Using Steady Flow Force for Unstable Valve Design: Modeling and Experiments

2004 ◽  
Vol 127 (3) ◽  
pp. 451-462 ◽  
Author(s):  
Qinghui Yuan ◽  
Perry Y. Li
Keyword(s):  
Steady Flow ◽  
Transient Flow ◽  
Experimental Studies ◽  
Single Stage ◽  
Low Flow ◽  
Cfd Analysis ◽  
Valve Design ◽  
Viscosity Effect ◽  
Modeling And Experiments ◽  
Negative Damping

In single stage electrohydraulic valves, solenoid actuators are usually used to stroke the main spools directly. They are cheaper and more reliable than multistage valves. Their use, however, is restricted to low bandwidth and low flow rate applications due to the limitation of the solenoid actuators. Our research focuses on alleviating the need for large and expensive solenoids in single stage valves by advantageously using fluid flow forces. For example, in a previous paper, we proposed to improve spool agility by inducing unstable transient flow forces by the use of negative damping lengths. In the present paper, how steady flow forces can be manipulated to improve spool agility is examined through fundamental momentum analysis, CFD analysis, and experimental studies. Particularly, it is found that two often ignored components—viscosity effect and non-metering momentum flux, have strong influence on steady flow forces. For positive damping lengths, viscosity increases the steady flow force, whereas for negative damping lengths, viscosity has the tendency to reduce steady flow forces. Also, by slightly modifying the non-metering port geometry, the non-metering flux can also be manipulated to reduce steady flow force. Therefore, both transient and steady flow forces can be used to improve the agility of single stage electrohydraulic valves. Experimental results confirm the contributions of both transient and steady flow force in improving spool agility.

Hybrid Analysis of Gas Annular Seals With Energy Equation

2013 ◽  
Author(s):  
Patrick J. Migliorini ◽  
Alexandrina Untaroiu ◽  
William C. Witt ◽  
Neal R. Morgan ◽  
Houston G. Wood
Keyword(s):  
Experimental Data ◽  
Hybrid Method ◽  
Energy Equation ◽  
Flow Analysis ◽  
Experimental Studies ◽  
Rotor System ◽  
Bulk Flow ◽  
Outlet Temperature ◽  
Cfd Analysis ◽  
Annular Seals

Annular seals are used in turbomachinery to reduce secondary flow between regions of high and low pressure. In a vibrating rotor system, the non-axisymmetric pressure field developed in the small clearance between the rotor and the seal generate reactionary forces that can affect the stability of the entire rotor system. Traditionally, two analyses have been used to study the fluid flow in seals, bulk-flow analysis and computational fluid dynamics (CFD). Bulk-flow methods are computational inexpensive, but solve simplified equations that rely on empirically derived coefficients and are moderately accurate. CFD analyses generally provide more accurate results than bulk-flow codes, but solution time can vary between days and weeks. For gas damper seals, these analyses have been developed with the assumption that the flow can be treated as isothermal. Some experimental studies show that the difference between the inlet and outlet temperature temperatures is less than 5% but initial CFD studies show that there can be a significant temperature change which can have an effect on the density field. Thus, a comprehensive analysis requires the solution of an energy equation. Recently, a new hybrid method that employs a CFD analysis for the base state, unperturbed flow and a bulk-flow analysis for the first order, perturbed flow has been developed. This method has shown to compare well with full CFD analysis and experimental data while being computationally efficient. In this study, the previously developed hybrid method is extended to include the effects of non-isothermal flow. The hybrid method with energy equation is then compared with the isothermal hybrid method and experimental data for several test cases of hole-pattern seals and the importance of the use of energy equation is studied.

Optimization of a Hydraulic Valve Design Using CFD Analysis

2005 ◽  
Author(s):  
Manohari D. Ramesh ◽  
Yan A. Tan ◽  
XueKui Lan
Keyword(s):  
Cfd Analysis ◽  
Valve Design ◽  
Hydraulic Valve

A Numerical Investigation on the Volute/Diffuser Interaction due to the Axial Distortion at Impeller Exit

2000 ◽  
Author(s):  
Fahua Gu ◽  
Abraham Engeda ◽  
Mike Cave ◽  
Jean-Luc Di Liberti
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Numerical Investigation ◽  
Steady Flow ◽  
Centrifugal Compressor ◽  
Vortex Structure ◽  
Flow Model ◽  
Single Stage ◽  
Mass Flows

Abstract A numerical simulation is performed on a single stage centrifugal compressor using the commercially available CFD software, CFX-TASCflow. The steady flow is obtained by circumferentially averaging the exit fluxes of the impeller. Three runs are made at design condition and off-design conditions. The predicted performance is in agreement with experimental data. The flow details inside the stationary components are investigated, resulting in a flow model describing the volute/diffuser interaction at design and off-design conditions. The recirculation and twin vortex structure are found to explain the volute loss increase at lower and higher mass flows, respectively.

scholarly journals EXPERIMENTAL STUDIES ON THE THRESHOLD OF VEHICLE INSTABILITY IN FLOODWATERS

2018 ◽  
Vol 80 (5) ◽  
Author(s):  
Syed Muzzamil Hussain Shah ◽  
Zahiraniza Mustaffa ◽  
Khamaruzaman Wan Yusof
Keyword(s):  
Experimental Studies ◽  
Orientation Angle ◽  
High Water ◽  
Road Surface ◽  
The Other ◽  
Low Flow ◽  
Flood Risks ◽  
Die Cast ◽  
Cast Model ◽  
Water Depths

Flood risks concerned to vehicle’s instability have become more conspicuous and it is thus necessary to understand the behaviour of vehicles exposed to floodwaters. Therefore, this paper aims at investigating the thresholds of vehicle instability in floodwaters at different orientations. A stationary die-cast model vehicle (1:24) was used with the condition of rear tires being locked only, positioned at different orientation angles on a flat road surface in the partially submerged zone. Measurements were taken including the approaching velocities and water depths, through which the instability was computed. The study concludes that a partially submerged vehicle becomes instable at high water depths and low flow velocities and vice versa. Further, the vehicle was observed to be most stable when positioned at orientation angle of 0°/360°, with the limiting depth × velocity (D*V) value of 0.0168 m2/s. On the other hand, it was noted to be least stable when positioned at the orientation angle of 90° and 270°, with the limiting (D*V) value of 0.0144 m2/s. The outcomes from this study were later translated into guidelines.

scholarly journals To model or not to model?

2011 ◽  
Vol 22 (7) ◽  
pp. 909-910 ◽  
Author(s):  
Daniel A. Fletcher
Keyword(s):  
Mathematical Modeling ◽  
Annual Meeting ◽  
Cell Biology ◽  
Experimental Studies ◽  
Personal Experiences ◽  
Modeling And Experiments

In theory, the combination of mathematical modeling with experimental studies can be a powerful and compelling approach to understanding cell biology. In practice, choosing appropriate problems, identifying willing and able collaborators, and publishing the resulting research can be remarkably challenging. To provide perspective on the question of whether and when to combine modeling and experiments, a panel of experts at the 2010 ASCB Annual Meeting shared their personal experiences and advice on how to use modeling effectively.

Pulsatile Flow and Oxygen Transport Past Cylindrical Fiber Arrays for an Artificial Lung: Computational and Experimental Studies

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Jennifer R. Zierenberg ◽  
Hideki Fujioka ◽  
Keith E. Cook ◽  
James B. Grotberg
Keyword(s):  
Right Ventricular ◽  
Steady Flow ◽  
Oxygen Transport ◽  
Pulsatile Flow ◽  
Experimental Studies ◽  
Artificial Lung ◽  
Transport Efficiency ◽  
Fiber Arrays ◽  
Cylindrical Fiber ◽  
The Right

The influence of time-dependent flows on oxygen transport from hollow fibers was computationally and experimentally investigated. The fluid average pressure drop, a measure of resistance, and the work required by the heart to drive fluid past the hollow fibers were also computationally explored. This study has particular relevance to the development of an artificial lung, which is perfused by blood leaving the right ventricle and in some cases passing through a compliance chamber before entering the device. Computational studies modeled the fiber bundle using cylindrical fiber arrays arranged in in-line and staggered rectangular configurations. The flow leaving the compliance chamber was modeled as dampened pulsatile and consisted of a sinusoidal perturbation superimposed on a steady flow. The right ventricular flow was modeled to depict the period of rapid flow acceleration and then deceleration during systole followed by zero flow during diastole. Experimental studies examined oxygen transfer across a fiber bundle with either steady, dampened pulsatile, or right ventricular flow. It was observed that the dampened pulsatile flow yielded similar oxygen transport efficiency to the steady flow, while the right ventricular flow resulted in smaller oxygen transport efficiency, with the decrease increasing with Re. Both computations and experiments yielded qualitatively similar results. In the computational modeling, the average pressure drop was similar for steady and dampened pulsatile flows and larger for right ventricular flow while the pump work required of the heart was greatest for right ventricular flow followed by dampened pulsatile flow and then steady flow. In conclusion, dampening the artificial lung inlet flow would be expected to maximize oxygen transport, minimize work, and thus improve performance.

The Effect of Mass Flow Rate on the Reflection Behaviour of Small-Amplitude Pressure Waves from Duct Terminations

1978 ◽  
Vol 20 (4) ◽  
pp. 229-235 ◽  
Author(s):  
M. A. Ali ◽  
K. F. Gill ◽  
B. W. Imrie
Keyword(s):  
Reflection Coefficient ◽  
Steady Flow ◽  
Mass Flow ◽  
Small Amplitude ◽  
Binary Sequence ◽  
Low Flow ◽  
Correlation Technique ◽  
Pressure Waves ◽  
Flow Number ◽  
Wide Range

This paper describes an investigation of the reflection characteristics of small-amplitude pressure waves in the presence of steady flow in a duct. A correlation technique employing pseudo-random binary-sequence (p.r.b.s.) pulses is introduced. A theoretical model of the process is presented together with considerations of correlation analysis. The results show agreement between the experimental results and the model; they further indicate that, in the presence of a steady flow component, there is a significant effect on the reflection behaviour of plane pressure waves for a reduction in the area terminating a duct. The experimental technique is effective at very low flow velocities (Mach number = 0·02, Reynolds number = 30 times 103) and establishes a linear relationship between a reflection coefficient and a non-dimensional mass flow number. A reflection coefficient of flow is introduced as an appropriate parameter for such conditions. The procedure could be applied to a wide range of industrial processes to determine flow coefficients of duct elements in situ, to optimize flow processes and to locate leakage flows.

scholarly journals Distribution of kinetic energy losses between nozzles and turbine impeller on partial gas supply modes

2021 ◽  
pp. 122-126
Author(s):  
Ю.В. Соломахин ◽  
Л.П. Цыганкова ◽  
В.Н. Коршунов
Keyword(s):  
Kinetic Energy ◽  
Pressure Ratio ◽  
Experimental Studies ◽  
Average Diameter ◽  
Rotor Blades ◽  
Low Flow ◽  
Energy Losses ◽  
Outlet Section ◽  
Technical Literature ◽  
Actual Flow Rate

В статье приведены результаты экспериментальных исследований связанных с распределением потерь кинетической энергии между сопловым аппаратом и рабочим колесом у осевых малорасходных турбинных ступеней. У всех ступеней конструктивные углы выхода сопел были менее 9°, что повлекло за собой необходимость выполнения рабочих колес с относительным шагом установки рабочих лопаток значительно большим, рекомендованного в технической литературе. Исследования проведены для ступеней со средним диаметром 250 мм. Диапазон изменения факторов составил: отношение давлений перед соплами к давлению за ступенью от 2.0 до 5.0; частоты вращения вала с рабочим колесом от 0 до 14000 . Эффективность использования кинетической энергии приведена в виде коэффициентов скорости соплового аппарата и рабочего колеса. Коэффициенты представляют собой отношение реальной скорости потока на выходе из соплового аппарата (рабочего колеса) к теоретически возможной скорости газа в выходном сечении рассматриваемого элемента ступени. Выявлено, что коэффициенты скорости сопловых аппаратов и рабочих колес изменяются не только при смене режимных параметров, таких как частота вращения ротора и отношения давлений на ступень, но и при изменении степени парциальности ступени. The article presents the results of experimental studies related to the distribution of kinetic energy losses between the nozzle apparatus and the impeller at axial low-flow turbine stages. At all stages, the design angles of the nozzle exit were less than 9 °, which entailed the necessity of making impellers with a relative pitch of the rotor blades that was much larger, as recommended in the technical literature. The studies were carried out for steps with an average diameter of 250 mm. The range of variation of the factors was the ratio of the pressures in front of the nozzles to the pressure behind the stage from 2.0 to 5.0; rotation speed of the shaft with the impeller from 0 to 14000 rpm. The efficiency of using the kinetic energy is given in the form of the coefficients of the speed of the nozzle apparatus and the impeller. The coefficients represent the ratio of the actual flow rate at the outlet of the nozzle apparatus (impeller) to the theoretically possible gas velocity in the outlet section of the stage element under consideration. It was found that the speed coefficients of the nozzle apparatus and impellers change not only when changing operating parameters, such as the rotor speed and the pressure ratio per stage, but also when changing the degree of stage partiality.

scholarly journals CFD Analysis to Understand the Flow Behaviour of a Single Stage Transonic Axial Flow Compressor

2013 ◽  
Author(s):  
M. T. Shobhavathy ◽  
Premakara Hanoca
Keyword(s):  
Axial Flow ◽  
Flow Behaviour ◽  
Single Stage ◽  
Cfd Analysis ◽  
Flow Conditions ◽  
Blade Passage ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Design Speed ◽  
Flow Compressor

This paper comprises the Computational Fluid Dynamic (CFD) analysis to investigate the flow behaviour of a high speed single stage transonic axial flow compressor. Steady state analyses were carried out at design and part speed conditions to obtain the overall performance map using commercial CFD software ANSYS FLUENT. Radial distribution of flow parameters were obtained at 90% of design speed for the choked flow and near stall flow conditions. The predicted data were validated against available experimental results. The end wall flow fields were studied with the help of velocity vector plots and Mach number contours at peak efficiency and near stall flow conditions at 60% and 100% design speeds. This study exhibited the nature of a transonic compressor, having strong interaction between the rotor passage shock and the tip leakage vortex at design speed, which generates a region of high blockage in the rotor blade passage. The influence of this interaction extends around15% of the blade outer span at design speed and in the absence of blade passage shock at 60% design speed, the influence of tip leakage flow observed was around 8%.

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