Onset Of Turbulence Research Articles

Dynamo instabilities in plasmas with inhomogeneous chiral chemical potential

We study the dynamics of magnetic fields in chiral magnetohydrodynamics, which takes into account the effects of an additional electric current related to the chiral magnetic effect in high-energy plasmas. We perform direct numerical simulations, considering weak seed magnetic fields and inhomogeneities of the chiral chemical potential ${\ensuremath{\mu}}_{5}$ with a zero mean. We demonstrate that a small-scale chiral dynamo can occur in such plasmas if fluctuations of ${\ensuremath{\mu}}_{5}$ are correlated on length scales that are much larger than the scale on which the dynamo growth rate reaches its maximum. Magnetic fluctuations grow by many orders of magnitude due to the small-scale chiral dynamo instability. Once the nonlinear backreaction of the generated magnetic field on fluctuations of ${\ensuremath{\mu}}_{5}$ sets in, the ratio of these scales decreases and the dynamo saturates. When magnetic fluctuations grow sufficiently to drive turbulence via the Lorentz force before reaching maximum field strength, an additional mean-field dynamo phase is identified. The mean magnetic field grows on a scale that is larger than the integral scale of turbulence after the amplification of the fluctuating component saturates. The growth rate of the mean magnetic field is caused by a magnetic $\ensuremath{\alpha}$ effect that is proportional to the current helicity. With the onset of turbulence, the power spectrum of ${\ensuremath{\mu}}_{5}$ develops a universal ${k}^{\ensuremath{-}1}$ scaling independently of its initial shape, while the magnetic energy spectrum approaches a ${k}^{\ensuremath{-}3}$ scaling.

Flow resistance and convective heat transfer by elastic turbulence in 1D/2D/3D geometries

Inducing elastic turbulence is a promising method to intensify flow and heat transfer at low Reynolds number Re. Different geometries shall have great impacts on the occurrence of elastic turbulence and its heat transfer effect, which are however seldom investigated especially for flow in 3D geometry. This work conducts a comparative experimental study of the dimension effect on elastic turbulence on 3D, 2D and 1D geometries with similar hydraulic diameters. Polyacrylamide is used to induce elastic turbulence and the corresponding flow resistance and heat transfer performance are obtained for different geometries under laminar flow conditions. The results provide strong evidence that curvatures are necessary for the onset of elastic turbulence in 1D geometry as shown by similar flow resistance and heat transfer coefficient between the Newtonian and viscoelastic fluids. Comparing to the 2D geometry, flow in 3D geometry achieves both reduced pressure drop gradient and increased heat transfer at the same time due to the unique interaction of elastic stress with the torsion and rotation effects. New correlations of Nusselt number Nu and Weissenberg number Wi are proposed in curved geometries as Nu∝Wi2.2 and Wi1.9 for the 3D and 2D flow structures, respectively, under the boundary condition of constant heat flux. The mechanisms of flow and heat transfer of elastic turbulence in different geometries are also discussed to help further optimization.

Particle‐resolved turbulent flow in a packed bed: RANS, LES, and DNS simulations

AbstractPacked bed reactors are widely used to perform solid‐catalyzed gas‐phase reactions and local turbulence is known to influence heat and mass transfer characteristics. We have investigated turbulence characteristics in a packed bed of 113 spherical particles by performing particle‐resolved Reynolds‐averaged Navier–Stokes (RANS) simulations, Large Eddy Simulation (LES), and Direct Numerical Simulation (DNS). The predictions of the RANS and LES simulations are validated with the lattice Boltzmann method (LBM)–based DNS at particle Reynolds number (Rep) of 600. The RANS and LES simulations can predict the velocity, strain rate, and vorticity with a reasonable accuracy. Due to the dominance of enhanced wall‐function treatment, the turbulence characteristics predicted by the ε‐based models are found to be in a good agreement with the DNS. The ω‐based models under‐predicted the turbulence quantities by several orders of magnitude due to their inadequacy in handling strongly wall‐dominated flows at low Rep. Using the DNS performed at different Rep, we also show that the onset of turbulence occurs between .

The role of heart rate variability and heart rate turbulence in diabetic retinopathy.

The aim of this study was to evaluate the cardiac autonomic functions of individuals with asymptomatic diabetic retinopathy (DR) and no obvious heart disease by heart rate turbulence (HRT) and heart rate variability (HRV) analysis. A total of 72 patients with type 2 diabetes mellitus: 20 non-retinopathic (NRDM), 26 non-proliferative retinopathic patients (NPDR) and 26 proliferative retinopathic patients (PDR) were enrolled in this cross-sectional study. The HRV parameters of Standard deviation of NN intervals (SDNN) (119.8±11.7, 101.1±20.2, 100.6±17.04), standard deviation of the average NN intervals (108.3±10.8, 91.2±17.5, 93.6±18.4), SDNN Index (49.5±5.1, 40.1±13.4, 38.6±12.7), Root mean square of successive RR interval differences (28.3±5.1, 22.3±7.5, 26±9.2) and Triangular index (34.4±4.3, 29.7±8.8, 27.3±6.7) were significantly lower in the NPDR and PDR groups than in the NRDM group (for all P<0.05). Also, there was a statistically significant higher Turbulence Onset (-1.80±0.7, -1.1±0.9, -0.43±0.81) and lower Turbulence Slope (8.05±2.59, 5.82±3.39, 4.53±2.07) in HRT parameters in patients in the NPDR and PDR groups than in the NRDM group (P<0.001). We found that HRV and HRT parameters had a significant deterioration in retinopathic individuals compared to the group without retinopathy. We think that HRV and HRT analysis can have an important role in the evaluation of these patients.

Characterization of Turbulent Flow Behind a Transcatheter Aortic Valve in Different Implantation Positions.

The development of turbulence after transcatheter aortic valve (TAV) implantation may have detrimental effects on the long-term performance and durability of the valves. The characterization of turbulent flow generated after TAV implantation can provide fundamental insights to enhance implantation techniques. A self-expandable TAV was tested in a pulse replicator and the three-dimensional flow field was extracted by means of tomographic particle image velocimetry. The valve was fixed inside a silicone phantom mimicking the aortic root and the flow field was studied for two different supra-annular axial positions at peak systole. Fluctuating velocities and turbulent kinetic energy were compared between the two implantations. Velocity spectra were derived at different spatial positions in the turbulent wakes to characterize the turbulent flow. The valve presented similar overall flow topology but approximately 8% higher turbulent intensity in the lower implantation. In this configuration, axial views of the valve revealed smaller opening area and more corrugated leaflets during systole, as well as more accentuated pinwheeling during diastole. The difference arose from a lower degree of expansion of the TAV's stent inside the aortic lumen. These results suggest that the degree of expansion of the TAV in-situ is related to the onset of turbulence and that a smaller and less regular opening area might introduce flow instabilities that could be detrimental for the long-term performance of the valve. The present study highlights how implantation mismatches may affect the structure and intensity of the turbulent flow in the aortic root.

Phase Transition to Turbulence in Spatially Extended Shear Flows.

Directed percolation (DP) has recently emerged as a possible solution to the century old puzzle surrounding the transition to turbulence. Multiple model studies reported DP exponents, however, experimental evidence is limited since the largest possible observation times are orders of magnitude shorter than the flows' characteristic timescales. An exception is cylindrical Couette flow where the limit is not temporal, but rather the realizable system size. We present experiments in a Couette setup of unprecedented azimuthal and axial aspect ratios. Approaching the critical point to within less than 0.1% we determine five critical exponents, all of which are in excellent agreement with the 2+1D DP universality class. The complex dynamics encountered at the onset of turbulence can hence be fully rationalized within the framework of statistical mechanics.

Heart rate turbulence measurements in patients with dipper and non-dipper hypertension: the effects of autonomic functions

Hypertensive patients have shown autonomic dysfunction that is closely associated with the measurements of heart rate variability (HRV) and heart rate turbulence (HRT). We aimed to show the alterations of HRV and HRT measurements in patients with both dipper and non-dipper hypertension. This was a retrospective study consisting of one hundred and twenty-three participants (mean age ± SD, 55.7 ± 14.8 years; range, 18–90 years). The participants were divided into two groups: Group1: The patients with dipper hypertension, Group2: The patients with non-dipper hypertension. Two cardiologists performed HRV and HRT using 24-h electrocardiography (ECG) Holter and ambulatory blood pressure monitoring (ABPM) of patients. The results indicated that patients in group 2 had higher low frequency power/high frequency power ratio (LF/HF), lower high frequency power (HF) , root mean square of standard deviation (RMSSD) values than group 1 (p = 0.007, p = 0.008, and p = 0.002, respectively). Group 2 also showed higher heart rate turbulence onset (HRTTO) and lower heart rate turbulence slope (HRTTS) values than Group 1 (p = 0.004, p = 0.001, respectively). We performed multivariate analysis and observed that HRTTS and HRTTO have statistically significant associations with the presence of dipper or non-dipper hypertension [F = 7.755, p = 0.001], LF/HF [F = 7.868, p = 0.001], and HF [F = 4.081, p = 0.020]. This study shows a statistically significant difference in HRT measurements between dipper and non-dipper hypertensive patients. Deteriorated autonomic circadian rhythm and autonomic functions may contribute to these results.

Statistical interpretation of LDA measurements in naturally developing turbulent drag-reducing flow using invariant theory

Turbulent drag reduction by an extremely diluted aqueous solution of polyacrylamide was studied in a fully developed plane channel flow under non-tripped flow conditions allowing the natural development of turbulence presumably from the initially laminar like a flow state. Using laser-Doppler anemometry, all components of the Reynolds stress tensor were measured. This permitted the determination of the turbulence anisotropy and independent invariants of the anisotropy tensor. Introducing a measure for the departure of the Reynolds stress tensor from the statistically axisymmetric state that ensures laminarity, fundamental insights relating the origin of turbulence and turbulent drag reduction were analyzed in light of the measured results and existing databases of direct numerical simulations. The chief mechanism relevant to the onset of turbulence and turbulent drag reduction deduced from analytic considerations involving only kinematic constraints was confirmed by the experimental data. Parametrization of the drag reduction effect in terms of the Deborah number based on turbulence quantities evaluated at the wall supports the deduction of the polymer-turbulence interaction in terms of the elastic properties of the polymer and the near-wall turbulence structure.

Container size effects on the validity for the concept of sedimentation turbulence studied using coagulated suspension of Na-montmorillonite in the semi-dilute regime

In our previously proposed concept of sedimentation turbulence, the feed-forward mechanism of flocculation induced by a sequential cohesive collision between settling flocs during the sedimentation process resulted in the monotonous increase of the settling velocity with increments of the settling cylinder height. However, the monotonous increase of the settling velocity and the size of flocs onset of the sedimentation turbulence are considered to meet across their limiting values. In order to confirm this conjecture, the effects of container sizes, i.e., the diameter and the height of the settling cylinder, on the validity of this concept were investigated on the basis of maximum floc size, which was maintained during the sedimentation process. The sedimentation experiments of highly coagulated Na-montmorillonite in the semi-dilute regime were extended using cylinders taller in height and smaller in diameter. The results obtained demonstrate that the maximum velocity becomes much faster than that of the free settling of a single floc. A notable observation was made when a cylinder with a diameter of 10 mm was used and in which the corresponding floc size was in the same order of magnitude. In this case, the clogged large floc essentially stopped its sedimentation motion. The crude estimation of the fluid force exerted on the floc during the sedimentation process was found to be consistent with this drastic change. • Sedimentation rate was enhanced by a collision of flocs resulted from a feed-forward mechanism. • The validity of sedimentation turbulence concept against the diameter and the height of the settling cylinder was examined. • Limiting behavior of sedimentation was found in the relation of cylinder diameter and size of developed flocs. • Crude estimation of the fluid force exerted on the floc was discussed.

Collisional properties of cm-sized high-porosity ice and dust aggregates and their applications to early planet formation

ABSTRACT In dead zones of protoplanetary discs, it is assumed that micrometre-sized particles grow Brownian, sediment to the mid-plane and drift radially inward. When collisional compaction sets in, the aggregates collect slower and therefore dynamically smaller particles. This sedimentation and growth phase of highly porous ice and dust aggregates is simulated with laboratory experiments in which we obtained mm- to cm-sized ice aggregates with a porosity of 90 per cent as well as cm-sized dust agglomerates with a porosity of 85 per cent. We modelled the growth process during sedimentation in an analytical calculation to compute the agglomerate sizes when they reach the mid-plane of the disc. In the mid-plane, the dust particles form a thin dense layer and gain relative velocities by, e.g. the streaming instability or the onset of shear turbulence. To investigate these collisions, we performed additional laboratory drop tower experiments with the high-porosity aggregates formed in the sedimentary-growth experiments and determined their mechanical parameters, including their sticking threshold velocity, which is important for their further collisional evolution on their way to form planetesimals. Finally, we developed a method to calculate the packing-density-dependent fundamental properties of our dust and ice agglomerates, the Young’s modulus, the Poisson ratio, the shear viscosity, and the bulk viscosity from compression measurements. With these parameters, it was possible to derive the coefficient of restitution which fits our measurements. In order to physically describe these outcomes, we applied a collision model. With this model, predictions about general dust-aggregate collisions are possible.

Abstract 10923: Heart Rate Turbulence and Severity of Atherosclerotic Coronary Lesion in Patients with History of Myocardial Infarction

Introduction: Prediction of adverse outcomes in patients after myocardial infarction (MI) remains a serious and not completely resolved problem, which pushes researchers to search for new technologies. One of the relatively promising non-invasive methods for predicting sudden coronary death in patients with coronary heart disease may be an assessment of heart rate turbulence (HRT). Hypothesis: to study the association between components of heart rate turbulence (HRT) and severity of atherosclerotic coronary lesion assessed by the SYNTAX and SYNTAX II Scores in patients with a history of myocardial infarction. Methods: study enrolled 106 patients with a history of MI in the mean age of 63.6±8.3 years (median age 64 [58; 69] years). The severity of coronary lesions was estimated by diagnostic selective coronary angiography with an assessment of SYNTAX and SYNTAX II Scores. All patients underwent 24-h Holter ECG monitoring. HRT was determined using two indicators: Turbulence Onset (To, %) and Turbulence Slope (Ts, ms/RRi). Results: after HRT quantification measurements were as follows: To= -1.28±1.75% (-1.09 [-2.21; -0.40]); Ts= 4.98±4.51 ms/RRi (3.66 [1.65; 7.24]). Mean SYNTAX Score was 16.8±8.5 (16.0 [10.0; 21.5]); SYNTAX Score II PCI - 30.8±8.9 (30.2 [24.7; 37.0]); SYNTAX Score II CABG - 23.8±7.7 (23.6 [19.0; 29.1]); 4 year PCI mortality - 9.4±9.1% (6.9 [4.4; 11.9]); 4 year CABG mortality - 5.0±3.7% (4.1 [2.8; 6.4]). Spearmen analysis revealed positive correlation between To (r=0.266; p=0.047) and SYNTAX Score II PCI and estimated 4-year PCI mortality rate (r=0.267; p=0.047). Negative correlation relationships were observed between Ts indicator and SYNTAX Score II PCI (r= -0.539; p&lt;0.001), SYNTAX Score II CABG (r= -0.318; p=0.017), 4-year PCI mortality rate (r= -0.539; p&lt;0.001) and 4-year CABG mortality rate (r= -0.348; p=0.008). There were no significant correlations between the rests of the analyzed indicators. Conclusions: Components of HRT have an association with SYNTAX and SYNTAX II scores. In patients with a history of MI, progressive impairment of baroreflex activity, as evidenced by changes in HRT parameters may indicate a more pronounced lesion of coronary arteries.

Channel flows of shear-thinning fluids that mimic the mechanical response of a Bingham fluid

The linear stability of channel flows driven by pressure drops is carried out for fluids that exhibit a yield stress, the mechanical response of which is prescribed by the Bingham constitutive relation or two of its regularizations: the model due to Allouche and co-workers that is usually referred to as the “simple model”, and Papanastasiou model. Despite the fact that these two regularized models provide a good approximation of the steady Poiseuille flow of a Bingham fluid, they fail to predict the stability characteristics of the exact Bingham model. The critical thresholds for the onset of turbulence predicted by using the simple and Papanastasiou models are essentially the same, but they differ significantly from that of the exact Bingham model. This discrepancy is shown to be due to the absence of energy dissipation in the rigid core of a Bingham fluid.

Transition to Turbulence Downstream of a Stenosis for Whole Blood and a Newtonian Analog Under Steady Flow Conditions.

Blood, a multiphase fluid comprised of plasma, blood cells, and platelets, is known to exhibit a shear-thinning behavior at low shear rates and near-Newtonian behavior at higher shear rates. However, less is known about the impact of its multiphase nature on the transition to turbulence. In this study, we experimentally determined the critical Reynolds number at which the flow began to transition to turbulence downstream of eccentric stenosis for whole porcine blood and a Newtonian blood analog (water-glycerin mixture). Velocity profiles for both fluids were measured under steady-state flow conditions using an ultrasound Doppler probe placed 12 diameters downstream of eccentric stenosis. Velocity was recorded at 21 locations along the diameter at 11 different flow rates. Normalized turbulent kinetic energy was used to determine the critical Reynolds number for each fluid. Blood rheology was measured before and after each experiment. Tests were conducted on five samples of each fluid inside a temperature-controlled in vitro flow system. The viscosity at a shear rate of 1000 s-1 was used to define the Reynolds number for each fluid. The mean critical Reynolds numbers for blood and water-glycerin were 470 ± 27.5 and 395 ± 10, respectively, indicating a ∼19% delay in transition to turbulence for whole blood compared to the Newtonian fluid. This finding is consistent with a previous report for steady flow in a straight pipe, suggesting some aspect of blood rheology may serve to suppress, or at least delay, the onset of turbulence in vivo.

Heart rate turbulence as potential adjuvant index for optimal treatment guidance in severe pulmonary artery hypertension

Abstract Purpose Despite significant progress achieved in the management of pulmonary arterial hypertension (PAH), the prognosis remains poor. Sudden cardiac death is one main cause of death in advanced disease. It is already known that in pts with PAH there is an alteration in cardiac autonomic nervous activity. Heart rate turbulence (HRT) is an ECG–related autonomic marker, helpful in risk stratification of proarrhythmia and sudden cardiac death. Aim of the study was to examine HRT in patients with severe idiopathic PAH (IPAH) and its relation to disease's progress. Methods The study population consisted of 46 pts, (32 men and 14 women), mean age 50±9 years, Group A 20 pts: NYHA III, III–IV diagnosed as severe IPAH and Group B 26 pts: NYHA II, II–III diagnosed as moderately severe IPAH. They underwent 24h Holter monitoring-HRT analysis with calculation of 2 parameters, turbulence onset (TO) and turbulence slope (TS) (Abnormal values: TO&amp;gt;0, TS&amp;lt;2.5msec/RR). Pts were defined as HRT(+) when TO and/or TS were abnormal and as HRT(−) when both TO and TS were normal or when HRT could not be calculated because of none or too few suitable PVCs. Reassessment of HRT was undertaken in 6 mo and 1 year in case of change in clinical status. Six pts from group A and 7 pts from group B underwent HRT reassessment because of change in clinical status. Results Initially abnormal HRT was found in 12 out of 20 pts (n=12, 60%) in group A and in none out of 26 (n=0, 0%) in group B (p=0,001). In 5 pts out of 8 with clinical improvement and 4 pts with clinical deterioration who had HRT reassessed, significant positive correlation was found between TS and change of clinical status (r=0,64, p=0,04). There was a tendency to greater normal TS mean values with clinical improvement even in group where TS was already normal (6,95±4,5 vs 3±0,3 p=0.077). Conclusion In severe IPAH cardiac autonomic system impairment was demonstrated mainly as abnormal TS in HRT. Significant positive correlation between normalization of TS and clinical improvement was revealed and that raises promises for use of HRT optimization as adjuvant index to guide optimal IPAH therapy and efficacy. Funding Acknowledgement Type of funding sources: None.

How intravenous iron therapy affects arrhythmia burden and functional status in patients with advanced heart failure and implantable devices

Abstract Background Heart failure with reduced ejection fraction (HFrEF) is a disease that confers significant morbidity and mortality to patients. Patients suffer from increased arrhythmia burden; lethal ventricular arrhythmias are frequent. Iron deficiency (ID) is increasingly recognized as a common comorbidity that constitutes a further detriment to patients' cardiorespiratory capacity and an independent prognosticator of mortality. ID treatment with intravenous ferric carboxymaltose (IV FCM) has proven beneficial, improving QoL and exercise capacity in HFrEF patients with ID. Iron depletion is linked to disturbed myocyte electromechanical balance, especially in HF. However, the role of IV FCM arrhythmic burden in HFrEF patients with ID has not been examined. Purpose Investigate the effect of IV FCM treatment on the functional capacity, QoL and arrhythmic burden of in HFrEF patients with ID and cardiac implantable electronic devices (CIED). Methods HFrEF patients with ID and CIEDs were recruited from our outpatient HF clinic. CIED telemetry revealed their arrhythmic burden for the 6 months preceding IV FCM administration. Patients underwent physical examination, blood testing, 6-minute walk testing, 24-hour Holter monitoring, QoL quantification with the KCCQ and EQ-5D-5L questionnaires and repeat CIED telemetry at study baseline (IV FCM administration) and 6-months. Microvolt T-wave alternans (MTWA) and heart rate turbulence (HRT) slope and onset were quantified through the 24-hour ECG recordings. HRT results are reported as HRT0, HRT1 or HRT2 based on the number of abnormal HRT parameters. Results So far, 83 (aged 68.3±8.7 years, 82% male) out of a total of 96 recruited patients have completed the 6-month follow-up (3 of 83 died before the 6-month mark). Picture 1 contains patients' baseline characteristics and 6-month results. Patients received a mean of 1.43±0.61g of IV FCM during the follow-up period, which significantly ameliorated iron status (Picture 1). The 6MWD increased by 32.4m (95% CI: 14.7–47.2, P&amp;lt;0.001), as did the KCCQ total score (P=0.008). Patients' CIEDs recorded significantly more nsVTs in the 6 months preceding IV FCM administration (2.2±15.7 per month) opposed to the subsequent period (0.06±3.1 per month, P=0.006). Patients' MTWA improved at 6-months over baseline (P=0.004), and a trend for improvement in HRT scores was observed (P=0.06). Hospitalization-free survival curves of these time periods reveal a non-significant trend for lower hospitalization risk following IV FCM (HR=1.9, P=0.09). Conclusions After 6 months of IV FCM treatment, HFrEF patients with ID had significantly better exercise capacity and quality of life. Regarding arrhythmias, a tentative improvement in CIED- and Holter-derived arrhythmic markers was observed. Extended follow-up of a larger sample size will provide further insight for the effect of IV FCM in these patients' arrhythmic burden. Funding Acknowledgement Type of funding sources: None. Baseline and 6-month resultsHospitalization curves pre-post IV FCM

Spectral Transfer and Kármán–Howarth–Monin Equations for Compressible Hall Magnetohydrodynamics

Abstract We derive two new forms of the Kármán–Howarth–Monin (KHM) equation for decaying compressible Hall magnetohydrodynamic (MHD) turbulence. We test them on results of a weakly compressible, 2D, moderate-Reynolds-number Hall MHD simulation and compare them with an isotropic spectral transfer (ST) equation. The KHM and ST equations are automatically satisfied during the whole simulation owing to the periodic boundary conditions and have complementary cumulative behavior. They are used here to analyze the onset of turbulence and its properties when it is fully developed. These approaches give equivalent results characterizing the decay of the kinetic + magnetic energy at large scales, the MHD and Hall cross-scale energy transfer/cascade, the pressure dilatation, and the dissipation. The Hall cascade appears when the MHD one brings the energy close to the ion inertial range and is related to the formation of reconnecting current sheets. At later times, the pressure dilatation energy exchange rate oscillates around zero, with no net effect on the cross-scale energy transfer when averaged over a period of its oscillations. A reduced 1D analysis suggests that all three methods may be useful to estimate the energy cascade rate from in situ observations.

Modeling and simulation of transitional Taylor-Green vortex flow with partially averaged Navier-Stokes equations

The PANS equations model is used to predict the transitional Taylor-Green vortex (TGV) flow at Re=3000. A new form of the closure is proposed, in which the PANS procedure is applied to a variant of the BHR turbulence model. The TGV is a benchmark case for transitional flows in which the onset of turbulence is driven by vortex-stretching and reconnection mechanisms. Since these physical phenomena are observed in numerous flows of variable-density, this study constitutes the first step toward extending the PANS method to such a class of problems. We start by deriving the governing equations of the model and analyze the selection of the parameters controlling its physical resolution, fe and fk, through a-priori testing. Afterward, we conduct PANS computations at different constant physical resolutions to evaluate the model's accuracy and cost predicting the TGV flow. This is performed through simple verification and validation exercises, and the physical and modeling interpretation of the numerical predictions. The results confirm that PANS can efficiently (accuracy vs. cost) predict the present flow problem. Yet, this is closely dependent on the physical resolution of the model. Whereas high-physical resolution (fk<0.50) computations are in good agreement with the reference DNS studies, low-physical resolution (fk>=0.50) simulations lead to large discrepancies with the reference data. The physical and modeling interpretation of the results demonstrates that the origin of these distinct behaviors lies in the model's ability to resolve the phenomena driving the onset of turbulence not amenable to modeling by the closure. The comparison of the computations' cost indicates that high-physical resolution PANS achieves the accuracy of DNS (fk=0.00) at a fraction of the cost. We observe a cost reduction of one order of magnitude at the current Re, which is expected to grow with Re.

Relationship between heart rhythm turbulence and ventricular arrhythmia in patients with multivessel lesion of coronary arteries

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): MoH Research Grant "Development of methods for differentiated prevention and treatment of potentially dangerous heart rhythm disorders" Prediction of adverse outcomes in patients after myocardial infarction (MI) remains a serious and not completely resolved problem, which pushes researchers to search for new technologies. One of the relatively promising new non-invasive methods for predicting sudden coronary death in patients with coronary heart disease and ventricular arrhythmias (VA) may be an assessment of heart rate turbulence (HRT). Given its important prognostic role, primarily in patients after MI, the aim of this work was to study the relationship between HRT and cardiovascular remodeling in patients with VA with history of MI and multivessel nature of coronary lesions. Materials and research methods 123 patients with history of MI, aged 38 to 76 years (average age 61.0 ± 7.6 years), were included into the study. The multivessel nature of coronary lesions was established based on the results of diagnostic selective coronary angiography. All patients underwent Holter monitoring of the electrocardiogram (HMECG). HRT was determined using two indicators, in accordance with the guidelines: Turbulence Onset (To, %) and Turbulence Slope (Ts, ms/RRi). Results Potentially dangerous ventricular arrhythmias (PDVA) were noted in more than half of the examined patients (n = 67; 54.5%). In analyze of the structure of PDVA, II class of VA, as the highest class, was not observed in any of the examined patients, class III was detected in 35% of cases, IVA – in 37.5%, and IVB – in 27.5%. In assessing the frequency of VAs, according to the Bigger classification, frequent PVC &amp;gt;10 VA/hour was detected in 41.5% of patients. The analysis of the HRT indicators did not reveal a decrease in the mean values both To (-1.2 ± 1.5%) and Ts (3.9 ± 3.1 ms/RRi) indicators in the main group of patients. However, after appropriate separation of the main group, 21.1% of them had disorders of only one (category 1; 15.4%) or both of the HRT indicators (category 2; 5.7%). Category 0 included patients without any disorder of HRT indicators. In analysis of the relationship between the PDVA and the category of HRT reduction, a significant interrelation between them was revealed (Table 1). Result Our study demonstrates presence of strong interrelation between HRT parameters disorder and severity of PDVA. Thus, study of HRT in patients after MI could be a strong and independent predictor of cardiovascular events including sudden cardiac death. Abstract Figure. Tab. 1. Interrelation between HRT and VA

Transition to turbulence in nonuniform coronal loops driven by torsional Alfvén waves

Both observations and numerical simulations suggest that Alfvénic waves may carry sufficient energy to sustain the hot temperatures of the solar atmospheric plasma. However, the thermalization of wave energy is inefficient unless very short spatial scales are considered. Phase mixing is a mechanism that can take energy down to dissipation lengths, but it operates over too long a timescale. Here, we study how turbulence, driven by the nonlinear evolution of phase-mixed torsional Alfvén waves in coronal loops, is able to take wave energy down to the dissipative scales much faster than the theory of linear phase mixing predicts. We consider a simple model of a transversely nonuniform cylindrical flux tube with a constant axial magnetic field. The flux tube is perturbed by the fundamental mode of standing torsional Alfvén waves. We solved the three-dimensional ideal magnetohydrodynamics equations numerically to study the temporal evolution. Initially, torsional Alfvén waves undergo the process of phase mixing because of the transverse variation of density. After only few periods of torsional waves, azimuthal shear flows generated by phase mixing eventually trigger the Kelvin-Helmholtz instability (KHi), and the flux tube is subsequently driven to a turbulent state. Turbulence is very anisotropic and develops transversely only to the background magnetic field. After the onset of turbulence, the effective Reynolds number decreases in the flux tube much faster than in the initial linear stage governed by phase mixing alone. We conclude that the nonlinear evolution of torsional Alfvén waves, and the associated KHi, is a viable mechanism for the onset of turbulence in coronal loops. Turbulence can significantly speed up the generation of small scales. Enhanced deposition rates of wave energy into the coronal plasma are therefore expected.

The centre-mode instability of viscoelastic plane Poiseuille flow

Abstract