Turbulent fluctuations in the viscous wall region for Newtonian and drag reducing fluids

1977 ◽  
Vol 20 (10) ◽  
pp. S112 ◽  
Author(s):  
Thomas J. Hanratty ◽  
Larry G. Chorn ◽  
Dimitrios T. Hatziavramidis
Keyword(s):  
Wall Region ◽  
Turbulent Fluctuations

The autonomous cycle of near-wall turbulence

1999 ◽  
Vol 389 ◽  
pp. 335-359 ◽  
Author(s):  
JAVIER JIMÉNEZ ◽  
ALFREDO PINELLI
Keyword(s):  
Reynolds Numbers ◽  
Wall Turbulence ◽  
Wall Region ◽  
Streamwise Vortices ◽  
Outer Flow ◽  
Turbulent Fluctuations ◽  
The Mean ◽  
Turbulence Generation ◽  
Near Wall Turbulence ◽  
Near Wall

Numerical experiments on modified turbulent channels at moderate Reynolds numbers are used to differentiate between several possible regeneration cycles for the turbulent fluctuations in wall-bounded flows. It is shown that a cycle exists which is local to the near-wall region and does not depend on the outer flow. It involves the formation of velocity streaks from the advection of the mean profile by streamwise vortices, and the generation of the vortices from the instability of the streaks. Interrupting any of those processes leads to laminarization. The presence of the wall seems to be only necessary to maintain the mean shear. The generation of secondary vorticity at the wall is shown to be of little importance in turbulence generation under natural circumstances. Inhibiting its production increases turbulence intensity and drag.

Structure Control of the Wall Region in a Turbulent Boundary.

1995 ◽  
Author(s):  
John Guckenheimer ◽  
Sidney Leibovich ◽  
Philip Holmes ◽  
John L. Lumley
Keyword(s):  
Wall Region ◽  
Structure Control

Structure of Turbulent Velocity and Temperature Fluctuations in Fully Developed Pipe Flow

1979 ◽  
Vol 101 (1) ◽  
pp. 15-22 ◽  
Author(s):  
M. Hishida ◽  
Y. Nagano
Keyword(s):  
Pipe Flow ◽  
Dominant Role ◽  
Temperature Fluctuations ◽  
Temperature Fields ◽  
Inertial Subrange ◽  
Wall Region ◽  
Turbulent Heat ◽  
Temperature Spectrum ◽  
Axial Heat ◽  
Heat Transport Process

An experimental investigation of the turbulent structure of velocity and temperature fields has been made in fully developed pipe flow of air. In the near-wall region, the coherent quasi-ordered structure plays a dominant role in the turbulent heat transport process. The turbulent axial heat flux as well as the intensities of velocity and temperature fluctuations reach their maximums in this region, but these maximum points are different. The nondimensional intensities of velocity and temperature fluctuations are well described with the “logarithmic law” in the turbulent part of the wall region where the velocity-temperature cross-correlation coefficient is nearly constant. In the turbulent core, the velocity and temperature fluctuations are less correlated. The spectra of velocity and temperature fluctuations present −1 slope at low wavenumbers in the wall region and −5/3 slope in the inertial subrange. The temperature spectrum for the inertial-diffusive subrange indicates the −8/3 power-law.

Regional cardiac uptake of 99-Tc-DPD is a novel powerful and independent prognostic marker in cardiac ATTR wild type amyloidosis

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
P Milani ◽  
G Cavenaghi ◽  
L Obici ◽  
R Mussinelli ◽  
C Klersy ◽  
...  
Keyword(s):  
Prognostic Value ◽  
Cox Regression ◽  
Expectation Maximization Algorithm ◽  
Linear Increase ◽  
Whole Body ◽  
Wall Region ◽  
Cardiac Spect ◽  
Risk Of Death ◽  
Cardiac Wall

Abstract Background Skeletal scintigraphy with bone tracers is a key tool for cardiac ATTR diagnosis. However its prognostic value has not been systematically assessed. Purpose We evaluated the prognostic relevance of a quantitative method to assess regional 99mTc-DPD uptake by SPECT in the heart of ATTRwt patients. Methods All ATTRwt patients (n=229) undergoing clinical assessment and bone scintigraphy at our center (from 2012 to 2019) were enrolled. Theyreceived approximately 700 MBq of 99mTc-DPD. Planar whole body acquisition 10' after the injection followed by cardiac SPECT after 3 hours were performed. SPECT data were reconstructed into 64x64 matrices with an ordered-subset expectation maximization algorithm. For each wall region and for the apex, a circular region of interest (ROI, 20 pixels) was manually drawn and a value equating to the number of counts contained in the ROI was obtained. Partial correlation of ln-transformed ROI and biomarkers was retrieved from a multivariable regression model, while controlling for each cardiac wall region. Multivariable Cox regression was used to assess the prognostic role of lnROI while adjusting for wall region, NT-proBNP, cTnI and eGFR. Hazard ratios and 95% confidence intervals (HR, 95% CI) were computed. The Harrell's c statistic was reported for model discrimination. The interaction of biomarker and regional wall on survival was assessed; also, to account for intra-subject correlation of measures, within subject robust standard errors were computed. Results Median follow-up was 21 months (IQR 11, 40) and 39 (17%) patients died. Median age was 76 years (IQR, 72–80), NT-proBNP 2944 ng/L (IQR, 1815–5319), cTnI 0.095 ng/L (IQR, 0.062–0.144) and eGFR 62 mL/min (IQR, 51–77). ROI did not correlate with any of NT-proBNP, eGFR, age, cTnI or mLVWT (R<1% in all cases). All analyses were adjusted for cardiac wall. At the multivariable Cox regression (Harrell's c=0.75), there was a linear increase in the risk of death associated with lnROI (HR 2.14, P=0.014), which was independent of cardiac wall region, NTproBNP, cTnI and eGFR. Only cTnI maintained a significant prognostic value. The association of lnROI and mortality was not modified by the site of measurement test for interaction with cardiac wall p=0.818). At the predefined subgroup analysis, the risk of death was similar for all walls; we computed the optimal cut-off for 12 months survival at the apex (a region usually lately involved) to 4193 (AUC: 0.68, sensitivity 80%, specificity 68%). At the multivariable Cox regression (Harrell's c 0.76), apex ROI>4193 was an independent predictor of death (HR 3.60, 95% CI 1.45–8.93, p=0.006) and outperformed all the biomarkers tested. Conclusions Quantitative assessment of ROI uptake at cardiac SPECT is a powerful predictor of survival in ATTRwt patients, independent of and outperforming the other known prognostic factors. This observation warrants validation with prolonged follow-up and in independent patient series. Funding Acknowledgement Type of funding source: None

Sign in / Sign up

Export Citation Format

Share Document