An Approach for the Scanning and Construction of Biofouled Surfaces to be used for Drag Measurements

2017 ◽  
Author(s):  
Christina Dehn ◽  
Eric Holm ◽  
Peter Chang ◽  
Abel Vargas ◽  
Scott Storms
Keyword(s):  
Channel Flow ◽  
Laser Scanning ◽  
Surface Characterization ◽  
Rough Surfaces ◽  
Surface Preparation ◽  
Turbulent Channel Flow ◽  
Geometric Parameters ◽  
Navier Stokes ◽  
Ship Hulls ◽  
Cfd Method

A methodology for digitizing and processing calcareous biofouling typically found on US Navy ship hulls has been developed. Panels that were immersed in seawater and allowed to grow biofouling were captured using 3-D laser scanning. The advantage of these digital replicas over real biofouled rough surfaces are many-fold: the surfaces can be manipulated to meet channel flow and large eddy simulation (LES) viscous size constraints; 3-D printing can then be used to build scaled rough surfaces that can be used in the fully developed turbulent channel flow; complex statistical and geometric parameters that encapsulate drag-producing physics can be computed; subregions of the surfaces can be tiled together to create composite surfaces that can span various parameter spaces. This paper describes, in detail, the digitizing, surface preparation, and 3-D printing methodologies. In addition, it describes the surface characterization software. Data from nine scanned surfaces, with biofouling from coastal Florida and Pearl Harbor, Hawaii are shown with preliminary correlations between pierside data and more complex geometric parameters. The work described herein is part of a larger project to develop a fast and accurate ReynoldsAveraged Navier Stokes (RANS) computational fluid dynamics (CFD) method to predict the drag penalty of fouled ships based on data obtained from pierside underwater surveys.

Burgers turbulence model for a channel flow

1971 ◽  
Vol 47 (2) ◽  
pp. 321-335 ◽  
Author(s):  
Jon Lee
Keyword(s):  
Channel Flow ◽  
Stokes Equations ◽  
Turbulent Channel Flow ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Amplitude Equations ◽  
Fourier Amplitude ◽  
Navier Stokes Equations ◽  
Burgers Model ◽  
Model Dynamics

The truncated Burgers models have a unique equilibrium state which is defined continuously for all the Reynolds numbers and attainable from a realizable class of initial disturbances. Hence, they represent a sequence of convergent approximations to the original (untruncated) Burgers problem. We have pointed out that consideration of certain degenerate equilibrium states can lead to the successive turbulence-turbulence transitions and finite-jump transitions that were suggested by Case & Chiu. As a prototype of the Navier–Stokes equations, Burgers model can simulate the initial-value type of numerical integration of the Fourier amplitude equations for a turbulent channel flow. Thus, the Burgers model dynamics display certain idiosyncrasies of the actual channel flow problem described by a truncated set of Fourier amplitude equations, which includes only a modest number of modes due to the limited capability of the computer at hand.

scholarly journals Parametric forcing approach to rough-wall turbulent channel flow

2012 ◽  
Vol 712 ◽  
pp. 169-202 ◽  
Author(s):  
A. Busse ◽  
N. D. Sandham
Keyword(s):  
Numerical Simulations ◽  
Channel Flow ◽  
Stokes Equations ◽  
Rough Surfaces ◽  
Turbulent Channel Flow ◽  
Rough Wall ◽  
Force Term ◽  
Shape Functions ◽  
Mean Flow ◽  
The Mean

AbstractThe effects of rough surfaces on turbulent channel flow are modelled by an extra force term in the Navier–Stokes equations. This force term contains two parameters, related to the density and the height of the roughness elements, and a shape function, which regulates the influence of the force term with respect to the distance from the channel wall. This permits a more flexible specification of a rough surface than a single parameter such as the equivalent sand grain roughness. The effects of the roughness force term on turbulent channel flow have been investigated for a large number of parameter combinations and several shape functions by direct numerical simulations. It is possible to cover the full spectrum of rough flows ranging from hydraulically smooth through transitionally rough to fully rough cases. By using different parameter combinations and shape functions, it is possible to match the effects of different types of rough surfaces. Mean flow and standard turbulence statistics have been used to compare the results to recent experimental and numerical studies and a good qualitative agreement has been found. Outer scaling is preserved for the streamwise velocity for both the mean profile as well as its mean square fluctuations in all but extremely rough cases. The structure of the turbulent flow shows a trend towards more isotropic turbulent states within the roughness layer. In extremely rough cases, spanwise structures emerge near the wall and the turbulent state resembles a mixing layer. A direct comparison with the study of Ashrafian, Andersson & Manhart (Intl J. Heat Fluid Flow, vol. 25, 2004, pp. 373–383) shows a good quantitative agreement of the mean flow and Reynolds stresses everywhere except in the immediate vicinity of the rough wall. The proposed roughness force term may be of benefit as a wall model for direct and large-eddy numerical simulations in cases where the exact details of the flow over a rough wall can be neglected.

scholarly journals Identifying eigenmodes of averaged small-amplitude perturbations to turbulent channel flow

2019 ◽  
Vol 875 ◽  
pp. 758-780
Author(s):  
A. S. Iyer ◽  
F. D. Witherden ◽  
S. I. Chernyshenko ◽  
P. E. Vincent
Keyword(s):  
Channel Flow ◽  
Small Amplitude ◽  
Direct Evidence ◽  
Graphics Processing Unit ◽  
Turbulence Models ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Processing Unit ◽  
Graphics Processing ◽  
First Time

Eigenmodes of averaged small-amplitude perturbations to a turbulent channel flow – which is one of the most fundamental canonical flows – are identified for the first time via an extensive set of high-fidelity graphics processing unit accelerated direct numerical simulations. While the system governing averaged small-amplitude perturbations to turbulent channel flow remains unknown, the fact such eigenmodes can be identified constitutes direct evidence that it is linear. Moreover, while the eigenvalue associated with the slowest-decaying anti-symmetric eigenmode mode is found to be real, the eigenvalue associated with the slowest-decaying symmetric eigenmode mode is found to be complex. This indicates that the unknown linear system governing the evolution of averaged small-amplitude perturbations cannot be self-adjoint, even for the case of a uni-directional flow. In addition to elucidating aspects of the flow physics, the findings provide guidance for development of new unsteady Reynolds-averaged Navier–Stokes turbulence models, and constitute a new and accessible benchmark problem for assessing the performance of existing models, which are used widely throughout industry.

The Effect of the Earth’s Rotation on Channel Flow

1986 ◽  
Vol 53 (1) ◽  
pp. 198-202 ◽  
Author(s):  
C. G. Speziale
Keyword(s):  
Channel Flow ◽  
Stokes Equations ◽  
Rectangular Channel ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Earth’S Rotation ◽  
Earth's Rotation ◽  
The Earth ◽  
Laminar Channel Flow ◽  
Rotation Of The Earth

The influence that the rotation of the earth has on laminar channel flow is investigated theoretically. The full nonlinear Navier-Stokes equations relative to a reference frame rotating with the earth are solved numerically for laminar flow in a rectangular channel whose axis is aligned east-west: the orientation which yields the most drastic effect. It is demonstrated that for channels of moderate width (less than 1 ft for the flow of most liquids), the rotation of the earth can give rise to a roll instability which has a severe distortional effect on the classical parabolic velocity profile. Consequently, the usual assumption made of neglecting the effect of the earth’s rotation in the calculation of channel flow can lead to serious errors unless the channel is substantially smaller than this size. It is briefly shown that similar effects would be expected for turbulent channel flow when the channel width is approximately an order of magnitude larger.

A Novel Fix to Reduce the Log-Layer Mismatch in Wall-Modeled Large-Eddy Simulations of Turbulent Channel Flow

2016 ◽  
Author(s):  
Rey DeLeon ◽  
Inanc Senocak
Keyword(s):  
Pressure Gradient ◽  
Channel Flow ◽  
Friction Velocity ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Gradient Term ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Mean Pressure ◽  
Les Model

The log-layer mismatch arises when a Reynolds-averaged Navier-Stokes (RANS) model is blended with a large-eddy simulation (LES) model in a hybrid fashion. Numerous researchers have tackled this problem by simulating a turbulent channel flow. We show that the log-layer mismatch in hybrid RANS-LES can be reduced substantially by splitting the mean pressure gradient term in the wall-normal direction in a manner that keeps the mass flow rate constant. Additionally, an analysis of the wall-normal variation of the friction velocity shows a constant value is recovered in the resolved LES region different than the value at the wall. Second-order turbulence statistics agree very well with direct numerical simulation (DNS) benchmarks when scaled with the friction velocity extracted from the resolved LES region. In light of our findings, we suggest that the current convention to drive a turbulent periodic channel flow with a uniform mean pressure gradient be revisited in testing eddy-viscosity-based hybrid RANS-LES models as it appears to be the culprit behind the log-layer mismatch.

Turbulence statistics in fully developed channel flow at low Reynolds number

1987 ◽  
Vol 177 ◽  
pp. 133-166 ◽  
Author(s):  
John Kim ◽  
Parviz Moin ◽  
Robert Moser
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Channel Flow ◽  
Stokes Equations ◽  
Turbulent Channel Flow ◽  
Navier Stokes ◽  
Turbulence Statistics ◽  
Navier Stokes Equations ◽  
Statistical Correlations ◽  
Grid Points

A direct numerical simulation of a turbulent channel flow is performed. The unsteady Navier-Stokes equations are solved numerically at a Reynolds number of 3300, based on the mean centreline velocity and channel half-width, with about 4 × 106 grid points (192 × 129 × 160 in x, y, z). All essential turbulence scales are resolved on the computational grid and no subgrid model is used. A large number of turbulence statistics are computed and compared with the existing experimental data at comparable Reynolds numbers. Agreements as well as discrepancies are discussed in detail. Particular attention is given to the behaviour of turbulence correlations near the wall. In addition, a number of statistical correlations which are complementary to the existing experimental data are reported for the first time.

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