Sinusoidal Excitation of a Free Turbulent Jet With Constant Amplitude Transverse Pressure Gradients Near the Nozzle Exit: Part II: An A-C Fluidic Model for the Jet Gain

1973 ◽  
Vol 95 (2) ◽  
pp. 174-179
Author(s):  
A. K. Stiffler ◽  
J. L. Shearer
Keyword(s):  
Pressure Gradient ◽  
Control Region ◽  
Input Signal ◽  
Nozzle Exit ◽  
Flow Direction ◽  
Turbulent Jet ◽  
Pressure Gradients ◽  
Constant Amplitude ◽  
Transverse Pressure ◽  
Sinusoidal Excitation

A free turbulent jet is perturbed transverse to the flow direction by a sinusoidal pressure gradient near the nozzle exit. An a-c model for the jet gain, based upon the control region dynamics and a uniform deflection of the jet downstream of this region, is generally verified in conjunction with attenuated mean shear velocities. A method is given to experimentally determine the effective amplitude of the input signal at the interface of the jet.

Signal Transit Velocities in a Turbulent Plane Jet

1976 ◽  
Vol 98 (3) ◽  
pp. 443-446
Author(s):  
A. K. Stiffler
Keyword(s):  
Nozzle Exit ◽  
Flow Direction ◽  
Turbulent Jet ◽  
Measured Signal ◽  
Centerline Velocity ◽  
Pressure Gradients ◽  
Periodic Pressure ◽  
Turbulent Plane ◽  
Plane Jet ◽  
Signal Time

A turbulent jet is perturbed transverse to the flow direction by periodic pressure gradients near the nozzle exit. Transit velocities are defined in terms of the measured signal time delay for stations 8, 12, 16 nozzle widths downstream of the nozzle exit. Excitation frequencies to 800 cps are considered. Transit velocities are found to be much less than the jet centerline velocity. The results are related to the convection velocity of turbulence.

Sinusoidal Excitation of a Free Turbulent Jet With Constant Amplitude Transverse Pressure Gradients Near the Nozzle Exit: Part I: Measurement of Mean Shear Velocities

1973 ◽  
Vol 95 (2) ◽  
pp. 167-173
Author(s):  
A. K. Stiffler ◽  
J. L. Shearer
Keyword(s):  
Nozzle Exit ◽  
Flow Direction ◽  
Excitation Frequency ◽  
Velocity Profiles ◽  
Turbulent Jet ◽  
Pressure Gradients ◽  
Mean Velocity ◽  
Effective Velocity ◽  
Gaussian Distribution Function ◽  
The Mean

A free turbulent jet is perturbed transverse to the flow direction by a sinusoidal pressure gradient near the nozzle exit. Velocities in the jet are determined by hot wire anemometer measurements. Moving effective mean velocity profiles are defined and reconstructed from the point-by-point stationary measurements of the mean velocity and of the harmonic content of the time varying signal. The effective velocity profiles are described by the Gaussian distribution function where the spread parameter decays as the cube of the product of the excitation frequency and the downstream location from the nozzle. These profile measurements and analysis of their characteristics lead to a better understanding of the factors determining the gain of a fluidic amplifier under conditions of high frequency operation.

Competing 3D Mechanisms in Compressor Flows

2015 ◽  
Author(s):  
James V. Taylor ◽  
Robert J. Miller
Keyword(s):  
Pressure Gradient ◽  
Design Space ◽  
Flow Direction ◽  
Three Dimensional ◽  
Transverse Pressure ◽  
Compressor Design ◽  
Design Systems ◽  
3D Stacking ◽  
Profile Loss ◽  
Different Levels

Even though three-dimensional design is central to all modern compressor design systems, many of these methods still rely, at the their core on a two-dimensional, sectional, view of blade aerodynamics. This paper argues that this view fundamentally limits design by not correctly considering the way in which pressure gradient transverse to the flow direction affects both separation and loss. The first part of the paper details how 3D blade stacking and the transverse pressure gradient fundamentally alters the behaviour of the corner separations and trailing edge separations. By controlling this design parameter it is possible to switch between the two. The transverse pressure gradient is also shown to be responsible for a substantial increase in profile loss. In the second part this understanding is used to explore the uncertainty of the design space by simultaneously varying pitch-chord ratio and 3D stacking. It is shown that the design space is split in half by two different levels of risk.

scholarly journals Determinants of valve gating in collecting lymphatic vessels from rat mesentery

2011 ◽  
Vol 301 (1) ◽  
pp. H48-H60 ◽  
Author(s):  
Michael J. Davis ◽  
Elaheh Rahbar ◽  
Anatoliy A. Gashev ◽  
David C. Zawieja ◽  
James E. Moore
Keyword(s):  
Pressure Gradient ◽  
Muscle Tone ◽  
Lymphatic Vessels ◽  
Vessel Diameter ◽  
Intraluminal Pressure ◽  
Pressure Gradients ◽  
Rat Mesentery ◽  
Temporal Relationships ◽  
Wide Range ◽  
Valve Opening

Secondary lymphatic valves are essential for minimizing backflow of lymph and are presumed to gate passively according to the instantaneous trans-valve pressure gradient. We hypothesized that valve gating is also modulated by vessel distention, which could alter leaflet stiffness and coaptation. To test this hypothesis, we devised protocols to measure the small pressure gradients required to open or close lymphatic valves and determine if the gradients varied as a function of vessel diameter. Lymphatic vessels were isolated from rat mesentery, cannulated, and pressurized using a servo-control system. Detection of valve leaflet position simultaneously with diameter and intraluminal pressure changes in two-valve segments revealed the detailed temporal relationships between these parameters during the lymphatic contraction cycle. The timing of valve movements was similar to that of cardiac valves, but only when lymphatic vessel afterload was elevated. The pressure gradients required to open or close a valve were determined in one-valve segments during slow, ramp-wise pressure elevation, either from the input or output side of the valve. Tests were conducted over a wide range of baseline pressures (and thus diameters) in passive vessels as well as in vessels with two levels of imposed tone. Surprisingly, the pressure gradient required for valve closure varied >20-fold (0.1–2.2 cmH2O) as a passive vessel progressively distended. Similarly, the pressure gradient required for valve opening varied sixfold with vessel distention. Finally, our functional evidence supports the concept that lymphatic muscle tone exerts an indirect effect on valve gating.

Protein osmotic pressure gradients and microvascular reflection coefficients

1997 ◽  
Vol 273 (2) ◽  
pp. H997-H1002 ◽  
Author(s):  
R. E. Drake ◽  
S. Dhother ◽  
R. A. Teague ◽  
J. C. Gabel
Keyword(s):  
Reflection Coefficient ◽  
Pressure Gradient ◽  
Osmotic Pressure ◽  
Reflection Coefficients ◽  
Pressure Gradients ◽  
Fluid Filtration ◽  
The Mean ◽  
Osmotic Reflection Coefficient ◽  
New Equation ◽  
Osmotic Pressure Gradient

Microvascular membranes are heteroporous, so the mean osmotic reflection coefficient for a microvascular membrane (sigma d) is a function of the reflection coefficient for each pore. Investigators have derived equations for sigma d based on the assumption that the protein osmotic pressure gradient across the membrane (delta II) does not vary from pore to pore. However, for most microvascular membranes, delta II probably does vary from pore to pore. In this study, we derived a new equation for sigma d. According to our equation, pore-to-pore differences in delta II increase the effect of small pores and decrease the effect of large pores on the overall membrane osmotic reflection coefficient. Thus sigma d for a heteroporous membrane may be much higher than previously derived equations indicate. Furthermore, pore-to-pore delta II differences increase the effect of plasma protein osmotic pressure to oppose microvascular fluid filtration.

scholarly journals Simulation Analysis on Water’s Micro Seepage Laws under Different Pressure Gradients Using Computed Tomography Method

2018 ◽  
Vol 2018 ◽  
pp. 1-26 ◽  
Author(s):  
Gang Zhou ◽  
Lei Qiu ◽  
Wenzheng Zhang ◽  
Jiao Xue
Keyword(s):  
Pressure Gradient ◽  
Mass Flow ◽  
Simulation Analysis ◽  
Effective Porosity ◽  
Pressure Gradients ◽  
Seepage Velocity ◽  
Average Mass ◽  
Depth Analysis ◽  
Tomography Method ◽  
Insight Into

The aim of this paper was to develop a model that can characterize the actual micropore structures in coal and gain an in-depth insight into water’s seepage rules in coal pores under different pressure gradients from a microscopic perspective. To achieve this goal, long-flame coals were first scanned by an X-ray 3D microscope; then, through a representative elementary volume (REV) analysis, the optimal side length was determined to be 60 μm; subsequently, by using Avizo software, the coal’s micropore structures were acquired. Considering that the porosity varies in the same coal sample, this study selected four regions in the sample for an in-depth analysis. Moreover, numerical simulations on water’s seepage behaviors in coal under 30 different pressure gradients were performed. The results show that (1) the variation of the simulated seepage velocity and pressure gradient accorded with Forchheimer’s high-velocity nonlinear seepage rules; (2) the permeability did not necessarily increase with the increase of the effective porosity; (3) in the same model, under different pressure gradients, the average seepage pressure decreased gradually, while the average seepage velocity and average mass flow varied greatly with the increase of the seepage length; and (4) under the same pressure gradient, the increase of the average mass flow from the inlet to the outlet became more significant under a higher inlet pressure.

Predicting Turbulent Boundary Layer Wall Pressure Fluctuations in Adverse Pressure Gradients

2005 ◽  
Author(s):  
Frank J. Aldrich
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Pressure Fluctuations ◽  
Adverse Pressure Gradient ◽  
Wall Pressure ◽  
Prediction Tool ◽  
Pressure Gradients ◽  
Wall Pressure Fluctuations ◽  
The Difference

A physics-based approach is employed and a new prediction tool is developed to predict the wavevector-frequency spectrum of the turbulent boundary layer wall pressure fluctuations for subsonic airfoils under the influence of adverse pressure gradients. The prediction tool uses an explicit relationship developed by D. M. Chase, which is based on a fit to zero pressure gradient data. The tool takes into account the boundary layer edge velocity distribution and geometry of the airfoil, including the blade chord and thickness. Comparison to experimental adverse pressure gradient data shows a need for an update to the modeling constants of the Chase model. To optimize the correlation between the predicted turbulent boundary layer wall pressure spectrum and the experimental data, an optimization code (iSIGHT) is employed. This optimization module is used to minimize the absolute value of the difference (in dB) between the predicted values and those measured across the analysis frequency range. An optimized set of modeling constants is derived that provides reasonable agreement with the measurements.

scholarly journals Numerical Analysis of the Mud Inflow Model of Fractured Rock Mass Based on Particle Flow

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Yongjian Pan ◽  
Huajun Wang ◽  
Yanlin Zhao ◽  
Qiang Liu ◽  
Shilin Luo
Keyword(s):  
Rock Mass ◽  
Pressure Gradient ◽  
Flow Direction ◽  
Fractured Rock ◽  
Water Pressure ◽  
Water Inrush ◽  
Quadratic Function ◽  
Particle Flow ◽  
Fractured Rock Mass ◽  
Particle Flows

Water inrush and mud outburst are one of the crucial engineering disasters commonly encountered during the construction of many railways and tunnels in karst areas. In this paper, based on fluid dynamics theory and discrete element method, we established a fractured rock mass mud inflow model using particle flow PFC3D numerical software, simulated the whole process of fractured rock mass mud inflow, and discussed the effect of particle size and flow velocity on the change of pressure gradient. The numerical simulation results show that the movement of particles at the corner of the wall when the water pressure is first applied occurs similar to the vortex phenomenon, with the running time increases, the flow direction of particles changes, the vortex phenomenon disappears, and the flow direction of particles at the corner points to the fracture; in the initial stage, the slope of the particle flows rate curves increases in time, and the quadratic function is used for fitting. After the percolation velocity of particles reaches stability, the slope of the curve remains constant, and the primary function is used for fitting; the particle flow rate and pressure gradient are influenced by a variety of factors, and they approximately satisfy the exponential function of an “S” curve.

The Effect of Real Turbine Roughness With Pressure Gradient on Heat Transfer

2003 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Combined Effects ◽  
Pressure Gradients ◽  
Smooth Wall ◽  
Reynolds Analogy ◽  
Integral Boundary ◽  
Favorable Pressure Gradient

Experimental measurements of heat transfer (St) are reported for low speed flow over scaled turbine roughness models at three different freestream pressure gradients: adverse, zero (nominally), and favorable. The roughness models were scaled from surface measurements taken on actual, in-service land-based turbine hardware and include samples of fuel deposits, TBC spallation, erosion, and pitting as well as a smooth control surface. All St measurements were made in a developing turbulent boundary layer at the same value of Reynolds number (Rex≅900,000). An integral boundary layer method used to estimate cf for the smooth wall cases allowed the calculation of the Reynolds analogy (2St/cf). Results indicate that for a smooth wall, Reynolds analogy varies appreciably with pressure gradient. Smooth surface heat transfer is considerably less sensitive to pressure gradients than skin friction. For the rough surfaces with adverse pressure gradient, St is less sensitive to roughness than with zero or favorable pressure gradient. Roughness-induced Stanton number increases at zero pressure gradient range from 16–44% (depending on roughness type), while increases with adverse pressure gradient are 7% less on average for the same roughness type. Hot-wire measurements show a corresponding drop in roughness-induced momentum deficit and streamwise turbulent kinetic energy generation in the adverse pressure gradient boundary layer compared with the other pressure gradient conditions. The combined effects of roughness and pressure gradient are different than their individual effects added together. Specifically, for adverse pressure gradient the combined effect on heat transfer is 9% less than that estimated by adding their separate effects. For favorable pressure gradient, the additive estimate is 6% lower than the result with combined effects. Identical measurements on a “simulated” roughness surface composed of cones in an ordered array show a behavior unlike that of the scaled “real” roughness models. St calculations made using a discrete-element roughness model show promising agreement with the experimental data. Predictions and data combine to underline the importance of accounting for pressure gradient and surface roughness effects simultaneously rather than independently for accurate performance calculations in turbines.

Possible Reason of the Dependence of an Apparent Permeability on the Pressure Gradient at low Flow Rates in Laboratory Study

2021 ◽  
Author(s):  
Nikolay Baryshnikov ◽  
Evgeniy Zenchenko ◽  
Sergey Turuntaev
Keyword(s):  
Pressure Gradient ◽  
Pore Pressure ◽  
Pore Space ◽  
Low Flow ◽  
Pressure Gradients ◽  
Apparent Permeability ◽  
Flow Rates ◽  
Rock Samples ◽  
Pore Pressure Gradient ◽  
Filtration Properties

<p>Currently, a number of studies showing that the injection of fluid into the formation can cause induced seismicity. Usually, it is associated with a change in the stress-strain state of the reservoir during the pore pressure front propagation. Modeling this process requires knowledge of the features of the filtration properties of reservoir rocks. Many researchers note the fact that the measured permeability of rock samples decreases at low pressure gradients. Among other things, this may be due to the formation of boundary adhesion layers with altered properties at the interfaces between the liquid and solid phases. The characteristic thickness of such layer can be fractions of a micron, and the effect becomes significant when filtering the fluid in rocks with a comparable characteristic pore size. The purpose of this work was to study the filtration properties of rock samples with low permeability at low flow rates. Laboratory modeling of such processes is associated with significant technical difficulties, primarily with the accuracy limit of measuring instruments when approaching zero speed values. The technique used by us to conduct the experiment and data processing allows us to study the dependence of the apparent permeability on the pore pressure gradient in the range of 0.01 MPa/m, which is comparable to the characteristic pressure gradients during the development of oil fields. In the course of the study, we carried out laboratory experiments on limestone core samples, during which the dependencies of their apparent permeability on the pore pressure gradient were obtained. We observed a significant decrease in their permeability at low flow rates. In the course of analyzing the experimental results, we proposed that a decrease in apparent permeability may occur due to the effect of even a small amount of residual gas in the pore space of the samples. This has been confirmed by additional experiments. The possibility of clogging of core sample pore space must be considered when conducting when conducting laboratory studies of the core apparent permeability.</p>

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