Average Pressure Measurement in Low-Velocity Nonuniform Gas Flows

1972 ◽  
Vol 94 (2) ◽  
pp. 91-97
Author(s):  
G. B. Gilbert
Keyword(s):  
Power Plant ◽  
Pressure Loss ◽  
Flow Model ◽  
Stagnation Pressure ◽  
Gas Flows ◽  
Low Velocity ◽  
Order Of Magnitude ◽  
Mathematical Techniques ◽  
Nonuniform Gas ◽  
Acceptable Measure

An accurate measurement of the average stagnation pressure at a duct cross section is necessary when trying to determine the loss characteristics of low-pressure loss components such as power plant ducts and electrostatic precipitators. In these components, the pressure loss is usually of the same order of magnitude as the gas velocity head. This paper describes how to calculate average stagnation pressure for flows with nonuniform velocity profiles. Guidelines are presented on the techniques needed to achieve an acceptable measure of the average stagnation pressure. These guidelines were developed for use by power plant engineers and experimental flow-model investigators. The required mathematical techniques, a computer program, and some experimental model results are presented.

Non-stationary process characteristics of the gas outflow into a liquid

2019 ◽  
Vol 14 (2) ◽  
pp. 82-88
Author(s):  
M.V. Alekseev ◽  
I.S. Vozhakov ◽  
S.I. Lezhnin
Keyword(s):  
Numerical Simulation ◽  
Liquid Column ◽  
Gas Content ◽  
Liquid Lead ◽  
Gas Flows ◽  
Asymptotic Model ◽  
Process Characteristics ◽  
Significant Difference ◽  
Order Of Magnitude ◽  
Volume Method

A numerical simulation of the process of the outflow of gas under pressure into a closed container partially filled with liquid was carried out. For comparative theoretical analysis, an asymptotic model was used with assumptions about the adiabaticity of the gas outflow process and the ideality of the liquid during the oscillatory one-dimensional motion of the liquid column. In this case, the motion of the liquid column and the evolution of pressure in the gas are determined by the equation of dynamics and the balance of enthalpy. Numerical simulation was performed in the OpenFOAM package using the fluid volume method (VOF method) and the standard k-e turbulence model. The evolution of the fields of volumetric gas content, velocity, and pressure during the flow of gas from the high-pressure chamber into a closed channel filled with liquid in the presence of a ”gas blanket“ at the upper end of the channel is obtained. It was shown that the dynamics of pulsations in the gas cavity that occurs when the gas flows into the closed region substantially depends on the physical properties of the liquid in the volume, especially the density. Numerical modeling showed that the injection of gas into water occurs in the form of a jet outflow of gas, and for the outflow into liquid lead, a gas slug is formed at the bottom of the channel. Satisfactory agreement was obtained between the numerical calculation and the calculation according to the asymptotic model for pressure pulsations in a gas projectile in liquid lead. For water, the results of calculations using the asymptotic model give a significant difference from the results of numerical calculations. In all cases, the velocity of the medium obtained by numerical simulation and when using the asymptotic model differ by an order of magnitude or more.

Discontinuous low-velocity zones in southern Tibet question the viability of the channel flow model

2011 ◽  
Vol 353 (1) ◽  
pp. 99-108 ◽  
Author(s):  
György Hetényi ◽  
Jérôme Vergne ◽  
Laurent Bollinger ◽  
Rodolphe Cattin
Keyword(s):  
Channel Flow ◽  
Flow Model ◽  
Low Velocity ◽  
Southern Tibet

Aerodynamic Similarity Principles and Scaling Laws for Windmilling Fans

2018 ◽  
Author(s):  
Dilip Prasad
Keyword(s):  
Rotational Speed ◽  
Pressure Loss ◽  
Scaling Laws ◽  
Dynamic Pressure ◽  
Stagnation Pressure ◽  
Design Parameters ◽  
Similarity Parameter ◽  
Wide Range ◽  
Simulation Results ◽  
Good Agreement

Windmilling requirements for aircraft engines often define propulsion and airframe design parameters. The present study is focused is on two key quantities of interest during windmill operation: fan rotational speed and stage losses. A model for the rotor exit flow is developed, that serves to bring out a similarity parameter for the fan rotational speed. Furthermore, the model shows that the spanwise flow profiles are independent of the throughflow, being determined solely by the configuration geometry. Interrogation of previous numerical simulations verifies the self-similar nature of the flow. The analysis also demonstrates that the vane inlet dynamic pressure is the appropriate scale for the stagnation pressure loss across the rotor and splitter. Examination of the simulation results for the stator reveals that the flow blockage resulting from the severely negative incidence that occurs at windmill remains constant across a wide range of mass flow rates. For a given throughflow rate, the velocity scale is then shown to be that associated with the unblocked vane exit area, leading naturally to the definition of a dynamic pressure scale for the stator stagnation pressure loss. The proposed scaling procedures for the component losses are applied to the flow configuration of Prasad and Lord (2010). Comparison of simulation results for the rotor-splitter and stator losses determined using these procedures indicates very good agreement. Analogous to the loss scaling, a procedure based on the fan speed similarity parameter is developed to determine the windmill rotational speed and is also found to be in good agreement with engine data. Thus, despite their simplicity, the methods developed here possess sufficient fidelity to be employed in design prediction models for aircraft propulsion systems.

Aerodynamic Similarity Principles and Scaling Laws for Windmilling Fans

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Dilip Prasad
Keyword(s):  
Rotational Speed ◽  
Pressure Loss ◽  
Scaling Laws ◽  
Dynamic Pressure ◽  
Stagnation Pressure ◽  
Design Parameters ◽  
Similarity Parameter ◽  
Wide Range ◽  
Simulation Results ◽  
Good Agreement

Windmilling requirements for aircraft engines often define propulsion and airframe design parameters. The present study is focused on two key quantities of interest during windmill operation: fan rotational speed and stage losses. A model for the rotor exit flow is developed that serves to bring out a similarity parameter for the fan rotational speed. Furthermore, the model shows that the spanwise flow profiles are independent of the throughflow, being determined solely by the configuration geometry. Interrogation of previous numerical simulations verifies the self-similar nature of the flow. The analysis also demonstrates that the vane inlet dynamic pressure is the appropriate scale for the stagnation pressure loss across the rotor and splitter. Examination of the simulation results for the stator reveals that the flow blockage resulting from the severely negative incidence that occurs at windmill remains constant across a wide range of mass flow rates. For a given throughflow rate, the velocity scale is then shown to be that associated with the unblocked vane exit area, leading naturally to the definition of a dynamic pressure scale for the stator stagnation pressure loss. The proposed scaling procedures for the component losses are applied to the flow configuration of Prasad and Lord (2010). Comparison of simulation results for the rotor-splitter and stator losses determined using these procedures indicates very good agreement. Analogous to the loss scaling, a procedure based on the fan speed similarity parameter is developed to determine the windmill rotational speed and is also found to be in good agreement with engine data. Thus, despite their simplicity, the methods developed here possess sufficient fidelity to be employed in design prediction models for aircraft propulsion systems.

Modeling of Wall Friction for Multispecies Solid-Gas Flows

1986 ◽  
Vol 108 (4) ◽  
pp. 486-488 ◽  
Author(s):  
E. D. Doss ◽  
M. G. Srinivasan
Keyword(s):  
Shear Stress ◽  
Flow Model ◽  
Flow Characteristics ◽  
Wall Friction ◽  
Gas Flows ◽  
Two Phase ◽  
One Dimensional ◽  
Friction Models ◽  
Wall Interaction ◽  
The One

The empirical expressions for the equivalent friction factor to simulate the effect of particle-wall interaction with a single solid species have been extended to model the wall shear stress for multispecies solid-gas flows. Expressions representing the equivalent shear stress for solid-gas flows obtained from these wall friction models are included in the one-dimensional two-phase flow model and it can be used to study the effect of particle-wall interaction on the flow characteristics.

Combustion Turbine Exhaust Duct, Silencer, and Stack Scale Modeling

2021 ◽  
Author(s):  
Robert Craven ◽  
Keith Kirkpatrick ◽  
Stephen Idem
Keyword(s):  
Reynolds Number ◽  
Power Plant ◽  
Pressure Loss ◽  
Total Pressure ◽  
Exhaust System ◽  
Total Pressure Loss ◽  
Scale Model ◽  
Pressure Losses ◽  
Exhaust Duct ◽  
On Line

Abstract After constructing a scale model of planned changes to a power plant exhaust system, tests were performed to measure pressure losses in the transition, silencer, and stack. A dimension of 0.30 m (1.0 ft) for the scale model corresponded to 3.7 m (12.0 ft) at full scale. To the extent possible, the scale model tests exhibited geometric similarity with the actual power plant. Total pressure loss coefficients varied between 2.122, 1.969, and 1.932, for three separate scale model configurations that were considered. A combination of turning vanes and splitter vanes in the five-gore elbow, coupled with the use of turning vanes in the rectangular elbow yielded the lowest total pressure loss. Although Reynolds number similarity between the scale model experiments and the actual power plant was not attained, Reynolds number independence was achieved in the tests. The results from this study was applied to model pressure loss in the actual power plant. The scale model testing revealed that utilization of the exhaust ducting design designated as Case A would yield a sufficiently low pressure loss that it would not degrade the performance of the combustion turbine in the power plant to be repaired. Therefore it was selected for inclusion in the retro-fitting of the power plant to facilitate its being quickly brought back on-line.

Simulations to Determine Laminar Loss Coefficients for Flow in Circular Ducts With Arbitrary Planar Bifurcation Geometries

2008 ◽  
Author(s):  
Tim A. Handy ◽  
Evan C. Lemley ◽  
Dimitrios V. Papavassiliou ◽  
Henry J. Neeman
Keyword(s):  
Pressure Loss ◽  
Three Dimensional ◽  
Computer Code ◽  
Two Dimensions ◽  
Stagnation Pressure ◽  
Loss Coefficient ◽  
Pressure Losses ◽  
Common Plane ◽  
Loss Coefficients ◽  
Inlet Duct

The goal of this study was to determine laminar stagnation pressure loss coefficients for circular ducts in which flow encounters a planar bifurcation. Flow conditions and pressure losses in these laminar bifurcations are of interest in microfluidic devices, in porous media, and in other networks of small ducts or pores. Until recently, bifurcation geometries had been studied almost exclusively for turbulent flow, which is often found in fluid supply and drain systems. Recently, pressure loss coefficients from simulations of a few arbitrary bifurcation geometries in two-dimensions have been published — the present study describes the extension of these two-dimensional simulations to three-dimensional circular ducts. The pressure loss coefficients determined in this study are intended to allow realistic simulation of existing laminar flow networks or the design of these networks. This study focused on a single inlet duct with two outlet ducts, which were allowed to vary in diameter, flow fraction, and angle — all relative to the inlet duct. All ducts considered in this study were circular with their axes in a common plane. Laminar stagnation pressure loss coefficients were determined by simulating incompressible flow through 475 different geometries and flow condition combinations. In all cases, the flow was laminar in the inlet and outlet ducts with a Reynolds number of 15 in the inlet duct. Simulations of the dividing flow geometries were done using FLUENT and a custom written computer code, which automated the process of creating the three-dimensional flow geometries. The outputs, pressure and velocity distributions at the inlet and outlets, were averaged over the circular ducts and then used to calculate pressure loss coefficients for each of the geometries and flow fraction scenarios simulated. The results for loss coefficient for the geometries considered ranged from 2.0 to 70. The loss coefficient for any geometry increased significantly as the outlet flow fraction increased. A consistent increase in loss coefficient was also observed as a function of decreasing outlet duct diameter. Less significant variation of the loss coefficient was observed as a function of the angles of the outlet ducts.

scholarly journals Regulation of accretion by its outflow in a symbiotic star: the 2016 outflow fast state of MWC 560

2020 ◽  
Vol 492 (3) ◽  
pp. 3107-3127 ◽  
Author(s):  
Adrian B Lucy ◽  
J L Sokoloski ◽  
U Munari ◽  
Nirupam Roy ◽  
N Paul M Kuin ◽  
...  
Keyword(s):  
Symbiotic Star ◽  
Fast State ◽  
Low Velocity ◽  
X Ray ◽  
Broad Absorption Line ◽  
Multi Wavelength ◽  
Order Of Magnitude ◽  
The Stability ◽  
Ultraviolet Observations ◽  
Optical Flux

ABSTRACT How are accretion discs affected by their outflows? To address this question for white dwarfs accreting from cool giants, we performed optical, radio, X-ray, and ultraviolet observations of the outflow-driving symbiotic star MWC 560 (≡V694 Mon) during its 2016 optical high state. We tracked multi-wavelength changes that signalled an abrupt increase in outflow power at the initiation of a months-long outflow fast state, just as the optical flux peaked: (1) an abrupt doubling of Balmer absorption velocities; (2) the onset of a 20 μJy per month increase in radio flux; and (3) an order-of-magnitude increase in soft X-ray flux. Juxtaposing to prior X-ray observations and their coeval optical spectra, we infer that both high-velocity and low-velocity optical outflow components must be simultaneously present to yield a large soft X-ray flux, which may originate in shocks where these fast and slow absorbers collide. Our optical and ultraviolet spectra indicate that the broad absorption-line gas was fast, stable, and dense (≳106.5  cm−3) throughout the 2016 outflow fast state, steadily feeding a lower density (≲105.5 cm−3) region of radio-emitting gas. Persistent optical and ultraviolet flickering indicate that the accretion disc remained intact. The stability of these properties in 2016 contrasts to their instability during MWC 560’s 1990 outburst, even though the disc reached a similar accretion rate. We propose that the self-regulatory effect of a steady fast outflow from the disc in 2016 prevented a catastrophic ejection of the inner disc. This behaviour in a symbiotic binary resembles disc/outflow relationships governing accretion state changes in X-ray binaries.

scholarly journals Optimization and Extended Applicability of Simplified Slug Flow Model for Liquid-Gas Flow in Horizontal and Near Horizontal Pipes

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 842
Author(s):  
Tea-Woo Kim ◽  
Nam-Sub Woo ◽  
Sang-Mok Han ◽  
Young-Ju Kim
Keyword(s):  
Slug Flow ◽  
Pressure Loss ◽  
Gas Flow ◽  
Flow Model ◽  
Flow Coefficient ◽  
Coefficient Of Determination ◽  
Liquid Holdup ◽  
Two Phase ◽  
Horizontal Pipes ◽  
Image Velocimetry

The accurate prediction of pressure loss for two-phase slug flow in pipes with a simple and powerful methodology has been desired. The calculation of pressure loss has generally been performed by complicated mechanistic models, most of which require the iteration of many variables. The objective of this study is to optimize the previously proposed simplified slug flow model for horizontal pipes, extending the applicability to turbulent flow conditions, i.e., high mixture Reynolds number and near horizontal pipes. The velocity field previously measured by particle image velocimetry further supports the suggested slug flow model which neglects the pressure loss in the liquid film region. A suitable prediction of slug characteristics such as slug liquid holdup and translational velocity (or flow coefficient) is required to advance the accuracy of calculated pressure loss. Therefore, the proper correlations of slug liquid holdup, flow coefficient, and friction factor are identified and utilized to calculate the pressure gradient for horizontal and near horizontal pipes. The optimized model presents a fair agreement with 2191 existing experimental data (0.001 ≤ μL ≤ 0.995 Pa∙s, 7 ≤ ReM ≤ 227,007 and −9 ≤ θ ≤ 9), showing −3% and 0.991 as values of the average relative error and the coefficient of determination, respectively.

Experimental study on the characteristics of axisymmetric cavity actuated supersonic flow

2016 ◽  
Vol 231 (14) ◽  
pp. 2570-2577
Author(s):  
S Jeyakumar ◽  
Shan M Assis ◽  
K Jayaraman
Keyword(s):  
Supersonic Flow ◽  
Pressure Loss ◽  
Static Pressure ◽  
Effective Means ◽  
Supersonic Nozzle ◽  
Stagnation Pressure ◽  
Complex Flow ◽  
Wall Angle ◽  
Blow Down ◽  
Axisymmetric Cavity

The effective means of air fuel mixing and flame holding can be achieved by incorporating cavity in supersonic combustor. Understanding the complex flow field of cavity flow is essential for the design of supersonic combustor. An attempt is made to understand the characteristics of supersonic flow past axisymmetric cavity, and a series of nonreacting experiments are carried out in a blow-down type supersonic flow facility. The facility consists of a supersonic nozzle, issues a flow Mach number of 1.80 into a circular cross sectional supersonic combustor in which axisymmetric cavity is placed. Cavity of two consecutive aft wall angles is the key parameter for the study. The performance of the cavity is investigated based on the static pressure measurement, momentum flux distribution at the exit plane of the combustor, and the stagnation pressure loss of the flow. Wall static pressure distribution revealed that pressure increases with decrease in the secondary aft wall angle below 45° due to stronger recompression of shear layers. Moreover, decreasing primary aft wall angle provides a uniform mixing profile along with decrease in stagnation pressure loss across the combustor.

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