Pressure Pulsations in Reciprocating Compressor Delivery Systems

1966 ◽  
Vol 8 (2) ◽  
pp. 141-151 ◽  
Author(s):  
F. J. Wallace
Keyword(s):  
Theoretical Approach ◽  
Wave Theory ◽  
Delivery Systems ◽  
Pressure Pulsations ◽  
Mean Flow ◽  
Gas Generator ◽  
Free Piston ◽  
Mean Pressure ◽  
Gas Generators ◽  
The Mean

In an earlier paper (1)†, the author discussed the nature of pressure pulsations in suction systems of free-piston gas generators, and in particular various forms of pulsation damping devices. A theoretical approach was based on a simple linear treatment of the system, i.e. (1) regarding all pressure pulsations as small in relation to the mean pressure on which they are superimposed, (2) treating dissipative elements (pipe friction or concentrated restrictions) as having linear pressure drop-velocity relationships about the mean flow condition, and (3) treating all distributed elements as having wave motion in accordance with small wave (2) or acoustic theory (rather than the non-linear finite wave theory (3) (4)). Although the physical conditions in compressor delivery systems are very different from those in gas generator suction systems, a similar theoretical approach, verified by acoustic model tests, has been found both to provide a good insight into the problem, and to give an acceptably accurate quantitative indication of pressure pulsation amplitudes. For this purpose systems have been divided into: (1) lumped impedance systems, (2) distributed impedance systems.

A theoretical study of viscous effects in peristaltic pumping

1994 ◽  
Vol 279 ◽  
pp. 177-195 ◽  
Author(s):  
Alden M. Provost ◽  
W. H. Schwarz
Keyword(s):  
Wave Propagation ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Mean Flow ◽  
Viscous Effects ◽  
Transverse Waves ◽  
Peristaltic Pumping ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean

Intuition and previous results suggest that a peristaltic wave tends to drive the mean flow in the direction of wave propagation. New theoretical results indicate that, when the viscosity of the transported fluid is shear-dependent, the direction of mean flow can oppose the direction of wave propagation even in the presence of a zero or favourable mean pressure gradient. The theory is based on an analysis of lubrication-type flow through an infinitely long, axisymmetric tube subjected to a periodic train of transverse waves. Sample calculations for a shear-thinning fluid illustrate that, for a given waveform, the sense of the mean flow can depend on the rheology of the fluid, and that the mean flow rate need not increase monotonically with wave speed and occlusion. We also show that, in the absence of a mean pressure gradient, positive mean flow is assured only for Newtonian fluids; any deviation from Newtonian behaviour allows one to find at least one non-trivial waveform for which the mean flow rate is zero or negative. Introduction of a class of waves dominated by long, straight sections facilitates the proof of this result and provides a simple tool for understanding viscous effects in peristaltic pumping.

Oscillatory forcing of flow through porous media. Part 2. Unsteady flow

2002 ◽  
Vol 465 ◽  
pp. 237-260 ◽  
Author(s):  
D. R. GRAHAM ◽  
J. J. L. HIGDON
Keyword(s):  
Porous Medium ◽  
Porous Media ◽  
Pressure Gradient ◽  
Flow Rate ◽  
Flow Through Porous Media ◽  
Mean Flow ◽  
Two Fluids ◽  
Mean Pressure ◽  
Flow Through ◽  
The Mean

Numerical computations are employed to study the phenomenon of oscillatory forcing of flow through porous media. The Galerkin finite element method is used to solve the time-dependent Navier–Stokes equations to determine the unsteady velocity field and the mean flow rate subject to the combined action of a mean pressure gradient and an oscillatory body force. With strong forcing in the form of sinusoidal oscillations, the mean flow rate may be reduced to 40% of its unforced steady-state value. The effectiveness of the oscillatory forcing is a strong function of the dimensionless forcing level, which is inversely proportional to the square of the fluid viscosity. For a porous medium occupied by two fluids with disparate viscosities, oscillatory forcing may be used to reduce the flow rate of the less viscous fluid, with negligible effect on the more viscous fluid. The temporal waveform of the oscillatory forcing function has a significant impact on the effectiveness of this technique. A spike/plateau waveform is found to be much more efficient than a simple sinusoidal profile. With strong forcing, the spike waveform can induce a mean axial flow in the absence of a mean pressure gradient. In the presence of a mean pressure gradient, the spike waveform may be employed to reverse the direction of flow and drive a fluid against the direction of the mean pressure gradient. Owing to the viscosity dependence of the dimensionless forcing level, this mechanism may be employed as an oscillatory filter to separate two fluids of different viscosities, driving them in opposite directions in the porous medium. Possible applications of these mechanisms in enhanced oil recovery processes are discussed.

Pulmonary hysteresis

1962 ◽  
Vol 17 (1) ◽  
pp. 51-53 ◽  
Author(s):  
G. Cavagna ◽  
G. Brandi ◽  
F. Saibene ◽  
G. Torelli
Keyword(s):  
Experimental Data ◽  
Airway Resistance ◽  
Human Lung ◽  
Minute Ventilation ◽  
Mean Flow ◽  
Mean Pressure ◽  
The Mean

The pressure-volume (P-V) diagram of the human lung was recorded on three subjects at minute ventilation from 2.5 to 180 liters/min. The area included between the inspiratory and expiratory curve is the expression of the work necessary to overcome a) airway resistance to the flow, b) lung viscosity, and c) eventual pulmonary hysteresis. From the experimental data the mean pressure (Pm) and the mean flow (Vm) have been calculated, and the mean pressure plotted against the mean flow; the extrapolation of the Pm data to Vm = o leads to a positive value of Pm of 0.5-0.9 cm H2O, and this is interpreted as being due to pulmonary hysteresis. This is almost equal to the pressure necessary to overcome the airway resistance and the lung viscosity during respiration at rest. Submitted on April 17, 1961

scholarly journals Surface-roughness effects on the mean flow past circular cylinders

1980 ◽  
Vol 98 (4) ◽  
pp. 673-701 ◽  
Author(s):  
O. Güven ◽  
C. Farell ◽  
V. C. Patel
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Pressure Rise ◽  
Boundary Layer Separation ◽  
Circular Cylinders ◽  
Mean Flow ◽  
Roughness Effects ◽  
Number Range ◽  
Mean Pressure ◽  
The Mean

Measurements of mean-pressure distributions and boundary-layer development on rough-walled circular cylinders in a uniform stream are described. Five sizes of distributed sandpaper roughness have been tested over the Reynolds-number range 7 × 104to 5·5 × 105. The results are examined together with those of previous investigators, and the observed roughness effects are discussed in the light of boundary-layer theory. It is found that there is a significant influence of surface roughness on the mean-pressure distribution even at very large Reynolds numbers. This observation is supported by an extension of the Stratford–Townsend theory of turbulent boundary-layer separation to the case of circular cylinders with distributed roughness. The pressure rise to separation is shown to be closely related, as expected, to the characteristics of the boundary layer, smaller pressure rises being associated with thicker boundary layers with greater momentum deficits. Larger roughness gives rise to a thicker and more retarded boundary layer which separates earlier and with a smaller pressure recovery.

 Generation of planetary waves by gravity-wave drag in the middle atmosphere

2021 ◽  
Author(s):  
Hye-Yeong Chun ◽  
Byeong-Gwon Song ◽  
In-Sun Song
Keyword(s):  
Large Scale ◽  
Middle Atmosphere ◽  
Weather Forecasting ◽  
Wave Theory ◽  
Wave Drag ◽  
Planetary Waves ◽  
Mean Flow ◽  
Long Time ◽  
The Mean

<p>Large-scale atmospheric circulation has been represented mostly by interaction between the mean flow and planetary waves (PWs). Although the importance of gravity waves (GWs) has been recognized for long time, contribution of GWs to the large-scale circulation is receiving more attention recently, with conjunction to GW drag (GWD) parameterizations for climate and global weather forecasting models that extend to the middle atmosphere. As magnitude of GWD increases with height significantly, circulations in the middle atmosphere are determined largely by interactions among the mean flow, PWs and GWs. Classical wave theory in the middle atmosphere has been represented mostly by the Transformed Eulerian Mean (TEM) equation, which include PW and GW forcing separately to the mean flow. Recently, increasing number of studies revealed that forcing by combined PWs and GWs is the same, regardless of different PW and GW forcings, implying a compensation between PWs and GWs forcing. There are two ways for GWs to influence on PWs: (i) changing the mean flow that either influences on waveguide of PWs or induces baroclinic/brotropic instabilities to generate in situ PWs, and (ii) generating PWs as a source of potential vorticity (PV) equation when asymmetric components of GWD exist. The fist mechanism has been studies extensively recently associated with stratospheric sudden warmings (SSWs) that are involved large amplitude PWs and GWD. The second mechanism represents more directly the relationship between PWs and GWs, which is essential to understand the dynamics in the middle atmosphere completely (among the mean flow, PWs and GWs). In this talk, a recently reported result of the generation of PWs by GWs associated with the strongest vortex split-type SSW event occurred in January 2009 (Song et al. 2020, JAS) is presented focusing on the second mechanism.  </p>

Effect of Vascular Stiffness on Pulmonary Flow in Normotensive and Hypertensive States: Numerical Study With Fluid Structure Interaction

2008 ◽  
Author(s):  
Zhenbi Su ◽  
Kendall Hunter ◽  
Robin Shandas
Keyword(s):  
Numerical Study ◽  
Vascular Stiffness ◽  
Mean Flow ◽  
Pulmonary Flow ◽  
Vascular Flow ◽  
Primary Determinant ◽  
Mean Pressure ◽  
Pulmonary Arterial ◽  
The Mean ◽  
The Right

Invasive measurement of pulmonary vascular flow and pressure provides the hemodynamic status of the pulmonary circulation for children with pulmonary arterial hypertension (PAH). Clinicians are primarily interested in pulmonary vascular resistance, which is the mean pressure of the circuit divided by the mean flow through it [1], in that it is believed to well-quantify the right ventricular (RV) afterload, the primary determinant of mortality. However, previous and current investigations on the pulmonary vascular stiffness (PVS), input impedance and RV power [2–4] have found PVS to be an important contributor to power, and thus, afterload. These previous and current investigations focus on the analysis of clinical data, which is limited by the clinical equipment and techniques.

scholarly journals Comments on “The Three-Dimensional Current and Surface Wave Equations”

2008 ◽  
Vol 38 (6) ◽  
pp. 1340-1350 ◽  
Author(s):  
Fabrice Ardhuin ◽  
Alastair D. Jenkins ◽  
Konstadinos A. Belibassakis
Keyword(s):  
Momentum Flux ◽  
Large Scale ◽  
Wave Equations ◽  
Three Dimensional ◽  
Wave Theory ◽  
Correction Method ◽  
Vertical Flux ◽  
Mean Flow ◽  
Wave Forcing ◽  
The Mean

Abstract The lowest order sigma-transformed momentum equation given by Mellor takes into account a phase-averaged wave forcing based on Airy wave theory. This equation is shown to be generally inconsistent because of inadequate approximations of the wave motion. Indeed the evaluation of the vertical flux of momentum requires an estimation of the pressure p and coordinate transformation function s to first order in parameters that define the large-scale evolution of the wave field, such as the bottom slope. Unfortunately, there is no analytical expression for p and s at that order. A numerical correction method is thus proposed and verified. Alternative coordinate transforms that allow a separation of wave and mean flow momenta do not suffer from this inconsistency nor do they require a numerical estimation of the wave forcing. Indeed, the problematic vertical flux is part of the wave momentum flux, thus distinct from the mean flow momentum flux, and not directly relevant to the mean flow evolution.

Relaxation of Spatially Advancing Coherent Structures in a Turbulent Curved Channel Flow

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
Koji Matsubara ◽  
Tomoya Ohishi ◽  
Keisuke Shida ◽  
Takahiro Miura
Keyword(s):  
Small Scale ◽  
Computational Domain ◽  
Mean Flow ◽  
Curved Channel ◽  
Concave Wall ◽  
Convex Wall ◽  
Mean Pressure ◽  
Coherent Vortex ◽  
The Mean ◽  
Scale Turbulence

A direct numerical simulation is made for the incompressible turbulent flow in the 180 deg curved channel with a long straight portion connected to its exit port. An examination is made for how the organized coherent vortex grows and decays in the curved channel: the radius ratio of 0.92, the aspect ratio of 7.2, and the succeeding straight section length of 75 times the channel half width. The 1552 × 91 × 128 ( = 18,427,136) grids are allocated to the computational domain. The frictional-velocity-based Reynolds number is kept at 150 to resolve the long domain including curved and straight regions. In contrast to that the coherent vortex grows along the concave wall, the vortex remains strong in the convex-wall side after the curvature accompanying a tail of the small-scale turbulence near the convex wall. The dissimilarity between the onset and disappearing of the coherent vortex essentially comes from the mean pressure gradient, which aids or averts the near-wall fluid oppositely between the curvature inlet and the exit. The mean flow is decelerated near the inlet of the convex wall to destabilize the flow and to trigger the onset of the coherent vortex. Contrary, the mean flow is accelerated near the exit of the convex wall to weaken the coherent vortex, and is decelerated near the exit of the concave wall to enhance the turbulence. Therefore, the turbulence enhancement and attenuation occurs oppositely between the inlet and exit of the curvature, and the coherent vortex draws a wake in the convex-side rather than the concave-side where it starts.

Peristaltic Waves in Circular Cylindrical Tubes

1969 ◽  
Vol 36 (3) ◽  
pp. 579-587 ◽  
Author(s):  
F. Yin ◽  
Y. C. Fung
Keyword(s):  
Pressure Gradient ◽  
Wall Motion ◽  
Amplitude Ratio ◽  
Cylindrical Tube ◽  
Critical Value ◽  
Mean Flow ◽  
Navier Stokes Equation ◽  
Mean Pressure ◽  
The Mean ◽  
Set Up

Peristaltic pumping in a circular cylindrical tube is analyzed. The problem is a viscous fluid flow induced by an axisymmetric traveling sinusoidal wave of moderate amplitude imposed on the wall of a flexible tube. A perturbation method of solution is sought. The amplitude ratio (wave amplitude/tube radius) is chosen as a parameter. The nonlinear convective acceleration terms in the Navier-Stokes equation is retained. The governing equations are developed up to the second order in the amplitude ratio. The zeroth-order terms yield the classical Poiseuille flow, the first-order terms yield the Sommerfeld-Orr equation. If there is no pressure gradient in the absence of wall motion, the mean flow and mean pressure gradient (averaged over time) are both shown to be proportional to the square of the amplitude ratio. Numerical results are obtained for this simple case by approximating a complicated group of products of Bessel functions by a polynomial. The results show that the mean axial velocity is dominated by two terms. One term corresponds to a parabolic profile which is due to the mean pressure gradient set up by the wall motion. The other term arises from satisfying the no-slip boundary condition at the wavy wall rather than at the mean position of the wall. In addition, there are perturbations arising from the convective acceleration. If the mean pressure gradient set up by the wall motion itself reaches a certain positive critical value, the velocity becomes zero on the axis. Values of the mean pressure gradient larger than the critical value will induce backward flow in the fluid. Values of the critical pressure gradient for several cases are presented.

Sympathetic stimulation and small artery constriction

1964 ◽  
Vol 206 (2) ◽  
pp. 262-264 ◽  
Author(s):  
Darrell L. Davis
Keyword(s):  
Atmospheric Pressure ◽  
High Frequency ◽  
Sympathetic Stimulation ◽  
Digital Artery ◽  
Pressure Pulsations ◽  
Artery Pressure ◽  
Mean Pressure ◽  
Stimulation Period ◽  
The Mean ◽  
Stimulation Of

The outflow of blood from a digital artery of the dog hind paw to the atmosphere was recorded to determine if this outflow could be stopped completely in response to high-frequency sympathetic stimulation. In 5 of the 12 dogs studied, the outflow was stopped completely by stimulation of the peripheral stump of the sciatic nerve at 15 v, 20–25 stimuli/sec, a pulse duration of 5 msec, and a total stimulation period of approximately 60 sec. In those experiments in which complete cessation of flow was achieved, pressure pulsations were obliterated from the digital artery pressure tracing and the mean pressure decreased to atmospheric pressure levels. In the remaining dogs, in which flow was not stopped, pressure pulsations were evident in the digital artery pressure tracings throughout the stimulation period and mean pressures decreased to values ranging from 15 to 2 mm Hg.

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