On Pressure-Velocity Correlation of Steady and Oscillating Flows in Regenerators Made of Wire Screens

1999 ◽  
Vol 121 (1) ◽  
pp. 52-56 ◽  
Author(s):  
Chin-Tsau Hsu ◽  
Huili Fu ◽  
Ping Cheng
Keyword(s):  
Pressure Drop ◽  
Reynolds Numbers ◽  
Steady Flows ◽  
Oscillating Flows ◽  
Velocity Correlation ◽  
Boundary Layer Effect ◽  
Wide Range ◽  
Layer Effect ◽  
High Reynolds ◽  
Very High

A facility capable of generating steady and oscillating flows was constructed and experiments were conducted to investigate the pressure-drop characteristics of regenerators packed with wire screens. Both the velocity and pressure-drop across the regenerator were measured. To accurately determine the correlation between pressure-drop and velocity, the experiments covered a wide range from very low to very high Reynolds numbers, Reh. The steady flow results reveal that a three-term correlation with a term proportional to Reh−1/2 in addition to the Darcy-Forchheimer two-term correlation will fit best to the data. This Reh−1/2 term accounts for the boundary layer effect at intermediate Reynolds number. The results also show that the correlation for oscillating flows coincides with that for steady flows in 1 < Reh < 2000. This suggests that the oscillating flows in the regenerators behave as quasi-steady at the frequency range of less than 4.0 Hz, which is the maximum operable oscillating flow frequency of the facility.

Experimental evidence for the theory of local isotropy

1948 ◽  
Vol 44 (4) ◽  
pp. 560-565 ◽  
Author(s):  
A. A. Townsend ◽  
Geoffrey Taylor
Keyword(s):  
Isotropic Turbulence ◽  
Reynolds Numbers ◽  
Velocity Correlation ◽  
Integral Scale ◽  
Local Isotropy ◽  
High Reynolds Numbers ◽  
Wide Range ◽  
Skewness Factor ◽  
High Reynolds ◽  
Image Position

Some new measurements of isotropic turbulence produced behind a biplane grid have been made at high Reynolds numbers, and these results are compared with the predictions of the theory of local isotropy developed by A. N. Kolmogoroff. The transverse double-velocity correlation has been measured at mesh Reynolds numbers up to 3·2 × 105, and the observed form agrees well with the predicted form. Measurements of the skewness factor of velocity differences over finite intervals have also been made, and the factor is nearly constant and equal to −0·38, if the interval is small compared with the integral scale. The invariance of dimensionless functions of the velocity derivatives has been confirmed for the flattening factor of ∂u/∂x, namely,which is nearly constant over a wide range of conditions. It is concluded that the theory of local isotropy is substantially correct for isotropic turbulence of high Reynolds number.

scholarly journals Spectral modelling for passive scalar dynamics in homogeneous anisotropic turbulence

2016 ◽  
Vol 799 ◽  
pp. 159-199 ◽  
Author(s):  
A. Briard ◽  
T. Gomez ◽  
C. Cambon
Keyword(s):  
Isotropic Turbulence ◽  
Reynolds Numbers ◽  
Passive Scalar ◽  
Homogeneous Isotropic Turbulence ◽  
Scalar Flux ◽  
Anisotropic Turbulence ◽  
Theoretical Predictions ◽  
High Reynolds ◽  
Shear Driven Flows ◽  
Very High

The present work aims at developing a spectral model for a passive scalar field and its associated scalar flux in homogeneous anisotropic turbulence. This is achieved using the paradigm of eddy-damped quasi-normal Markovian (EDQNM) closure extended to anisotropic flows. In order to assess the validity of this approach, the model is compared to several detailed direct numerical simulations (DNS) and experiments of shear-driven flows and isotropic turbulence with a mean scalar gradient at moderate Reynolds numbers. This anisotropic modelling is then used to investigate the passive scalar dynamics at very high Reynolds numbers. In the framework of homogeneous isotropic turbulence submitted to a mean scalar gradient, decay and growth exponents for the cospectrum and scalar energies are obtained analytically and assessed numerically thanks to EDQNM closure. With the additional presence of a mean shear, the scaling of the scalar flux and passive scalar spectra in the inertial range are investigated and confirm recent theoretical predictions. Finally, it is found that, in shear-driven flows, the small scales of the scalar second-order moments progressively return to isotropy when the Reynolds number increases.

scholarly journals Radiation and Energetic Analysis of Nanofluid Based Volumetric Absorbers for Concentrated Solar Power

Nanomaterials ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 838 ◽  
Author(s):  
Jan Eggers ◽  
Eckart Lange ◽  
Stephan Kabelac
Keyword(s):  
Radiation Energy ◽  
Reynolds Numbers ◽  
Numerical Approach ◽  
Working Fluid ◽  
Concentrated Solar Power ◽  
Optical Efficiency ◽  
Solar Absorber ◽  
Energetic Analysis ◽  
High Reynolds ◽  
Very High

Recently, several publications gave attention to nanofluid based solar absorber systems in which the solar radiation energy is directly absorbed in the volume of the fluid. This idea could provide advantages over conventionally used surface absorbers regarding the optical and thermal efficiency. For the evaluation of this concept, a numerical approach is introduced and validated in this contribution. The results show that the optical efficiency of a volumetric absorber strongly depends on the scattering behavior of the nanofluid and can reach competitive values only if the particle size distribution is narrow and small. If this is achieved, the surface temperature and therefore the heat loss can be lowered significantly. Furthermore, the surface absorber requires very high Reynolds numbers to transfer the absorbed energy into the working fluid and avoid overheating of the absorber tube. This demand of pumping power can be reduced significantly using the concept of volumetric absorption.

scholarly journals Stagnation Region Heat Transfer Augmentation at Very High Turbulence Levels

2015 ◽  
Author(s):  
J. E. Kingery ◽  
F. E. Ames
Keyword(s):  
Heat Transfer ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Bypass Transition ◽  
Stagnation Region ◽  
Heat Transfer Augmentation ◽  
Wide Range ◽  
High Turbulence ◽  
Very High ◽  
Turbulence Generator

A database for stagnation region heat transfer has been extended to include heat transfer measurements acquired downstream from a new high intensity turbulence generator. This work was motivated by gas turbine industry heat transfer designers who deal with heat transfer environments with increasing Reynolds numbers and very high turbulence levels. The new mock aero-combustor turbulence generator produces turbulence levels which average 17.4%, which is 37% higher than the older turbulence generator. The increased level of turbulence is caused by the reduced contraction ratio from the liner to the exit. Heat transfer measurements were acquired on two large cylindrical leading edge test surfaces having a four to one range in leading edge diameter (40.64 cm and 10.16 cm). Gandvarapu and Ames [1] previously acquired heat transfer measurements for six turbulence conditions including three grid conditions, two lower turbulence aero-combustor conditions, and a low turbulence condition. The data are documented and tabulated for an eight to one range in Reynolds numbers for each test surface with Reynolds numbers ranging from 62,500 to 500,000 for the large leading edge and 15,625 to 125,000 for the smaller leading edge. The data show augmentation levels of up to 136% in the stagnation region for the large leading edge. This heat transfer rate is an increase over the previous aero-combustor turbulence generator which had augmentation levels up to 110%. Note, the rate of increase in heat transfer augmentation decreases for the large cylindrical leading edge inferring only a limited level of turbulence intensification in the stagnation region. The smaller cylindrical leading edge shows more consistency with earlier stagnation region heat transfer results correlated on the TRL (Turbulence, Reynolds number, Length scale) parameter. The downstream regions of both test surfaces continue to accelerate the flow but at a much lower rate than the leading edge. Bypass transition occurs in these regions providing a useful set of data to ground the prediction of transition onset and length over a wide range of Reynolds numbers and turbulence intensity and scales.

Entry Length Requirements for Two- and Three-Dimensional Laminar Couette–Poiseuille Flows

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Bayode E. Owolabi ◽  
David J. C. Dennis ◽  
Robert J. Poole
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Channel Height ◽  
Development Length ◽  
Square Duct ◽  
Entry Length ◽  
Wide Range ◽  
High Reynolds ◽  
Pressure Driven Flow ◽  
Poiseuille Flows

In this study, we examine the development length requirements for laminar Couette–Poiseuille flows in a two-dimensional (2D) channel as well as in the three-dimensional (3D) case of flow through a square duct, using a combination of numerical and experimental approaches. The parameter space investigated covers wall to bulk velocity ratios, r, spanning from 0 (purely pressure-driven flow) to 2 (purely wall driven-flow; 4 in the case of a square duct) and a wide range of Reynolds numbers (Re). The results indicate an increase in the development length (L) with r. Consistent with the findings of Durst et al. (2005, “The Development Lengths of Laminar Pipe and Channel Flows,” ASME J. Fluids Eng., 127(6), pp. 1154–1160), L was observed to be of the order of the channel height in the limit as Re→0, irrespective of the condition at the inlet. This, however, changes at high Reynolds numbers, with L increasing linearly with Re. In all the cases considered, a uniform velocity profile at the inlet was found to result in longer entry lengths than in a flow developing from a parabolic inlet profile. We show that this inlet effect becomes less important as the limit of purely wall-driven flow is approached. Finally, we develop correlations for predicting L in these flows and, for the first time, also present laser Doppler velocimetry (LDV) measurements of the developing as well as fully-developed velocity profiles, and observe good agreement between experiment, analytical solution, and numerical simulation results in the 3D case.

A multiple relaxation time extension of the constant speed kinetic model

2016 ◽  
Vol 27 (08) ◽  
pp. 1650088 ◽  
Author(s):  
Abed Zadehgol ◽  
Mahmud Ashrafizaadeh
Keyword(s):  
Relaxation Time ◽  
Kinetic Model ◽  
Reynolds Numbers ◽  
Constant Speed ◽  
Benchmark Problems ◽  
Multiple Relaxation Time ◽  
Time Extension ◽  
High Reynolds ◽  
The Stability ◽  
Very High

In this work, a multiple relaxation time (MRT) extension of the recently introduced constant speed kinetic model (CSKM) is proposed. The CSKM, which is an entropic kinetic model and based on unconventional entropies of Burg and Tssalis, was introduced in [A. Zadehgol and M. Ashrafizaadeh, J. Comput. Phys. 274, 803 (2014)]; [A. Zadehgol Phys. Rev. E 91, 063311 (2015)] as an extension of the model of Boghosian et al. [Phys. Rev. E 68, 025103 (2003)] in the limit of fixed speed continuous velocities. The present extension improves the stability of the previous models at very high Reynolds numbers, while allowing for a more convenient orthogonal lattice. The model is verified by solving the following benchmark problems: (i) the lid driven square cavity and (ii) the Kelvin–Helmholtz instability of thin shear layers in a doubly periodic square domain.

Numerical Integration Procedure for the Steady State Navier-Stokes Equations

1969 ◽  
Vol 11 (5) ◽  
pp. 445-453 ◽  
Author(s):  
A. K. Runchal ◽  
M. Wolfshtein
Keyword(s):  
Stokes Equations ◽  
Computing Time ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Square Cavity ◽  
Constant Property ◽  
Navier Stokes Equations ◽  
High Reynolds ◽  
Very High ◽  
Numerical Integration Procedure

A procedure is proposed for the integration of the full Navier-Stokes equations for constant-property two-dimensional flows. In contrast with earlier procedures, the present one is capable of dealing with cases of very high Reynolds number. The power of the new procedure is demonstrated in two cases: (1) the square recirculating eddy, for which no solution was previously available for Reynolds numbers larger than about 400, and (2) an impinging jet, for which no solution was available previously. The procedure has also been applied to the square cavity at Reynolds numbers below 400; it gives results of an accuracy comparable with that of previous solutions, but with a smaller computing time.

Investigations of the Flow in Curved Ducts at Large Reynolds Numbers

1948 ◽  
Vol 15 (4) ◽  
pp. 344-348
Author(s):  
J. R. Weske
Keyword(s):  
Reynolds Number ◽  
Pressure Drop ◽  
Boundary Layers ◽  
Reynolds Numbers ◽  
Equation Of Motion ◽  
Radius Ratio ◽  
High Reynolds Numbers ◽  
Net Pressure ◽  
High Reynolds ◽  
Curved Ducts

Abstract It is found that the flow in curved ducts at high Reynolds numbers may be analyzed by methods adapted from the theory of boundary layers. Integration of the equation of motion of the “shedding layer” led to relations for the net pressure drop of curved ducts as a function of radius ratio and of Reynolds number.

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