Nonideal mixer as a source of random fluctuations

1984 ◽  
Vol 49 (4) ◽  
pp. 772-792
Author(s):  
Vladimír Kudrna ◽  
Pavel Hasal ◽  
Jitka Vyhlídková
Keyword(s):  
Turbulent Flow ◽  
Flow Velocity ◽  
Linear Filter ◽  
Residence Times ◽  
Random Fluctuations

An attempt is made here to describe distribution of residence times of a fluid in a nonideal flow mixer for turbulent flow of the charge, i.e. for the case when the flow velocity exhibits random fluctuations. The analysis is based on the assumption that the flow of fluid in mixer may be considered as a stationary Markov's process and is aimed at application of the mixer as a linear filter.

Smoothing of stationary random signal in continuous flow mixer with gamma-distribution of residence times

1985 ◽  
Vol 50 (11) ◽  
pp. 2545-2557
Author(s):  
Pavel Hasal ◽  
Vladimír Kudrna ◽  
Jitka Vyhlídková
Keyword(s):  
Theoretical Analysis ◽  
Gamma Distribution ◽  
Continuous Flow ◽  
Random Signal ◽  
Linear Filter ◽  
Residence Times ◽  
Statistical Parameters ◽  
Basic Parameters

The paper is focused on a theoretical analysis of the function of continuous flow mixer with the so-called gamma-distribution of fluid residence times, used as a linear filter smoothing undesirable fluctuations of input properties. A relation is derived expressing the degree of smoothing of the signal passing through the system, as a function of statistical parameters of this signal and of gamma-distribution of fluid-residence times in the mixer. The analysis of this relation leads to conclusions concerning the prediction of the operation of smoothing mixers or the design of their basic parameters.

Rate of advancement of reactions in turbulent flows

1964 ◽  
Vol 17 (8) ◽  
pp. 821 ◽  
Author(s):  
RCL Bosworth ◽  
CM Groden
Keyword(s):  
Laminar Flow ◽  
Turbulent Flow ◽  
Turbulent Flows ◽  
Residence Time ◽  
Time Distribution ◽  
Residence Time Distribution ◽  
Residence Times ◽  
Cylindrical Reactor ◽  
The Times ◽  
Very High

When a reacting substance or mixture is caused to flow in a cylindrical reactor, all portions of the stream will not flow at the same rate and will exhibit different residence times and, accordingly, are subject to different extents of degrees of reaction. The average degrees of reaction following the residence time distribution proper to laminar flow are given in the earlier publication1 and this paper extends the treatment to that of turbulent flow. In the earlier treatment of laminar flow the ratio of average extent of reaction with non-interacting streams to that of complete intermingling, or the C/Cm, is plotted against the ratio of the times of flow with those of reaction (S). The C/Cm versus S curves are all above unity and increase with increasing S, with the exception of very high orders of chemical reaction for which values of C/Cm are all unity. In the case of turbulent flow the values of C/Cm are more nearly unity at all values of S.

The determination of transverse pulsations of turbulent flow velocity in fast-axial flow CO2 laser by phase-conjugation method

2005 ◽  
Author(s):  
S. A. Buyarov ◽  
M. G. Galuskin ◽  
V. D. Dubrov ◽  
V. Y. Panchenko ◽  
Yu. N. Zavalov
Keyword(s):  
Turbulent Flow ◽  
Flow Velocity ◽  
Phase Conjugation ◽  
Axial Flow ◽  
Conjugation Method

Direct numerical simulation of turbulent flow over a modeled riblet covered surface

1995 ◽  
Vol 302 ◽  
pp. 333-376 ◽  
Author(s):  
D. Goldstein ◽  
R. Handler ◽  
L. Sirovich
Keyword(s):  
Turbulent Flow ◽  
Drag Reduction ◽  
Flow Velocity ◽  
Body Force ◽  
Complex Geometry ◽  
Cross Flow ◽  
Immersed Boundary ◽  
Computational Domain ◽  
Mean Flow ◽  
Velocity Fluctuations

An immersed boundary technique is used to model a riblet covered surface on one wall of a channel bounding fully developed turbulent flow. The conjecture that the beneficial drag reduction effect of riblets is a result of the damping of cross-flow velocity fluctuations is then examined. This possibility has been discussed by others but is unverified. The damping effect is explicitly modelled by applying a cross-flow damping force field in elongated streamwise zones with a height and spacing corresponding to the riblet crests. The same trends are observed in the turbulence profiles above both riblet and damped surfaces, thus supporting cross-flow damping as a beneficial mechanism. It is found in the examples presented that the effect of the riblets on the mean flow field quantities (mean velocity profile, velocity fluctuations, Reynolds shear stress, and low–speed sreak spacing) is small. The riblests cause a relatively small drag reduction of about 4%, a figure that is in rough agreement with experiments and other computations. The simulations also suggest a mechanism for the observed displacement of the turbulence quantities away from the wall.The immersed boundary technique used to model the riblets consists of creating an externally imposed spatially localized body force which opposes the flow velocity and creates a riblet-like surface. For unstead viscous flow the calculation of the force is done with a feedback scheme in which the velocity is used to iteratively determine the desired value. In particular, the surface body force is determined by the relation f(xs, t) = α ∫ t0U(xs,t′)dt′ + βU(xs, t) for surface points xs, velocity U time t and negative constants α and β. All simulations are done with a spectral code in a single computational domain without any mapping of the mesh. The combination of the immersed boundary and spectral techniques can potentially be used to solve other problems having complex geometry and flow physics.

The effect of turbulence on the cost of swimming for juvenile Atlantic salmon (Salmo salar)

2003 ◽  
Vol 60 (9) ◽  
pp. 1149-1160 ◽  
Author(s):  
Eva C Enders ◽  
Daniel Boisclair ◽  
André G Roy
Keyword(s):  
Atlantic Salmon ◽  
Turbulent Flow ◽  
Flow Velocity ◽  
Turbulent Flows ◽  
Salmo Salar ◽  
Forced Swimming ◽  
Mean Flow ◽  
Atlantic Salmon Salmo Salar ◽  
Juvenile Atlantic Salmon ◽  
Wide Range

Fish activity costs are often estimated by transforming their swimming speed in energy expenditures with respirometry models developed while forcing fish to swim against a flow of constant velocity. Forced swimming models obtained using a procedure that minimizes flow heterogeneity may not represent the costs of swimming in rivers characterized by turbulence and by a wide range of instantaneous flow velocities. We assessed the swimming cost of juvenile Atlantic salmon (Salmo salar) in turbulent flows using two means (18 and 23 cm·s–1) and two standard deviations of flow velocity (5 and 8 cm·s–1). Twenty respirometry experiments were conducted at 15 °C with fish averaging 10 g. Our results confirmed that swimming costs are affected by the level of turbulence. For a given mean flow velocity, swimming costs increased 1.3- to 1.6-fold as turbulence increased. Forced swimming models under estimated actual swimming costs in turbulent flow by 1.9- to 4.2-fold. Spontaneous swimming models overestimated the real cost of swimming in turbulent flow by 2.8- to 6.6-fold. Our analyses suggest that models in which both the mean and the standard deviation of flow velocity are explicitly represented are needed to adequately estimate the costs of swimming against turbulent flows.

scholarly journals Analysis of Turbulent Flow Structure with Its Fluvial Processes around Mid-Channel Bar

2021 ◽  
Vol 14 (1) ◽  
pp. 392
Author(s):  
Md. Amir Khan ◽  
Nayan Sharma ◽  
Jaan Pu ◽  
Faisal M. Alfaisal ◽  
Shamshad Alam ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flow ◽  
Flow Velocity ◽  
Turbulent Kinetic Energy ◽  
Production Rate ◽  
Energy Transport ◽  
Vertical Distance ◽  
Scour Hole ◽  
The Impact ◽  
Channel Bar

Researchers have recognized that the successive growth of mid-channel bar deposits can be entertained as the raison d’être for the initiation of the braiding process, which is closely interlinked with the growth, decay, and vertical distribution of fluvial turbulent kinetic energy (TKE). Thus, focused analysis on the underlying mechanics of turbulent flow structures in the proximity of a bar deposit occurring in the middle of the channel can afford crucial scientific clues for insight into the initiating fluvial processes that give rise to braiding. In the study reported herein, a physical model of a mid-channel bar is constructed in an experimental flume to analyze the turbulence parameters in a region close to the bar. Notably, the flow velocity plays an important role in understanding the flow behavior in the scour-hole location in the upstream flow divergence zone as well as near the downstream zone of flow convergence in a mid-channel bar. Therefore, the fluctuating components of turbulent flow velocity are herein discussed and analyzed for the regions located close to the bar. In the present study, the impact of the mid-channel bar, as well as its growth in turbulent flow, on higher-order velocity fluctuation moments are investigated. For near-bed locations, the results show the dominance of ejection events in upstream zones and the dominance of sweep events at locations downstream of the mid-channel bar. In scour-hole sections, the negative value of the stream-wise flux of turbulent kinetic energy and the positive value of the vertical flux of turbulent kinetic energy indicate energy transport in downward and forward directions, respectively. The downward and forward energy transport processes lead to scouring at these locations. The maximum turbulent production rate occurs in the wake region of the bar. The high rate of turbulence production has occurred in that region, which can be ascribed to the process of shedding turbulent vortices. The results show that the impact of the presence of the bar is mainly restricted to the lower layers of flow. The turbulent dissipation rate monotonically decreases with an increase in the vertical distance from the bed. The turbulent production rate first increases and then decreases with successive increases in the vertical distance from the bed. The paper concludes with suggestions for the future potential use of the present research for the practical purpose of examining braid bar occurrences in alluvial rivers to develop an appropriate response through training measures.

Prediction of mean turbulent flow velocity in a permeable-walled pipe

2019 ◽  
Vol 573 ◽  
pp. 648-660 ◽  
Author(s):  
Shuolin Li ◽  
Wenxin Huai ◽  
Nian-Sheng Cheng ◽  
Giovanni Coco
Keyword(s):  
Turbulent Flow ◽  
Flow Velocity

Turbulent Flow Structure around a Horizontal Circular Cylinder Placed on a Rough Bed

2021 ◽  
Author(s):  
prashanth hanmaiahgari ◽  
kalpana devi
Keyword(s):  
Boundary Layer ◽  
Circular Cylinder ◽  
Turbulent Flow ◽  
Flow Velocity ◽  
Reynolds Shear Stress ◽  
Reynolds Numbers ◽  
Reattachment Length ◽  
Natural Streams ◽  
Rough Bed ◽  
Horizontal Circular Cylinder

<p>Pipelines that traverse a river are often buried beneath the river bed. However, the pipeline may be exposed due to scoured riverbed during floods. The exposed pipeline vibrates in a frequency band depending upon the flow velocity, size, and shape of the pipe. These vibrations are detrimental to the pipeline safety and stability due to their cyclic nature. In fact, these vibrations are induced by the turbulence around the cylinder which is a function of the flow velocity apart from the diameter of the cylinder and the bed roughness. The main objective of this paper is to investigate the structure of turbulent flow in the recirculation, reattachment and recovery regions behind a horizontal circular cylinder placed on the rough bed. In this direction, different experiments were conducted in a wide flume for various flow Reynolds numbers and cylinder Reynolds numbers. The Acoustic Doppler Velocimetry (ADV) was used for measuring the instantaneous point velocities. The raw velocity data were properly processed before the analysis. The approach flow was found to be a canonical near wall turbulent flow. In the immediate downstream of the cylinder, flow is characterized by recirculation, boundary layer reattachment and recovery. The reattachment length was determined using the established forward fraction method and reattachment length is independent of the flow Reynolds number. In addition, enhanced turbulence intensities, Reynolds shear stress, and turbulent kinetic energy were observed in the separated shear layer and they rapidly decreased in the recovery region. The present investigation will boost the understanding of hydraulics of flow around the horizontal bed-mounted cylindrical objects in rough bed natural streams under different flow conditions.</p><p><strong>Keywords: </strong>Wall mounted horizontal cylinder; Boundary layer; Separated and reattached turbulent flows; Wall Wake flows; ADV; Open channel flow.</p>

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