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Investigation of flow over a ground sill using OpenFOAM

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Investigation of the flow over a ground sill using OpenFOAM
Katharina Teuber, Technische Universit¨at Berlin,
Tabea Broecker, Technische Universit¨at Berlin,
Waldemar Elsesser, Technische Universit¨at Berlin,
Berken Agaoglu, Technische Universit¨at Berlin,
Reinhard Hinkelmann, Technische Universit¨at Berlin
Key words: two-phase flow, OpenFOAM, interFoam,
ground sill, turbulence modelling, CFD
Introduction
Computational Fluid Dynamics (CFD) gains an in-
creasing importance in the field of hydraulic engineer-
ing. One application, the open source C+ + libraries
OpenFOAM will be analysed in the following.
In this contribution, flow over a two-dimensional
ground sill is simulated using the volume of fluid (VoF)
method and its suitability to describe such complex hy-
draulic phenomena is investigated. Validation is per-
formed by comparing the results with measurements
by [1].
Computational framework
Governing equations Surface water flow is calcu-
lated by using the two-phase flow solver interFoam
based on a VoF approach for one- and two-phase
flows. Both phases are considered as one fluid with
rapidly changing material properties, therefore one set
of Navier-Stokes-equations is solved. The phases are
defined by an additional transport equation which is
used as a marker to describe the distribution of the
phases throughout the domain [2].
Turbulence modelling Different turbulence mod-
els are applied and the results are compared. Con-
stant turbulent viscosities between υ= 103m2/s and
υ= 106m2/s are used as the simplest model. Fur-
ther, different RANS models such as k-ε, k-ωas well
as k-ωSST and LES are analysed.
Results and discussion
Water level drawdown The water level drawdown
can be calculated analytically by using continuity and
Bernoulli’s equation. Due to additional energy losses
caused by the angular structure of the sill as well as
losses due to sidewalls when a three-dimensional model
is chosen, the drawdown is smaller but reasonably co-
incides. The drawdown also differs depending on the
turbulence model.
Eddy structures The results of a one-phase val-
idation testcase show a good agreement with the
measurements by [1]. Both the one- and two-phase
testcases show differences in the eddy structures
behind the ground sill (cf. Figure 1 and 2) and the
length of the recirculation zone depending on the
chosen turbulence model.
Figure 1: Velocity distribution in recirculation zone (con-
stant turbulent viscosity υ= 103m2/s)
Figure 2: Velocity distribution in recirculation zone (con-
stant turbulent viscosity υ= 106m2/s)
Conclusions
The suitability of OpenFOAM’s two-phase solver in-
terFoam to simulate a complex hydraulic testcase has
been investigated using two- and three-dimensional
model setups. Different turbulence models have been
compared and the water level drawdown due to the
ground sill has been compared to an analytical solu-
tion.
The VoF method implemented is able to reproduce the
effects of a complex hydraulic testcase with differences
in the accuracy depending on the chosen turbulence
model.
Future research will analyse the effects of further hy-
draulic structures and take the behaviour of the air
phase into account.
References
[1] G. Almeida, D. Durao and M. Heitor. Wake flows be-
hind two-dimensional model hill. Experimental Thermal
and Fluid Science, 7(1): 87-101 (1993).
[2] G. C. Morgan. Application of the interFoam VoF code
to coastal wave/structure interaction, PhD thesis, Uni-
versity of Bath, United Kingdom (2013).
Conference Paper
Full-text available
In the field of hydraulic engineering, attention towards Computational Fluid Dynamics (CFD) has increased within the last years. In this study, flow over a two-dimensional ground sill is simulated and analyzed using the open source model OpenFOAM. Single-phase flow simulations are compared to experimental results obtained by Almeida et al. (1993) and two-phase flow simulations are compared to analytical solutions by using Bernoulli’s and continuity equation. The results show that the model is capable of simulating such hydraulic testcases. Different RANS and LES simulations were found to reproduce the analyzed flow behavior well.
Article
Laser-Doppler measurements of velocity characteristics are reported for the recirculating flow established in the wake of two-dimensional, polynomial-shaped obstacles that are axisymmetrical about a vertical axis and mounted in a water channel downstream of a fully developed channel flow for Re = 6 × 104. The study involves measurements of the mean and fluctuating flow properties in the streamwise and spanwise directions and includes comparison of the flow around a single obstacle with that resulting from the interaction of consecutive obstacles. The results include analysis of the turbulent stresses in local flow coordinates and reveal flow structure qualitatively similar to that found in other turbulent flows with a reattachment zone and, for the case of multiple hills, resembling the flow over wavy surfaces of large amplitude. The implications of the results for the calculation of turbulent flows over curved boundaries using turbulence models are discussed.
Application of the interFoam VoF code to coastal wave/structure interaction
  • G C Morgan
G. C. Morgan. Application of the interFoam VoF code to coastal wave/structure interaction, PhD thesis, University of Bath, United Kingdom (2013).