Structure and motion design of a mock circulatory test rig

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

Machinability and Optimization of Shrouded Centrifugal Impellers for Implantable Blood Pumps

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

Influence of curvature distribution smoothing on the reduction of aerofoil self-noise

Purpose – The 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 – The paper performed Large Eddy Simulation (LES) approach 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 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 and the vortex shedding phenomenon. Findings – The paper provides quantitative insights about how the flapping process of the laminar separation bubble within the boundary layer near the trailing edge affects the aerofoil self-noise. It is found that the aerofoil A7 with smooth curvature distributions presents a 10% smaller laminar separation bubble compared to the aerofoil E387 at Reynolds number 100,000 and Angle of Attack 4-degree. The LES results also suggests 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

Experimental study of surface curvature effects on aerodynamic performance of a low Reynolds number airfoil for use in small wind turbines

This paper presents the wind tunnel experimental results to investigate the effects of surface gradient-of-curvature on aerodynamic performance of a low Reynolds number airfoil Eppler 387 for use in small-scale wind turbines. The prescribed surface curvature distribution blade design method is applied to the airfoil E387 to remove the gradient-of-curvature discontinuities and the redesigned airfoil is denoted as A7. Both airfoils are manufactured with high precision to reflect the design. Low-speed wind tunnel experiments are conducted to both airfoils at chord based Reynolds numbers 100 000, 200 000, and 300 000. Surface pressure measurements are used to calculate the lift and pitching-moment data, and the wake survey method is applied to obtain the drag data. The experimental results of E387 are compared with NASA Low Turbulence Pressure Tunnel (LTPT) results for validation. The gradient-of-curvature discontinuities of E387 result in a larger laminar separation bubble which causes higher drag at lower angles of attack. As the angle of attack increases the separation bubble of the airfoil E387 moves faster towards the leading edge than that of A7, resulting in a premature bubble bursting and earlier stall on E387. The impact of the gradient-of-curvature distribution on the airfoil performance is more profound at higher angles of attack and lower Reynolds number. The aerodynamic improvements are integrated over the 3D geometry of a 3 kW small wind turbine, resulting in up to 10% increase in instantaneous power and 1.6% increase in annual energy production. It is experimentally concluded that an improved curvature distribution results in a better airfoil performance, leading to higher energy output efficiency

Assessment of elliptic flame front propagation characteristics of iso-octane, gasoline, M85 and E85 in an optical engine

Premixed fuel–air flame propagation is investigated in a single-cylinder, spark-ignited, four-stroke optical test engine using high-speed imaging. Circles and ellipses are fitted onto image projections of visible light emitted by the flames. The images are subsequently analysed to statistically evaluate: flame area; flame speed; centroid; perimeter; and various flame-shape descriptors. Results are presented for gasoline, isooctane, E85 and M85. The experiments were conducted at stoichiometric conditions for each fuel, at two engine speeds of 1200 rpm (rpm) and 1500 rpm, which are at 40% and 50% of rated engine speed. Furthermore, different fuel and speed sets were investigated under two compression ratios (CR: 5.00 and 8.14). Statistical tools were used to analyse the large number of data obtained, and it was found that flame speed distribution showed agreement with the normal distribution. Comparison of results assuming spherical and non-isotropic propagation of flames indicate non-isotropic flame propagation should be considered for the description of in-cylinder processes with higher accuracy. The high temporal resolution of the sequence of images allowed observation of the spark-ignition delay process. The results indicate that gasoline and isooctane have somewhat similar flame propagation behaviour. Additional differences between these fuels and E85 and M85 were also recorded and identified

Blade-loading effects on the propagation of unsteady flow and on forcing functions in axial-turbine cascades

This article investigates the effect of tangential blade loading on the propagation of time-dependent pressure disturbance due to potential-flow interaction ans viscous-wake interaction from upstream blade rows in axial-turbine-blade rotor cascades. Results are obtained by modeling the effects of the stator viscous wake and tha stator-rotor potential-flow field on the rotor flow field. A computer program is used to calculate the unsteady flows in the rotor passages. The amplitudes for the two types of interaction are based on a review of available experimental and computational data. We study the propagation of the isolated potential-flow interaction (no viscous-wake interaction), of the isolated viscous wake interaction (no potential-flow interaction), and of the combination of interactions. We examine the propagation of both interactions in three frotor cascades of high, medium and low tangential-loading coefficient (1.2, 1.0 and 0.8 respectively) for typical values of reduced frequency. The discussion uses as example a stator-to-rotor-pitch ration $R$ = 2. We investigate the differences when the stator-to-rotor pitch ratio is decreased (to $R$ = 1) and increased (to $R$ = 4). We offer new explanations of the mechanisms of generation of unsteady forces on the blades and study the effects of tangential blade and of axial gap between blade rows on th time-dependent forces acting on the blades. The potential-flow field of the rotor-leading-edge region cuts the potential-flow field of the upstream stator, and distorts and cuts the wake centerlines. The potential-flow field cut into the rotor passage propagates downstream as a potential-flow disturbance superimposed on the rotor flow field. The direction and decay rate of this interaction are determined respectively by the stator-outlet flow angle and by the stator-cascade pitch. The cut wake is sheared into the rotor passage and it results in a region of increased unsteady pressure upstream of the wake centerline and a region of decreased unsteady pressure downstream of the wake centerline. The wake shearing is more pronounced in highly-loaded cascades, and for lower stator outlet-flow angles. The potential flow interaction dominates the unsteadiness for high values of $R$ and the wake interaction dominates the unsteadiness for low values of $R$. The above explanations can be used to determine locations unsteady-pressure regions, and the shape of the unsteady forcing functions

A design method for the prediction of unsteady forces on subsonic, axial gas-turbine blades

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1987.Bibliography: p. 214-225.by Theodosios Prokopios Korakianitis.Sc.D