Evaluating the effect of non-Newtonian turbulent blood models within a double-stenosed artery

This article describes the numerical investigation of blood rheology within an artery that includes two narrowing areas via Computational Fluid Dynamics (CFD). Elliptic blending Reynolds stress model and two models of viscosity have been used in this investigation utilizing STAR-CCM+ 2021.2.1. The test model includes two elliptical stenosis with a 2mm distance between them, and the area of stenosis is 75%. Results of normalized axial velocity, turbulent kinetic energy (TKE) and turbulent viscosity ratio (TVR) were evaluated before, through and after the stenosis in order to predict and avoid the real problems that occur from changing the area of the artery. Furthermore, Fractional flow reserve (FFR) was employed to assess the level of risk of stenosis through the artery, which depends on pressure measurements. Corresponding to the author's observation, it was found that the recirculation regions in the area between the stenosis are larger than the area after the stenosis. Moreover, the results of TKE and TVR are almost identical through and downstream of the stenosis, whereas the TKE is slightly higher with the Carreau model than with the Newtonian flow at the upstream and through the first stenosis.

Evaluating the effect of non-Newtonian fluid turbulent flowing for blood within a double-stenosed artery

This article describes the numerical investigation of blood rheology within an artery that includes two narrowing areas via Computational Fluid Dynamics (CFD) to offer guidance to the community, especially surgeons, and help them to avoid the risk of stenosis. Elliptic blending Reynolds stress model and two models of viscosity have been used in this investigation utilizing STAR-CCM+ 2021.2.1. The test model includes two elliptical stenosis with a 2mm distance between them, and the area of stenosis is 75%. Results of normalized axial velocity, turbulent kinetic energy (TKE) and turbulent viscosity ratio (TVR) were evaluated before, through and after the stenosis in order to predict and avoid the real problems that occur from changing the area of the artery. Furthermore, Fractional flow reserve (FFR) was employed to assess the level of risk of stenosis through the artery, which depends on pressure measurements. Corresponding to the author's observation, it was found that the recirculation regions in the area between the stenosis are larger than the area after the stenosis. Moreover, the results of TKE and TVR are almost identical through and downstream of the stenosis, whereas the TKE is slightly higher with the Carreau model (arrive to 0.54 J/kg) than with the Newtonian flow (arrive to o.47 J/kg) at the upstream and through the first stenosis.

Direct Numerical Simulation of Real-gas Effects within Turbulent Boundary Layers for Fully-developed Channel Flows

Real-gas effects have a significant impact on compressible turbulent flows of dense gases, especially when flow properties are in proximity of the saturation line and/or the thermodynamic critical point. Understanding of these effects is key for the analysis and improvement of performance for many industrial components, including expanders and heat exchangers in organic Rankine cycle systems. This work analyzes the real-gas effect on the turbulent boundary layer of fully developed channel flow of two organic gases, R1233zd(E) and MDM - two candidate working fluids for ORC systems. Compressible direct numerical simulations (DNS) with real-gas equations of state are used in this research. Three cases are set up for each organic vapour, representing thermodynamic states far from, close to and inside the supercritical region, and these cases refer to weak, normal and strong real-gas effect in each fluid. The results within this work show that the real-gas effect can significantly influence the profile of averaged thermodynamic properties, relative to an air baseline case. This effect has a reverse impact on the distribution of averaged temperature and density. As the real-gas effect gets stronger, the averaged centre-to-wall temperature ratio decreases but the density drop increases. In a strong real-gas effect case, the dynamic viscosity at the channel center point can be lower than at channel wall. This phenomenon can not be found in a perfect gas flow. The real-gas effect increases the normal Reynolds stress in the wall-normal direction by 7–20% and in the spanwise direction by 10–21%, which is caused by its impact on the viscosity profile. It also increases the Reynolds shear stress by 5–8%. The real-gas effect increases the turbulence kinetic energy dissipation in the viscous sublayer and buffer sublayer <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mo stretchy="false">(</mml:mo><mml:msup><mml:mi>y</mml:mi><mml:mo>∗</mml:mo></mml:msup><mml:mo><</mml:mo><mml:mn>30</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math></inline-formula> but not in the outer layer. The turbulent viscosity hypthesis is checked in these two fluids, and the result shows that the standard two-function RANS model (<inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>k</mml:mi><mml:mo>−</mml:mo><mml:mi>ϵ</mml:mi></mml:math></inline-formula> and <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mi>k</mml:mi><mml:mo>−</mml:mo><mml:mi>ω</mml:mi></mml:math></inline-formula>) with a constant <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi>C</mml:mi><mml:mi>μ</mml:mi></mml:msub><mml:mo>=</mml:mo><mml:mn>0.09</mml:mn></mml:math></inline-formula> is still suitable in the outer layer <inline-formula><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:mo stretchy="false">(</mml:mo><mml:msup><mml:mi>y</mml:mi><mml:mo>∗</mml:mo></mml:msup><mml:mo>></mml:mo><mml:mn>70</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math></inline-formula>, with an error in ±10%.

Testing Basic Gradient Turbulent Transport Models for Swirl Burners Using PIV and PLIF

The present paper reports on the combined stereoscopic particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) measurements of turbulent transport for model swirl burners without combustion. Two flow types were considered, namely the mixing of a free jet with surrounding air for different swirl rates of the jet (Re = 5 × 103) and the mixing of a pilot jet (Re = 2 × 104) with a high-swirl co-flow of a generic gas turbine burner (Re = 3 × 104). The measured spatial distributions of the turbulent Reynolds stresses and fluxes were compared with their predictions by gradient turbulent transport models. The local values of the turbulent viscosity and turbulent diffusivity coefficients were evaluated based on Boussinesq’s and gradient diffusion hypotheses. The studied flows with high swirl were characterized by a vortex core breakdown and intensive coherent flow fluctuations associated with large-scale vortex structures. Therefore, the contribution of the coherent flow fluctuations to the turbulent transport was evaluated based on proper orthogonal decomposition (POD). The turbulent viscosity and diffusion coefficients were also evaluated for the stochastic (residual) component of the velocity fluctuations. The high-swirl flows with vortex breakdown for the free jet and for the combustion chamber were characterized by intensive turbulent fluctuations, which contributed substantially to the local turbulent transport of mass and momentum. Moreover, the high-swirl flows were characterized by counter-gradient transport for one Reynolds shear stress component near the jet axis and in the outer region of the mixing layer.

Estimation of the turbulent Schmidt number in a model gas turbine combustor

This article presents the estimation of turbulent Schmidt number in a model gas turbine combustor. Different gases are used as the model fuel while maintaining the mass flow rate. The simplest closure models for Reynolds stress and turbulent flux are considered. The anisotropy of turbulent viscosity is demonstrated.

Modeling of the Wind/Disk Outflow from Be Stars

The objective of this work is to reproduce the formation of the fast polar wind and viscous disk outflow from Be stars in a unified physical picture. Numerical modeling of the plasma outflow from fast rotating stars was performed taking into account the acceleration of the plasma due to scattering of the radiation of the star in lines of plasma ions and excitation of the hydrodynamic turbulence in the outflow. The fast polar wind naturally arises in this picture with an expected flow rate. For the first time, it is shown that a disk-like outflow with a relatively high level of turbulence is formed at the equator of fast rotating stars emitting radiation-driven wind. However, the level of turbulent viscosity is well below the level necessary for the formation of a Keplerian disk.

FEATURES OF MODELING THE TRACTION OF MOVEMENT OF MATERIAL PARTICLES IN A VORTICAL LAYER

In the given article the actual modern scientific problem is solved — on the basis of experimental data the mathematical model of movement of a particle in a vortex layer at heat treatment taking into account multiphase of a stream is created. At the current level of development of vortex devices, the relevance of research aimed at in-depth study of processes, improvement of structures and manufacturing technology of individual components has increased. The lack of a strict theory is felt most acutely in the design of systems and installations in which the vortex apparatus is one of the main units. In this regard, the priority remains the development of a theory that allows to obtain a fairly reliable mathematical description of the processes occurring in the vortex chamber of the apparatus. The patterns of propagation of the swirling jet depend on a large number of different conditions (design features of the nozzle, the intensity of the twist) and flow parameters (their density and speed). The flow in the jet has a complex non-automodal character, in connection with which in other works it was considered expedient to use for calculation numerical methods of integration of equations of motion to describe the non-automodal flow in ordinary jets. The disadvantage of these models is that when solving the model of vortex flows go into the model of laminar flows. In this case, many quantities cannot be determined analytically or experimentally. When dividing the flow into the zone of the vortex and the zone of the main vortex, the error in the calculations of the hydrodynamics of the flow, and especially the particles, increases significantly due to the use of different equations of the turbulent viscosity, which is taken for each zone constant. These models are written for a continuous medium and are therefore not suitable for multiphase flow. The peculiarities of the trajectory of the material particle in the vortex apparatus are determined and the dependences are obtained, which allow to control the heat treatment time and on the basis of which it is possible to design the optimal vortex device for drying dispersed materials. The mathematical models obtained in this work can be used in methods of calculations and design of vortex heat and mass transfer devices. The calculations performed according to the equations of the proposed model show satisfactory agreement with the experimental data. When estimating the relative velocities of the particle in the unloading part of the vortex apparatus, it is obvious that the use of equations for laminar flow, which are traditionally used in calculations, leads to significant errors.

Convective Heat Exchange and Friction in a Thin Laminar-to-Turbulent Boundary Layer on the Impermeable Lateral Surfaces of Blunted Cones Featuring a Low Aspect Ratio

In order to provide a high-quality solution to the problem of computing convective heat transfer parameters in a laminar-to-turbulent boundary layer, it is necessary to numerically integrate differential equations describing that layer, completed by semi-empirical turbulent viscosity models, said models having been tested by comparing their output to the results of experimental investigations where the gas dynamics of a gas flow around a body is correctly simulated. Developing relatively simple yet adequately accurate computation methods becomes crucial for practical applications. To date, the effective length method, being simple yet apparently boasting an acceptable accuracy, has become the most widespread technique for solving this problem in aircraft design and aerospace technology. However, this statement is not correct for large Reynolds numbers on a hemisphere. Under these conditions, semi-empirical apparent turbulent viscosity models provide significantly better matches to experimental data. The paper analyses the feasibility of using a similar approach for the lateral surface of a blunted cone featuring a low aspect ratio. We describe a new efficient approach to solving this problem, demonstrating a high accuracy and maximum simplicity when used in practice. We check the results of systematic computations using our method against comparable data obtained via the most frequently cited approaches to solving this problem

Обґрунтування моделі турбулентної в’язкості для дослідження характеристик співвісного гвинтовентилятора і вхідного пристрою ГТД

The issues of substantiation of the most rational, based on adequacy, model of turbulent viscosity for mathematical modeling of the flow near the propfan and in the inlet of the turbine-propeller engine are considered. It was found that at present there is no universal turbulence model for determining the parameters of the boundary layer, energy loss in the flow, and laminar-turbulent transition. Analysis of the results of previous studies showed that there is a need to select and justify a turbulent viscosity model for each type of research object. The task of modeling the flow near the propfan and in the inlet device of the power plant was performed using the ANSYS CFX software product, which allows using various standard mathematical models and tools for modeling turbulent flow. The object of research is an annular axial inlet device, in front of which there is a coaxial propfan with two rows of propellers: the first row has eight blades, the second - six. 7 types of models of turbulent viscosity, which most fully describe the phenomena in the flow around the propfan and the inlet device, have been investigated: k-ωmodel; SSТ (shear stress transport) SST Transitional №1 Fully turbulence; SST Transitional №2 Specified Intermittency; SST Transitional №3 Gamma model; SST Transitional №4 Gamma theta model; SST Transitional №5 Intermittency. The results of mathematical modeling of the flow near the propfan and in the inlet device at the corresponding operating mode of the turbopropfan engine using the selected models of turbulent viscosity, the total pressure value in front of and behind the inlet device was obtained to determine the total pressure recovery coefficient in it and the value of the propfan thrust. The value of the recovery factor of the total pressure in the inlet device and the propfan thrust are compared with the flight test data of the prototype. An analysis of the comparison of the values of the total pressure recovery factor in the inlet device and the propfan thrust showed that the use of the SST Transitional №4 Gamma theta model allows obtaining the value of the total pressure recovery factor in the inlet device and the propfan thrust that is closest to the flight test results.

Моделювання течії в співвісному гвинтовентиляторі з управлінням примежовим шаром

The development and improvement of turboprop engines are one of the important tasks of modern aircraft engine building. Propeller performance significantly affects the overall efficiency of turboprop engines. An important issue is to increase the trust of the propeller or propfan. In this matter, promising energy methods for increasing lift deserve special attention. Energy methods for increasing the lift force are based on the use of additional energy from the power plant to improve the flow around the blade and increase its bearing properties. The purpose of this work is to assess the influence of the boundary layer control on the blades of a coaxial propfan on the thrust. A coaxial propfan was chosen as the object of research. The rotor fan consists of two rows of blades, the first row has eight blades, the second - six. The peripheral diameter of the blades of the propfan is the same and amounts to 4.5 m. The cruise mode of operation was selected for the study. Modeling the flow in a coaxial propfan was based on the solution of the Navier-Stokes system of equations, which was closed by the SST Gamma Theta Transition model of turbulent viscosity. The computational grid consisted of 20 million cells, type-block, structured and unstructured with an adaptation of the boundary layer. In this study, an active boundary layer control method was chosen. The boundary layer was controlled only on the blades of the first row of the propfan. In the peripheral region of the blade, an additional mass of air was blown out through the slot, at a distance of 70 % of the profile chord. Blowing out a thin jet near the blade wall to increase the flow energy serves as an effective means of controlling the flow separation and increasing the bearing capacity of the propfan blade. Analysis of the simulation of the flow in a propfan with control of the boundary layer showed that the addition of energy to the boundary layer contributes to the filling of the velocity profile in the boundary layer, leads to a decrease in resistance and an increase in the thrust of the propfan. The results of the study showed that for the studied scheme of blowing out an additional mass of air on the propeller blades, it is possible to increase the thrust force up to 100 N. In the future, it is planned to investigate other schemes for controlling the boundary layer to increase the thrust of the coaxial propfan.