Abstract
Particle Image Velocimetry measurements of the liquid velocity fields in the flow over the backward-facing step were performed in the same flow configuration as in the existing Direct Numerical Simulation (DNS). The experiment and the simulation were performed in an identical cross-section geometry with step expansion rate 2.25 and the square shape of the outlet duct at the Reynolds number in an inlet part of the section 7100. The experiment was performed in transparent test section, 1.2 m long, with 20 × 45 mm2 cross-section upstream and 45 × 45 mm2 downstream, while a domain that was three times shorter was used in the DNS. A 2D-2C PIV system with a single high-speed camera and a pulse laser was used for a series of two-dimensional measurements of the velocity field at several cross-sections from two different perspectives. Variables analyzed in the experiment are time-averaged fluid velocities, velocity RMS fluctuations and two components of the Reynolds stress tensor. The key novelty is the comparison of two very accurate approaches, PIV and DNS, in the same cross-section geometry. Comparison of the similarities, and especially the differences between the two approaches, elucidates uncertainties of both studies and answers the question on what kind of agreement is expected when two very accurate approaches are compared.
Highlights
The separation and reattachment of turbulent flows occur in many industrial applications and natural systems, and as such, represent an important field of study
Since the final geometry and the Reynolds number of liquid metal experiment [4] were slightly different than in Direct Numerical Simulation (DNS), the second Backward-Facing Step (BFS) experiment related to the SESAME project was developed: adiabatic experiment performed with water and without heating
We have not found the specific cases of the rectangular channel with expansion ratio of around 2 and with moderate Reynolds numbers, which can be accurately described with DNS studies
Summary
The separation and reattachment of turbulent flows occur in many industrial applications and natural systems, and as such, represent an important field of study. Since the final geometry and the Reynolds number of liquid metal experiment [4] were slightly different than in DNS, the second BFS experiment related to the SESAME project was developed: adiabatic experiment performed with water and without heating This experiment is described in the present paper. We have not found the specific cases of the rectangular channel with expansion ratio of around 2 and with moderate Reynolds numbers, which can be accurately described with DNS (or LES) studies Since such a numerical study was performed by Oder et al [2], we decided to build a test-section based on this simulation. The RANS models remain the key tool for high Reynolds number industrial flows [30], where DNS approaches are typically not feasible and even LES models are too expensive due to the enormous computational power required
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