameters are varied from and. The achieved results are projected graphically through streamlines, isotherms, and local and average Nusselt numbers. Tabular data for kinetic energy and wall heat flux are also calculated. It is inferred through the analysis that, with uplift in the Rayleigh number elevation in the magnitude of kinetic energy and convective heat transfer arises, whereas the reverse pattern is depicted versus the power–law index


2021 ◽  
Author(s):  
Hemant Kumar ◽  
Chetan S. Mistry

Abstract A surge in the small jet engine market due to aero-propulsion purposes generates a requirement to develop compact and robust high-performance compressors. Mixed flow compressors can provide a comparatively higher pressure ratio compared to axial compressors and have less frontal area than centrifugal compressors. Rapid progress in manufacturing and computational capabilities has resulted in the successful design of mixed flow compressors in recent decades. In the present study, the mixed flow compressor was designed to operate at 3,000 rpm with a small total-to-total pressure ratio of 1.03 and a mass flow rate = 1.98 kg/s to carry at low-speed testing for university-level research. Meanline design for the compressor with air as working fluid was done. The blade geometry was developed using commercial Ansys® Bladegen module. The flow domain mesh was generated by the TurboGrid module. Ansys CFX was used as a solver and post-processing tool for the present numerical study. The present work describes the detailed design procedure, overall performance, and flow field features of a low-speed mixed-flow compressor with the special requirement of axial flow exit. The parametric analysis was carried out on splitter blade placement, wrap angle (10°, 20°, 30°, and 50°), and exit cone angle (30°, 40°, 50°, 60°, and 65°), at constant tip clearance and keeping the other parameters constant to observe their effect on performance and flow structure. The use of splitter blades smoothen the flow structure along both stream-wise and span-wise direction, which minimizes flow the separation issue and thereby helping in extending the overall operating range. Comparing the flow field characteristic and performance of each parametric variable, the optimum range of design values is exhibited. The numerical observation and analysis done on parametric variations in this paper can be used for the design of such a future low-speed mixed flow compressor for different performance expectations and installation requirements.


Author(s):  
Sugeng Hadi Susilo ◽  
Hangga Wicaksono

A further investigation of premixed biogas combustion towards the NOx formation is presented in this study. The purpose of the simulation is to determine the addition of CO2 in biogas fuel to the combustion behavior of premixed biogas on NOx formation, and to determine the occurrence of NOx in the pre-mixed biogas combustion. In this study, the Counterflow Premixed Flame class is used where this class is based on the One Dim class which is the basis for simulations with a 1-dimensional domain. The Counterflow Premixed Flame class uses an axisymmetric stagnation flow domain which has been written based on the equations. Cantera uses Newton's method to solve them. Completion is carried out in two stages. The first stage is to solve the solution using the equilibrium at each z coordinate point that has been determined. Many estimation starting points are determined from the start of the program. The second stage is the recalculation process at each point and then subdivided to get a smoother solution. The premixed excess CO2 biogas fuel and air combustion analyzed using a 1-dimensional numerical study. The diluted CO2 mass fraction ranged between 0–40 %. The CH4/CO2/air volume flow rate was maintained in ±L/min. The analysis implements the 1-D Counter Flow approach. Two counterflow nozzles were 20mm in diameter and the flame stagnation point at 10 mm. The results show that NOx mass fraction formed only on a fuel-lean mixture of CH4/CO2/air and its values decreased along with CO2 added. The addition of CO2 could reduce the NO species mass fraction down to 18 %, and NO2 reduction down to 7 %. This is mainly caused by a decreasing heat release rate of NO+N↔N2+O, N+O2↔NO+O, N+OH↔NO+H, and N+CO2↔NO+CO reactions. The N+CO2↔NO+CO reaction increased as CO2 was added but its values were not as much as the decline of three other reactions


Author(s):  
Yue-Lin Hsieh ◽  
Dan Wang ◽  
Xiaobing Xu ◽  
Dengtao Yu ◽  
Yongzhen Wu ◽  
...  

There has been a growing interest in the investigation of hydroacoustic characteristics of pulsatile tinnitus (PT). However, a proper technique for computational fluid dynamics (CFD) simulation has yet to be discussed. The primary goal of this paper was to investigate the intrasinus hydroacoustic characteristics of PT at the transverse-sigmoid junction (TSJ) using Doppler ultrasound and examine the validity of CFD techniques in simultaneity. The preoperative and intraoperative Doppler ultrasound were performed on a patient with PT at upper jugular vein and TSJ, respectively. Canonical CFD techniques were applied to solve the computational transverse-sigmoid sinus flow domain and compared with the Doppler’s measurements. In addition, the spectro-temporal analysis was performed for the sonification of PT. PT was associated with the recirculating flows at the TSJ according to ultrasonographic detection. This pathogenic region was characterized by a sudden deceleration of flow velocity and inverse increase of flow static pressure, which large eddy simulation (LES) resulted in the smallest 6% velocity difference compared to the measured Doppler data, albeit with little differences compared to other solvers. Therefore, based on this case study, the transient LES approach is an optimal CFD method for the computational simulation of the complex hemodynamics at the TSJ. Further numerical studies with large case series are warrranted.


2021 ◽  
Vol 9 (11) ◽  
pp. 1217
Author(s):  
Sunao Murashige ◽  
Wooyoung Choi

This paper describes a numerical investigation of ripples generated on the front face of deep-water gravity waves progressing on a vertically sheared current with the linearly changing horizontal velocity distribution, namely parasitic capillary waves with a linear shear current. A method of fully nonlinear computation using conformal mapping of the flow domain onto the lower half of a complex plane enables us to obtain highly accurate solutions for this phenomenon with the wide range of parameters. Numerical examples demonstrated that, in the presence of a linear shear current, the curvature of surface of underlying gravity waves depends on the shear strength, the wave energy can be transferred from gravity waves to capillary waves and parasitic capillary waves can be generated even if the wave amplitude is very small. In addition, it is shown that an approximate model valid for small-amplitude gravity waves in a linear shear current can reasonably well reproduce the generation of parasitic capillary waves.


2021 ◽  
Author(s):  
Z. Z. Rashed

Abstract This paper examines the controlling of the three dimensional dusty nanofluid flow using the two circular cylinders having different thermal conditions. The cylinders are located in the middle area while the location of the right cylinder is changeable. The 3D cubic flow domain is filled by a non-Darcy porous medium and a magnetic field in Z-direction is taken place. The non-homogeneous two phase model of the nanofluid is applied while the permeability and thermal conductivity of the porous medium are assumed heterogonous. The current situation is represented by two systems of the equations for the nanofluid and dusty phases. The solutions methodology is depending on the 3D SIMPLE scheme together with the finite volume method. The major outcomes indicating to that the flow can be well controlled using the inner isothermal cylinders. Also, the cases of the heterogeneity in \(X-Y\) and \(X-Z\) directions give the lowest values of \({Nu}_{av}\).


2021 ◽  
Vol 2116 (1) ◽  
pp. 012026
Author(s):  
Lisa Lampunio ◽  
Yu Duan ◽  
Raad Issa ◽  
Matthew D. Eaton

Abstract This paper investigates the effects of different inlet velocities on thermal stripping phenomena within a T-junction. The computational flow domain is modelled using the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model implemented within the commercial CFD code STAR-CCM+ 12.04. The computational model is validated against the OECD-NEA-Vattenfall T-junction Benchmark data. The influence of flat and fully developed inlet velocity profiles is then assessed. The results are in good agreement with the experimental data. The different inlet velocity profiles have a non-negligible effect on the mean wall temperature. The mean velocity shows lower sensitivity to changes in inlet velocity profiles, whose influence is confined mainly to the recirculation zone near the T-junction.


SIMULATION ◽  
2021 ◽  
pp. 003754972110551
Author(s):  
Laurie A Florio

This work describes a unique technique to simulate continuously and directly coupled fluid flow and moving particles including both mechanical and thermal interactions between the flow, particles, and flow paths. The particles/flow paths are discretized within a computational fluid dynamics flow domain so that the local flow and temperature field conditions surrounding each particle or other solid body are known along with the local temperature distribution within the particle and other solids. Contact conduction between solid bodies including contact resistance, conjugate heat transfer at the fluid–solid interfaces, and even radiation exchanges between solid surfaces and between solid surfaces and the fluid are incorporated in the thermal interactions and a soft collision model simulates the solid body mechanical contact. The ability to capture these local flow and thermal effects removes reliance on correlations for fluid forces and for heat transfer coefficients/exchange and removes restrictions on the flow regime and particle size and volume fraction considered. Larger particle sizes and higher particle concentration conditions can be studied with local effects captured. The method was tested for a range of particle thermal and mechanical properties, driving pressures, and for limited radiation parameters. The results reveal important information about the basic thermal and flow phenomena that cannot be obtained in standard modeling methods and demonstrate the utility of the modeling method. The technique can be applied to examine phenomena dependent on local thermal conditions such as chemical reactions, material property variation, agglomerate formation, and phase change. The methods can also be used as a basis for machine learning algorithm development for flows with large particle counts so that more detailed phenomena can be considered compared to those provided by standard techniques with reduced computational costs compared to those with fully resolved particles in the flow.


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