MODELING THE LUBRICATING INTERFACES OF ULTRA-HIGH PRESSURE RADIAL PISTON MACHINES

Ramchandran, Gautham. M.S.M.E., Purdue University, August 2016. Modeling the Lubricating Interfaces of Ultra-High Pressure Radial Piston Machines. Major Professor: Andrea Vacca, School of Mechanical Engineering

Low-thrust chemical propulsion system pump technology

Candidate pump and driver systems for low thrust cargo orbit transfer vehicle engines which deliver large space structures to geosynchronous equatorial orbit and beyond are evaluated. The pumps operate to 68 atmospheres (1000 psi) discharge pressure and flowrates suited to cryogenic engines using either LOX/methane or LOX/hydrogen propellants in thrust ranges from 445 to 8900 N (100 to 2000 lb F). Analysis of the various pumps and drivers indicate that the low specific speed requirement will make high fluid efficiencies difficult to achieve. As such, multiple stages are required. In addition, all pumps require inducer stages. The most attractive main pumps are the multistage centrifugal pumps

Characterization of Flow Dynamics in a Heart Simulator by means of PIV = Charakterisierung der Strömungsdynamik in einem Herzsimulator mittels PIV

Diese Arbeit konzentriert sich auf die strömungsmechanische Charakterisierung von Regurgitationsjets, die durch insuffiziente Mitralklappen entstehen. Die Untersuchungen wurden mit Particle Image Velocimetry (PIV) Messtechnik und eigens entwickelten Post-Processing-Skripten durchgeführt. Die Mitralinsuffizienz ist die häufigste Form der Herzklappenerkrankung und bezeichnet den Rückfluss von Blut in den linken Vorhof aufgrund einer insuffizienten Mitralklappe, was zu verschiedenen gesundheitlichen Komplikationen führt. Eine genaue Diagnose der Mitralinsuffizienz ist für eine erfolgreiche Behandlung von entscheidender Bedeutung. Bei komplexen Regurgitationsjets ist die Aussagekraft herkömmlicher Methoden jedoch limitiert. Diese Studie zielt darauf ab, das Verständnis für die komplexe Strömungssituation von Regurgitationsjets zu verbessern und so zur Verbesserung der Diagnose und damit der Therapie beizutragen. Dazu wurden phasengemittelte und phasenaufgelöste 2D2C-PIV-Experimente für verschiedene Mitralklappengeometrien im Herzsimulator durchgeführt. Der Laserlichtschnitt wurde traversiert, um quasi 3D Geschwindigkeitsdaten zu erhalten. Drei generische Mitralklappengeometrien unterschiedlicher Größe wurden untersucht: eine runde Lochblende, ein spitzes Oval und eine Tropfenform. Zusätzlich wurden eine exzentrische Klappengeometrie und eine patienten-spezifische Klappe untersucht. Die Geschwindigkeitsdaten wurden bezüglich zeitlichem Strömungsverlauf und Form des Jets untersucht. Die Wirbeldynamische Untersuchung basierte auf der Wirbelstärke, sowie dem Q- und $\Gamma_1$-Kriterium. Die Ergebnisse der generischen Mitralklappen zeigten typische Merkmale von pulsierenden Jets. Unterschiede in der radialen Geschwindigkeitsverteilung konnten mit den unterschiedlichen Öffnungsformen in Verbindung gebracht werden. Die Sattel-behafteten radialen Profile der Axialgeschwindigkeit am Auslass können durch die geringe Einlasslänge und die scharfen Öffnungsränder erklärt werden. Zusätzlich zu periodisch wiederkehrenden Anfangswirbeln wurden Kelvin-Helmholtz-Instabilitäten in der Grenzschicht stromaufwärts detektiert. Die exzentrische Klappengeometrie zeigte ähnliche Beobachtungen, jedoch um den Winkel der Exzentrizität gedreht. Die patientenspezifische Mitralklappe ergab, im Vergleich zu den generischen Fällen,eine deutlich instabilere und turbulentere Strömungssituation, was auf die komplexere Öffnungsform, die höhere Reynoldszahl und die größere Flexibilität der Klappenblätter zurückzuführen ist. Form und Richtung des Jets unterlagen starken zeitlichen und räumlichen Schwankungen. Gemittelte PIV-Auswertungen ergaben ein dominantes Anfangswirbelpaar, während Einzelbildpaarauswertungen keine eindeutige Wirbelerkennung zeigten. Für zukünftige Untersuchungen wird empfohlen, das Innere des Atriums mit einer realistischeren Geometrie zu modellieren und Hochgeschwindigkeits-PIV zu verwenden

Smart Flow Control Processes in Micro Scale

In recent years, microfluidic devices with a large surface-to-volume ratio have witnessed rapid development, allowing them to be successfully utilized in many engineering applications. A smart control process has been proposed for many years, while many new innovations and enabling technologies have been developed for smart flow control, especially concerning “smart flow control” at the microscale. This Special Issue aims to highlight the current research trends related to this topic, presenting a collection of 33 papers from leading scholars in this field. Among these include studies and demonstrations of flow characteristics in pumps or valves as well as dynamic performance in roiling mill systems or jet systems to the optimal design of special components in smart control systems

Studies of exit pressure recovery coefficient and its effects on dynamic characteristics of annular water seals

Rotordynamic instability and vibration due to fluid forces within annular seals are well-known phenomenons that can occur in pumps as well as in turbines. Traditional theoretical predictions for the fluid reaction forces and equivalent dynamic characteristics of annular seals are computationally efficient compared with CFD method. Exit pressure loss coefficient is one of the main factors that influence the precisions of theoretical analysis. In this paper, exit pressure recovery coefficients at three different static eccentricity ratios under different operating conditions are investigated using CFD method. The numerical result shows that exit coefficient increases exponentially with the ratio of circumferential velocity to axial velocity at all these three eccentricity ratios. Besides, an analysis method for annular plain seals with the introduction of exit pressure recovery coefficient varied with operating conditions is proposed based on the previous analysis results. Comparisons are made between theoretical predictions calculated by the two methods with and without exit coefficient over a wide range of pressure drops and running speeds. The result suggests that damping coefficients are much more sensitive to the change of the exit boundary conditions compared to stiffness coefficients. In addition, the new prediction results of cross-coupled stiffness and direct damping coefficient show relatively smooth change with the increase of velocity ratio than the previous results

An Investigation of Micro-Surface Shaping on the Piston/Cylinder Interface of Axial Piston Machines

Presently, axial piston machines of the swash plate type are commonly used in industry due to their many benefits. However, with recent technological advancements in hydraulic hybrid powertrains and displacement-controlled actuation, the application of such machines has been broadened demanding a more cost-effective reliable and efficient, yet versatile machine. The fluid film geometry of the lubricating interfaces is a very complex and sensitive phenomena that must simultaneously fulfill a competing bearing and sealing function. Therefore, the design process of such machines is a difficult process while tightly constrained manufacturing tolerances are essential thereby increasing the initial production costs. Accordingly, virtual prototyping through analytical simulation in this field has emerged as an ideal tool not only to improve the performance of existing units, but to also design new and innovative axial piston machines that fulfill the demands of advanced technology. The aim of this dissertation is to investigate more efficient and reliable designs of the piston/cylinder interface of an axial piston machine over a broad range of operating conditions. Primarily, an extensive simulation study was conducted in which the design of a commercially available machine was modified to accommodate piston micro-surface shaping where the relative improvements were then quantified in comparison. This study utilizes a novel fully-coupled fluid structure interaction model considering both thermal and pressure deformations of the solid bodies to accurately predict the dynamic behavior of the lubricating interface. Having analyzed the phenomena of the lubricating gap and the effects of micro-surface shaping, an optimization technique was utilized to design this interface. The optimization scheme determines the best balance between improving the sealing function while maintaining or even improving the bearing function. A surface shaped piston was then measured and compared back to the simulation results realizing the capabilities of such a novel methodology. Ultimately, this cost-effective design process demonstrated that micro-surface shaping is beneficial as it allows for reduced clearances, achieving a reduction in volumetric losses, while increasing fluid film support, resulting in superior efficiency as well as enhanced reliability and overall performance

Research on the Piston with Damping Hole and Pressure Recess of Axial Piston Motor

Based on the principle of hydrostatic bearing, in this study, several novel kinds of pistons were designed out, and the mathematic model of hydrostatic bearing on piston was established and analyzed. It was also found that, the diameter of damping hole and the width of pressure recess had impact on the radial load capacity of piston, the overall efficiency of axial piston motor, and the friction and wear capacity of piston. Results from tests shown that in the case of the pressure difference of 10MPa to 22MPa and the different speed of 500rpm to 2000rpm, the overall efficiency of axial piston motor could be improved by 0.1%-0.6%, compared to the ordinary piston. On the other hand, the wear scar of the piston modified was circular, and the one of the ordinary piston was longitudinal and deep, which shown that the piston modified could improve the wear capacity

Piston / Cylinder Interface Of Axial Piston Machines – Effect Of Piston Micro-Surface Shaping

Axial piston machines are widely used in current industries such as aerospace, agriculture, automotive, heavy machinery, military, etc. Thus new cost-effective and highly efficient designs with better performance and reliability are needed. These new, high efficient pumps and motors will also aid in new applications such as hybrid hydrostatic transmissions and displacement controlled actuation. The aim of this work is to study how to reduce the energy dissipation (increase efficiency) while also improving the load carrying ability of the fluid film between the piston and the cylinder through surface shaping of the piston over a wide range of operating conditions. The impacts of this study also include the utilization of modern manufacturing technologies as low tolerances are necessary such that this could affect the overall efficiency of the machine drastically. This study could also open up ways to use water as a lubricating fluid in order to significantly reduce costs. In doing so, a comprehensive understanding of the phenomena occurring between the piston and cylinder will also be achieved in order to find a balance between the viscous friction of the fluid, while reducing any contact occurring, and the leakage. In order to verify the code used in this surface shaping study, a comprehensive study was conducted on the baseline and then compared to measurements

Multi-physics for integrated analysis of flexible body dynamics with tribological conjunction in IC engines

Since the inception of internal combustion engine, there has been a continual strive to improve its efficiency and refinement. Until very recently, the developments in this regard have been largely based on an experiential basis, or backed by analytical investigations, confined to particular features of the engines. This has been due to lack of computational power, and analysis tools of an integrative nature. In recent years enhanced computing power has meant that complex models, chiefly based on multi-body dynamics could be developed, and further enhanced by the inclusion of component flexibility in the form of structural modes, obtained through finite element analysis. This approach has enabled study of dynamics/vibration response of engines in a more quantitative manner than hitherto possible. Structural integrity issues, as well as noise and vibration (refinement) can then be studied in an integrated manner. However, earlier models still lack sufficient detail to include, within the same analysis, issues related to efficiency, chiefly prediction of parasitic losses due to mechanical imbalance and friction. [Continues.

Rotordynamic Instability Problems in High-Performance Turbomachinery, 1986

The first rotordynamics workshop proceedings (NASA CP-2133, 1980) emphasized a feeling of uncertainty in predicting the stability of characteristics of high-performance turbomachinery. In the second workshop proceedings (NASA CP-2250, 1982) these uncertainities were reduced through programs established to systematically resolve problems, with emphasis on experimental validiation of the forces that influence rotordynamics. In third proceedings (NASA CP-2338, 1984) many programs for predicting or measuring forces and force coefficients in high-performance turbomachinery produced results. Data became available for designing new machines with enhanced stability characteristics or for upgrading existing machines. The present workshop proceedings illustrates a continued trend toward a more unified view of rotordynamic instability problems and several encouraging new analytical developments