scholarly journals ENTRAINMENT DUE TO MEAN FLOW IN TWO-LAYERED FLUID

1988 ◽  
Vol 1 (21) ◽  
pp. 189
Author(s):  
Masaru Ura ◽  
Nobuhiro Matsunaga
Keyword(s):  
Grid Turbulence ◽  
Mean Flow ◽  
Mean Velocity ◽  
Entrainment Velocity ◽  
Turbulent Entrainment ◽  
The Mean ◽  
Flow Turbulence ◽  
Turbulence Factor ◽  
Relationship Of ◽  
The Relationship

The entrainment phenomena have been investigated across an interface between two-layered stratified flow induced by wind shear stress. The velocities of mean flow, turbulence and entrainment have been measured under three different conditions of water surface by using a wind-wave tank. When the entrainment velocity ue is expressed on the basis of the turbulent quantities at the interface, the turbulent entrainment coefficient E ( = ue/u) is given by E = A-(egl/u2)-3I1 ( A = 0.7). Here Eg, u and 1 are the effective buoyancy, the turbulence intensity and the integral lengthscale of turbulence at the interface, respectively. This result coincides with the relationship of entrainment due to oscillating grid turbulence, in which the mean flow does not exist. When, for the practical purpose, the estimation of ue is made by using the mean velocity Um and the depth h of mixed layer, Em ( - Ue/Um ) = Am•(egh/Um 2)"3/2 is derived from the transformation of E = A-(egl/u2)-3/2. There holds Am = A-Tf between Am and Tf, Tf being a turbulence factor given by (u/Um)4•(1/h)-3/2. It has been found that this relationship is also valid in various types of two-layered stratified flows as well as the wind-induced two-layered flows.

Intra-Task Reliability and Specificity of Individual Consistency

1970 ◽  
Vol 30 (2) ◽  
pp. 583-587 ◽  
Author(s):  
Albert V. Carron
Keyword(s):  
Motor Response ◽  
Present Report ◽  
Motor Task ◽  
Response Component ◽  
Linear Movement ◽  
The Mean ◽  
Individual Consistency ◽  
Response Consistency ◽  
Relationship Of ◽  
The Relationship

The present report is based on reanalysis of data of Marisi (1969) in order to examine the relationship of consistency of motor response among the component responses of a single motor task. 120 high school Ss were tested on a special task, the rho. A single trial on this motor task can be logically separated into three component motor responses: reaction time, a short circular movement, and a short linear movement. The results indicated that consistency of motor response was moderately reliable within the response components but tended to be response-component specific. Further, both the reliability and specificity of motor-response consistency were independent of the size of the mean performance scores.

Relationship between temporal and spatial averages in grid turbulence

2013 ◽  
Vol 730 ◽  
pp. 593-606 ◽  
Author(s):  
L. Djenidi ◽  
S. F. Tardu ◽  
R. A. Antonia
Keyword(s):  
Strong Support ◽  
Statistical Properties ◽  
Grid Turbulence ◽  
Mean Flow ◽  
Lateral Direction ◽  
Ergodic Hypothesis ◽  
Long Time ◽  
The Mean ◽  
Temporal And Spatial ◽  
Boltzmann Method

AbstractA long-time direct numerical simulation (DNS) based on the lattice Boltzmann method is carried out for grid turbulence with the view to compare spatially averaged statistical properties in planes perpendicular to the mean flow with their temporal counterparts. The results show that the two averages become equal a short distance downstream of the grid. This equality indicates that the flow has become homogeneous in a plane perpendicular to the mean flow. This is an important result, since it confirms that hot-wire measurements are appropriate for testing theoretical results based on spatially averaged statistics. It is equally important in the context of DNS of grid turbulence, since it justifies the use of spatial averaging along a lateral direction and over several realizations for determining various statistical properties. Finally, the very good agreement between temporal and spatial averages validates the comparison between temporal (experiments) and spatial (DNS) statistical properties. The results are also interesting because, since the flow is stationary in time and spatially homogeneous along lateral directions, the equality between the two types of averaging provides strong support for the ergodic hypothesis in grid turbulence in planes perpendicular to the mean flow.

The structure of a highly decelerated axisymmetric turbulent boundary layer

2021 ◽  
Vol 929 ◽  
Author(s):  
N. Agastya Balantrapu ◽  
Christopher Hickling ◽  
W. Nathan Alexander ◽  
William Devenport
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Large Scale ◽  
Convection Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean

Experiments were performed over a body of revolution at a length-based Reynolds number of 1.9 million. While the lateral curvature parameters are moderate ( $\delta /r_s < 2, r_s^+>500$ , where $\delta$ is the boundary layer thickness and r s is the radius of curvature), the pressure gradient is increasingly adverse ( $\beta _{C} \in [5 \text {--} 18]$ where $\beta_{C}$ is Clauser’s pressure gradient parameter), representative of vehicle-relevant conditions. The mean flow in the outer regions of this fully attached boundary layer displays some properties of a free-shear layer, with the mean-velocity and turbulence intensity profiles attaining self-similarity with the ‘embedded shear layer’ scaling (Schatzman & Thomas, J. Fluid Mech., vol. 815, 2017, pp. 592–642). Spectral analysis of the streamwise turbulence revealed that, as the mean flow decelerates, the large-scale motions energize across the boundary layer, growing proportionally with the boundary layer thickness. When scaled with the shear layer parameters, the distribution of the energy in the low-frequency region is approximately self-similar, emphasizing the role of the embedded shear layer in the large-scale motions. The correlation structure of the boundary layer is discussed at length to supply information towards the development of turbulence and aeroacoustic models. One major finding is that the estimation of integral turbulence length scales from single-point measurements, via Taylor's hypothesis, requires significant corrections to the convection velocity in the inner 50 % of the boundary layer. The apparent convection velocity (estimated from the ratio of integral length scale to the time scale), is approximately 40 % greater than the local mean velocity, suggesting the turbulence is convected much faster than previously thought. Closer to the wall even higher corrections are required.

Respiratory Periodicity and Electroencephalogram Arousals During Sleep in Older Adults

2007 ◽  
Vol 8 (4) ◽  
pp. 249-260 ◽  
Author(s):  
Barbara Waag Carlson ◽  
Virginia J. Neelon ◽  
John R. Carlson ◽  
Marilyn Hartman ◽  
Sunil Dogra
Keyword(s):  
Older Adults ◽  
Exploratory Study ◽  
High Variability ◽  
Arterial Oxygenation ◽  
Type B ◽  
Breathing Patterns ◽  
The Mean ◽  
Relationship Of ◽  
The Relationship ◽  
Electroencephalogram Eeg

The aim of this exploratory study was to examine the relationship of electroencephalogram (EEG) arousals to breathing patterns and the relationship of both arousals and breathing patterns to arterial oxygenation during sleep in older adults. Five older adults were monitored using standard polysomnography. Records were divided into 5-min segments and breathing patterns identified based on the level of respiratory periodicity and the variability in the frequency of breathing cycles. Standard criteria were used to determine sleep states and occurrence of EEG arousals. High respiratory periodicity was seen in 23% of the segments, whereas 24% had low respiratory periodicity with minimal variability in the frequency of breathing (Type A low respiratory periodicity) and 53% had low respiratory periodicity with high variability in the frequency of breathing (Type B low respiratory periodicity). Nearly all (97%) segments with high respiratory periodicity had EEG arousals, whereas fewer segments (33%) with low respiratory periodicity had arousals, regardless of the stage of sleep. Desaturations occurred more often in segments with high respiratory periodicity, F (2,4) = 57.3, p < .001, but overall, the mean SaO2 of segments with high respiratory periodicity did not differ from levels seen in segments with low respiratory periodicity, F( 2,4) = 0.77, ns. Our findings suggest that high respiratory periodicity is a common feature of EEG arousals and, in older adults, may be important for maintaining oxygen levels during desaturations during sleep.

scholarly journals Relationship of altitude mountain sickness and smoking: a Catalan traveller’s cohort study

BMJ Open ◽  
2017 ◽  
Vol 7 (9) ◽  
pp. e017058 ◽  
Author(s):  
Alba Sánchez-Mascuñano ◽  
Cristina Masuet-Aumatell ◽  
Sergio Morchón-Ramos ◽  
Josep M Ramon
Keyword(s):  
Smoking Status ◽  
Medical Advice ◽  
Health Clinic ◽  
Travel Health ◽  
Systemic Corticosteroids ◽  
The Mean ◽  
Mountain Sickness ◽  
Relationship Of ◽  
The Relationship ◽  
Chronic Use

ObjectivesThe aim of this study is to analyse the relationship between smoking andaltitude mountain sicknessin a cohort of travellers to 2500 metres above sea level (masl) or higher.SettingTravel Health Clinic at the Hospital Universitari de Bellvitge, in Barcelona, Spain.ParticipantsA total of 302 adults seeking medical advice at the travel clinic, between July 2012 and August 2014, before travelling to 2500 masl or above, who agreed to participate in the study and to be contacted after the trip were included. Individuals who met the following criteria were excluded: younger than 18 years old, taking carbonic anhydrase inhibitors for chronic use, undergoing treatment with systemic corticosteroids and taking any medication that might prevent or treat altitude mountain sickness (AMS) prior to or during the trip. The majority of participants were women (n=156, 51.7%). The mean age was 37.7 years (SD 12.3). The studied cohort included 74 smokers (24.5%), 158 (52.3%) non-smokers and 70 (23.2%) ex-smokers. No statistical differences were observed between different sociodemographic characteristics, constitutional symptoms or drug use and smoking status.OutcomesThe main outcome was the development of AMS, which was defined according to the Lake Louise AMS criteria.ResultsAMS, according to the Lake Louise score, was significantly lower in smokers; the value was 14.9%, 95% CI (6.8 to 23.0%) in smokers and 29.4%, 95% CI (23.5 to 35.3%) in non-smokers with an adjusted OR of 0.54, 95% CI (0.31 to 0.97) independent of gender, age and maximum altitude reached.ConclusionsThese results suggest that smoking could reduce the risk of AMS in non-acclimated individuals. Further studies should be performed in larger cohorts of travellers to confirm these results. Despite the results, smoking must be strongly discouraged because it greatly increases the risk of cardiorespiratory diseases, cancer and other diseases.

scholarly journals Frequency of non-motor symptoms in Peruvian patients with Parkinson's disease

2013 ◽  
Vol 71 (4) ◽  
pp. 216-219 ◽  
Author(s):  
Carlos Cosentino ◽  
Yesenia Nuñez ◽  
Luis Torres
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Progressive Increase ◽  
Motor Symptoms ◽  
Number Of Patients ◽  
Progression Of Disease ◽  
The Mean ◽  
Relationship Of ◽  
The Relationship ◽  
Non Motor Symptoms

Introduction: Non-motor symptoms in Parkinson's disease are often not well recognized in clinical practice. Non-motor symptoms questionnaire (NMSQuest) is a simple instrument that allows patients or caregivers to report non-motor symptoms in a practical manner. Objective: We attempted to determine the prevalence of non-motor symptoms in three hundred Parkinson's disease outpatients. Results: The mean total non-motor symptoms was 12.41, ranging from 0 to 27 of a maximum of 30. At least one was present in 99.3% of patients. A progressive increase in mean total score was observed across each 5-year interval. Depression domain scored the most “positive” answers while urinary and anxiety /memory were secondly and thirdly most prevalent respectively. Conclusion: The large number of patients included in this study allowed evaluation of the occurrence of non-motor symptoms in early and advanced disease in addition to the relationship of these kinds of symptoms with progression of disease.

Scaling laws for pipe-flow turbulence

1975 ◽  
Vol 67 (2) ◽  
pp. 257-271 ◽  
Author(s):  
A. E. Perry ◽  
C. J. Abell
Keyword(s):  
Pipe Flow ◽  
Scaling Laws ◽  
Dynamic Calibration ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Number Range ◽  
Static Calibration ◽  
Calibration Methods ◽  
The Mean ◽  
Flow Turbulence

Using hot-wire-anemometer dynamic-calibration methods, fully developed pipe-flow turbulence measurements have been taken in the Reynolds-number range 80 × 103 to 260 × 103. Comparisons are made with the results of previous workers, obtained using static-calibration methods. From the dynamic-calibration results, a consistent and systematic correlation for the distribution of turbulence quantities becomes evident, the resulting correlation scheme being similar to that which has previously been established for the mean flow. The correlations reported have been partly conjectured in the past by many workers but convincing experimental evidence has always been masked by the scatter in the results, no doubt caused by the difficulties associated with static-calibration methods, particularly the earlier ones. As for the mean flow, the turbulence intensity measurements appear to collapse to an inner and outer law with a region of overlap, from which deductions can be made using dimensional arguments. The long-suspected similarity of the turbulence structure and its consistency with the established mean-flow similarity appears to be confirmed by the measurements reported here.

632 Family History of Children Diagnosed with Obstructive Sleep Apnea

SLEEP ◽  
2021 ◽  
Vol 44 (Supplement_2) ◽  
pp. A248-A248
Author(s):  
Kristi Porterfield-Pruss ◽  
Denise Willis ◽  
Beverly Spray ◽  
Supriya Jambhekar
Keyword(s):  
Family History ◽  
Family Members ◽  
Biological Father ◽  
Medical Problems ◽  
Obstructive Sleep ◽  
Familial Association ◽  
History Of ◽  
The Mean ◽  
Relationship Of ◽  
The Relationship

Abstract Introduction Limited evidence suggests a familial association of OSA. It is not known how often children who require positive airway pressure (PAP) devices have a family member with OSA or that requires PAP. It is felt that PAP adherence in children is affected by PAP adherence in parents. We wanted to explore the relationship of OSA in children requiring PAP to OSA in immediate family members as well as the association of obesity and adherence between children and family members. Methods Caregivers of children who utilize PAP devices at home were invited to complete an electronic questionnaire regarding family history of OSA. Descriptive statistics were utilized to summarize results. Results The study was completed by 75 participants. The majority of children were male (64%, 48/75), black (47%, 35/75) and non-Hispanic (88%, 66/75). The mean age was 11.8 years (median 13) and mean BMI was 32.8 (median 29.8). The mean AHI on the diagnostic polysomnogram was 28.4 events per hour (median 15.3). Mean adherence to PAP &gt; 4 hours per night was 56.5 (Median 68.2). Most, 87% (65/75), have other underlying medical problems. Twenty-four percent (18/75) have a biological father with OSA of whom 61% (11/18) are considered moderately/extremely obese. Of mothers, 13% (10/75) have OSA and 70% (7/10) are obese. Overall, 29% (22/75) had either a paternal (11%, 8/75) or maternal (19%, 14/75) grandfather with OSA of which 36% (8/22) are obese. For grandmothers, 31% (23/75) have OSA and 22% (5/23) are obese with more being paternal (19%, 14/75) compared to maternal (12%, 9/75). Of the 73 total family members reported to have OSA, 86% (63/73) use PAP and most (65%, 41/63) use it for &gt; 4 hours every night. Few participants had siblings with OSA. Conclusion There were more fathers with OSA than mothers, but mothers were reported to be obese more often. Grandparents were reported to have OSA but were reported to be obese less often than parents. Maternal grandparents with OSA were reported to be obese more than paternal grandparents. The majority of family members with OSA who use CPAP report nightly use. Support (if any):

A Mean Flow Model for Polymer and Fiber Turbulent Drag Reduction

2005 ◽  
Vol 15 (6) ◽  
pp. 370-389 ◽  
Author(s):  
Anshuman Roy ◽  
Ronald G. Larson
Keyword(s):  
Drag Reduction ◽  
Weissenberg Number ◽  
Extensional Viscosity ◽  
Mean Flow ◽  
Dimensionless Numbers ◽  
Zero Shear Viscosity ◽  
Mean Velocity ◽  
Fiber Concentration ◽  
Turbulent Drag ◽  
The Mean

Abstract We present a one-parameter model that fits quantitatively the mean velocity profiles from experiments and numerical simulations of drag-reduced wall-bounded flows of dilute solutions of polymers and non-Brownian fibers in the low and modest drag reduction regime. The model is based on a viscous mechanism of drag reduction, in which either extended polymers or non-Brownian fibers increase the extensional viscosity of the fluid and thereby suppress both small and large turbulent eddies and reduce momentum transfer to the wall, resulting in drag reduction. Our model provides a rheological interpretation of the upward parallel shift S+ in the mean velocity profile upon addition of polymer, observed by Virk. We show that Virk’s correlations for the dependence on polymer molecular weight and concentration of the onset wall shear stress and slope increment on the Prandtl-Karman plot can be translated to two dimensionless numbers, namely an onset Weissenberg number and an asymptotic Trouton ratio of maximum extensional viscosity to zero-shear viscosity. We believe that our model, while simple, captures the essential features of drag reduction that are universal to flexible polymers and fibers, and, unlike the Virk phenomenology, can easily be extended to flows with inhomogeneous polymer or fiber concentration fields.

scholarly journals On the streamwise evolution of turbulent boundary layers in arbitrary pressure gradients

2002 ◽  
Vol 461 ◽  
pp. 61-91 ◽  
Author(s):  
A. E. PERRY ◽  
IVAN MARUSIC ◽  
M. B. JONES
Keyword(s):  
Boundary Layers ◽  
Scaling Laws ◽  
Power Spectra ◽  
Adverse Pressure Gradient ◽  
Turbulent Boundary Layers ◽  
Stream Velocity ◽  
Mean Flow ◽  
Mean Velocity ◽  
Law Of The Wall ◽  
The Mean

A new approach to the classic closure problem for turbulent boundary layers is presented. This involves, first, using the well-known mean-flow scaling laws such as the log law of the wall and the law of the wake of Coles (1956) together with the mean continuity and the mean momentum differential and integral equations. The important parameters governing the flow in the general non-equilibrium case are identified and are used for establishing a framework for closure. Initially closure is achieved here empirically and the potential for achieving closure in the future using the wall-wake attached eddy model of Perry & Marusic (1995) is outlined. Comparisons are made with experiments covering adverse-pressure-gradient flows in relaxing and developing states and flows approaching equilibrium sink flow. Mean velocity profiles, total shear stress and Reynolds stress profiles can be computed for different streamwise stations, given an initial upstream mean velocity profile and the streamwise variation of free-stream velocity. The attached eddy model of Perry & Marusic (1995) can then be utilized, with some refinement, to compute the remaining unknown quantities such as Reynolds normal stresses and associated spectra and cross-power spectra in the fully turbulent part of the flow.

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