Turbulent wake behavior with axial pressure gradients

1975 ◽  
Vol 2 (5-6) ◽  
pp. 261-266
Author(s):  
F. Pittaluga
Keyword(s):  
Turbulent Wake ◽  
Pressure Gradients ◽  
Axial Pressure

Investigation on Header Manifold Model Effect at CANDU6 Large Loss of Cooling Accident

2008 ◽  
Author(s):  
Daniel Dupleac ◽  
Ilie Prisecaru ◽  
Mirea Mladin ◽  
Gheorghe Negut ◽  
Petre Ghitescu
Keyword(s):  
Nuclear Power ◽  
Flow Distribution ◽  
Strong Impact ◽  
Pressure Gradients ◽  
Axial Pressure ◽  
Nuclear Power Reactor ◽  
Pressure Drops ◽  
Candu Reactors ◽  
Loss Of Coolant Accident ◽  
Pressure Tubes

In a CANDU 6 nuclear power reactor fuel bundles are supported in horizontal Zircaloy pressure tubes tube through which the heavy-water coolant flows. 95 pressure tubes are connected by individual feeders to a common header. For CANDU 6 safety analyses, even when multiple channels model is employed, only one node is used for header. In this approach, all the channels are subjected to the same boundary condition. However, site inlet and outlet header pressure measurements and ultrasonic feeder flow data, confirm the existence of axial pressure gradients along the inlet and outlet headers. These axial pressure gradients would give rise to individual header-to-header pressure drops for each channel and also to flow distribution throughout both the inlet and outlet headers. In this paper, the header manifold model effect on the large break loss of coolant accident analyses of CANDU reactors has been performed by RELAP5/ mod 3.4 code. The 35% reactor inlet header break was selected for this study, as this break size produce the highest fuel clad temperature among all postulated breaks size. The results obtained considering the header manifold model, show that location of fuel channel upon break location has a strong impact on peak clad temperature calculation.

On steady columnar vortices under local compression

1995 ◽  
Vol 299 ◽  
pp. 367-388 ◽  
Author(s):  
Roberto Verzicco ◽  
Javier Jiménez ◽  
Paolo Orlandi
Keyword(s):  
Turbulent Flows ◽  
Reynolds Numbers ◽  
Pressure Gradients ◽  
Axial Pressure ◽  
Velocity Signal ◽  
Long Time Behaviour ◽  
Long Time ◽  
Axial Stretching ◽  
Theoretical Analyses ◽  
Massive Separation

Numerical simulations are presented of the long time behaviour of viscous columnar vortices subject to non-uniform axial stretching. The relevant result is that the vortices reach a steady state even when the axial average of the strain is zero, such that they are being compressed during half of their extent. The structure of the flow is analysed and shown to range from local Burgers equilibrium to massive separation. For an intermediate range of Reynolds numbers the vortices are more or less uniform and compact, and it is suggested that this condition is related to the strong vortices observed in turbulent flows. The reason for the survival of the vortices under compression is traced to induced axial pressure gradients and to the viscous cancellation of outgoing vorticity. Theoretical analyses of the linear Burgers’ regime and of the onset of separation are presented and compared to the numerical experiments. The results are related to the observation of intermittency in turbulence, and shown to be consistent both with the observed scaling of vortex diameter, and with the lack of intermittency of the velocity signal.

Arbitrary Mean Flow in Adverse Pressure Gradients

1971 ◽  
Vol 93 (4) ◽  
pp. 495-499 ◽  
Author(s):  
G. M. Bragg ◽  
J. K. Suk
Keyword(s):  
Adverse Pressure Gradient ◽  
Maximum Error ◽  
Velocity Profiles ◽  
Turbulent Wake ◽  
Pressure Gradients ◽  
Local Velocity ◽  
Calculation Methods ◽  
Mean Flow ◽  
Mean Velocity ◽  
Made In

Measurements of mean velocity profiles were made in the turbulent wake behind a single cylinder as well as a row of parallel, arbitrarily spaced and arbitrarily sized cylinders with an adverse pressure gradient. Two currently available calculation methods, based on a simple superposition of momentum, and a step-by-step finite difference procedure, were applied to the prediction of mean velocity profiles in the wake. The agreement between the predicted and the observed results is good in most cases with maximum error less than 18 percent of significant velocity defects or 3 percent of local velocity.

Axially Symmetric Laminar Free Mixing With Large Swirl

1962 ◽  
Vol 84 (4) ◽  
pp. 370-374 ◽  
Author(s):  
Martin H. Steiger ◽  
Martin H. Bloom
Keyword(s):  
Boundary Layer ◽  
Compressible Flow ◽  
Free Stream ◽  
A Priori ◽  
Radial Pressure ◽  
Pressure Gradients ◽  
Axially Symmetric ◽  
Axial Pressure ◽  
Integral Methods ◽  
Special Case

Viscous laminar axially symmetric free mixing with large swirl is investigated by a boundary-layer type of analysis with integral methods. Large swirl generates axial pressure gradients as well as large radial pressure gradients, and therefore alters the streamwise flow. Examples calculated for both incompressible and compressible flow show that the wake may be significantly lengthened by large swirl. However, this effect is shown to be diminished in the compressible case where higher free-stream Mach numbers lead to decreased densities, and to decreased centrifugal effects, decreased radial pressure gradients, and decreased axial pressure gradients. In the limiting special case of small or moderate swirl the results agree with those previously obtained by Steiger and Bloom [1] in analysis wherein the induced pressure gradients were neglected a priori.

Laminar Mixing in the Presence of Axial Pressure Gradients

1961 ◽  
Vol 28 (1) ◽  
pp. 73-75 ◽  
Author(s):  
L. G. Napolitano ◽  
A. Pozzi
Keyword(s):  
Pressure Gradients ◽  
Axial Pressure ◽  
Laminar Mixing

Free Turbulent Mixing in Axial Pressure Gradients

1973 ◽  
Vol 40 (2) ◽  
pp. 375-380 ◽  
Author(s):  
G. J. Hokenson ◽  
J. A. Schetz
Keyword(s):  
Flow Field ◽  
Turbulent Mixing ◽  
Eddy Viscosity ◽  
Static Pressure ◽  
Initial Conditions ◽  
Near Field ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Axial Pressure ◽  
Flow Equations

The results of an experimental investigation of the free turbulent mixing of wakes and jets in axial pressure gradients are presented. The data include static pressure and velocity profiles and the turbulent intensity which is presented in terms of the parameter u′cL2¯(Δu)max2. It is hypothesized that the representation of the Reynolds stress by a generalized Clauser eddy viscosity model is scaled by this parameter. The experimentally observed dependence of this turbulence quantity on flow field dimensionality and the imposed pressure gradient places more stringent demands on the form of the eddy viscosity than has been shown before. However, the experimental data reveal some fortuitous behavior which aids in the specification of the spatial dependence of the turbulence parameter, leaving the scaling to be determined primarily by the initial conditions, i.e., the state of the turbulence in the near field. Substantial lateral static pressure gradients were observed in all two-dimensional cases studied. It is shown that the boundary-layer form of the viscous flow equations are inadequate in such cases, and a numerical solution of a system of equations that includes an approximate form of the lateral momentum equation provides predictions in good agreement with the data for the mean flow field.

scholarly journals Bidirectional Brush Seals – Post-Test Analysis

1999 ◽  
Vol 5 (3) ◽  
pp. 167-180 ◽  
Author(s):  
Robert C. Hendricks ◽  
Jack Wilson ◽  
Tom Y. Wu ◽  
Ralph Flower ◽  
Robert L. Mullen
Keyword(s):  
Pressure Gradients ◽  
Wave Rotor ◽  
Axial Pressure ◽  
Test Analysis ◽  
Pressure Drops ◽  
Pressure Profiles ◽  
Response Range ◽  
Post Test ◽  
Brush Seals ◽  
Outside Diameter

A post-test analysis of a set of inside-diameter/outside-diameter (ID/OD) bidirectional brush seals used in three-port wave rotor tests was undertaken to determine brush bristle and configuration wear, pullout, and rotor coating wear. The results suggest that sharp changes in the pressure profiles were not well reflected in bristle tip configuration patterns or wear. Also, positive-to-negative changes in axial pressure gradients appeared to have little effect on the backing plates. Although the brushes had similar porosities, they had very different unpacked arrays. This difference could explain the departure of experimental data from computational fluid dynamics flow predictions for well-packed arrays at higher pressure drops. The rotor wear led to “car track” scars (upper and lower wear bands) with a whipped surface between the bands. Those bands may have resulted from bristle stiffening at the fence and gap plates during alternate portions of the rotor cycle. Within the bristle response range the wear surface reflected the pressure distribution effect on bristle motion. No sacrificial metallurgical data were taken. The bristles did wear, with correspondingly more wear on the ID brush configurations than on the OD configurations; the complexity in constructing the ID brush was a factor.

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