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Purpose This paper aims to investigate the influence of smooth curvature distributions on the self-noise of a low Reynolds number aerofoil and to unveil the flow mechanisms in the phenomenon. Design/methodology/approach In this paper, large Eddy simulation (LES) approach was performed to investigate the unsteady aerodynamic performance of both the original aerofoil E387 and the redesigned aerofoil A7 in a time-dependent study of boundary layer characteristics at Reynolds number 100,000 and angle of attack (AoA) 4-degree. The aerofoil A7 is redesigned from E387 by removing the irregularities in the surface curvature distributions and keeping a nearly identical geometry. Flow vorticity magnitude of both aerofoils, along with the spectra of the vertical fluctuating velocity component and noise level, are analysed to demonstrate the bubble flapping process near the trailing edge (TE) and the vortex shedding phenomenon. Findings This paper provides quantitative insights about how the flapping process of the laminar separation bubble (LSB) within the boundary layer near the TE affects the aerofoil self-noise. It is found that the aerofoil A7 with smooth curvature distributions presents a 10% smaller LSB compared to the aerofoil E387 at Reynolds number 100,000 and AoA 4-degree. The LES results also suggest that curvature distribution smoothing leads to a 6.5% reduction in overall broadband noise level. Originality/value This paper fulfils an identified need to reveal the unknown flow structure and the boundary layer characteristics that resulted in the self-noise reduction phenomenon yielded by curvature distribution smoothing.

With advancement of nanoscience, "nanofluids" are becoming quite popular among thermal engineers. High thermal conductivity, relatively less settling speed, and higher surface area of nanoparticles are a few key promoting properties. The last two decades have seen dramatic progress towards using nanoparticles in industrial applications. However, the stability and rheological characteristics of prepared nanofluids have serious effects on their transport characteristics, but unfortunately, this has not found proper attention from researchers. In this study, stability and rheological characteristics of ZnO nanoparticles within deionized water, ethylene glycol, and their blends have been extensively tested. Stability was observed using UV-vis spectroscopy, while the viscosity was measured with the help of a rheometer. The data was collected with 0.011-0.044 wt.% loading of nanoparticles, while experiments were conducted within 15-55?C temperature range. Better stability was recorded when nanofluids were prepared with pure ethylene glycol. Experiments showed that the viscosity increased with particle loading, whereas the effect of surfactants appeared to be insignificant. Research results were used to assess predictions of different viscosity models. Experimental data was overpredicted by Einstein, Brinkman, and Batchelor?s models.

Nanofluids have recently attracted attention of many researchers due to their growing potential applications in heat transfer devices. They possess extraordinary thermal and rheological characteristics compared to the respective base fluids. However, the preparation of nanofluids and their dispersion stability is a matter of serious concern, several research investigations have been done in the present era to address these issues. Through this review article, an attempt has been made to critically analyze the published literature on the preparation and dispersion stability of different kinds of aqueous metal oxide nanofluids. In this context, general preparation and stabilization methods, types of instruments for stability inspection, as well as factors affecting stability of aqueous metal oxide nanofluids, are discussed in detail. The current research needs, possible solutions to research challenges in exploring uniformly dispersed nanofluids under optimized operating conditions is the heart of this review article. An effort has been made to determine the status as well as the possible future directions, the preparation and stability related research may take.

Increasing the gas temperature at the inlet to the high pressure turbine of gas turbine engines is known as a proven method to increase the efficiency of these engines. However, this will expose the blades’ surface to very high heat load and thermal damages. In the case of the un-shrouded turbine blades, the blade tip will be exposed to a significant thermal load due to the developed leakage flows in the tip gap, this leads to in-service burnout which degrades the blade tip and shortens its operational life. This paper studies the in-service burnout effect of the transonic tip flows over a cavity tip which is a configuration commonly used to reduce the tip leakage flows. This investigation is carried out experimentally within a transonic wind tunnel and computationally using steady and unsteady Reynolds Averaged Navier Stokes approaches. Various flow measurements are established and different flow behaviour including separation bubbles, shockwave development and distinct flow interactions are captured and discussed. It is found that when the tip is exposed to the in-service burnout, leakage flow behaves in a significantly different way. In addition, the effective tip gap becomes much larger and allows higher leakage mass flow rate in comparison to the sharp-edge tip (i.e. a tip at the beginning of its operational life). The tip leakage losses are found much higher for the round-edge cavity tip (i.e. a tip exposed to burn-out effect). Experimental and computational flow visualisations, surface pressure measurements and discharge coefficient variation are given and analysed for several pressure ratios across the tip gap.

Gas path diagnostics is a key aspect of the engine health monitoring (EHM) process that aims to detect, identify and predict engine component faults, using information from installed sensors, in order to guide maintenance action, maintain engine efficiency and prevent catastrophic failures. To achieve high prediction accuracies, current data-derived diagnostic models tend to be engine specific while the model-based methods are known to be time-consuming, especially for complex engine configurations. This paper proposes an integrated approach for accurate and accelerated isolation and prediction of multiple-degraded gas turbine component faults that comprises 3 steps — feature extraction using the Principal Component Analysis (PCA), machine learning classification with a multi-layer perceptron, artificial neural network (MLP-ANN) and model-based fault prediction via the non-linear Gas Path Analysis (GPA) technique. In this hybrid approach, the PCA first transforms the measurement fault signature into a fault-feature domain, which becomes an input to the multi-label ANN classifier used to isolate the potential faulty components. The non-linear GPA finally quantifies the magnitude of degradation that produced the recorded fault signature. Once trained and validated, the PCA-ANN model is deployed as part of the data processing mechanism prior to the actual GPA calculation. This method was assessed and validated using the thermodynamic performance model of a 2-shaft, high-bypass ratio, turbofan engine. For training and testing the PCA-ANN classifier, a total of 28,000 final samples for 14 measurement parameters, each averaged from 10 data points with Gaussian noise of zero mean and unit standard deviation, and implanted with single-, double- and triple-component fault cases of various magnitude, were generated by steady-state performance simulation of the engine model at its reference operating condition. Correlation analysis of this data set revealed the optimum sensor subset to be used for multi-component diagnostics. A quantitative analysis of the PCA-ANN fault isolation on the test set produced a classification accuracy of 96.6% and performed better on all metrics, compared to other multi-label classification algorithms. Finally, the proposed integrated approach achieved an average of 94.35% reduction in processing time, when compared to the conventional non-linear GPA by component-fault-cases (CFCs), while predicting implanted faults to the same accuracy.

Un-shrouded turbine blades are more common than shrouded ones in gas turbine aero-engines since they reduce the weight and avoid the centrifugal loading caused by the blades’ shrouds. Despite these important advantages, the absence of the shroud leads to leakage flows across the tip gap and exposes the blade tip to high thermal load and thermal damages. In addition, the leakage flows can contribute up to 30% of the aerodynamic loss in a turbine stage. In this study, the effect of in-service burnout is explored using a fundamental flat tip model of a high-pressure gas turbine blade. This investigation is carried out both experimentally in a transonic wind tunnel and computationally using the Reynolds Averaged Navier-stokes approach at high-speed conditions. It is found that exposing the tip to the in-service burnout effect changes the leakage flow behaviour significantly when compared with the tip with sharp edges (i.e. the tip at the start of its operational life). Different flow acceleration, flow structure and shockwave pattern and interactions are captured for the round-edge flat tip (i.e. the tip exposed to in-service burnout). The effective tip gap is found to be much larger for the round-edge flat tip allowing more leakage flow into the tip gap which results into higher tip leakage losses in comparison to the sharp-edge tip. Experimental and computational flow visualisations, surface pressure distributions and discharge coefficient are given and analysed for several pressure ratios over the tip gap.

Reliable transient performance is crucial in handling an aircraft gas turbine engine from one steady state to another. The assessment of transient performance stability is normally done during the detailed design stage when component design details become available. Consequently, design iterations may be necessary and costly if engine transient handling and stability are not satisfactory. To make engine design more cost and time effective, it has become important to assess the transient performance stability at conceptual and preliminary design stage with the inclusion of key impact factors such as fuel control schedule, rotor dynamics and heat soakage. However, due to lack of detailed engine structural and geometrical information at the initial design stage, such transient performance simulation and assessment may have to ignore heat soakage effect. In this paper, a novel generically simplified heat soakage model for three major gas path components of gas turbine engines including compressors, turbines and combustors has been introduced to support more realistic transient performance simulation of gas turbine engines at conceptual and preliminary design stage. Such heat soakage model only requires thermodynamic design parameters as input, which is normally available during such design stages. The model has been implemented into in-house transient performance simulation software and applied to a model twin-spool turbojet engine to test its effectiveness. A comparison between transient performance simulated with and without the heat soakage effects demonstrate that the results are promising. Although the introduced heat soakage model is less accurate than that using detailed component geometrical information, it is able to include the major heat soakage effect in transient performance simulation and provide engine transient stability analysis to support conceptual and preliminary engine designs.

Low Reynolds number blade profiles of ReC=105–2×105 as based on the chord length and used for small unnamed air vehicles, and near space applications are investigated for single and counter-rotating (co-axial) proprotors, i.e. acting as rotors or propellers. Such profiles are prone for early stall, significantly reducing their maximum lift to drag ratio. Two profiles previously designed by our continuous surface curvature design approach named as CIRCLE are investigated in order to improve the performance of the proprotors. The profiles are redesigns of the common symmetric NACA0012 and asymmetric E387 profiles. Using general arguments based on composite efficiency and rotor’s lift to drag ratio, the performance envelope is noticeably increased when using the redesigned profiles for high angles of attack due to stall delay.A new approach is derived to account for the distance between the rotors of a co-axial proprotor. It is coupled with a blade element method and is verified against experimental results. Single and co-axial CIRCLE-based proprotors are investigated against the corresponding non-CIRCLE-based proprotors at hover and axial translation. Noticeable improvements are observed in thrust increase and power reduction at high angles of attack of the blade’s profiles, particularly for the co-axial configuration. Plots of thrust, torque, power, composite efficiency and aerodynamic efficiency distributions are given and analysed.

Higher unburned hydrocarbon emissions are attributed to the relatively low temperature combustion of natural gas in compression ignition engines whereas the combustion of hydrogen in compression ignition environment results in higher NOX. These emissions characteristics are explained on the basis of different physio-chemical properties of the two gaseous fuel: higher Cp value in case of natural gas and higher diffusion coefficient, wider flammability limits and shorter quenching gaps for hydrogen are held responsible for these trends. This study assesses the potential of hydrogen being used in combination with natural gas with diesel and rapeseed methyl ester (RME) as pilot fuels. This type of fueling can be referred as ‘triple fueling of the compression ignition engines’ and has the potential to achieve a better trade-off between the higher NOX associated with hydrogen and higher hydrocarbon emissions associated with natural gas based dual fueling of compression ignition engines. The present study has investigated the potential of the triple fueling of the compression ignition engines so far the attainment of a better trade-off between NOX and hydrocarbon emissions are concerned. Comparing the specific NOX and hydrocarbon emissions in different cases reveals that a significant drop in specific hydrocarbon emissions can be achieved at the cost of a small increment in specific NOX. At both speeds (1000 rev/min and 1500 rev/min), the reduction in hydrocarbon emissions is more prominent at relatively lower loads, which can be a potential solution of reducing specific hydrocarbon emissions at lower loads in diesel engine operations. The stoichiometric equation for the triple fueling (Diesel or RME piloted mixture of natural gas and hydrogen) is also presented.

The application of axial pumps as ventricular assist devices (VADs) requires significant modifications to the size and characteristics of industrial pumps due to the difference in flow fields of industrial and medical pumps. Industrial pumps operate in the region of Reynolds number Re = 10, whereas axial blood pumps operate in Re < 10. The common pump design technique is to rely on the performance of previously designed pumps using the concept of fluid dynamic similarity. Such data are available for industrial pumps as specific speed-specific diameter (ns-ds) graphs. The difference between the flow fields of industrial and medical pumps makes the industrial ns-ds graphs unsuitable for medical pumps and consequently several clinically available axial blood pumps operate with low efficiencies. In this article, numerical and experimental techniques were used to design 62 axial pump impellers with different design characteristics suitable for VADs and mechanical circulatory support devices (MCSDs). The impellers were manufactured and experimentally tested in various operating conditions of flow, pressure, and rotational speed. The hemocompatibility of the impellers was numerically investigated by modeling shear stress and hemolysis. The highest efficiency of each pump impeller was plotted on an ns-ds diagram. The nondimensional results presented in this article enable preliminary design of efficient and hemocompatible axial flow pumps for VADs and MCSDs.

In centrifugal rotary blood pumps (RBP), clearances are a critical parameter in determining blood trauma. This study investigates the effect of axial clearance (Cax) and radial clearance (Crad) on the hydrodynamic and hemolytic performance of a centrifugal RBP. A centrifugal pump was parameterized so that it could be defined by geometric variables Cax and Crad. Optimal Latin hypercube sampling was used to determine design points based on Cax, Crad, and rotor speed (ω). For each design point, a computational simulation was conducted to determine efficiency (η) and normalized index of hemolysis (NIH). Next, a response surface (RS) was created to estimate these performance parameters based on the design variables. The results show that for a given Cax, when Crad is decreased, η increases until Crad = 0.15 mm, beyond which η deceases. For a given Crad, Cax has a unimodal relationship with η. The NIH has a unimodal relationship with both Cax and Crad. The mechanisms behind these relationships were investigated by various analytical methods. It was found that vortices in the secondary flow paths were a critical factor in determining efficiency and hemolysis. The optimal clearance values discerned in this study are only valid for the specific impeller geometry and operating conditions analyzed.

The finite block method (FBM) is developed to determine stress intensity factors with orthotropic functionally graded materials under static and dynamic loads in this paper. By employing the Lagrange series, the first order partial differential matrix for one block is derived with arbitrary distribution of nodes. The higher order derivative matrix for two dimensional problems can be constructed directly. For linear elastic fracture mechanics, the COD and J-integral techniques to determine the stress intensity factors are formulated. For the dynamic problems, the Laplace transform method and Durbin's inverse technique are employed. Several examples are given and comparisons have been made with both the finite element method and analytical solutions in order to demonstrate the accuracy and convergence of the finite block method.

In this paper, the integral equations are formulated and solved numerically for a cracked orthotropic strip with Functionally Graded Materials (FGMs) subjected to both static and dynamic loads. The Green's function of displacement discontinuity in an orthotropic FGM strip is derived by using the Fourier transform and the Laplace transform techniques with the shear modulus and the mass density varying exponentially, and constant Poisson's ratio for functionally graded materials. It has been shown that the transformed Green's solutions have the same order of singularities as that in the static case. The normalized time-dependent stress intensity factors are obtained with the Durbin’s inversion method for the Laplace transform. The static stress intensity factors are compared with the results given by finite element analysis and excellent agreements are achieved.

Purpose Contact interaction and contact detection (CD) remain key components of any discontinua simulations. The methods of discontinua include combined finite-discrete element method (FDEM), discrete element method, molecular dynamics, etc. In recent years, a number of CD algorithms have been developed, such as Munjiza–Rougier (MR), Munjiza–Rougier–Schiava (MR-S), Munjiza-No Binary Search (NBS), Balanced Binary Tree Schiava (BBTS), 3D Discontinuous Deformation Analysis and many others. This work aims to conduct a numerical comparison of certain algorithms often used in FDEM for bodies of the same size. These include MR, MR-S, NBS and BBTS algorithms. Design/methodology/approach Computational simulations were used in this work. Findings In discrete element simulations where particles are introduced randomly or in which the relative position between particles is constantly changing, the MR and MR-S algorithms present an advantage in terms of CD times. Originality/value This paper presents a detailed comparison between CD algorithms. The comparisons are performed for problem cases with different lattices and distributions of particles in discrete element simulations. The comparison includes algorithms that have not been evaluated between them. Also, two new algorithms are presented in the paper, MR-S and BBTS.

This paper describes an investigation into journal bearings with geometries and working fluid similar to centrifugal blood pumps. The aim is to describe the phenomena that cause these journal bearings to deviate from classical predictions. Experimental, analytical and numerical methods are used to investigate the behaviour of a range of bearings with geometries and working fluid similar to blood pumps. It was found that the clearance had a significant effect on the force-eccentricity characteristic of the bearing, with smallest and largest clearances deviating from classical predictions. Experimentally measured pressure distributions show that slip occurs when the clearance is small and that turbulence occurs with the largest clearances. The effects of these phenomena on lubricant pressure and blood compatibility are discussed.

Mock circulatory test rig (MCTR) is the essential and indispensable facility in the cardiovascular in vitro studies. The system configuration and the motion profile of the MCTR design directly influence the validity, precision, and accuracy of the experimental data collected. Previous studies gave the schematic but never describe the structure and motion design details of the MCTRs used, which makes comparison of the experimental data reported by different research groups plausible but not fully convincing. This article presents the detailed structure and motion design of a sophisticated MCTR system, and examines the important issues such as the determination of the ventricular motion waveform, modelling of the physiological impedance, etc., in the MCTR designing. The study demonstrates the overall design procedures from the system conception, cardiac model devising, motion planning, to the motor and accessories selection. This can be used as a reference to aid researchers in the design and construction of their own in-house MCTRs for cardiovascular studies.

Aquatic vegetation dramatically shifts the main flow, secondary flow and turbulent structures in a meandering channel. In this study, hydrodynamics in a bending channel with a vegetation patch (VP) has been numerically studied under the variation of curvature ratios (CRs=0.5, 1.0, 1.5, 2.0) and the vegetation density i.e. Solid Volume Fractions (SVF=1.13%, 4.86%). Both effects on vegetation shear flow, helical flow, bed shear stress and bulk drag coefficients are studied in twelve cases by using Ansys Fluent package. Unsteady Reynolds Averaging Navier-Stokes (URANS) framework coupled with the Reynolds Stress turbulence Model (RSM) and Volume Of Fluid (VOF) approach is successfully applied to predict the entire flow field including multi-circulation cells as well as the free surface. The conclusions are summarized as three points. Firstly, an increase of CR moves the main circulation cell and thalweg's location towards the outer bank, while decreasing the drag coefficients in streamwise and spanwise. However, the CR weakly affects the normalised shear flow velocity profiles and dominant eddy frequencies downstream of the VP. Secondly, the trend of the dominant shedding frequency to fall with the increase of SVF that has been known only for SVF S t p SVF N , links Stp and SVF, where N is the number of stems in the patch. This number stays almost constant for each case series regardless of the variation of SVF (for SVF S t p SVF N is strongly determined by the patch shape factor, mildly influenced by the patch Reynolds number, but it excludes the influence of the SVF and N. The insights from the present study unveil the complicated eco-hydro-morphic interactions among the bio-mass density, turbulent flow and channel meanders’ variation. It provides a better understanding of natural bending river systems’ development and fundamentals for the recovery of urban channel ecosystems by vegetated re-meandering.

The application of artificial mechanical pumps as heart assist devices impose power and size limitations on the pumping mechanism, and therefore requires careful optimization of pump characteristics. Typically new pumps are designed by relying on the performance of other previously designed pumps of known performance using concepts of fluid dynamic similarity. Such data are readily available for industrial pumps, which operate in Reynolds numbers region of 108. Heart assist pumps operate in Reynolds numbers of 105. There are few data available for the design of centrifugal pumps in this characteristic range. This article develops specific speed versus specific diameter graphs suitable for the design and optimization of these smaller centrifugal pumps concentrating in dimensions suitable for ventricular assist devices (VADs) and mechanical circulatory support (MCS) devices. A combination of experimental and numerical techniques was used to measure and analyze the performance of 100 optimized pumps designed for this application. The data are presented in the traditional Cordier diagram of nondimensional specific speed versus specific diameter. Using these data, nine efficient designs were selected to be manufactured and tested in different operating conditions of flow, pressure, and rotational speed. The nondimensional results presented in this article enable preliminary design of centrifugal pumps for VADs and MCS devices.

This article describes the effects of ambulatory accelerations on the stability of a magnetically suspended impeller for use in implantable blood pumps. A magnetic suspension system is developed to control the radial position of a magnetic impeller using coils in the pump casing. The magnitude and periodicity of ambulatory accelerations at the torso are measured. A test rig is then designed to apply appropriate accelerations to the suspension system. Accelerations from 0 to 1 g are applied to the suspended impeller with ambulatory periodicity while the radial position of the impeller and power consumption of the suspension system are monitored. The test is carried out with the impeller suspended in air, water, and a glycerol solution to simulate the viscosity of blood. A model is developed to investigate the effects of the radial magnetic suspension system and fluid damping during ambulatory accelerations. The suspension system reduces the average displacement of the impeller suspended in aqueous solutions within its casing to 100 µm with a power consumption of below 2 W during higher magnitude ambulatory accelerations (RMS magnitude 0.3 g). The damping effect of the fluid is also examined and it is shown that buoyancy, rather than drag, is the primary cause of the damping at the low displacement oscillations that occur during the application of ambulatory accelerations to such a suspension system.

Based on the interpolation of the Lagrange series and the Finite Block Method (FBM), the formulations of the Boundary Node Petrov–Galerkin Method (BNPGM) are presented in the weak form in this paper and their applications are demonstrated to the elasticity of functionally graded materials, subjected to static and dynamic loads. By introducing the mapping technique, a block of quadratic type is transformed from the Cartesian coordinate to the normalized coordinate with 8 seeds for two-dimensional problems. The first-order partial differential matrices of boundary nodes are obtained in terms of the nodal values of the boundary node, which can be utilized to determine the tractions on the boundary. Time-dependent partial differential equations are analyzed in the Laplace transformed domain and the Durbin’s inversion method is applied to determine the physical values in the time domain. Illustrative numerical examples are given and comparison has been made with the analytical solutions, the Boundary Element Method (BEM) and the Finite Element Method (FEM).

Diesel and water emulsions have the potential to be used in compression ignition engines to control the emissions of NOx and PM. Very little is known about the influence emulsification will have on the fuel sprays formed during injection. This paper outlines the measurement of the momentum flux of injection sprays of Diesel fuel and Diesel fuel emulsions containing 10% and 20% water, with the goal of hydraulically characterizing the sprays and identifying the influence emulsification may have on them. The momentum flux, mass flow, instantaneous mass flow, discharge coefficient, injection velocity, momentum coefficient and momentum efficiency have been examined. The injections were carried out in a high pressure chamber filled with nitrogen. The measured momentum flux is observed to increase with increasing injection pressure in a linear form. Increasing the ambient density in the chamber resulted in a decrease in the measured momentum flux. The emulsified fuel sprays had a very similar momentum flux as the neat Diesel fuel sprays. The total mass of emulsified fuel injected was less than for neat Diesel at corresponding condition. The instantaneous mass flow rate was determined using a normalized form of the momentum flux measurement and the independently measured total mass injected. The emulsions tended to have a lower discharge coefficient and there is no evidence that the nozzle is cavitating at these conditions. The emulsified fuels have tended to have a higher injection velocity than the neat Diesel fuel sprays. The momentum efficiency is introduced, which uses the instantaneous mass measurement and the theoretical velocity of the spray. The emulsified fuels have a larger momentum efficiency, a result of their high injection velocity compared with the neat Diesel fuel., Advanced Engine Research, Basildon, UK

This is a review of some of the recent developments in the application of 3D printing to medicine. The topic is introduced with a brief explanation as to how and why 3D is changing practice, teaching, and research in medicine. Then, taking recent examples of progress in the field, we illustrate the current state of the art. This article concludes by evaluating the current limitations of 3D printing for medical applications and suggesting where further progress is likely to be made.

This paper describes a new method to predict emissions in internal combustion (IC) engines. The method couples a multi-dimensional engine modeling program with pre-integrated non-equilibrium chemical kinetics reaction results. Prior to engine simulation, detailed chemical kinetics reactions of air/fuel mixture at different temperatures, pressures, and compositions, are calculated using SENKIN, a subprogram in the CHEMKIN-II computer package. The reaction results are decoupled from their chemical eigenvalue (order of about 10 - 10 s), then integrated and saved in physical time scale (order of about 10 - 5 s) in a database file. In the database reaction results of different initial conditions (temperature, pressure, and species composition) are stored in different zones; the zones are indexed using their respective reaction conditions. Fluid dynamics and thermal dynamics of the movement of piston and valves, and spray droplets interaction are simulated by KIVA-3 V. Instead of calculating directly the non-equilibrium chemical reactions of the air/fuel mixture, reaction results are obtained from the database file via an interpolating subroutine, which returns temperature, heat release, and species concentrations after reaction to the main program. The approach avoids direct time consuming calculation of detailed chemical reactions as well as the errors introduced by coupling the physical and chemical processes. Emissions are predicted accurately since reaction of air/fuel mixture is calculated using the detailed chemical kinetics mechanism. The approach is applied to model a Caterpillar 3401 direct injection compression ignition (CI) diesel engine. In addition we carried out experimental tests on a Toledo 1500 SI gasoline engine, and those results are compared with the proposed computational approach. In all cases the predicted results agree well with the experimental data.

The prescribed surface curvature distribution blade design (CIRCLE) method optimises aerofoils and blades by controlling curvature continuity and slope of curvature distribution along their surfaces. The symmetrical NACA0012 exhibits a surface curvature discontinuity at the leading edge point, and the non-symmetrical E387 exhibits slope-of-curvature discontinuities in the surface. The CIRCLE method is applied to both aerofoils to remove both surface curvature and slope-of-curvature discontinuities. Computational fluid dynamics analyses are used to investigate the curvature effects on aerodynamic performance of the original and modified aerofoils. These results are compared with experimental data obtained from tests on the original aerofoil geometry. The computed aerodynamic advantages of the modified aerofoil are analysed in different operating conditions. The leading edge singularity of NACA0012 is removed and it is shown that the surface curvature discontinuity affects the aerodynamic performance near the stalling angle of attack. The discontinuous slope-of-curvature distribution of E387 influences the size of the laminar separation bubble at lower Reynolds numbers, and it affects the inherent profile of the aerofoil at higher Reynolds numbers. It is concluded that the surface curvature distribution of aerofoils has a significant effect on aerofoil aerodynamic performance, which can be improved by redesigning the surface curvature distribution of the original aerofoil geometry.

This paper presents the performance and emissions contours of a hydrogen dual fueled compression ignition (CI) engine with two pilot fuels (diesel and rapeseed methyl ester), and compares the performance and emissions iso-contours of diesel and rapeseed methyl ester (RME) single fueling with diesel and RME piloted hydrogen dual fueling throughout the engines operating speed and power range. The collected data have been used to produce iso-contours of thermal efficiency, volumetric efficiency, specific oxides of nitrogen (NOX), specific hydrocarbons (HC) and specific carbon dioxide (CO2) on a power-speed plane. The performance and emission maps are experimentally investigated, compared, and critically discussed. Apart from medium loads at lower and medium speeds with diesel piloted hydrogen combustion, dual fueling produced lower thermal efficiency everywhere across the map. For diesel and RME single fueling the maximum specific NOX emissions are centered at the mid speed, mid power region. Hydrogen dual fueling produced higher specific NOX with both pilot fuels as compared to their respective single fueling operations. The range, location and trends of specific NOX varied significantly when compared to single fueling cases. The volumetric efficiency is discussed in detail with the implications of manifold injection of hydrogen analyzed with the conclusions drawn.

Traditional implantation techniques of assist devices from the apex of left ventricle to the ascending or descending aorta are highly invasive and carry substantial complications for end-stage heart failure patients. This study has shown that the descending aorta can be a promising location to install an implantable mechanical circulatory support with minimally invasive surgery. Herein, the hemodynamic effect of an in-house prototyped pump implanted in the descending aorta was investigated numerically as well as experimentally. The objective of the experimental study is met by using the in-house simulator of the cardiovascular loop replicating congestive heart failure conditions. The objective of the numerical study was met by using the modified version of the concentrated lumped parameter model developed by the same team. The results show that the pump placement in the descending aorta can lead to an improvement in pulsatility. The pressure drop, generated at the upstream of the pump, facilitates the cardiac output as a result of after-load reduction, but at the same time, it induces a slight drop in the carotid as well as the coronary perfusion. The pressure rise, generated at the downstream of the pump, improves the blood perfusion in the renal circulation.

This paper presents wind tunnel experiments to illustrate the effects of surface curvature on the aeroacoustic performance of airfoil E387. For the first time, surface curvature effects are considered in an investigation of the airfoil’s self-noise. To distinguish the effects of surface curvature, the CIRCLE method is applied to the airfoil E387 to remove slope-of-curvature discontinuities and the redesigned airfoil is denoted A7. Anechoic wind tunnel tests were performed with E387 and A7 at three low Reynolds numbers to investigate aeroacoustic performance by measuring airfoil self-noise at different angles of attack (AoA) and spatial positions. At 2° and 4° AoA, A7 presents a tone with a reduced amplitude compared with E387 due to its improved slope-of-curvature distribution. It is concluded that improving surface curvature distribution improves airfoil aeroacoustic performance.

Previous numerical models of impeller pumps for ventricular assist devices utilize curve-fitted polynomials to simulate experimentally-obtained pressure difference versus flow rate characteristics of the pumps, with pump rotational speed as a parameter. In this paper the numerical model for the pump pressure difference versus flow rate characteristics is obtained by analytic derivation. The mass, energy and angular momentum conservation laws are applied to the working fluid passing through the impeller geometry and coupled with the turbomachine's velocity diagram. This results in the construction of a pressure difference versus flow rate characteristic for the specific pump geometry, with pump rotational speed as parameter. Overall this model allows modifications of the pump geometry, so that the pump avoids undesirable operating conditions, such as regurgitant flow. The HeartMate III centrifugal pump is used as an example to demonstrate the application of the technique. The parameterised numerical model for HeartMate III derived by this technique is coupled with a numerical model for the human cardiovascular system, and the combination is used to investigate the cardiovascular response under different conditions of impeller pump support. Conditions resulting in regurgitant pump flow, the pump resulting in aortic valve closure and taking over completely the pumping action from the diseased heart, and inner ventricular wall suction at pump inlet are predicted by the model. The simulation results suggest that for normal HeartMate III operation the pump speed should be maintained between 3,100 and 4,500 r p m to avoid regurgitant pump flow and ventricular suction. To obtain optimal overall cardiovascular system plus pump response, the pump operating speed should be 3,800 r p m .

This paper describes the use of analytical methods to determine machinable centrifugal impeller geometries and the use of computational fluid dynamics (CFD) for predicting the impeller performance. An analytical scheme is described to determine the machinable geometries for a shrouded centrifugal impeller with blades composed of equiangular spirals. The scheme is used to determine the maximum machinable blade angles for impellers with three to nine blades in a case study. Computational fluid dynamics is then used to analyze all the machinable geometries and determine the optimal blade number and angle based on measures of efficiency and rotor speed. The effect of tip width on rotor speed and efficiency is also examined. It is found that, for our case study, a six- or seven-bladed impeller with a low blade angle provides maximum efficiency and minimum rotor speed.

This article presents computational algorithms for the design, analysis, and optimization of airfoil aerodynamic performance. The prescribed surface curvature distribution blade design (CIRCLE) method is applied to a symmetrical airfoil NACA0012 and a non-symmetrical airfoil E387 to remove their surface curvature and slope-of-curvature discontinuities. Computational fluid dynamics analysis is used to investigate the effects of curvature distribution on aerodynamic performance of the original and modified airfoils. An inviscid–viscid interaction scheme is introduced to predict the positions of laminar separation bubbles. The results are compared with experimental data obtained from tests on the original airfoil geometry. The computed aerodynamic advantages of the modified airfoils are analyzed in different operating conditions. The leading edge singularity of NACA0012 is removed and it is shown that the surface curvature discontinuity affects aerodynamic performance near the stalling angle of attack. The discontinuous slope-of-curvature distribution of E387 results in a larger laminar separation bubble at lower angles of attack and lower Reynolds numbers. It also affects the inherent performance of the airfoil at higher Reynolds numbers. It is shown that at relatively high angles of attack, a continuous slope-of-curvature distribution reduces the skin friction by suppressing both laminar and turbulent separation, and by delaying laminar-turbulent transition. It is concluded that the surface curvature distribution has significant effects on the boundary layer behavior and consequently an improved curvature distribution will lead to higher aerodynamic efficiency.

In this study, the design aspects of optically accessible pressure vessels are investigated via a case study of a High Pressure Combustor experimental rig. The rig was designed to take optical measurements of combustion, simulating the conditions found in internal combustion engines and turbines. Although, it is not new to equip chambers and reactors with sight windows, important aspects of design and relevant information regarding optical access is missing or are insufficiently explored or not readily accessible in the existing literature. A comprehensive review of requirements for optical access to such high-pressure, high-temperature systems has been conducted. It is shown in a readily-navigable format as function of application and precision, with data and technical correlations hitherto not found in a ‘user-friendly’ style. The material selection procedure is detailed and supported by a complete comparison of optical materials and relevant properties. The review revealed a significant inconsistency in mechanical properties claimed in the literature for optical materials. As a response to this, increased safety factor values are suggested as function of level of uncertainties and effects of failure, typically three to four times higher than the industrial standard. Moreover, newly developed equations are presented linking performance analysis to the design criteria. Keywords: Optically-accessible reactor, Optical engine, Pressure vessel, Sapphire, Window design, Combustion

International audience; In this paper, two-dimensional (2-D) analytical magnetic field calculations are used to compute crucial quantities of Brushless permanent-magnet (PM) machines with surface-inset PMs. The analytical magnetic field distribution is based on the subdomain technique in which the slotting and tooth-tip effects have been considered. It includes both different magnetization patterns (e.g.,radial, parallel and Halbach) and different spatial distribution of winding (e.g., concentrated and distributed with one or more layers). The saturation effect of the magnetic circuit is neglected. In this investigation, the phase and line induced back electromotive force (EMF) waveforms, electromagnetic/cogging/reluctance torques, self-/mutual-inductances and unbalanced magnetic forces(UMFs) have been analytically calculated. The analytical expressions can be used for Brushless machines having surface-inset PMs with any radius-independent magnetization pattern. In this study, two slotted Brushless PM machines with surface-inset PMs have been selected to evaluate the efficacy of the analytical expressions by comparing the results with those obtained by the finite-element method (FEM). One of the case studies is a 9-slots/8-poles Brushless DC (BLDC) machine with radially magnetized PMs, non-overlapping all teeth wound winding and six-step rectangular armature current waveforms. The other is a 15-slots/4-poles Brushless AC (BLAC) machine with Halbach magnetization PMs, double-layer overlapping winding and sinusoidal armature current waveforms.

When natural gas is port/manifold injected into a compression ignition engine, the mixture of air and the natural gas is compressed during the compression stroke of the engine. Due to the difference in the values of specific heat capacity ratio between air and natural gas, the temperature and pressure at the time of pilot fuel injection are different when compared to a case where only air is compressed. Also, the presence of natural gas affects the peak in-cylinder (adiabatic flame) temperature. This significantly affects the performance as well as emissions characteristics of natural gas based dual fueling in CI engine. Natural gas has been extensively tested in a single cylinder compression ignition engine to obtain performance and emissions maps.Two pilot fuels, diesel and RME, have been used to pilot natural gas combustion. The performance of the two liquid fuels used as pilots has also been assessed and compared. Tests were conducted at 48 different operating conditions (six different speeds and eight different power output conditions for each speed) for single fueling cases. Both the diesel and RME based single fueling cases were used as baselines to compare the natural gas based dual fueling where data was collected at 36 operating conditions (six different speeds and six different power output conditions for each speed). Performance and emissions characteristics were mapped on speed vs brake power plots. The thermal efficiency values of the natural gas dual fueling were lower when compared to the respective pilot fuel based single fueling apart from the highest powers. The effect of engine speed on volumetric efficiency in case of the natural gas based dual fueling was significantly different from what was observed with the single fueling. Contours of specific NOX for diesel and RME based single fueling differ significantly when these fuels were used to pilot natural gas combustion. For both of the single fueling cases, maximum specific NOX were centered at the intersection of medium speeds and medium powers and they decrease in all directions from this region of maximum values. On the other hand, an opposite trend was observed with dual fueling cases where minimum specific NOX were observed at the center of the map and they increase in all direction from this region of minimum NOX. RME piloted specific NOX at the highest speeds were the only exception to this trend. Higher specific HC and lower specific CO2 emissions were observed in case of natural gas based dual fueling. The emissions were measured in g/MJ of engine power.

Natural gas and hydrogen have been extensively tested in dual fuel mode in a compression ignition engine. Many studies conclude that the emissions, especially those oxides of nitrogen (NOx) are expected to form in the region around the pilot spray where high temperatures exist and the equivalence ratio is close to stoichiometric. The effect of changing the pilot fuel quantity has not been widely reported. This study investigates the effect of changing pilot fuel quantity, and type and the effect of this change on various combustion (ignition delay, in-cylinder pressure and rate of energy release) and emission (specific NOx and hydrocarbons) parameters. Dual fueling of natural gas and hydrogen exhibit an increased ignition delay compared to the ignition delay exhibited by the pilot fuel at similar operating conditions. For dual fueling cases, the ignition delay is reduced as the quantity of pilot fuel is increased.

The application of centrifugal pumps as heart assist devices imposes design limitations on the impeller geometry. Geometry and operating parameters will affect the performance and the hemocompatibility of the device. Among all the parameters affecting the hemocompatibility, pressure, rotational speed, blade numbers, angle, and width have significant impact on the blood trauma. These parameters directly (pressure, speed) and indirectly (geometry) affect the efficiency of the pump as well. This study describes the experimental investigation on geometric parameters and their effect on the performance of small centrifugal pumps suitable for Mechanical Circulatory Support (MCS) devices. Experimental and numerical techniques were implemented to analyze the performance of 15 centrifugal impellers with different characteristics. The effect of each parameter on the pump performance and hemolysis was studied by calculating the normalized index of hemolysis (NIH) and the shear stress induced in each pump. The results show five and six blades, 15-35° outlet angle, and the lowest outlet width that meets the required pressure rise are optimum values for an efficient hemocompatible pump.

The paper examined the case study of the Saudi electricity sector and provided projections for energy use and respective carbon dioxide (CO2) emissions for the period 2010–2025 with and without cleaner energy technologies. Based on two sets of 20 life cycle assessment studies for carbon capture and storage and solar photovoltaic technologies, CO2 emission reduction rates were used for projecting future CO2 emissions. Results showed enormous savings in CO2 emissions, for the most likely case, year 2025 reported savings that range from 136 up to 235 MtCO2. Including low growth and high growth cases, these savings could range from 115 up to 468 MtCO2 presenting such an unrivalled opportunity for Saudi Arabia. These projections were developed as a way of translating the inherent advantages that cleaner energy technologies could provide for CO2 emissions savings. It is hoped that the results of this paper would inform energy policymaking in Saudi Arabia.

A finite integration method is proposed in this paper to deal with partial differential equations in which the finite integration matrices of the first order are constructed by using both standard integral algorithm and radial basis functions interpolation respectively. These matrices of first order can directly be used to obtain finite integration matrices of higher order. Combining with the Laplace transform technique, the finite integration method is extended to solve time dependent partial differential equations. The accuracy of both the finite integration method and finite difference method are demonstrated with several examples. It has been observed that the finite integration method using either radial basis function or simple linear approximation gives a much higher degree of accuracy than the traditional finite difference method.

Many studies presenting performance and emissions characteristics of compression-ignition (CI) engines operating with various fuels present these characteristics at a few load settings and engine rotational speed combinations. In general engine performance and emissions contours have not been investigated throughout the operating speed and power range of engines. In this paper the performance and specific emissions contours of a diesel and rapeseed methyl ester (RME) fueled CI engine are experimentally investigated, assessed, compared, and critically discussed. The contours are plotted on load (brake power) versus engine rotating speed figures throughout the engine operating range. The thermal efficiency with diesel and RME are comparable for all ranges of speeds and power outputs. At the maximum power range RME has slightly higher thermal efficiency. From the location of maximum NOX contours in the central region of the power–speed range, any increase or decrease in either power or speed across the map shall result in lower specific NOX. RME produces lower NOX compared to the diesel fuel. At the higher loads RME produces fewer unburned hydrocarbon emissions than diesel, but in medium and intermediate loads the unburned hydrocarbon emissions are comparable. CO2 is lower with RME than diesel throughout the engine operating range.

The absence of carbon content of hydrogen fuel makes it an attractive candidates for future energy carriers. Hydrogen or dual fuelled engines are a practical alternative to pure hydrocarbon fuelling modes. However, fine tuning of current engines is necessary. In this study premixed hydrogen flame propagation is investigated in a single-cylinder, spark-ignited, four-stroke optically accessible spark ignition test engine using high-speed imaging. Ellipses were fitted on the flame contours during the analysis to obtain flame speeds and flame centre motion. The test conditions covered a range of engine speeds from 1000 rpm to 2000 rpm with 100 rpm increments using a lean mixture, ϕ = 0.67. The fine temporal resolution allowed the time, at which spark governed kernel formation becomes a function of engine parameters to be determined. The few data that have been published in the literature regarding hydrogen flame speeds were compared with the finding of this study.

In this paper, the electromagnetic torque, reluctance torque, inductance, and back-EMF are analytically calculated for brushless slotless machines with surface inset magnets. The calculations are based on the 2-D analytical magnetic field distributions. Although the expressions can be used for any magnetization patterns, the effects of three different magnetization patterns, i.e., radial, parallel, and Halbach, on the developed torque, back-EMF and inductances are examined. Besides, the influences of three types of armature current waveforms (sinusoidal, ideal rectangular, and six-step rectangular) on the mentioned quantities are investigated. The effects of pole arc per pole pitch ratio on the performance of slotless brushless machines are also studied. To evaluate the proposed 2-D analytical expressions, the analytical results are compared with those obtained by finite element analyses.

This article presents a new device designed to simulate in vitro flow rates, pressures, and other parameters representing normal and diseased conditions of the human cardiovascular system. Such devices are sometimes called bioreactors or "mock" simulator of cardiovascular loops (SCVLs) in literature. Most SCVLs simulate the systemic circulation only and have inherent limitations in studying the interaction of left and right sides of circulation. Those SCVLs that include both left and right sides of the circulation utilize header reservoirs simulating cycles with constant atrial pressures. The SCVL described in this article includes models for all four chambers of the heart, and the systemic and pulmonary circulation loops. Each heart chamber is accurately activated by a separate linear motor to simulate the suction and ejection stages, thus capturing important features in the perfusion waveforms. Four mechanical heart valves corresponding to mitral, pulmonary, tricuspid, and aortic are used to control the desired unidirectional flow. This SCVL can emulate different physiological and pathological conditions of the human cardiovascular system by controlling the different parameters of blood circulation through the vascular tree (mainly the resistance, compliance, and elastance of the heart chambers). In this study, four cases were simulated: healthy, congestive heart failure, left ventricular diastolic dysfunction conditions, and left ventricular dysfunction with the addition of a mechanical circulatory support (MCS) device. Hemodynamic parameters including resistance, pressure, and flow have been investigated at aortic sinus, carotid artery, and pulmonary artery, respectively. The addition of an MCS device resulted in a significant reduction in mean blood pressure and re-establishment of cardiac output. In all cases, the experimental results are compared with human physiology and numerical simulations. The results show the capability of the SCVL to replicate various physiological and pathological conditions with and without MCS.

The finite integration method is proposed in this paper to approximate solutions of partial differential equations. The coefficient matrix of this finite integration method is derived and its superior accuracy and efficiency is demonstrated by making comparison with the classical finite difference method. For illustration, the finite integration method is applied to solve a nonlocal elastic straight bar under different loading conditions both for static and dynamic cases in which Laplace transform technique is adopted for the dynamic problems. Several illustrative examples indicate that high accurate numerical solutions are obtained with no extra computational efforts. The method is readily extendable to solve more complicated problems of nonlocal elasticity.

A comprehensive analytical open-circuit magnetic field distribution of slotless brushless permanent magnet machines with surface mounted magnets is presented for six different magnetization patterns. The stator and rotor back-irons are assumed to be finite permeable. Therefore, the analytical model covers five annular regions: rotor; magnet; air–gap/winding; stator; and exterior. The expressions of the five regions are presented in a convenient form to ease the numerical computation for both internal and external rotor motors. The induced back-EMF is also expressed analytically. The efficacy of the analytical model is validated by comparing the results with finite element analyses (FEAs).

The PresCrIbed suRface Curvature distribution bLade dEsign (CIRCLE) method, proposed by T Korakianitis, is a direct method for designing (or redesigning) high efficiency turbomachinery and fan blades, and isolated airfoils. It was initially introduced to improve the design of high efficiency turbomachinery blades. It is now extended for use with 2D and 3D turbomachinery blades and isolated airfoils. The connection of the profile's leading edge (LE) to the trailing edge (TE), on both sides, is defined using continuity in the surface curvature and its derivatives. Improvements to the aerodynamic performance of the Eppler airfoil are presented in this paper. Improved geometries with continuous curvature have been produced using the CIRCLE method. The performances of Eppler and the redesigned A5 and A6 have been studied using CFD analysis. They are analyzed considering low subsonic flow condition (Reynolds number~105). These are compared to a previous airfoil A4. The redesigned blades’ LE proved favorable as they succeeded in removing pressure ‘spikes’ on the suction side. Comparative analysis with the original results showed significant aerodynamic improvements. Airfoils A4, A5 and A6 have comparatively thicker TE section compared to Eppler. Despite the changes made to the geometry and continuous curvature distribution in A4, A5 and A6 (from Eppler), there appear a separated region on the suction side at about 60% of the chord downstream from the LE. The new blades exhibit higher aerodynamic efficiencies, in terms of overall lift-to-drag ratio up to 40% than the original. The investigations are perfo med at on and off design conditions.

This study investigates the hemodynamic responses of the cardiovascular system when a rotary blood pump is operating in the descending aorta, with a focus on the cerebral, coronary and renal autoregulation, using our in-house cardiovascular emulator. Several improvements have been made from our previous studies. A novel coronary system was developed to replicate the native coronary perfusion. Three pinch valves actuated by stepper motors were used to simulate the regional autoregulation systems of the native cerebral, coronary and renal circulations. A rotary pump was installed in the descending aorta, in series with the heart, and the hemodynamic responses of the cardiovascular system were investigated with a focus on cerebral, coronary and renal circulation over a wide range of pump rotor speeds. Experiments were performed twice, once with the autoregulation systems active and once with the autoregulation systems inactive, to reflect that there will be some impairment of autoregulatory systems in a patient with heart failure. It was shown that by increasing the rotor speed to 3000 rpm, the cardiac output was improved from 2.9 to 4.1 L/min as a result of an afterload reduction induced by the pressure drop upstream of the pump. The magnitudes of changes in perfusion in the cerebral, coronary and renal circulations were recorded with regional autoregulation systems active and inactive.

The effect of surface waves on the hydrodynamic performance of a marine current turbine (MCT) is studied using the unsteady BEM method. The calculation are found to be in a very good agreement with experimental results of a small scale MCT. It is shown that a large amplitude wave, but still a long wave can affect the time-averaged coefficient of power and also introduce non-linearity in the time response of the turbine particularly at low tip speed ratio. This can have consequence for an effective control of the turbine. Instantaneous blade loading and power spectra are given and analyzed.