Theoretical approximations to analyse the onset of self-excited oscillations in flow through collapsible tubes

2010 ◽  
Vol 224 (2) ◽  
pp. 337-343
Author(s):  
V Oruç ◽  
M Ö Çarpınlıoğlu
Keyword(s):  
Theoretical Calculations ◽  
Input Parameter ◽  
Elastic Tube ◽  
Linear Stability Theory ◽  
Sectional Area ◽  
Cross Sectional ◽  
Collapsible Tubes ◽  
Theoretical Predictions ◽  
Flow Through ◽  
Critical Oscillation

In this study, flow through collapsible tubes is analysed theoretically for the case of the onset of collapse which induces self-excited oscillations. The basic tools in the theoretical calculations are the linear stability theory and the tube law. The experimental data in the form of measured oscillation frequency at the onset of collapse of an elastic tube is supplied as a base input parameter for the theoretical approximations. The calculations offer a possibility for estimating the unmeasured parameters such as critical oscillation speed, speed index, and tube cross-sectional area at the onset of collapse. It was seen by referring to the obtained results that theoretical predictions agreed with the experimental measurements.

Effect of Tapering on Pulsatile Flow Through a U-Tube Model of the Human Aortic Arch

2010 ◽  
Author(s):  
Masaru Sumida
Keyword(s):  
Velocity Profile ◽  
Pulsatile Flow ◽  
Velocity Profiles ◽  
Cross Sectional Area ◽  
Flow Rate Ratio ◽  
Sectional Area ◽  
Cross Sectional ◽  
Turn Angle ◽  
Flow Through ◽  
The Cross

An experimental investigation of pulsatile flow through a tapered U-tube was performed to study the blood flow in the aorta. The experiments were carried out in a U-tube with a curvature radius ratio of 3.5 and a 50% reduction in the cross-sectional area from the entrance to the exit of the curved section. Velocity measurements were conducted by a laser Doppler velocimetry for a Womersley number of 10, a mean Dean number of 400 and a flow rate ratio of 1. The velocity profiles for pulsatile flow in the tapered U-tube were compared with the corresponding results in a U-tube having a uniform cross-sectional area. The striking effects of the tapering on the flow are exhibited in the axial velocity profiles in the section from the latter half of the bend to the downstream tangent immediately behind the bend exit. A depression in the velocity profile appears at a smaller turn angle Ω in the case of tapering, although the magnitude of the depression relative to the cross-sectional average velocity decreases. The value of β, which indicates the uniformity in the velocity profile over the cross section, decreases with increasing Ω, whereas it rapidly increases immediately behind the bend exit.

Identification of the piston machine combustion chamber tightness

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Piotr Jan Bielawski
Keyword(s):  
Combustion Chamber ◽  
Measurement System ◽  
Gas Flow ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Cross Sectional ◽  
Content Type ◽  
Flow Through ◽  
The Cross ◽  
Pneumatic Sensor

PurposeThe lack of integrity of the piston machine combustion chamber manifests itself in leakages of the working fluid between the piston and the cylinder liner, at valves mounted in the cylinder head and between the head and the liner. An untight combustion chamber leads to decreased power output or efficiency of the engine, while leaks of a fluid may cause damage to many components of the chamber. The actual value of working chamber leak is a desired and essential piece of information for planning operations of a given machine.Design/methodology/approachThis research paper describes causes and mechanisms of leakage from the working chamber of internal combustion engines. Besides, the paper outlines presently used methods and means of leak identification and states that their further development and improvements are needed. New methods and their applicability are presented.FindingsThe methods of leak identification have been divided into diagnostic and non-working machine leak identification methods. The need has been justified for the identification of leakage from the combustion chamber of a non-working machine and for using the leakage measure as the value of the cross-sectional area of the equivalent leak, defined as the sum of cross-section areas of all leaking paths. The analysis of possible developments of tightness assessment methods referring to the combustion chamber of a non-working machine consisted in modelling subsequent combustion chamber leaks as gas-filled tank leak, leak from another element of gas-filled tank and as a regulator of gas flow through a nozzle.Originality/valueA measurement system was built allowing the measurement of pressure drop in a tank with the connected engine combustion chamber, which indicated the usefulness of the system for leakage measurement in units as defined in applicable standards. A pneumatic sensor was built for measuring the cross-sectional area of the equivalent leak of the combustion chamber connected to the sensor where the chamber functioned as a regulator of gas flow through the sensor nozzle. It has been shown that the sensor can be calibrated by means of reference leaks implemented as nozzles of specific diameters and lengths. The schematic diagram of a system for measuring the combustion chamber leakage and a diagram of a sensor for measuring the cross-sectional area of the equivalent leak of the combustion chamber leakage are presented. The results are given of tightness tests of a small one-cylinder combustion engine conducted by means of the set up measurement system and a pre-prototype pneumatic sensor. The two solutions proved to be practically useful.

Kinematic description of fluids in motion and approximations

2018 ◽  
Author(s):  
Marcel Escudier
Keyword(s):  
Fluid Velocity ◽  
Slip Boundary Condition ◽  
Cross Sectional Area ◽  
Constant Density ◽  
Sectional Area ◽  
Cross Sectional ◽  
Slip Boundary ◽  
Flow Problems ◽  
Mass Flowrate ◽  
Flow Through

In this chapter some of the terminology and simplifications which enable us to begin to describe and analyse practical fluid-flow problems are introduced. The terms ‘fluid particle’ and ‘streamline’ are defined. The principle of conservation of mass applied to steady one-dimensional flow through a streamtube of varying cross-sectional area resulted in the continuity equation. This important equation relates mass flowrate ṁ, volumetric flowrate Q̇, average fluid velocity V̄, fluid density ρ‎, and cross-sectional area A: m = ρ‎ Q̇ = ρ‎AV̅ = constant. For a constant-density fluid this result shows that fluid velocity increases if the cross-sectional area decreases, and vice versa. The no-slip boundary condition, a consequence of which is the boundary layer, is introduced.

Viscous flow in collapsible tubes of slowly varying elliptical cross-section

1977 ◽  
Vol 81 (2) ◽  
pp. 273-294 ◽  
Author(s):  
Rosemary Wild ◽  
T. J. Pedley ◽  
D. S. Riley
Keyword(s):  
Pressure Drop ◽  
Flow Rate ◽  
Transverse Velocity ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Collapsible Tube ◽  
Experimental Conditions ◽  
Cross Sectional ◽  
Elliptical Cross ◽  
Collapsible Tubes

This paper is concerned with steady flow in collapsible tubes, such as veins, at fairly low Reynolds number. Lubrication theory is used to calculate the velocity and pressure distribution in an elliptical tube whose cross-sectional area and eccentricity vary slowly and in a given way with longitudinal distance x. The transverse velocity field and the effect of inertia on the primary velocity and pressure distributions are calculated to first order in the relevant small parameter. The results of these calculations are combined with a relationship between transmural pressure and the cross-sectional area at any x which is close to that measured in (large) veins, and are used to predict the pressure and flow in a collapsible tube when a given distribution of external pressure is applied. Different relationships between the tube perimeter and cross-sectional area are examined. The theory is applied to an experiment in which a segment of collapsible tube is supported between two rigid segments, and squeezed; predictions of the relationship between the pressure drop and flow rate are made for various experimental conditions. In particular, when the resistance of the downstream rigid segment is held constant, a range of flow rates is found in which the pressure drop falls as the flow rate is raised; this agrees with experiment.

scholarly journals Comparison of the heat for rectangular and circle salt boiling stove in Ban Dung area, Udon Thani Province.

2018 ◽  
Vol 192 ◽  
pp. 02031
Author(s):  
Aphichat Srichat ◽  
Ponthep Vengsungnle ◽  
Kaweepongt Hongtong ◽  
Weeraphon Kaewka ◽  
Jarinee Jongpluempiti
Keyword(s):  
Fluid Dynamics ◽  
Thermal Efficiency ◽  
Thermal Parameter ◽  
Sectional Area ◽  
Cross Sectional ◽  
Hot Air ◽  
Boiling Process ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Through ◽  
The Cost

This research aims a study to compare the thermal parameter of the original (rectangular) and circle salt boiling stove by computational fluid dynamics (CFD) of the boiling salt process in Ban Dung area, Udon Thani province. The first study, the rectangular stove has U-shaped channel for heating flow through chimney that the stove size is 2.4 m of width, 6.0 m of long, 0.8 m of high and cross-sectional area of heating flue was 0.8 x 0.8 m2. The second study, the circle salt boiling stove has a similarly volume of the rectangular stove of 4.32 m3 and the diameter of 4.58 m. From the results of mathematical models by CFD found that the rectangular stove have the thermal efficiency, the highest fired temperature and the velocity outlet of hot air of 17.78%, 537.77oC and 4.862 m/s, respectively. Then, the circle stove have 24.59%, 758.32oC and 3.1424 m/s, respectively. it can be calculated the thermal efficiency reduce of the boiling salt production is 27.69%. Comparison between the rectangular and the circle salt boiling stove found that the circle stove have the thermal efficiency and heating flue more than the rectangular stove. It can reduce the cost of production and reduce the fuel consumption in the salt boiling process.

scholarly journals Steady analysis of transcritical flows in collapsible tubes with discontinuous mechanical properties: implications for arteries and veins

2013 ◽  
Vol 736 ◽  
pp. 195-215 ◽  
Author(s):  
A. Siviglia ◽  
M. Toffolon
Keyword(s):  
Mechanical Properties ◽  
Free Surface Flows ◽  
Cross Sectional Area ◽  
Sectional Area ◽  
Collapsible Tube ◽  
Cross Sectional ◽  
Collapsible Tubes ◽  
The Cross ◽  
Transcritical Flows ◽  
Arteries And Veins

AbstractWe study the conditions under which discontinuous mechanical properties of a collapsible tube can induce transcritical flows, i.e. the transition through the critical state where the speed index (analogous to the Mach or the Froude numbers for compressible and free surface flows, respectively) is one. Such a critical transition may strongly modify the flow properties, cause a significant reduction in the cross-sectional area of the tube, and limit the flow. General relationships are obtained for a short segment using a one-dimensional model under steady flow conditions. Marginal curves delimiting the transcritical regions are identified in terms of the speed index and the cross-sectional area ratio. Since there are many examples of such flows in physiology and medicine, we also analyse the specific case of prosthesis (graft or stent) implantation in blood vessels. We then compute transcritical conditions for the case of stiffness and reference area variations, considering a collapsible tube characterized by physiological parameters representative of both arteries and veins. The results suggest that variations in mechanical properties may induce transcritical flow in veins but is unrealistic in arteries.

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