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‣ Determinação da variação da pressão de pulso em cadelas mecanicamente ventiladas com e sem PEEP, submetidas à expansão volêmica durante cirurgia abdominal; Assessment of arterial pulse pressure variation in mechanically ventilated dogs with PEEP and ZEEP, submitted to volume load during abdominal surgery

Moreno, Luciana Montel Moreno
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 12/12/2008 Português
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Ao contrário dos indicadores estáticos, como a pressão venosa central e a pressão de oclusão da artéria pulmonar, a variação da pressão de pulso arterial tem se mostrado um indicador hemodinâmico preciso para a determinação da responsividade à administração de fluido. Objetivo: Este estudo objetivou mensurar a variação da pressão de pulso em cadelas mecanicamente ventiladas submetidas a expansão volêmica durante procedimento cirúrgico eletivo (ovário-salpingo-histerectomia) e determinar a relação deste indicador com os dados hemodinâmicos obtidos por meio do exame ecodopplercardiográfico transesofágico. Material e método: Quinze cadelas foram distribuídas aleatoriamente em dois grupos: sem pressão positiva ao final da expiração (GI - ZEEP, n = 7) e com pressão positiva ao final da expiração de 5cmH2O (GII - PEEP, n = 8). As avaliações hemodinâmicas incluindo freqüência cardíaca (FC), pressão arterial média invasiva (PaM), variação da pressão de pulso (VPP), pressão venosa central (PVC), volume sistólico (VE), índice cardíaco (IC), velocidade do fluxo aórtico (VFA) e gradiente de pressão do fluxo aórtico (Grad); análise de gases sangüíneos e parâmetros do sistema respiratório incluindo freqüência respiratória (FR) e pressão de pico inspiratória (PIP)...

‣ Modelo de mistura aplicado para a previsão de Holdup e gradiente de pressão bifásico em duto anular de grande diâmetro; Drift-flux model applied to predict holdup and two-phase pressure gradient in large annular duct

Carvalho, Sávider Conti
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 21/03/2013 Português
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O escoamento bifásico é muito importante para vários ramos industriais. As misturas bifásicas podem escoar em diversas configurações, as quais são chamadas de padrões de escoamento, e que, ao longo dos anos, receberam diversas classificações. Neste trabalho foi estudado o padrão bolhas dispersas em duto anular. Os trabalhos sobre escoamento bifásico em geometria anular são mais escassos, especialmente quando se trata de dutos anulares de grande dimensão. Dentre os modelos existentes para a modelagem do escoamento bifásico, trabalhamos com o modelo de mistura (Drift Flux), pois, apesar das altas velocidades superficiais, o escoamento em bolhas não possui um comportamento homogêneo, já que a fase gasosa ainda escoa na região central e com uma velocidade maior do que a velocidade da mistura. Foi utilizado o modelo de mistura unidimensional para a modelagem do escoamento bifásico água-ar, pois, além de bastante preciso, é de baixo custo computacional e fácil implementação. Neste trabalho empregamos, a princípio, equações elaboradas para dutos circulares, as quais foram adaptadas para a geometria anular fazendo-se uso do conceito de diâmetro hidráulico. As equações foram implementadas no software Mathematica® e as previsões para o holdup e queda de pressão foram comparadas com dados experimentais próprios. O trabalho experimental foi realizado no laboratório de escoamentos multifásicos do Núcleo de Engenharia Térmica e de Fluidos (NETeF) da EESC-USP...

‣ Correlação entre a contagem de plaquetas no sangue e o gradiente de pressão venosa hepática em pacientes cirróticos; Correlation between platelet blood levels and the hepatic venous pressure gradient among patients with cirrhosis

Dittrich, Sirlei; Mattos, Angelo Alves de; Cheinquer, Hugo; Araújo, Fernanda Schild Branco de
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
Português
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Racional - A medida do gradiente de pressão venosa hepática é o método mais utilizado para a avaliação da pressão portal. Mais recentemente, a contagem de plaquetas no sangue tem sido apontada como um marcador não-invasivo da presença de hipertensão portal. Objetivo - Correlacionar a contagem de plaquetas com os valores do gradiente de pressão venosa hepática em uma população de pacientes cirróticos. Pacientes e Métodos - Foram estudados 83 pacientes com hepatopatia crônica que realizaram estudo hemodinâmico hepático, em período de 6 anos. Os pacientes foram divididos em grupos conforme a classificação de Child-Pugh e todos realizaram endoscopia digestiva alta para constatar a presença de varizes de esôfago, assim como tiveram a contagem sérica de plaquetas determinada. Resultados - O número de plaquetas variou entre 45.000/mm3 e 389.000/mm3, com média 104.099 e desvio-padrão 58.776. O gradiente de pressão venosa apresentou média igual a 15,2 mm Hg e desvio-padrão igual a 6,4 mm Hg, variando de 1 a 29 mm Hg. Realizou-se regressão linear simples para verificar a correlação entre o gradiente de pressão venosa e o número de plaquetas, o que permitiu constatar fraca correlação entre ambos. Embora se tenha observado menor número de plaquetas...

‣ Axisymmetric motion of a second order viscous fluid in a circular straight tube under pressure gradients varying exponentially with time

Carapau, Fernando
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Artigo de Revista Científica Formato: 507066 bytes; application/pdf
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The aim of this paper is to analyze the axisymmetric unsteady flow of a non-Newtonian incompressible second order fluid in a straight rigid and impermeable tube with circular cross-section of constant radius. To study this problem, we use the 1D nine directors Cosserat theory approach which reduces the exact three-dimensional equations to a system depending only on time and on a single spatial variable. From this system we obtain the relationship between mean pressure gradient and volume flow rate over a finite section of the tube. Assuming that the pressure gradient rises and falls exponentially with time, the 3D exact solution for unsteady volume flow rate is compared with the corresponding 1D solution obtained by the Cosserat theory using nine directors.

‣ Average Pressure Gradient of Swirling Flow Motion of a Viscoelastic Fluid in a Circular Straight Tube with Constant Radius

Carapau, Fernando
Fonte: Universidade de Évora Publicador: Universidade de Évora
Tipo: Artigo de Revista Científica
Português
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Motived by the aim of modelling the behavior of swirling flow motion, we present a 1D hierarchical model for an Rivlin-Ericksen fluid with complexity n = 2 flowing in a circular straight tube with constant radius. Integrating the equation of conservation of linear momentum over the tube cross-section, with the velocity field approximated by the Cosserat theory, we obtain a one-dimensional system depending only on time and on a single spatial variable. The velocity field approximation satisfies both the incompressibility condition and the kinematic boundary condition exactly. From this new system, we derive the equation for the wall shear stress and the relationship between average pressure gradient, volume flow rate and swirling scalar function over a finite section of the tube. Also, we obtain the corresponding partial differential equation for the swirling scalar function.

‣ A model of a turbulent boundary layer with a nonzero pressure gradient

Barenblatt, G. I.; Chorin, A. J.; Prostokishin, V. M.
Fonte: The National Academy of Sciences Publicador: The National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 30/04/2002 Português
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According to a model of the turbulent boundary layer that we propose, in the absence of external turbulence the intermediate region between the viscous sublayer and the external flow consists of two sharply separated self-similar structures. The velocity distribution in these structures is described by two different scaling laws. The mean velocity u in the region adjacent to the viscous sublayer is described by the previously obtained Reynolds-number-dependent scaling law φ = u/u* = Aηα, A = 1/documentclass[12pt]{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} setlength{oddsidemargin}{-69pt} egin{document} egin{equation*}sqrt{3}end{equation*}end{document} ln ReΛ + 5/2, α = 3/2 In ReΛ, η = u*y/ν. (Here u* is the dynamic or friction velocity, y is the distance from the wall, ν the kinematic viscosity of the fluid, and the Reynolds number ReΛ is well defined by the data.) In the region adjacent to the external flow, the scaling law is different: φ = Bηβ. The power β for zero-pressure-gradient boundary layers was found by processing various experimental data and is close (with some scatter) to 0.2. We show here that for nonzero-pressure-gradient boundary layers...

‣ Mechanism of systolic anterior motion of mitral valve and site of intraventricular pressure gradient in hypertrophic obstructive cardiomyopathy.

Nagata, S; Nimura, Y; Beppu, S; Park, Y D; Sakakibara, H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1983 Português
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The mechanism of systolic anterior motion of the mitral valve and the localisation of the intraventricular pressure gradient were determined in 15 cases of hypertrophic obstructive cardiomyopathy by the combined use of real time two dimensional echocardiography and intracardiac manometry. We arrived at the following conclusions. The systolic anterior motion of the mitral echo in the M-mode echocardiogram can be classified into two types, I and II, based on two dimensional echocardiographic findings. In type I, the echo sources of systolic anterior motion are the anteriorly shifted mitral chordae and, in part, the papillary muscles. The intraventricular pressure gradient occurs at the level of the tip of the papillary muscle. The suprapapillary part of the outflow tract and the inflow part show a low pressure, while the apical cavity shows a high pressure. In type II, the echo sources of systolic anterior motion are the anterior and posterior mitral leaflets which are oriented in such a way as to obstruct the outflow tract. The pressure gradient occurs at the level of the anterior and posterior mitral leaflets. The inflow tract and the outflow tract just below the mitral leaflets show a high pressure, in contrast to type I systolic anterior motion. The inappropriate and maloriented papillary muscles play an essential role in causing both types of systolic anterior motion and outflow obstruction. The direction of the axis of the papillary muscle is changed in late systole...

‣ Comparison of ventricular emptying with and without a pressure gradient in patients with hypertrophic cardiomyopathy.

Siegel, R J; Criley, J M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1985 Português
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Thirty three patients with hypertrophic cardiomyopathy were studied to determine whether the presence of an intraventricular pressure gradient impaired left ventricular emptying. Patients with resting gradients had a higher mean left ventricular ejection fraction (92 (6.4)%) than patients without a resting or inducible pressure gradient (75.5 (9)%). The rate and degree of emptying increased when gradients greater than 85 mm Hg were induced in two patients with insignificant mitral regurgitation. If the induced gradients had been the result of obstruction a decrease in the rate or degree of ventricular emptying would be expected. Higher ejection fractions in patients with intracavitary pressure gradients as well as enhanced rate and degree of left ventricular emptying with induced gradients are inconsistent with outflow obstruction. These findings support the concept that cavity obliteration is responsible for the pressure gradient in these patients with hypertrophic cardiomyopathy.

‣ Transseptal pressure gradient with leftward septal displacement during the Mueller manoeuvre in man.

Guzman, P A; Maughan, W L; Yin, F C; Eaton, L W; Brinker, J A; Weisfeldt, M L; Weiss, J L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1981 Português
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Septal displacement is postulated as an important mediator of ventricular interdependence. During acute right ventricular loading with the Mueller manoeuvre the septum flattens and shifts leftward. To investigate the mechanism of this septal deformation, we measured transseptal pressures in nine patients during Mueller manoeuvres with simultaneous right and left ventricular micromanometers, and left ventricular configuration with two-dimensional echocardiograms. Data were analysed throughout diastole and at end-systole during control and maximum Mueller manoeuvre (-40 to -80 mmHg airway pressure). Leftward septal displacement during the Mueller manoeuvre was evidenced by an increase in septal radius of curvature at end-diastole persisting through end-systole. The left ventricular free wall radius of curvature was unchanged. During the Mueller manoeuvre, the left ventricular cavity area decreased significantly in the cross-sectional view. All Mueller manoeuvres were associated with a decrease in left-to-right ventricular transseptal pressure gradient throughout diastole. There was no significant change in the gradient at end-systole; septal flattening persisted, however, despite a pronounced left to right pressure gradient. Thus, diastolic septal flattening during right ventricular loading is associated with a decreased transseptal pressure gradient but does not require right ventricular diastolic pressure to exceed left ventricular diastolic pressure. The persistence of flattening in systole suggests that once septal shift occurs during diastole...

‣ Pressure-Controlled Motion of Single Polymers through Solid-State Nanopores

Lu, Bo; Hoogerheide, David Paul; Zhao, Qing; Zhang, Hengbin; Tang, Zhipeng; Yu, Dapeng; Golovchenko, Jene Andrew
Fonte: American Chemical Society (ACS) Publicador: American Chemical Society (ACS)
Tipo: Artigo de Revista Científica
Português
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Voltage-biased solid-state nanopores are well established in their ability to detect and characterize single polymers, such as DNA, in electrolytes. The addition of a pressure gradient across the nanopore yields a second molecular driving force that provides new freedom for studying molecules in nanopores. In this work, we show that opposing pressure and voltage bias enables nanopores to detect and resolve very short DNA molecules, as well as to detect near-neutral polymers.; Engineering and Applied Sciences; Physics

‣ An Experimental investigation of the effect of pressure gradient on gas-oil relative permeability in Iranian carbonate rocks

Keshavarz, A.; Vatanparast, H.; Zargar, M.; Kalantariasl, A.; Haghighi, M.
Fonte: Marcel Dekker Inc Publicador: Marcel Dekker Inc
Tipo: Artigo de Revista Científica
Publicado em //2012 Português
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The authors examine the effect of pressure gradient on gas-oil relative permeability in horizontal and vertical immiscible displacement. The experiments are conducted on a core from lower Dalan formation in the South Pars oilfield of Iran, in constant pressure, unsteady-state condition, and different pressure gradients. The Toth method is used for calculating the relative permeability and plotting proper curves. Data analysis and the effect of pressure gradient on gas-oil relative permeability are investigated. Results show that relative permeability curves are affected by pressure gradient and this effect is much prominent at low pressures due to end-effect phenomena. The dependence of relative permeability curves on pressure gradient is correlated as a function of dimensionless capillary number. The accuracy of this correlation for relative permeability prediction is examined and a new method is introduced to minimize the end-effect phenomena on relative permeability curves.; A. Keshavarz, H. Vatanparast, M. Zargar, A. Kalantari Asl and M. Haghighi

‣ On the pressure gradient force over steep topography in sigma coordinate ocean models

Haney, Robert L.
Fonte: American Meteorological Society Publicador: American Meteorological Society
Tipo: Artigo de Revista Científica Formato: 10 p.
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Approved for public release; distribution is unlimited; The error in computing the pressure gradient force near steep topography using terrain following (o) coordinates is investigated in an ocean model using the family of vertical differencing schemes proposed by Arakawa and Suarez. The truncation error is estimated by substituting known buoyancy profiles in the finite difference hydrostatic and pressure gradient terms. The error due to "hydrostatic inconsistency," which is not simply a space truncation error, is also documented. The results show that the pressure gradient error is spread throughout the water column, and it is sensitive to the vertical resolution and to the placement of the grid points relative to the vertical structure of the buoyancy field being modeled. Removing a reference state, as suggested for the atmosphere by Gary, reduces the truncation error associated with the two lowest vertical modes by a factor of 2 to 3. As an example, the error in computing the pressure gradient using a standard 10-level primitive equation model applied to buoyancy profiles and topographic slopes typical of the California Current region corresponds to a false geostrophic current of the order of 10-12 cm s(-1). The analogous error is a hydrostatically consistent 30-level model with the reference state removed is about an order of magnitude smaller.

‣ Direct Numerical Simulation of Compressible and Incompressible Wall Bounded Turbulent Flows with Pressure Gradients

Wei, Liang
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 3555645 bytes; application/pdf
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This thesis is focused on direct numerical simulation (DNS) of compressible and incompressible fully developed and developing turbulent flows between isothermal walls using a discontinuous Galerkin method (DGM). Three cases (Ma = 0.2, 0.7 and 1.5) of DNS of turbulent channel flows between isothermal walls with Re ~ 2800, based on bulk velocity and half channel width, have been carried out. It is found that a power law seems to scale mean streamwise velocity with Ma slightly better than the more usual log-law. Inner and outer scaling of second-order and higher-order statistics have been analyzed. The linkage between the pressure gradient and vorticity flux on the wall has been theoretically derived and confirmed and they are highly correlated very close to the wall. The correlation coefficients are influenced by Ma, and viscosity when Ma is high. The near-wall spanwise streak spacing increases with Ma. Isosurfaces of the second invariant of the velocity gradient tensor are more sparsely distributed and elongated as Ma increases. DNS of turbulent isothermal-wall bounded flow subjected to favourable and adverse pressure gradient (FPG, APG) at Ma ~ 0.2 and Reref ~ 428000, based on the inlet bulk velocity and the streamwise length of the bottom wall...

‣ Effect of Valsalva's manoeuvre and hyoscinbutylbromide on the pressure gradient across the wall of oesophageal varices.

Hosking, S W; Robinson, P; Johnson, A G
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1987 Português
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To assess whether Valsalva's manoeuvre might cause variceal bleeding, 22 patients with oesophageal varices were studied. In 12 patients who received no previous treatment to their varices the median pressure gradient across the varix wall at rest was 19 (6-36) mmHg, and in 10 patients whose varices were thrombosed at their distal end the median pressure gradient in the proximal patent varix was 8 (1-6) mmHg. In untreated patients groups, the pressure gradient rose by 6-12 mmHg during Valsalva's manoeuvre in four patients, fell by 4-11 mmHg in five patients and was virtually unchanged in the remainder. These changes seem unlikely to cause variceal bleeding. Patients who repeated Valsalva's manoeuvre showed similar changes on each occasion. Six patients in the untreated group also received hyoscinbutylbromide 20 mg iv. No change was seen in the pressure gradient in five patients, suggesting that it is of little value in preventing variceal bleeding.

‣ A Model of a Turbulent Boundary Layer With a Non-Zero Pressure Gradient

Barenblatt, G. I.; Chorin, A. J.; Prostokishin, V. M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 28/02/2002 Português
Relevância na Pesquisa
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According to a model of the turbulent boundary layer proposed by the authors, in the absence of external turbulence the intermediate region between the viscous sublayer and the external flow consists of two sharply separated self-similar structures. The velocity distribution in these structures is described by two different scaling laws. The mean velocity u in the region adjacent to the viscous sublayer is described by the previously obtained Reynolds-number-dependent scaling law $\phi = u/u_*=A\eta^{\alpha}$, $A=\frac{1}{\sqrt{3}} \ln Re_{\Lambda}+ \frac 52$, $\alpha=\frac{3}{2\ln Re_{\Lambda}}$, $\eta = u_* y/\nu$. (Here $u_*$ is the dynamic or friction velocity, y is the distance from the wall, $\nu$ the kinematic viscosity of the fluid, and the Reynolds number $Re_{\Lambda}$ is well defined by the data) In the region adjacent to the external flow the scaling law is different: $\phi= B\eta^{\beta}$. The power $\beta$ for zero-pressure-gradient boundary layers was found by processing various experimental data and is close (with some scatter) to 0.2. We show here that for non-zero-pressure-gradient boundary layers, the power $\beta$ is larger than 0.2 in the case of adverse pressure gradient and less than 0.2 for favourable pressure gradient. Similarity analysis suggests that both the coefficient B and the power $\beta$ depend on $Re_{\Lambda}$ and on a new dimensionless parameter P proportional to the pressure gradient. Recent experimental data of Perry...

‣ Finite element analysis for normal pressure hydrocephalus: The effects of the integration of sulci

Kim, Hakseung; Park, Dae-Hyeon; Yi, Seong; Jeong, Eun-Jin; Yoon, Byung C.; Czosnyka, Marek; Sutcliffe, Michael P. F.; Kim, Dong-Joo
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
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This is the author accepted manuscript. The final version is available from Elsevier via http://dx.doi.org/10.1016/j.media.2015.05.006; Finite element analysis (FEA) is increasingly used to investigate the brain under various pathological changes. Although FEA has been used to study hydrocephalus for decades, previous studies have primarily focused on ventriculomegaly. The present study aimed to investigate the pathologic changes regarding sulcal deformation in normal pressure hydrocephalus (NPH). Two finite element (FE) models?an anatomical brain geometric (ABG) model and the conventional simplified brain geometric (SBG) model?of NPH were constructed. The models were constructed with identical boundary conditions but with different geometries. The ABG model contained details of the sulci geometry, whereas these details were omitted from the SBG model. The resulting pathologic changes were assessed via four biomechanical parameters: pore pressure, von Mises stress, pressure, and void ratio. NPH was induced by increasing the transmantle pressure gradient (TPG) from 0 to a maximum of 2.0 mmHg. Both models successfully simulated the major features of NPH (i.e., ventriculomegaly and periventricular lucency). The changes in the biomechanical parameters with increasing TPG were similar between the models. However...

‣ Analytical and Experimental Investigation of a Turbulent Mixing Layer of Different Gases in a Pressure Gradient

Rebollo, Manuel R.
Fonte: California Institute of Technology Publicador: California Institute of Technology
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em //1973 Português
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An analytical and experimental study has been made of the turbulent mixing layer in a pressure gradient. Theory predicts the possible existence of equilibrium flows, and this was confirmed experimentally for turbulent shear layers between streams of helium and nitrogen. The only case for which similarity is possible is for ρ_2U_2%2 = ρ_1U1^2, since then P_2(x) = P_1(x). These equilibrium flows are of the form U_1 ~ x^α and δ ~ x where α = u/U-1 dU_1/dx is a non-dimensional pressure gradient parameter. The experimental investigation was conducted in the facility designed by Brown to produce turbulent flows at pressures up to 10 atmospheres. The adjustable walls of the test section of the apparatus were modified in order to set the pressure gradient. Shadowgraphs of the mixing zone for α = 0 and α = - 0.. 18, at different Reynolds numbers, revealed a large scale structure noticeably different for each α. The similarity properties of the shear layer were established from mean profiles of total head and density. In addition, the rms density fluctuations were found to be self-preserving. From the mean profiles, the spreading rate, turbulent mass diffusion, Reynolds stress and Schmidt number distributions were calculated from the equations of motion. The experimental results show that the spreading rate for the adverse pressure gradient is 60% greater than for the α = 0 case. The maximum shearing stress is 70% larger and the maximum value of the turbulent mass diffusion is 20% larger than their α = 0 counterparts. The maximum rms density fluctuations are approximately O.2 in both flows. Surprisingly low values of turbulent Schmidt numbers were found; e.g. ...

‣ Effects of Wall Roughness on Adverse Pressure Gradient Boundary Layers

Mottaghian, Pouya
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
Português
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Large-eddy Simulations were carried out on a flat-plate boundary layer over smooth and rough surfaces in the presence of an adverse pressure gradient, strong enough to induce separation. The inlet Reynolds number (based on freestream velocity and momentum thickness at the reference plane) is 2300. A sand-grain roughness model was implemented and spatial resolution requirements were determined. Two roughness heights were used and a fully-rough flow condition is achieved at the reference plane with roughness Reynolds numbers 60 and 120. As the friction velocity decreases due to the adverse pressure gradient the roughness Reynolds number varies from fully-rough to transitionally rough and smooth regime before the separation. The double-averaging approach illustrates how the roughness contribution decreases before the separation as the dispersive stresses decrease markedly compared to the upstream region. Before the flow detachment, roughness intensifies the Reynolds stresses. After the separation, the normal stresses, production and dissipation substantially increase through the adverse pressure gradient region. In the recovery region, the flow is highly three dimensional, as turbulent structures impinge on the wall at the reattachment region. Roughness initially increases the skin friction...

‣ VERTICAL WELL PRESSURE AND PRESSURE DERIVATIVE ANALYSIS FOR BINGHAM FLUIDS IN HOMOGENEOUS RESERVOIRS

MARTINEZ,JAVIER A.; H. ESCOBAR,FREDDY; MONTEALEGRE,MATILDE
Fonte: DYNA Publicador: DYNA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2011 Português
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This paper presents a technique for interpreting the behavior of pressure and pressure derivative for a Bingham-type fluid in a homogeneous reservoir drained by a vertical well using the TDS technique, by observing the influence of the minimum pressure gradient which characterizes this behavior, and characteristic points which are used for estimating formation permeability, drainage area, and skin factor. The pressure derivative for Bingham Non-Newtonian fluids is presented in the literature for the first time. The higher the minimum pressure gradient, the more asymmetrically concave the pressure derivative becomes. Also, it was observed in closed systems that the late unit-slope pressure derivative coincides with the same one for Newtonian fluids.

‣ Sludge pipe flow pressure drop prediction using composite power-law friction factor-Reynolds number correlations based on different non-Newtonian Reynolds numbers

Haldenwang,R; Sutherland,APN; Fester,VG; Holm,R; Chhabra,RP
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2012 Português
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When predicting pressure gradients for the flow of sludges in pipes, the rheology of the fluid plays an important role, especially with increasing concentration of the suspended matter in the sludge. The f-Re relationship is often applied when designing pipelines, but it depends on the rheological parameters of the fluid and what definition of non-Newtonian Reynolds number is used. In this work, a database of 586 AP - Q points from tests with 10 different sludges of concentration 3.4 to 7.2% by mass, in 3 test pipe diameters, was established and used to rheologically characterise the sludges as Bingham plastic fluids. Five published definitions of the non-Newtonian Reynolds number were used to create composite power law correlations for the f-Re relationship covering all flow regimes. Pressure gradient predictions based on each correlation were compared and ranked, based on 2 different statistical estimates of error. The correlations using the MetznerReed Reynolds number (ReMR) and a Reynolds number proposed by Slatter and Lazarus in 1993 (Re2) yielded the lowest errors in comparison with the experimental values. It is shown that these correlations can be used to predict pressure drop to within ±20% for a given sludge concentration and operating condition.