Search

A continuous-curvature parameterization method was coupled with the genetic algorithm and a RANS flow solver to optimize the cascade of VKI and Aachen turbine blades. The main advantage of the method is to generate blades with a continuous curvature distribution, which results in a smooth distribution of pressure and velocity on the blade surface. The geometry of the blade cascade was parameterized by 33 variables, and two objective functions were considered for the optimization. The first cost function was to reduce the total pressure loss with the constraints of mass flow rate, blade loading, and outlet flow angle. At the second cost function, the constraint of constant cross-sectional area was added to the previous constraints to preserve the structural strength of the turbine blade. The total pressure loss for the VKI blade decreased by 14.7 % and 10.6 % for the first and second objective functions, respectively. The total pressure loss for the Aachen blade was also reduced by 9.5 % and 7.5 % for the first and second objective functions, respectively. Due to the efficient geometry parameterization, the proposed method quickly converged to a high-efficiency blade at the early generations. The proposed method can be developed for optimizing the different blades of turbine, compressor, and airfoil types.

In this paper deformation and breakup of a non-Newtonian shear thinning droplet are studied parametrically. The effects of physical and geometrical properties are investigated by means of numerical methods. The flow is simulated in the range of 716 up to 2864 for Reynolds number and 8.5 to 70 for the Weber number. The VOF numerical method is used for capturing the droplet deformation and Carreau model is used to simulate non-Newtonian physical properties. The results are compared with those exist in literature. It is found that various non-Newtonian parameters of the fluid properties do affect the critical Weber number and the deformation of the droplet.

In this article, a simplified 3D magneto-thermal model to study the temperature distribution over the housing of a Switched Reluctance Machine (SRM) is proposed. The main objective of such model is to study the temperature distribution profile on the body of the machine under various working conditions in order to introduce a temperature based signature to develop condition monitoring procedures. The analysis of fluid flow and heat transfer inside the SRM supports the hypothesis that the effect of turbulent flow of the fluid and the complex heat transfer phenomenon of the rotating parts can be simplified to a heat flux boundary condition representation of the heat loss. The accuracy of the model is validated through simulation and experimental results on a prototype SRM. The developed simplified model can be used as for prediction of temperature profile on SRM surface, well suited for fault diagnosis in SRM. The proposed methodology can be modified applied in developing a thermal model for other types of electric machines.

Nonequilibrium molecular dynamics simulations is applied to investigate the simultaneous effect of rarefaction and wall force field on the heat conduction characteristics of nano-confined rarefied argon gas. The interactive thermal wall model is used to specify the desired temperature on the walls while the Irving– Kirkwood expression is implemented for calculating the heat flux. It is observed that as the temperature differences between the walls increases by lowering the temperature of the cold wall, the number of adsorbed gas atoms on the cold wall increases notably due to the increment in the residence time of the gas atoms. Consequently, the interfacial thermal resistance between the gas and the cold wall reduces which results in a reduction of the temperature jump. Meanwhile, the increase in the temperature of the hot wall leads to a reduction of the residence time of gas atoms in the near-wall region which decreases the number of absorbed gas atoms on the hot wall. This results in an increase in interfacial thermal resistance which leads to a higher temperature jump. It is observed that the bulk, wall force field and interface regions form approximately 10%, 45% and 45% of the total thermal resistance, respectively. Furthermore, unlike the interfacial thermal resistance, the bulk and the wall force field thermal resistance are approximately independent of the implemented temperature difference.

Computational modeling of biological systems is a powerful tool to clarify diverse processes contributing to cancer. The aim is to clarify the complex biochemical and mechanical interactions between cells, the relevance of intracellular signaling pathways in tumor progression and related events to the cancer treatments, which are largely ignored in previous studies.A three-dimensional multiscale cell-based model is developed, covering multiple time and spatial scales, including intracellular, cellular, and extracellular processes. The model generates a realistic representation of the processes involved from an implementation of the signaling transduction network.Considering a benign tumor development, results are in good agreement with the experimental ones, which identify three different phases in tumor growth. Simulating tumor vascular growth, results predict a highly vascularized tumor morphology in a lobulated form, a consequence of cells' motile behavior. A novel systematic study of chemotherapy intervention, in combination with targeted therapy, is presented to address the capability of the model to evaluate typical clinical protocols. The model also performs a dose comparison study in order to optimize treatment efficacy and surveys the effect of chemotherapy initiation delays and different regimens.Results not only provide detailed insights into tumor progression, but also support suggestions for clinical implementation. This is a major step toward the goal of predicting the effects of not only traditional chemotherapy but also tumor-targeted therapies.

The purpose of this study is to analyze the flow of wet foam and to study the effect of volume fraction, velocity and surface tension and other physical parameters on the foam flow. The most numerical researches done in this area are for single-phase flows. The numerical simulation in this study is the first simulation in the foam flow, in which both the bubbles and the water are simulated as two-phase flow. In this study, fluid containing a surfactant and bubbles are flowing in a duct. The dimensions of the duct cross section is 15 × 60 in millimeters. The numerical solution is performed for three Reynolds numbers of 50, 100 and 1000, three volume fractions of 48, 41 and 28, and three Weber numbers of 0.405, 0.27 and 0.203 (27 different modes), and the effect of the above parameters on the flow behavior and its physical properties have been investigated. It was found that in foam flow, the velocity fluctuations, due to the movement of bubbles in the flow, is in the order of magnitude of the mean velocity. The same is true for wall shear stress. By increasing the Reynolds number, the pressure loss increases, the magnitude of the velocity fluctuations decreases and the frequency of the velocity fluctuations increases. By increasing the Weber number, the pressure loss and the magnitude of the velocity fluctuations decrease and the mean shear stress increases. By increasing the foam quality, pressure loss increases, the mean shear stress and the magnitude of the velocity fluctuations decrease and its frequency increases. And the phenomenon of coalescence causes a sudden increase in momentum speed.

The structures of flow in laminar Couette-Taylor flow with periodic oscillation of the inner cylinder rotation velocity (which linearly increases from zero to a fixed maximum value and then goes to zero again in each period) for different three regimes; Couette flow, Taylor vortex and wavy vortex, with the effect of the Womersley number, Wo, for different periods and the critical Taylor number are investigated numerically. The Wo varies between. 0.38 ≤ Wo ≤ 8.59. To understand how the flow responds to a given boundary conditions, the critical Taylor number is calculated and the structure of vortices which formed in the flow field is investigated. The results show that if Wo is increased, i.e. when the slope of rotational velocity of inner cylinder is increased, more delay in changing the flow regime compare to the steady state (when the inner cylinder rotates with constant velocity) is observed. Also for large values of Wo, due to the inertia, the flow does not follow the given boundary condition so for the higher value of the Womersley number, Wo = 8.59, there is a time lag and vortices do not appear until the second period of the inner cylinder oscillations. The reason is that the time scale of the dynamics of flow is less than the time scale that is associated with the flow instability, thus the flow regime behaves like a laminar Couette flow at the initial period. Comparing the present results with that of steady state, it is appeared that for a minimum value of Wo used in this paper, i.e. Wo = 0.38, the primary critical Taylor number is 50% higher than that of steady state.

A 3-D simulation of red blood cells (RBCs) described as deformable cells in plasma flow is an indispensable element of blood flow analysis in the human vessels. To numerically investigate RBC motio...

Effects of geometric parameters of diffuser vanes as well as impeller micro grooves depth on the performance of a vertically suspended centrifugal pump have been studied. Different diffuser vanes height,leading angles, trailing angles, wrapping angles and furthermore, impeller micro grooves depths have been analyzed thoroughly. Numerical results have been verified by comparing experimental data. Results, without considering cavitation, reveal that diffuser vanes height has the profound impact on the vertically suspended centrifugal pump performance followed by vanes wrapping angle. Additionally, it is observed that delivered head and efficiency of micro-grooved impellers reduce more by flow rate enhancing rather than that of the original impeller.

Three-dimensional unsteady flow around a finite wall mounted square cylinder subjected to a steady secondary flow (blowing and suction) from the cylinder's front face has been studied with the aid of direct numerical simulations. The aspect ratio (AR) of the cylinder was varied as AR = 2, 4 and 7 while the ratio Г of the secondary flow to the freestream velocity was changed as −4 ≤ Г ≤ 4. All simulations were carried out at a Reynolds number (Re) of 250, based on the cylinder width, to investigate the influence of Г and AR on cylinder forces, vortex shedding frequency, and mean and instantaneous wake structures. The results show that, independent of AR, both blowing and suction have the potential to reduce the time-mean forces (e.g. more than 90% pressure drag reduction), fluctuating forces and vortex shedding frequency. Furthermore, a detailed investigation of vortex evolution reveals that the suction strategy considerably affects the shedding type and wake flow topology. Increasing the suction ratio changes the shedding from symmetric to asymmetric at AR = 4. Conversely, a planar jet attenuates vortical structures in the vicinity of the wall. Jet deflection is observed at Г = 2 and 4, which plays a key role in the success of the control approach and in the determination of the wake flow structure by changing the pressure distribution on the front face. The effect of AR on the shedding of large-scale vortical structures is also examined. Two critical AR values are determined where the flow and the mean wake structure changed from steady to unsteady (2

We present molecular dynamics simulations of stationary argon gas in nanoscale confinement and under various temperature differences between walls. For a channel of 5.4 nm height, we vary the gas density and find that in addition to the temperature difference between the walls, the absolute temperature of each wall plays an important role in the determination of the gas molecule distribution regardless of the level of rarefaction. The combined effect of the wall force field, the temperature difference between the walls and the wall temperature leads to the fact that the normalized temperature profile along the channel height does not coincide for various temperature differences between the walls. As the gas density is increased, it is observed that the wall force field effect on the density and temperature profiles reduces considerably due to the increment in the magnitude of the gas force field for all implemented temperature differences. Considering the temperature profiles and the distribution of the effective local thermal conductivity (ELTC) along the channel height, it is inferred that a diffusive transport mechanism is dominant throughout the dense gas medium. Besides, as the gas becomes rarefied, ballistic transport in the bulk region and diffusive transport in the regions close to the walls are observed. Furthermore, the effective thermal conductivity is a function of the implemented temperature differences between the walls and its value at 300 K varies from 0.18 to 12 mW / mK as the bulk gas density changes from 1.95 to 196 kg / m 3 .

In this work, water and water/Al2O3 nanofluid forced convection are studied numerically through a rotating U-shaped microchannel. The hydrophilic (no-slip flow) and hydrophobic (with slip length of 5 μm) conditions are used on the microchannel walls. Simulations are provided for various nanoparticle volume concentrations (ϕ=0-5%), and rotational speeds (ω =0-300 rad/s) and Reynolds numbers (Re=200-1000) to study their effects on the pressure drop, heat transfer, and thermal performance coefficient. A modified thermal performance criterion is suggested to include the variations of the working fluid properties relative to the reference case. It is observed that the existence of the nanoparticles in the base fluid provides considerable improvement on the heat transfer. The nanofluid flow also improves the thermal performance coefficient for volume concentrations of ϕ=0.5% and 2%, while it reduces for ϕ=5%. Although the thermal performance coefficient of the nanofluid flow at ϕ=5% decreases due to high pressure drop, but it is recommended to use water/Al2O3 at ϕ=5% as working fluid due to its high heat transfer enhancement (about 40%).

The dynamics of tumor growth and associated events cover multiple time and spatial scales, generally including extracellular, cellular and intracellular modifications. The main goal of this study is to model the biological and physical behavior of tumor evolution in presence of normal healthy tissue, considering a variety of events involved in the process. These include hyper and hypoactivation of signaling pathways during tumor growth, vessels’ growth, intratumoral vascularization and competition of cancer cells with healthy host tissue. The work addresses two distinctive phases in tumor development—the avascular and vascular phases—and in each stage two cases are considered—with and without normal healthy cells. The tumor growth rate increases considerably as closed vessel loops (anastomoses) form around the tumor cells resulting from tumor induced vascularization. When taking into account the host tissue around the tumor, the results show that competition between normal cells and cancer cells leads to the formation of a hypoxic tumor core within a relatively short period of time. Moreover, a dense intratumoral vascular network is formed throughout the entire lesion as a sign of a high malignancy grade, which is consistent with reported experimental data for several types of solid carcinomas. In comparison with other mathematical models of tumor development, in this work we introduce a multiscale simulation that models the cellular interactions and cell behavior as a consequence of the activation of oncogenes and deactivation of gene signaling pathways within each cell. Simulating a therapy that blocks relevant signaling pathways results in the prevention of further tumor growth and leads to an expressive decrease in its size (82% in the simulation)., Author summary Mathematical modeling and simulation of cancer across different biological scales is becoming increasingly important in the development of therapeutic strategies. In the current work, a multiscale model is presented to study the growth and progression of tumor and angiogenesis based on tumor-host interactions which allows investigating the effects of tumor-targeted therapy. Considering the signal-transduction networks involved in various types of cancers, we proposed a cascade that encompasses some significant signaling pathways. A Boolean network model is employed to describe the receptors cross-talk. As a result of the activation of oncogenes and deactivation of pertinent gene signaling pathways within each cell, the cellular interactions and cell behavior are modeled. By linking cells state with environmental cues, the tumor morphology is determined. Consistent with the experimental observations, the intratumoral vascularization density resulting from the simulation reports malignancy grade as a prognostic parameter. Moreover, our model permits to explore possible novel therapeutic procedures, including therapies targeting specific pathways. It captures cellular apoptosis by receptor inhibition in tumor development as a new area of mathematical modeling of targeted therapy.

The effect of the wall force field and the wall physical characteristics on the interfacial phenomena of a 5.4 nm nanoconfined gas medium are investigated by applying three-dimensional molecular dynamics simulations. Assuming that a range of 1 nm from each wall is affected by the wall force field, the gas distribution changes notably in this region which covers 40% of the channel height. Therefore, a combined effect of the wall force field and the wall stiffness, its mass as well as the interaction strength determines the interfacial phenomena such as interfacial thermal resistance (ITR) at the gas/solid interface. The increment in interaction strength of the gas/solid atoms leads to an increase in the amount of adsorbed gas on the wall which reduces the temperature jump and ITR notably. When the ratio between the interaction strengths of the gas/solid to the gas/gas atoms exceeds 4, the temperature jump and the ITR reduce to zero. As the wall becomes stiffer, the temperature jump and consequently the ITR are increased considerably. Simultaneously, the temperature distribution in the gas medium along the channel height becomes more and more independent of the gas density as the wall stiffness increases. It is observed that as the ratio between the mass of the wall and the gas atoms increases up to 2, the temperature jump reduces notably. Meanwhile, as the wall atoms become heavier, an increment in the temperature jump is observed. Consequently, the minimum ITR occurs at a ratio of 2. It is also shown that the temperature profile in the bulk region of the channel is approximately independent of the wall mass. Considering several metals as the wall material, our analysis reveals that silver, copper, and nickel experience the least ITR among the others.

In this paper, a parametric study of anode channel clogging of a proton exchange membrane fuel cell (PEMFC) is presented using the numerical volume of fluid method. The droplet size distribution in the present research is considered close to reality. Therefore, three droplets with different sizes are initially placed on the anode channel wall. The droplet sizes are obtained based on the distribution of the saturated liquid water along the whole channel under a specific working condition and the amount of condensed water in the channel, using the PEMFC code. Finally, the dynamic behavior of the droplets is investigated and compared to that of a single droplet with the same total volume. Numerical results show that, in the case of three droplets, the droplets coalesce during the removal time and form a larger droplet. Also, the droplets gradually spread over the channel walls and eventually reach the upper corners of the channel and form liquid slugs. Then, the slugs move slowly toward the channel outlet, and after a while, their shapes and positions are fixed and cause the channel clogging. Changing the number of droplets does not significantly change the time of channel clogging. The numerical results show that the time-averaged pressure drop of three droplets is about 85% less than that of a single droplet.

In this study the hemodynamic analysis of complete coronary bypass graft with elastic walls and different percentages of stenosis are investigated numerically. Blood flow is considered Newtonian and unsteady. The objective of this study is to deal with the influence of the wall elasticity, flow pulsatility and stenosis percentage on the flow configuration, Wall Shear Stress (WSS) and rotational flows. By comparing the rigid and elastic wall results of WSS, it is concluded that WSS obtains lower values in toe, heel and bed of the host vessel under the bifurcation in the elastic mode, which is closer to reality. Also it is concluded that with increasing the stenosis percentage, the possibility of occurring rotational flow will increase. The maximum and minimum values of WSS are observed in the stenosis of 70%. From the pulsatility of flow, it is observed that unsteady flow shows more accurate results also velocity and WSS have lower values compared with the steady state results.

The interactive thermal wall model is applied in three-dimensional molecular dynamics simulations to investigate the combined effect of the wall force field, the wall stiffness, the wall atom mass and the wall/gas interaction potential strength on the heat transfer characteristics of static rarefied argon gas within a nanochannel. By increasing the wall stiffness, a reduction in the heat flux through the gas medium occurs which leads to a higher temperature jump. As the wall atom mass is increased up to twice the argon atom mass, the heat flux is enhanced notably and a minimum temperature jump can be found at this point. Further increase in the wall atom mass results in reducing the heat flux and consequently increasing the temperature jump. The increment of the wall/gas interaction potential strength up to four times the one of gas/gas interactions is shown to enhance the heat flux and to reduce the temperature jump until it eventually vanishes. Furthermore, it is found that under such conditions, the density profile experiences a second peak. A further increase of this parameter is found to have a negligible effect on the heat flux through the gas medium and it only increases the second peak in the density profile.

Chaotic advection flow is one of the most useful methods to enhance mixing and heat transfer simultaneously in the laminar flow which is generated by spatially chaotic trajectories of the fluid particles. The present study aims to characterize the behavior of chaotic advection flow and heat transfer in a twisted pipe. The considered geometry consists of three 90° bends with an elliptical cross-section; the angle between curvature planes of consecutive bends is 90°. Numerical simulations are performed for both steady-state and pulsatile (unsteady) inlet velocity conditions with the Reynolds numbers in the range of 200 ≤ Re ≤ 450, wall temperatures 310 ≤ Tw (K) ≤ 340, velocity amplitude ratios (the ratio of peak oscillatory velocity component to the mean flow velocity) 1 ≤ β ≤ 3, and Womersley numbers 2.1118 ≤ α ≤ 7.9018. Mixing and heat transfer are analyzed both qualitatively and quantitatively for various considered conditions. The results revealed that the elliptical cross-section has a considerable impact besides the chaotic configuration on mixing and heat transfer enhancement. In the steady-state flow, the desirable system efficiency can be achieved either by increasing the wall temperature or decreasing the Reynolds number. Moreover, in the pulsatile flow, the Womersley numbers in the range of 2.1118 ≤ α ≤ 3.9509 provide a favorable condition to augment the mixing and heat transfer in the twisted pipe.

In the present study, influences of impeller splitter blades on the performance of a centrifugal pump when handling viscous fluids have been investigated numerically and experimentally. In order to approach this aim, various splitter blades have been inserted on the impellers that pump viscous fluids ranging from 1 cSt to 500 cSt and the optimum splitter blade length based on the numerical results were constructed and tested thoroughly. Effects of splitter blades with lengths of 0.3, 0.45, 0.6 and 0.75 times of the main impeller blades were analyzed numerically. Results revealed that splitter blades have significant effect on the performance of a centrifugal pump. In fact, splittered impellers extend the operating region of centrifugal pumps remarkably and also among different surveyed splitter blades the head and efficiency increase by 20% and 3% respectively by using splittered impeller of 0.75L in comparison with the original impeller (without splitter blade). Moreover, the data analyses shows that splittered impellers can be used for pumping viscous fluids in the almost all operating conditions of non-splittered impellers with less viscous working fluid and obtained reasonable performance.

The effect of changing the Knudsen number on the thermal properties of static argon gas within nanoscale confinement is investigated by three-dimensional molecular dynamics simulations. Utilizing thermalized channel walls, it is observed that regardless of the channel height and the gas density, the wall force field affects the density and temperature distributions within approximately 1 nm from each channel wall. As the gas density is increased for constant channel height, the relative effect of the wall force field on the motion of argon gas atoms and, consequently, the maximum normalized gas density near the walls is decreased. Therefore, for the same Knudsen number, the temperature jump for this case is higher than what is observed for the case in which the channel height changes at a constant gas density. The normalized effective thermal conductivity of the argon gas based on the heat flux that is obtained by implementation of the Irving-Kirkwood method reveals that the two cases give the same normalized effective thermal conductivity. For the constant density case, the total thermal resistance increases as the Knudsen number decreases while for the constant height case, it reduces considerably. Meanwhile, it is observed that regardless of the method used to change the Knudsen number, a considerable portion of the total thermal resistance refers to interfacial and wall force field thermal resistance even for near micrometer sized channels., 18 pages, 11 figures

The aim of this paper is to use the thermo-viscous expansion-contraction effect to enhance mixing in microchannels. To do this, numerical simulation of chaos flow generated by periodic thermal boundary condition in a 2-D microchannel is considered.The main objectives are to evaluate the effect of Reynolds number, Strouhal number and thermal penetration length on chaotic mixing. The vorticity is used as a criteria evaluating the chaos. It is shown that thermo-viscous expansion-contraction effect can be used as aconsiderable potential mean for micro-scale chaotic mixingpotential mean for micro-scale chaotic mixing. The results show that, the vorticity generated by change of density and viscosity due to the temperature difference caused by periodic heat transfer at flow boundary is mainly a function of dimensionless flow velocity and film thickness.

This research focuses on numerically investigating the self-diffusion coefficient and velocity autocorrelation function (VACF) of a dissipative particle dynamics (DPD) fluid as a function of the co...

We describe in this work a numerical simulation of chaotic heat transfer by laminar flow in a twisted pipe that consists of three bends. Observations on the secondary flow topology changed by the variation of Reynolds number and tube wall temperature as well as their coincidence with heat transfer enhancement are discussed. Both steady and pulsating flows with constant wall temperature are considered. Numerical simulations are performed for Reynolds numbers range 300 1) provide a more complex secondary flow and hence a better heat transfer. Pulsation energy consumption is higher than the energy needed for increasing Reynolds number of the steady flow to match the same heat transfer enhancement. However, a better heating uniformity is obtained in the pulsating flow, which is not the case in the steady flow.

Nanoparticles deposition is one of the most challenges for industrial use of nanofluids. In the present study, the heat transfer enhancement of Multi Wall Carbon Nano Tube, MWCNT-water nanofluid in a double pipe heat exchanger due to vibrating walls is examined for different mass fractions. This work is performed by a flexible double pipe heat exchanger made of PVDF. The forced vibration on the outer surface of the heat exchanger is imposed by electro-dynamic vibrators. Results demonstrate that imposing the vibrations increases the heat transfer coefficient remarkably, while decreases the nanoparticles deposition. Heat transfer increases by increasing the nanofluid temperature, mass flow rate, nano fluid mass fraction and vibtation level. The most increase in heat transfer coefficient is 100% which is obtained in the test of the lowest mass fraction (0.04%) with the highest vibration level (9 m/s2) in the experiment range.

This study aims to investigate experimentally the influence of rounding corners (r) as well as aspect ratio (AR) on the flow structures of a surface-mounted finite cylinder. The cylinders with sharp (r* = r/D = 0) and rounded corners (r*=0.167, 0.25 and 0.5) and aspect ratio or height-to-width/diameter ratio (AR = H/D) between 2 and 7 are utilized. The experiments are based on the five-hole probe and hot-wire measurements as well as the oil flow visualization. Wake measurements are made in an open return wind tunnel at the Reynolds number, Re = 1.6 × 104, where Re is defined based on the side width/diameter (D) of the cylinder cross-section and the freestream velocity. It is found that r* and AR have significant effects on the flow structure from the perspective of wake topology, strength of streamwise vortices, and vortex shedding frequency. For all r* considered, the wake is characterized by a quadrupole type (both the tip and base vortices are present) at AR = 7, while a dipole type occurs for AR = 2 and 4 (the base vortices are absent). The strength (circulation) of the streamwise vortex structures is affected by r*. For all AR examined in the present study, the strengths of tip and base vortex structures decrease with increasing r*. The oil flow visualization demonstrates that the features of the horseshoe vortex are sensitive to r* and AR. With increasing r*, the location of the separation line moves downstream and the distance between horseshoe vortex legs decreases. Velocity measurements reveal that the downwash flow enhances with increasing r*. It is also found that the Strouhal number increases progressively by 60% as r* increases from 0 to 0.5, regardless of AR.

Although the study of flow around buildings has a rich background, the development of construction material, the congestion of buildings, the urban ventilation and consideration of pedestrian wind condition make the necessity of further insightful flow-physic studies. This study numerically investigates the gap and wake flows associated with two inline non-identical-height (aspect ratios of 4 and 7 for the up- and downstream) buildings at a Reynolds number of 2.2 × 104 and gap spacing (G*) of 1, 3, and 5 through the large eddy simulation technique. It is found that an increase of G* mostly affects the flow pattern in the gap, so that the slender-body, alternate reattachment and semi-stable gap flow at the G* of 1 (or 3) turns into the co-shedding flow at the G* of 5. The pressure coefficients ( C ¯ p ) on the cylinders' faces show that an increase of G* from 1 to 3 increases/decreases the C ¯ p on the side (and top) faces of upstream/downstream cylinders, respectively. Further increasing G* from 3 to 5, however, drops the C ¯ p on the side and top faces of both cylinders. On the other hand, the flow regime produces a profound effect on the pedestrian level so that the strong wind condition appears in the small gap, and a very weak wind condition in the vortex cores. Hence a minimum gap of 3 is recommended for better pedestrian level wind conditions. Besides, increasing gap from 1 to 5 reduces the shielding effect of the interfering building markedly.

The impinging turbulent slot jet was investigated experimentally using tomographic particle image velocimetry technique. The jet Reynolds number was considered equal to 9000 and the nozzle to plate distance was 10 times the width of the nozzle. The mean flow and turbulent statistics were evaluated at different cross-sections. Then, the dominant three-dimensional structures of the turbulent flow were identified using the Proper orthogonal decomposition (POD) method, and the contribution of different energy modes to the total energy was determined. It is observed that the first 40 POD modes can be considered as the dominant flow modes which contain about 89 % of total kinetic energy of the flow. Also, horseshoe form structures were observed in some POD modes on both sides of the jet central plane. Finally, three-dimensional vortex structures were specified using vorticity, Q and λ2 criteria, and compared with each other.

Frostbite is considered the severest form of cold injury and can lead to necrosis and loss of peripheral appendages. Therefore, prediction of endurance time of limb's tissue in cold condition is not only necessary but also crucial to estimate cold injury intensity and to choose appropriate clothing. According to the previous work which applied a 3-D thermal model for human finger to analyze cold stress, in this study, an expression is presented for endurance time in cold conditions to prevent cold injury. A formula is also recommended to select a proper glove with specific thermal resistance based on the ambient situation and cold exposure time. By employing linear extrapolation and real physical conditions, the proposed formulas were drawn out from numerical simulation. Analytical results show good agreement with numerical data. The used numerical data had been also validated with experimental data existed in the literature. Furthermore, the effect of different parameters such as glove thermal resistance and ambient temperature is investigated analytically.

The transport coefficients of a dissipative particle dynamics system are investigated numerically taking into account the conservative force. The influence of the conservative force parameter on kinetic and dissipative viscosity is considered and compared with theoretical predictions. The analytical solution of the potential term that arises from the conservative force is generally very complicated; therefore, this term has been ignored in most previous work and deemed negligible. In the present work, an expression for the effect of the conservative force on potential viscosity is semi-empirically obtained revealing the dependence of the latter on various parameters such as conservative force strength, density number and temperature. This relation offers a proper approximation of conservative force impact on potential viscosity.

A new and rather accurate correlation for prediction of effective diffusion coefficient is proposed for the biological tissue in the brain. Blood flow in brain capillaries and mass diffusion process in the tissues as a porous media, surrounding the capillaries, are simulated by using the random nature of tissue structure and the lattice Boltzmann method. The present correlation which is obtained from the lattice Boltzmann method and is taken into account the effects of the pore or cell structure is validated by comparing it with that of theoretical, statistical and experimental data. A very good coincidence between experimental data and present results have been found. So, the results show that the new model for the effective diffusion coefficient is a good choice for normal and damaged brain tissue and it produces more accurate results than existing models.

Numerical simulations are performed to investigate the fluid flow and heat transfer in a three-dimensional rotating U-shaped microchannel with a square cross-section for Reynolds numbers of 200–1000. Water is employed as working fluid. The microchannel surface is considered to be hydrophilic (no-slip flow) and hydrophobic (slip flow). Effects of slip flow, temperature jump and rotational speed in the range of 0–300 rad/s are studied on the heat transfer, pressure drop and thermal performance coefficient. Various slip lengths ranging from zero (hydrophilic surface) to 10 μm are employed and their results are compared. It is observed that the effect of slip flow results on the leading and trailing walls is not similar due to the rotational effects. It is found that the slip flow augments the heat transfer rate in comparison with that of no-slip flow while using both slip flow and temperature jump reduces the heat transfer rate in comparison with that of slip flow. A relatively large reduction on the pressure drop and an improvement on the Nusselt number are found when the slip length increases from zero to 10 μm. The thermal performance coefficient increases about 90% for 10 μm slip length in comparison with that of no-slip condition. Moreover, for a rotating microchannel (300 rad/s), the thermal performance coefficient increases about 43% for low Reynolds numbers and about 11% for large Reynolds numbers in comparison with that of the stationary microchannel.

Molecular dynamics simulations of static argon gas at three different levels of rarefaction are conducted for a channel of 5.4 nm height to investigate the simultaneous effect of the wall force field and the gas temperature on the stress distribution along the channel height. Using the interactive thermal wall model, different temperatures are applied on the channel walls to be able to investigate the effect of the wall temperature and the induced heat flux through the gas medium on the stress distribution. Considering the monoatomic neutral argon gas, the kinetic, particle-particle virial, and surface-particle virial are considered for computing the stress distribution along the channel height. The normal stress components in the bulk gas region are distributed isotropically regardless of the gas density, temperature, and induced heat flux through the domain, while an anisotropy is observed due to the presence of the surface-particle virial. As the gas becomes hotter, the velocity of the gas atoms increases, and thus the kinetic stress component also increases. Besides, the gas density in the wall force field region reduces which eventually attenuates the surface-particle and particle-particle virial stress within 1 nm from each wall. This effect was also observed as the gas becomes cooler. It is shown that the combination of gas density, wall temperature, and induced heat flux are the main parameters which determine the distribution of stress within the gas medium especially in the wall force field region where repulsive and attractive interactions exist.

In the present study, a new mathematical model for mass transfer in extra-vascular space is presented to indicate the effect of dead cells in infarcted tissues. This model is useful for predicting the results of experiments which are designed to distinguish normal from infarcted tissues and it can be used to approximate the percent of damaged cells in the infarcted tissue. The increase of permeability due to existence of dead cells caused by infarction is modeled as a sink term. The present model is validated for two different solutes by comparing their results with the existing experimental data. It is shown that the presented model is an appropriate model for simulating mass transfer in tissues. Furthermore, the sensitivity of the model to the effective diffusion coefficient, Schmidt number, porosity and Damkohler number is examined. The simulations show that permeability of dead cells significantly affects the volume of the contrast agent in the infarcted tissue. The results also indicate that the Schmidt number not only affects the mass diffusion through damaged tissues, but also influences the partition coefficient. The other parameters mentioned above have effects on the amount of mass diffusion into the infarcted tissue when the extent of damage in tissues is changed.

In the present study, the ball-spine inverse design algorithm is developed for swirling viscous flow regime to improve the performance of an axisymmetric 90-degree bend duct between the radial and axial diffuser of a centrifugal compressor. Performance improvement of the 90-degree bend duct is accomplished to increase its pressure recovery without separation. First, the effects of geometric parameters on flow separation are numerically studied and a safe margin is obtained for prevention of flow separation and stall. Then, the safe margin is enlarged to reach a higher pressure recovery via the shape modification of duct walls. The shape modification process integrates the BSA as shape modification algorithm and an axisymmetric flow analysis code as flow solver. Shape modification process is carried out by improving the current wall pressure distribution and applying it to the inverse design algorithm. Results show merits and robustness of the BSA for duct design in swirling viscous flow regime whereby the pressure recovery coefficient of the 90-degree bend duct increases up to 7%.

Electroosmosis is the predominant mechanism for flow generation in lab-on-chip devices. Since most biofluids encountered in these devices reveal non-Newtonian behavior, a special understanding of the fundamental physics of the relevant transport phenomena seems vital for an accurate design of such miniaturized devices. In this study, a numerical analysis is presented to explore transport characteristics of typical non-Newtonian biofluids through annular microchannels under combined action of pressure and electrokinetic forces. The flow is considered steady and hydrodynamically fully developed. A finite difference method is used to solve the Poisson-Boltzmann and Cauchy momentum equations, while the classical boundary condition of no velocity-slip for the flow field is applied. The Poisson-Boltzmann equation is solved in the exact form without using the Debye-Huckel approximation. After numerically solving the governing equations, role of the key parameters in hydrodynamic behavior of the flow is analyzed and discussed.

The performance of standard Lattice Boltzmann, LB, is confined to the micro scale flows with a Knudsen number, Kn , less than 0.1. In the previous works we proposed a modified LB which is able to extend the ability of LBM to simulate wide range of Knudsen flow regimes. To study the ability of this model for porous media, in the present work we investigate nanoscale gaseous flows through porous media confined between parallel plates by means of LB, and molecular dynamics, MD, simulations. The comparison between modified LB and MD shows a very good agreement at sufficiently low solid fractions. In addition, flow characteristics through various porous structures are studied via the MD simulation and the effect of various parameters such as driving force, porosity and Knudsen number on the velocity and temperature distributions is investigated. Our results demonstrate the good ability of MDS for investigating different flow phenomena such as permittivity and Darcian flow in porous media.

In this paper, flow past a single Dissipative Particle Dynamics (DPD) particle with low Reynolds number is investigated and it is inquired that whether a single DPD particle immersed in a fluid, has an intrinsic size. Then a minimum length scale is determined such that the hydrodynamic behavior based on standard DPD formulation is modeled correctly. Almost all of the previous studies assume the DPD particles as point centers of repulsion with no intrinsic size. Hence to prescribe the size of a simulating sphere, a structure of frozen DPD particles is created. In this paper two effective radii, Stokes-Einstein radius and a radius based on the Stokes law, for DPD particles are introduced. For small Reynolds numbers; it is proved that the two radii approach each other. Finally in spite of the typical simulations which assume DPD particles as point centers of repulsion, it is concluded that each of the individual DPD particles interact with other particles as a sphere with non-zero radius. It results the reduction of the required number of particles and eventuates more economical simulations. Moreover contemplating the radius of the particles is necessary for the new Low-Dimensional model which is derived based on the DPD method.

In the present study, impinging of vertical twin jet against a horizontal plate is numerically and experimentally investigated. Four two equation RANS based turbulence models are used and their capabilities to simulate such complicated turbulent flow were examined. The two fluid jets are separated by a thin membrane. The inlet jet hydraulic diameters are the same and the Reynolds number of external flows of jets is 13500. The ratio of width of nozzles (e) to nozzle-to-plate distance (H) considered as 1:10. The turbulent models used in this work are k-e, k-e RNG, k-ω and k-ω SST. The results obtained by the models were compared with each other as well as two-dimensional PIV data to evaluate the capabilities of such models for this kind of flows. By comparing the numerical and experimental results, it is concluded that all of the models can predict acceptable results in the free jet area, but in the near wall region none of the models can predict flow characteristics with reasonable accuracy. It was observed that, at low nozzle-to-plate distances, the prediction results of the turbulence models are approximately in accordance with the experimental data, particularly for a zone near the midline separating the two jets.

The structure-function relation is one of the oldest hypotheses in biology and medicine; i.e., form serves function and function influences form. Here, we derive and validate form-function relations for volume, length, flow, and mean transit time in vascular trees and capillary numbers of various organs and species. We define a vessel segment as a “stem” and the vascular tree supplied by the stem as a “crown.” We demonstrate form-function relations between the number of capillaries in a vascular network and the crown volume, crown length, and blood flow that perfuses the network. The scaling laws predict an exponential relationship between crown volume and the number of capillaries with the power, λ, of 4/3 < λ < 3/2. It is also shown that blood flow rate and vessel lengths are proportional to the number of capillaries in the entire stem-crown systems. The integration of the scaling laws then results in a relation between transit time and crown length and volume. The scaling laws are both intra-specific (i.e., within vasculatures of various organs, including heart, lung, mesentery, skeletal muscle and eye) and inter-specific (i.e., across various species, including rats, cats, rabbits, pigs, hamsters, and humans). This study is fundamental to understanding the physiological structure and function of vascular trees to transport blood, with significant implications for organ health and disease.

In this paper a new analytical relation is presented to approximate pressure-flow rate relationship in terms of the dimensions of impeller and channel geometries for small regenerative turbine pumps (RTPs) using some simplifying assumptions. Numerical simulation of the pump is conducted to compare the results with that of the analytical one. It is demonstrated that the presented analytical relation approximates the P-Q curve of the real pump satisfactorily. Finally, sources of the deviation of the pump behavior from predictions made by the proposed analytical relations are examined and discussed.

There are two coefficients termed as “slip factor” and “shock loss (incidence) coefficient” that play an important role in performance and designing process of regenerative pumps. In this research, numerical simulation of regenerative pumps with incompressible flow and different dimensions of channel is conducted. A new technique is presented for accurate computation of “slip factor” and “shock loss coefficient” from numerical simulation of the pump. This technique is applicable to different sizes and models of regenerative pumps. By employing the presented technique, the influential coefficients and circulatory flow for two small regenerative pumps are examined quantitatively. Quantitative and accurate computation of shock loss coefficient and slip factor in regenerative pumps through numerical simulation is new to the literature. Finally, changes of the coefficients in a pump are examined as channel dimension changes.

In this research, a new method called elastic surface algorithm is presented for inverse design of 2-D airfoil in a viscous flow regime. In this method as an iterative one, airfoil walls are considered as flexible curved beams. The difference between the target and the current pressure distribution causes the flexible beams to deflect at each shape modification step. In modification shape algorithm, the finite element equations of two-node Timoshenko beam are solved to calculate the deflection of the beams. In order to validate the proposed method, various airfoils in subsonic and transonic regimes are studied, which show the robustness of the method in the viscous flow regime with separation and normal shock. Also, three design examples are presented here, which show the capability of the proposed method.

Growth of stenosis is mainly due to the high concentration of plasma lipoprotein such as low density lipoprotein (LDL) near the art ery walls. Accurate prediction of LDL concentration especially near the stenosis and where the shear stress is low, can help to predict the plaque growth. In this paper, a novel model is introduced to predict the LDL concentration near a plaque. This model is based on variable diffusion coefficient of LDL due to the non-Newtonian behavior of the blood flow in low shear stress regions such as flow around plaques. The new model for diffusion coefficient consists of two parts: the stationary and the shear- induced particle diffusivity due to rotation of red blood cells. The results show that the new model predicts the LDL concentration well and unlike the constant diffusion coefficient which is used by others, produces more physical and meaningful results.

In this work, for better understanding of microvessels disorders, mass transfer at a stenotic and the straight capillary wall in the presence of RBC motion is investigated. The immersed boundary- lattice Boltzmann method is used for this purpose. The erythrocyte is considered as an immersed biconcave shaped tissue around the capillary as a porous media. The gamma function for input concentration, which is close to the actual stenosis brain capillary, is used. The simulated results obtained for both stenosis and straight capillaries are compared. It is shown that while the RBC motion has negligibly small effects on wall mass transfer in straight capillaries, its effect is not negligible at stenosis capillaries.

Analytical relation for slow motion thin liquid films bounded by a fixed wall and free surface for Newtonian and non-Newtonian fluids are obtained in this work. Assuming long-wave approximation, the momentum and continuity equations for thin liquid films of power-law fluids are simplified and solved analytically to derive the evolution equation of thin liquid films. The evolution equation is derived for two- and three-dimensional cases. A relation for evolution of thin films is obtained for a simple case in which the liquid film is supported from below by a solid surface and subjected to gravity and constant surface tension forces. This evolution equation of thin film has been solved numerically in order to compare the behavior of Newtonian and non-Newtonian liquids for different Bond numbers. It is shown that the power-law model at low and high strain rates is invalid and it affects the results. The Rayleigh-Taylor instability is another subject that is studied in this work. This interesting phenomena is investigated by solving the evolution equation numerically for different Bond numbers. The results show that the evolution of the free surface thin film for pseudo plastic fluids is different from that of Newtonian and dilatant fluids