scholarly journals Scaling Turbulent Combustion Fields in Explosions

2020 ◽  
Vol 10 (23) ◽  
pp. 8577
Author(s):  
Allen Kuhl ◽  
David Grote ◽  
John Bell
Keyword(s):  
Turbulent Combustion ◽  
Scaling Laws ◽  
High Explosive ◽  
Length Scale ◽  
Roundoff Error ◽  
Reynolds Stresses ◽  
Phase 3 ◽  
Three Phase ◽  
The Mean ◽  
Thermodynamic Variables

We considered the topic of explosions from spherical high-explosive (HE) charges. We studied how the turbulent combustion fields scale. On the basis of theories of dimensional analysis by Bridgman and similarity theories of Sedov and Barenblatt, we found that all fields scaled with the explosion length scale r0. This included the blast wave, the mean and root mean squared (RMS) profiles of thermodynamic variables, combustion variables, velocities, vorticity, and turbulent Reynolds stresses. This was a consequence of the formulation of the problem and our numerical method, which both satisfied the similarity conditions of Sedov. We performed numerical simulations of 1 g charges and 1 kg charges; the solutions were identical (within roundoff error) when plotted in scaled variables. We also explored scaling laws related to three-phase pyrotechnic explosions. We show that although the scaling formally broke down, the fireball still essentially scaled with the explosion length scale r0. However, the discrete Lagrange particles (DLP) (phase 2) and the heterogeneous continuum model (HCM) of the DLP wakes (phase 3) did not scale with r0, and mean and RMS profiles could differ by a factor of 10 in some regions. This was because the DLP particles and wakes introduced an additional scale that broke the similarity conditions.

scholarly journals MP09: Canadian Community Utilization of Stroke Prevention Pilot Study-Emergency Department (C-CUSP ED)

CJEM ◽  
2017 ◽  
Vol 19 (S1) ◽  
pp. S68 ◽  
Author(s):  
R. Parkash ◽  
K. Magee ◽  
M. McMullen ◽  
M.B. Clory ◽  
M. D’Astous ◽  
...  
Keyword(s):  
Stroke Prevention ◽  
Phase 1 ◽  
Retrospective Chart Review ◽  
Phase 2 ◽  
Phase 3 ◽  
Three Phase ◽  
Rigorous Study ◽  
The Mean ◽  
Prior Risk

Introduction: Atrial fibrillation (AF) is the most common sustained arrhythmia affecting 1-2% of the population. Oral anticoagulation (OAC) reduces stroke risk by 60-80% in AF patients, but only 50% of indicated patients receive OAC. Many patients present to the ED with AF due to arrhythmia symptoms, however; lack of OAC prescription in the ED has been identified as a significant gap in the care of AF patients. Methods: This was a multi-center, pragmatic, three-phase before-after study, in three Canadian sites. Patients who presented to the ED with electrocardiographically (ECG) documented, nonvalvular AF and were discharged home were included. Phase 1 was a retrospective chart review to determine OAC prescription of AF patients in each ED; Phase 2 was a low-intensity knowledge translation intervention where a simple OAC-prescription tool for ED physicians with subsequent short-term OAC prescription was used, as well as an AF patient education package and a letter to family physicians; phase 3 incorporated Phase 2 interventions, but added immediate follow-up in a community AF clinic. The primary outcome of the study was the rate of new OAC prescriptions at ED discharge in AF patients who were OAC eligible and were not on OAC at presentation. Results: A total of 632 patients were included from June, 2015-November, 2016. ED census ranged from 30000-68000 annual visits. Mean age was 71±15, 67±12, 67±13 years, respectively. 47.5% were women, most responsible ED diagnosis was AF in 75.8%. The mean CHA2DS2-VASc score was 2.6±1.8, with no difference amongst groups. There were 266 patients eligible for OAC and were not on this at presentation. In this group, the prescription of new OAC was 15.8% in Phase 1 as compared to 54% and 47%, in Phases 2 and 3, respectively. After adjustment for center, components of the CHA2DS2-VASc score, prior risk of bleeding and most responsible ED diagnosis, the odds ratio for new OAC prescription was 8.0 (95%CI (3.5,18.3) p<0.001) for Phase 3 vs 1, and 10.0 (95%CI (4.4,22.9) p<0.001), for Phase 2 vs 1). No difference in OAC prescription was seen between Phases 2 and 3. Conclusion: Use of a simple OAC-prescription tool was associated with an increase in new OAC prescription in the ED for eligible patients with AF. Further testing in a rigorous study design to assess the effect of this practice on stroke prevention in the AF patients who present to the ED is indicated.

An Experimental Investigation of the Velocity and Temperature Fields of Cold Jets Injected Into a Hot Crossflow

1998 ◽  
Vol 120 (2) ◽  
pp. 320-326 ◽  
Author(s):  
H. A. Rydholm
Keyword(s):  
Scaling Laws ◽  
Temperature Fields ◽  
Reynolds Stresses ◽  
Experimental Conditions ◽  
Mean Values ◽  
Cooling Design ◽  
The Mean ◽  
Prandtl Numbers ◽  
Density Ratios ◽  
Cooling Air

It is shown here by dimensional analysis that the near-wall flow field of an effusion-cooled combustor can be scaled if the Reynolds, Mach, and Prandtl numbers and the temperature and velocity ratios are kept constant. It is also demonstrated that a practical model experiment can be designed, which fulfills all the scaling laws. A test rig meeting these requirements has been designed, built and tested. The experimental conditions have been chosen to correspond to the conditions usually met in a real effusion-cooled combustion chamber. One geometric configuration has been investigated. This consists of one transverse row of holes drilled with a 30 deg angle to the wall through which the cooling air enters a cross-flowing mainstream. The mean values of all three velocity components and the three normal fluctuating Reynolds stresses as well as the mean temperature have been measured in a large number of points surrounding the central injection hole. Experiments were carried out for jet-to-mainstream density ratios of 1.2 and 1.8. The results indicate that realistic density ratios are necessary to provide data directly applicable to effusion-cooling design.

Some Solutions of the Plane Turbulent Impinging Jet

1970 ◽  
Vol 92 (4) ◽  
pp. 915-922 ◽  
Author(s):  
M. Wolfshtein
Keyword(s):  
Reasonable Agreement ◽  
Eddy Viscosity ◽  
Order Differential Equation ◽  
Impinging Jet ◽  
Experimental Information ◽  
Length Scale ◽  
Reynolds Stresses ◽  
Finite Difference Technique ◽  
The Mean ◽  
Mean Strain

The impinging jet problem is solved by an iterative finite-difference technique. Reynolds stresses are assumed to be related to the mean strain by a scalar eddy viscosity. The eddy viscosity is assumed to depend on the level of energy fluctuations and a length scale. The level of energy fluctuations is obtained from a second-order differential equation, while the length scale of turbulence is prescribed on the basis of experimental information. The solutions show reasonable agreement with experiment.

scholarly journals An Experimental Investigation of the Velocity and Temperature Fields of Cold Jets Injected Into a Hot Crossflow

1996 ◽  
Author(s):  
Hans A. Rydholm
Keyword(s):  
Scaling Laws ◽  
Temperature Fields ◽  
Reynolds Stresses ◽  
Experimental Conditions ◽  
Mean Values ◽  
Cooling Design ◽  
The Mean ◽  
Prandtl Numbers ◽  
Density Ratios ◽  
Cooling Air

It is shown here by dimensional analysis that the near-wall flow field of an effusion cooled combustor, can be scaled if the Reynolds, Mach and Prandtl numbers and the temperature and velocity ratios are kept constant. It is also demonstrated that a practical model experiment can be designed, which fulfils all the scaling laws. A test rig meeting these requirements has been designed, built and tested. The experimental conditions have been chosen to correspond to the conditions usually met in a real effusion cooled combustion chamber. One geometrical configuration has been investigated. This consists of one transverse row of holes drilled with a 30° angle to the wall through which the cooling air enters into a cross flowing mainstream. The mean values of all three velocity components and the three normal fluctuating Reynolds stresses as well as the mean temperature have been measured in a large number of points surrounding the central injection hole. Experiments were carried out for jet-to mainstream density ratios of 1.2 and 1.8 and the results indicate that realistic density ratios are necessary to provide data directly applicable in effusion cooling design.

Fr256 RIFAXIMIN SIGNIFICANTLY IMPROVES BOWEL MOVEMENT URGENCY IN PATIENTS WITH IRRITABLE BOWEL SYNDROME WITH DIARRHEA: A POOLED ANALYSIS OF THREE PHASE 3 TRIALS

2021 ◽  
Vol 160 (6) ◽  
pp. S-281
Author(s):  
Philip S. Schoenfeld ◽  
Darren M. Brenner ◽  
Nipaporn Pichetshote ◽  
Zeev Heimanson ◽  
Brian E. Lacy
Keyword(s):  
Irritable Bowel Syndrome ◽  
Bowel Movement ◽  
Pooled Analysis ◽  
Phase 3 ◽  
Three Phase ◽  
Irritable Bowel

scholarly journals Jet Formation and Evolution in Baroclinic Turbulence with Simple Topography

2010 ◽  
Vol 40 (2) ◽  
pp. 257-278 ◽  
Author(s):  
Andrew F. Thompson
Keyword(s):  
Southern Ocean ◽  
Potential Vorticity ◽  
Baroclinic Instability ◽  
Length Scale ◽  
Reynolds Stresses ◽  
Mean Flow ◽  
Jet Formation ◽  
Meridional Transport ◽  
Jet Behavior ◽  
Jet Variability

Abstract Satellite altimetry and high-resolution ocean models indicate that the Southern Ocean comprises an intricate web of narrow, meandering jets that undergo spontaneous formation, merger, and splitting events, as well as rapid latitude shifts over periods of weeks to months. The role of topography in controlling jet variability is explored using over 100 simulations from a doubly periodic, forced-dissipative, two-layer quasigeostrophic model. The system is forced by a baroclinically unstable, vertically sheared mean flow in a domain that is large enough to accommodate multiple jets. The dependence of (i) meridional jet spacing, (ii) jet variability, and (iii) domain-averaged meridional transport on changes in the length scale and steepness of simple sinusoidal topographical features is analyzed. The Rhines scale, ℓβ = 2πVe/β, where Ve is an eddy velocity scale and β is the barotropic potential vorticity gradient, measures the meridional extent of eddy mixing by a single jet. The ratio ℓβ /ℓT, where ℓT is the topographic length scale, governs jet behavior. Multiple, steady jets with fixed meridional spacing are observed when ℓβ ≫ ℓT or when ℓβ ≈ ℓT. When ℓβ < ℓT, a pattern of perpetual jet formation and jet merger dominates the time evolution of the system. Zonal ridges systematically reduce the domain-averaged meridional transport, while two-dimensional, sinusoidal bumps can increase transport by an order of magnitude or more. For certain parameters, bumpy topography gives rise to periodic oscillations in the jet structure between purely zonal and topographically steered states. In these cases, transport is dominated by bursts of mixing associated with the transition between the two regimes. Topography modifies local potential vorticity (PV) gradients and mean flows; this can generate asymmetric Reynolds stresses about the jet core and can feed back on the conversion of potential energy to kinetic energy through baroclinic instability. Both processes contribute to unsteady jet behavior. It is likely that these processes play a role in the dynamic nature of Southern Ocean jets.

Prediction of Confined Coaxial Turbulent Jet Mixing With a Streamwise Differencing Scheme

1991 ◽  
Author(s):  
M. A. R. Sharif ◽  
M. A. Gadalla
Keyword(s):  
Reynolds Stresses ◽  
Low Velocity ◽  
Mean Velocity ◽  
Jet Mixing ◽  
Air Jet ◽  
Air Stream ◽  
Constant Diameter ◽  
Flow Domain ◽  
The Mean ◽  
Secondary Air

Abstract Isothermal turbulent mixing of an axisymmetric primary air jet with a low velocity annular secondary air stream inside a constant diameter cylindrical enclosure is predicted. The flow domain from the inlet to the fully developed downstream locations is considered. The predicted flow field properties include the mean velocity and pressure and the Reynolds stresses. Different velocity and diameter ratios between the primary and the secondary jets have been investigated to characterize the flow in terms of these parameters. A bounded stream-wise differencing scheme is used to minimize numerical diffusion and oscillation errors. Predictions are compared with available experimental data to back up numerical findings.

Hot Wire Measurements at the Exit of a Centrifugal Compressor Impeller

1979 ◽  
Vol 193 (1) ◽  
pp. 341-347
Author(s):  
A. Goulas ◽  
R. C. Baker
Keyword(s):  
Centrifugal Compressor ◽  
Magnetic Tape ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Mean Velocity ◽  
Isentropic Flow ◽  
Compressor Impeller ◽  
The Mean

Hot wire measurements at the exit of a small centrifugal compressor impeller are reported. Three different hot wire readings were obtained and stored on a magnetic tape for each point by gating the analogue hot wire signal with a pulse which indicated circumferential position. The combination of the three readings yielded the mean velocity and some Reynolds stresses at each point. The measurements show a ‘jet-wake’ profile towards the shroud and ‘isentropic’ flow near the hub.

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