Measurement and modelling of homogeneous axisymmetric turbulence

1998 ◽  
Vol 374 ◽  
pp. 59-90 ◽  
Author(s):  
TORBJÖRN SJÖGREN ◽  
ARNE V. JOHANSSON
Keyword(s):  
Transport Equation ◽  
Reynolds Stress ◽  
Turbulence Models ◽  
Theoretical Description ◽  
Wind Tunnel Experiments ◽  
Third Order ◽  
Point Velocity ◽  
First Time ◽  
Rapid Pressure

A new method for determining the slow and rapid pressure-strain rate terms directly from wind-tunnel experiments has been developed with the aid of a newly developed theoretical description of the kinematics of homogeneous axisymmetric turbulence. Both the straining and the return-to-isotropy process of homogeneous axisymmetric turbulence are studied with the aim of improving Reynolds stress closures. Direct experimental determination of the different terms in the transport equation for the Reynolds stress tensor plays a major role in the validation and development of turbulence models. For the first time it is shown that the pressure{strain correlation can be determined with good accuracy without balancing it out from the Reynolds stress transport equation (and without measuring the pressure). Instead it is determined through evaluation of integrals containing second- and third-order two-point velocity correlations. All the terms in the Reynolds stress equations are measured directly and balance is achieved.

Numerical investigation of flow features in the vaneless region of a centrifugal pump by large eddy simulation

2018 ◽  
Vol 35 (1) ◽  
pp. 395-410 ◽  
Author(s):  
Xianbei Huang ◽  
Yaojun Li ◽  
Zhuqing Liu ◽  
Wei Yang
Keyword(s):  
Experimental Data ◽  
Transport Equation ◽  
Centrifugal Pump ◽  
Reynolds Stress ◽  
Pressure Pulsation ◽  
Third Order ◽  
Production Term ◽  
Content Type ◽  
Blade Passing Frequency ◽  
Rotor Stator Interaction

Purpose The purpose of this paper is to obtain a better understanding of the rotor–stator interaction in the vaneless region of a centrifugal pump. Design/methodology/approach A third-order sub-grid scale (SGS) model containing the rotation rate tensor named the dynamic cubic non-linear model (DCNM) is used for simulating the flow field in a centrifugal pump with a vaned diffuser. The pressure coefficient and velocity distributions are compared with the experimental data. Focusing on the vaneless region, the pressure pulsation, Reynolds stress pulsation and Reynolds stress transport equation are analyzed. Findings The comparison of the calculation results with the experimental data indicates that the DCNM can accurately capture the distributions of pressure and velocity in the vaneless region. Based on the instantaneous pressure signals, the pressure pulsation is analyzed to show that in the vaneless region, the dominant frequency near the impeller is twice the blade passing frequency, whereas it is equal to the blade passing frequency near the diffuser. Further exploration of the Reynolds stress pulsation shows the correlation between the two variables. Additionally, the extreme low frequency of Reynolds stress near the diffuser is found to be related to the rotation instability. To explore the turbulence characteristics in the vaneless region, the Reynolds stress transportation equation is studied. In the vaneless region, the rotation term of the Reynolds stress transport equation is negligible compared to the production term, although the rotation instability is obvious near the diffuser. The production of the Reynolds stress plays the role of redistributing the energy from the uu component to the vv component, except for the region near the impeller outlet. Originality/value The third-order SGS model DCNM has proved to be promising in simulating the rotor–stator interaction. The analysis of the rotation instability and the Reynolds stress transport equation shed light on the further understanding of the rotor–stator interaction.

scholarly journals The Theoretical Description for the Electrochemical Determination of Anti-COVID-19 Drug Umifenovir, Assisted by a Poly(squaraine dye-co-naphthoquinones) Composite with CoO(OH), Paired with CoO2

2020 ◽  
Vol 10 (1) ◽  
pp. 1962-1968
Keyword(s):  
Mathematical Model ◽  
Bifurcation Analysis ◽  
Double Electric Layer ◽  
Electrochemical Determination ◽  
Theoretical Description ◽  
Oscillatory Behavior ◽  
Linear Stability Theory ◽  
Squaraine Dye ◽  
First Time

For the first time, the system with anti-COVID19 drug umivenofir electrochemical determination, assisted by a Squaraine Dye – CoO(OH)/CoO2 composite, has been described theoretically. The mechanism contains hydrolysis, chemical, and electrochemical oxidation stages. The correspondent mathematical model has been developed and analyzed using linear stability theory and bifurcation analysis. Despite the branched character of the mechanism, the composite of Squaraine Dye with CoO(OH)/CoO2 may be an efficient electrode modifier for the umivenofir determination. However, the oscillatory behavior may be possible, but only because of double electric layer influences on the electrochemical stage.

Modeling Separation-Induced Transition Using a Non-Linear Three Equation Turbulence Model and a Reynolds Stress Turbulence Model

2010 ◽  
Author(s):  
Zinon Vlahostergios ◽  
Kyros Yakinthos
Keyword(s):  
Transport Equation ◽  
Reynolds Stress ◽  
Turbulence Model ◽  
Eddy Viscosity ◽  
Turbulence Models ◽  
Viscosity Model ◽  
Transitional Flows ◽  
Eddy Viscosity Model ◽  
Non Linear ◽  
Stress Models

This paper presents an effort to model separation-induced transition on a flat plate with a semi-circular leading edge, by using two advanced turbulence models, the three equation non-linear model k-ε-A2 of Craft et al. [16] and the Reynolds-stress model of Craft [13]. The mechanism of the transition is governed by the different inlet velocity and turbulence intensity conditions, which lead to different recirculation bubbles and different transition onset points for each case. The use of advanced turbulence models in predicting the development of transitional flows has shown, in past studies, good perspectives. The k-ε-A2 model uses an additional transport equation for the A2 Reynolds stress invariant and it is an improvement of Craft et al. [12] non-linear eddy viscosity model. The use of the third transport equation gives improved results in the prediction of the longitudinal Reynolds stress distributions and especially, in flows where transitional phenomena may occur. Although this model is a pure eddy-viscosity model, it borrows many aspects from the more complex Reynolds-stress models. On the other hand, the use of an advanced Reynolds-stress turbulence model, such as the one of Craft [13], can predict many complex flows and there are indications that it can be applied to transitional flows also, since the crucial terms of Reynolds stress generation are computed exactly and normal stress anisotropy is resolved. The model of Craft [13], overcomes the drawbacks of the common used Reynolds-stress models regarding the computation of wall-normal distances and vectors in order to account for wall proximity effects. Instead of these quantities, it employs “normalized turbulence lengthscale gradients” which give the ability to identify the presence of strong inhomogeneity in a flow development, in an easier way. The final results of both turbulence models showed acceptable agreement with the experimental data. In this work it is shown that there is a good potential to model separation-induced transitional flows, with advanced turbulence modeling without any additional use of ad-hoc modifications or additional equations, based on various transition models.

THEORETICAL DESCRIPTION OF DOUBLE BETA DECAY TRACKS IN A GERMANIUM DETECTOR AND OF THEIR DEPENDENCE ON PARTICLE AND NUCLEAR PHYSICS — A REVIEW

2006 ◽  
Vol 21 (06) ◽  
pp. 1159-1188 ◽  
Author(s):  
H. V. KLAPDOR-KLEINGROTHAUS ◽  
I. V. KRIVOSHEINA ◽  
I. V. TITKOVA
Keyword(s):  
Beta Decay ◽  
Nuclear Matrix ◽  
Particle Physics ◽  
Nuclear Physics ◽  
Theoretical Description ◽  
Double Beta Decay ◽  
Matrix Elements ◽  
Ge Detector ◽  
First Time

In this review for the first time a theoretical description of the tracks of events of nuclear double beta decay in a large Ge detector is presented. It is obvious that in principle the shapes and sizes of these tracks — and the corresponding time structure of pulses — depend on particle physics and nuclear physics parameters such as neutrino mass, right-handed current parameters, and nuclear matrix elements. The knowledge of this dependence is of importance, since the key to probe the existence of 0νββ decay beyond observation of a signal at the Q value of the process, Qββ, is the discrimination of ββ events from background γ events (or other events), in almost any double beta decay experiment (see Refs. 2 and 3). In this review Monte-Carlo simulations of tracks of neutrino-accompanied (2νββ) and neutrinoless double beta decay (0νββ) events, and of various kinds of background processes such as multiple and other γ interactions are reported for a large Ge detector. The time history of the evolution of the individual events is followed and the sizes of the events (volumes in the detector inside which the energy of the event is released) are investigated. Effects of the angular correlations of the two electrons in ββ decay, which again depend on the above nuclear and (for 0νββ decay) particle physics parameters, are taken into account and have been calculated for this purpose for the first time on basis of the experimental half-life of 76 Ge and of realistic nuclear matrix elements. It is shown for ββ decay of 76 Ge , that 0νββ events are to a large extent separable from Compton scattering of γ events of the same energy, while double escape peaks of γ-lines show very similar behavior as 0νββ events, and in that sense can be useful for corresponding "calibration" of pulse shapes of the detector. The possibility to distinguish 0νββ events from γ events is found to be essentially independent of the particle physics parameters of the 0νββ process. A brief outlook is given on the potential of future experiments with respect to determination of the particle physics parameters 〈mν〉, 〈λ〉, 〈η〉. It is suggested, that the strategy in future 0νββ research should be, to combine confirmation of the HEIDELBERG-MOSCOW result with determination of the mechanism of the dominating decay, instead of repeating earlier experiments or ideas. The future experiment thus should not use 76 Ge or 136 Xe , but instead 124 Xe .

Disability as a social phenomenon

2020 ◽  
pp. 22-38
Author(s):  
Natalia Guseva ◽  
Vitaliy Berdutin
Keyword(s):  
Social Protection ◽  
Russian Society ◽  
Stage Model ◽  
High Quality ◽  
Rehabilitation Programs ◽  
Current State ◽  
The Social ◽  
Consistent Solution ◽  
First Time

At present, the problem of establishing disability is a point at issue in Russia. Despite the fact that medical criteria for disability are being developed very actively, high-quality methods for assessing social hallmarks are still lacking. Since disability is a phenomenon inherent in any society, each state forms a social and economic policy for people with disabilities in accordance with its level of development, priorities and opportunities. We have proposed a three-stage model, which includes a system for the consistent solution of the main tasks aimed at studying the causes and consequences of the problems encountered today in the social protection of citizens with health problems. The article shows why the existing approaches to the determination of disability and rehabilitation programs do not correspond to the current state of Russian society and why a decrease in the rate of persons recognized as disabled for the first time does not indicate an improvement in the health of the population. The authors proposed a number of measures with a view to correcting the situation according to the results of the study.

The Calculation of Turbulent Diffusion Coefficients in Aquatic Ecosystems

2019 ◽  
Vol 70 (11) ◽  
pp. 3903-3907
Author(s):  
Galina Marusic ◽  
Valeriu Panaitescu
Keyword(s):  
Transport Equation ◽  
Turbulent Diffusion ◽  
Diffusion Coefficients ◽  
Aquatic Ecosystems ◽  
Specific Area ◽  
Left Bank ◽  
The Right ◽  
Prut River

The paper deals with the issues related to the pollution of aquatic ecosystems. The influence of turbulence on the transport and dispersion of pollutants in the mentioned systems, as well as the calculation of the turbulent diffusion coefficients are studied. A case study on the determination of turbulent diffusion coefficients for some sectors of the Prut River is presented. A new method is proposed for the determination of the turbulent diffusion coefficients in the pollutant transport equation for specific sectors of a river, according to the associated number of P�clet, calculated for each specific area: the left bank, the right bank and the middle of the river.

Phytochemical Constituents of Annona reticulata and their Cytotoxic Activity

2020 ◽  
Vol 17 (3) ◽  
pp. 206-210
Author(s):  
Ty Viet Pham ◽  
Thang Quoc Le ◽  
Anh Tuan Le ◽  
Hung Quoc Vo ◽  
Duc Viet Ho
Keyword(s):  
Cytotoxic Activity ◽  
Cell Lines ◽  
Structural Determination ◽  
Phytochemical Investigation ◽  
Ic50 Values ◽  
Phytochemical Constituents ◽  
First Time ◽  
Annona Reticulata

A phytochemical investigation of the leaves of Annona reticulata led to the isolation and structural determination of β-sitosterol (1), ent-pimara-8(14),15-dien-19-oic acid (2), ent-pimara- 8(14),15-dien-19-ol (3), quercetin (4), quercetin 3-O-α-L-arabinopyranoside (5), and a mixture of quercetin 3-O-β-D-galactopyranoside (6a) and quercetin 3-O-β-D-glucopyranoside (6b). Of these, compounds 2 and 3 were isolated from the genus Annona for the first time. Compound 3 showed strong cytotoxicity against SK-LU-1 and SW626 cell lines with IC50 values of 17.64 ± 1.07 and 19.79 ± 1.41 μg mL-1, respectively.

Development of an HPLC-UV Method for Quantification of Stattic

2019 ◽  
Vol 15 (6) ◽  
pp. 568-573
Author(s):  
Soheil Sedaghat ◽  
Ommoleila Molavi ◽  
Akram Faridi ◽  
Ali Shayanfar ◽  
Mohammad Reza Rashidi
Keyword(s):  
High Performance ◽  
Accurate Method ◽  
Plasma Samples ◽  
Promising Target ◽  
Relative Standard ◽  
Dimerization Inhibitor ◽  
Oncogenic Protein ◽  
First Time ◽  
Transcription 3

Background: Signal transducer and activator of transcription 3 (STAT3), an oncogenic protein found constitutively active in many types of human malignancies, is considered to be a promising target for cancer therapy. Objective: In this study for the first time, a simple and accurate method has been developed for the determination of a STAT3 dimerization inhibitor called stattic in aqueous and plasma samples. Methods: A reverse-phase high-performance liquid chromatography (RP-HPLC) composed of C18 column as stationary phase, and the mixture of acetonitrile (60%) and water (40%) as mobile phase with a UV detection at 215 nm were applied for quantification of stattic. The developed method was validated by Food and Drug Administration (FDA) guideline. Results: The method provided a linear range between 1-40 and 2.5-40 µg mL-1 for aqueous and plasma samples, respectively, with a correlation coefficient of 0.999. The accuracy (as recovery) of the developed method was found to be between 95-105% for aqueous medium and 85-115% for plasma samples. The precision (as relative standard deviation) for aqueous and plasma samples was less than 6% and 15%, respectively. The sensitivity of the developed method based on FDA guideline was 1 µg mL-1 for aqueous and 2.5 µg mL-1 for plasma samples. Conclusion: These results show that the established method is a fast and accurate quantification for stattic in aqueous and plasma samples.

Carbon dots derived from Fusobacterium nucleatum for intracellular determination of Fe3+ and bioimaging both in vitro and in vivo

2021 ◽  
Author(s):  
Lijuan Liu ◽  
Shengting Zhang ◽  
Xiaodan Zheng ◽  
Hongmei Li ◽  
Qi Chen ◽  
...  
Keyword(s):  
Carbon Dots ◽  
Fusobacterium Nucleatum ◽  
Living Cells ◽  
First Time ◽  
Fluorescent Carbon Dots ◽  
Fluorescent Carbon

Fusobacterium nucleatum has been employed for the first time to synthesize fluorescent carbon dots which could be applied for the determination of Fe3+ ions in living cells and bioimaging in vitro and in vivo with excellent biocompatibility.

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