Fluid-Structure Interaction Simulation of Blood Flow Inside a Diseased Left Ventricle With Obstructive Hypertrophic Cardiomyopathy in Early Systole

Mitral-Septal contact has been proven to be the cause of obstruction in the left ventricle with hypertrophic cardiomyopathy (HC). This paper presents a study on the fluid mechanics of obstruction using two-way loosely coupled fluid-structure interaction (FSI) methodology. A parametric model for the geometry of the diseased left ventricular cavity, myocardium and mitral valve has been developed, using the dimensions extracted from magnetic resonance images. The three-element Windkessel model [1] was modified for HC and solved to introduce pressure boundary condition to the aortic aperture in the systolic phase. The FSI algorithm starts at the beginning of systolic phase by applying the left ventricular pressure to the internal surface of the myocardium to contract the muscle. The displacements of the myocardium and mitral leaflets were calculated using the nonlinear finite element hyperelastic model [2] and subsequently transferred to the fluid domain. The fluid mesh was moved accordingly and the Navier-Stokes equations were solved in the laminar regime with the new mesh using the finite volume method. In the next time step, the left ventricular pressure was increased to contract the muscle further and the same procedure was repeated for the fluid solution. The results show that blood flow jet applies a drag force to the mitral leaflets which in turn causes the leaflet to deform toward the septum thus creating a narrow passage and possible obstruction.

Research on the Design Method of the Centrifugal Pump With Splitter Blades

The research on a centrifugal pump of low specific speed with splitter blades was carried out in recent years by our group, is systematically introduced in this paper. The design method is summarized also. At the beginning, based on the former L9(34) orthogonal test, Particle Imagine Velocity (PIV) tests and Computational Fluid Dynamics (CFD) simulations were carried out for several designs with different splitter blade length. Results show that for an impeller with splitter blades the “jet-wake” flow at the impeller outlet is improved, and the velocity distribution inside the impeller is more uniform. This explains that the impeller with splitter blades shows higher performance (especially in head and efficiency). Meanwhile, the numerical simulation results were compared with the test results, which confirm that, CFD technology can be used to observe inner flow distribution and forecast pump performance tendency. Later, a further L9(34) orthogonal test, which adopt the blade number as a new variable, was designed to explore the relationship between geometry parameters of splitter blade and pump performance, and corresponding CFD simulations for the flow field with volute were also done. From the test results the influence of the main design parameters on the hydraulic performance of a centrifugal pump and its reasonable value range are determined. The simulations forecasted pump performance show good consistency with that from tests at the rated point, and the simulated error at other flow rates were analyzed. Thirdly, in order to save research cost, numerical simulations were done for the full flow field including the cavity inside the volute and impeller. By analyzing the distribution law of blade torque and turbulent kinetic energy in the impeller, the value fetching principle for the splitter blade inlet diameter is presented as “the splitter blades torque should be positive”, and by analyzing the distribution of blades loading, the flow distribution rules and pump performance influenced by different splitter blades off-setting angles and inlet diameters were discovered. The disk friction loss, which consuming much energy in centrifugal pumps, was also forecasted at various operating conditions. The results were compared with that from empirical formulas, which show great accordance at the rated point, and the forecasted results at off-design points were analyzed also. Finally, the research results and the design method for the centrifugal pump with splitter blades, such as how to select splitter blade number, the off-setting angle, the inlet diameter and the deflection angle, were summarized.

Analysis of Physical Properties and Experimental Behaviour of High Turbulent Flow in Cross-Flow Microfiltration of Ac¸ai Juice

This paper presents an experimental investigation of the cross-flow microfiltration process applied to the clarifying of ac¸ai (Euterpe oleracea Mart.) juice. Ac¸ai juice is a complex fluid, similar to a suspension of particles (fibers and cellulose) mixed in water, which contains ions of iron, zinc, maganese and pigments, as anthocyanins. In this study, a commercial membrane of α-alumina (Al2O3) in the form of a tube with 1.2μm of average pore size was utilized to investigate the clarifying of juice. This pore size of the ceramic structure was utilized in an attempt to reduce the polarization phenomenon and improve the permeate flux without utilizing the usual enzymatic treatment made in the microfiltration processes. The rheological behaviour of the suspension was investigated in a cone/plate rheometer (model, DVIII-Ultra) and a cylindrical rheometer (model, DVIII+), both by Brookfield/USA, as the shear stress (τ) in function of shear rate (γ) was fitted and analyzed with the power-law and Herschel-Bulkley’s models. All the mixtures showed flow behaviour index values (n) near to one, characterizing Newtonian fluids (pseudo-plastic). The particle size distribution (PSD) of the samples of suspension and permeate were analyzed by APS100 (ultrasound spectroscopy) by Matec/USA. The analysis of the suspension showed the presence of particles of size equal 0.16micra, while the permeate did not present particles. The experiments were performed in a turbulent range higher than 2400 until 57500 and with variation to values of transmembrane pressure from 1 to 4bar; the usual and direct correlation between transmembrane flux and transmembrane pressure was not observed in the experiments and a new correlation to the dimensionless of TMP (trans-membrane pressure) and Reynolds (Re) was presented.

Prediction of Transition Region in Flow Over the Flat Plates

A new model has been developed to predict the onset of transition from laminar to turbulent regime and also calculate the transition flow field. In developing the model, we have used the V2F turbulence model to predict the Reθ and velocity fluctuations, u′, at the onset of transition point, extracted from the same available experimental cases over a flat plate for several experimental cases. Then, we have correlated Reθ as a function of u′ at the transition point. This correlation has been used in conjunction with the V2F model to find the onset of transition point. The intermittency model has also been modified to calculate the probability of turbulence regime all over the flow field to improve the eddy viscosity calculated by V2F model. The model has been tested for different flat plate flows and the results compared with experimental data insuring the accuracy of the model. Comparison showed that the model is a powerful tool for prediction of transition onset and also transition region.

Experimental Investigation of the Complete Characteristics of Rotodynamic Pumps

Pump failure in a pipeline system can occur for several reasons and this undesirable event causes waterhammer phenomenon. While designing a pipeline system, minimum and maximum pressures caused by waterhammer and the variation of the pressure along the pipeline with respect to time must be determined. In order to calculate the time variation of the pressure, complete characteristics of a pump is used as one of the boundary conditions. In these unsteady conditions, the pump may turn in normal or reverse directions which define eight different working zones called pump, turbine, brake and booster. Specific speed is an essential parameter which affects characteristics of pumps. In the literature, for many years there have been only three complete pump characteristics obtained with the assistance of 1960’s measuring devices and techniques. Each one of those corresponds to pumps having centrifugal (nsq = 35), mixed flow (nsq = 147) or axial impeller (nsq = 261). Recently additional complete pump characteristics that belong to 14 different specific speeds have been published in the literature. By considering improvements in pump design during half a century and innovations in measurement techniques, the present study is performed to repeat experiments of complete characteristics of different specific speeds existing in the literature, and to obtain complete pump characteristics for different specific speeds. The complete characteristics of seven pumps with specific speeds of nsq = 20 – 23 – 33 – 55 – 105 – 209 and 261 are obtained experimentally. The results show that the complete characteristics of a pump is not only function of specific speed but also function of pump design. The number of the complete pump characteristics available in the literature is increased in this study. The obtained results revealed that, unlike the existing approach in the literature, the complete characteristics of pump that is used in the pipeline, must be used in the calculation of waterhammer pressures in the design of pipelines.

Compressible Advection Through an Elastomer Seal: A Porous Media Approach to Seals for Space Applications

Gas permeability characterization is of the utmost importance in space seals applications. Space seals must maintain acceptable mass losses in harsh environments where temperatures widely vary under vacuum conditions. Silicone elastomers are commonly used in space as they offer significant sealing performance at temperature extremes and are capable of meeting stringent outgassing requirements necessary for vacuum environments. Traditional models of leak rates solely rely on a diffusive transport mechanism; mass is transported across a membrane through molecular flow induced by a concentration gradient under isostatic conditions. In the application of space seals, the pressure gradients are large, resulting in advection dominated transport. Conventional applications of advection utilize Darcy’s law; however, the fluid is assumed incompressible and fails to capture the nonlinear pressure gradient under compressible situations. Consequently, employing Darcy’s law incorrectly predicts the leak rate. A novel model in compressible advection through an elastomer seal is presented. A phenomenological approach is taken to determine the specific discharge. Through the conservation of mass, the governing equation for pressure is derived. An exact analytical solution exists for one-dimensional flow in the form of a Generalized Emden-Fowler equation and as a result, an analytical expression for mass flow is developed. A series of experiments is presented to deduce permeability constants and Klinkenberg parameter of silicone S0383-70 under one-dimensional flow conditions. The leak rates of the model and experiments are compared. Through the presented compressible advection model, the mass leak rate of any candidate seal geometry can be evaluated.

Numerical Investigations About the Effect of Non-Condensable Gas on Cavitating Flows

A series of numerical investigations was carried out to study the behavior of cavitating turbulent flows in an orifice. In the present work, two different cavitation models were used for the simulation. In the first model, flow was modeled as two interpenetrating fluids (liquid and vapor), and in the second model, the working fluid was assumed to be a mixture of three fluids (liquid, vapor and non-condensable gas). In both cases, we used a finite volume method to discretize the equations and SIMPLEC algorithm to link the pressure and velocity fields. An upwind scheme was used to model convective fluxes and other transport equations. Turbulence effects were considered using the k-ε model. Computations were performed at various inlet pressures and a fixed outlet pressure. The values of discharge coefficient obtained from the simulations were compared with published experimental data. Better agreement was found with the second model. This revealed the importance of non-condensable gases on cavitation. Furthermore, the distributions of vapor volume fraction and velocity magnitude were investigated with using both models. The results showed considerable differences between two models in description of inception of cavitation, distributions of vapor volume fraction and velocity magnitude.

Two-Fluid CFD Model of Adiabatic Air-Water Upward Bubbly Flow Through a Vertical Pipe With a One-Group Interfacial Area Transport Equation

This paper describes in detail the assessment of the CFD code CFX to predict adiabatic liquid-gas two-phase bubbly flow. This study has been divided into two parts. In the first exercise, the effect of Lift Force, Wall Force and the Turbulent Diffusion Force have been assessed using experimental data from the literature for air-water upward bubbly flows through a pipe. The data used here had a characteristic near wall void peaking which was largely influenced by the joint action of the three forces mentioned above. The simulations were performed with constant bubble diameter assuming no bubble interactions. This exercise resulted in selection of the most appropriate closure form and closure coefficients for the above mentioned forces for the range of flow conditions chosen. In the second exercise, the One-Group Interfacial Area Transport equation was introduced in the two-fluid model of CFX. The interfacial area density plays important role in the correct prediction of interfacial mass, momentum and energy transfer and is affected by bubble breakup and coalescence processes in adiabatic flows. The One-Group Interfacial Area Transport Equation (IATE) has been developed and implemented for one-dimensional models and validated using cross-sectional area averaged experimental data over the last decade by various researchers. The original one-dimensional model has been extended to multidimensional flow predictions in this study and the results are presented in this paper. The paper also discusses constraints posed by the commercial CFD code CFX and the solutions worked out to obtain the most accurate implementation of the model.

Multi-Objective Design Optimization of a Mixed-Flow Pump

In most cases of high specific speed mixed-flow pump applications, it is necessary to satisfy more than one performance characteristic such as deign point efficiency, shut-off power/head and non-stall characteristic (no positive slope in flow-head curve). However, it is known that these performance characteristics are in relation of trade-offs. As a result, it is difficult to optimize these performance characteristics by conventional way such as trial and error approach by modifying geometrical parameters. This paper presents the results of the multi-objective optimization strategy of mixed-flow pump design by means of three dimensional inverse design approach, Computational Fluid Dynamics (CFD), Design of Experiments (DoE), response surface model (RSM) and Multi Objective Genetic Algorism (MOGA). The parameters to control blade loading distributions and meridional geometries for impeller and diffuser blades in inverse design were chosen as design variables of the optimization process. Pump efficiency, maximum slope in flow-head curve and shut-off power/head were selected as objective functions. Objective functions of pumps, designed by design variables specified in DoE, were evaluated by using CFD. Then, trade-off relations between objective functions were analyzed by using Pareto fronts obtained by MOGA. Some pumps which have specific performance characteristic (non-stall, low shut-off power, high efficiency etc.) designed along the Pareto front were numerically evaluated.

A Method to Optimize the Operation of Pumping System

There are many pumps working in generating plant for pumping water in the cooling system. The pumps consume a big amount of electricity especially in large generating plant which operates continuously for long time. Therefore, the electric power cost will increase with increasing of operation cost of the pumping system. It is very important to minimize the operation cost of the pumping system to optimize the use of generating plant assets. In order to optimize the operation of pumping system the method of adjusting pump rotation speeds are often adopted. The fundamental factor of optimizing pump operation is to obtain the operation performance. Theoretically the affinity law (special modeling Equation) of pumps can be applied to convert the performances of pumps under rated speeds to variable rotation speeds. However the affinity law can only be applied in the region of pump operation around Best Efficiency Point with an acceptable precision. Also the affinity law derived from the Modeling Equation can only be valid to pump or pump bowl rather than pumping system. In this paper a method was conducted to determine the performances of pumping system based on the computational and experimental results. The principle of optimizing the pumping system is discussed. Finally the optimizing operation alternative of the pumping system is presented.