Unsteady RANS Simulation of Flow Around a 5:1 Rectangular Cylinder at High Reynolds Numbers

2012 ◽  
Author(s):  
Muk Chen Ong
Keyword(s):  
Free Stream ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Stream Velocity ◽  
High Reynolds Numbers ◽  
Rectangular Cylinder ◽  
Mean Pressure ◽  
Unsteady Rans ◽  
High Reynolds

The unsteady flows around a stationary two dimensional rectangular cylinder with chord-to-thickness ratio B/D = 5.0 at high Reynolds numbers, ReB = 5×105, 1×106, 1.5×106 and 2×106 (based on the free stream velocity and the chord length), are investigated numerically by solving the Unsteady Reynolds-Averaged Navier Stokes (URANS) equations with a standard high Reynolds number k-ε turbulence model. The objective of the present study is to evaluate whether the model is applicable for engineering design within this flow regime. Hydrodynamic results (such as time-averaged drag coefficient, root-mean-square of fluctuating lift coefficient, Strouhal number and mean pressure distribution around the rectangular cylinder) are compared with published experimental data. The mechanism of vortex shedding is also discussed.

Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade

2000 ◽  
Author(s):  
Heinz-Adolf Schreiber ◽  
Wolfgang Steinert ◽  
Bernhard Küsters
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Reynolds Numbers ◽  
Boundary Layer Transition ◽  
Bypass Transition ◽  
Layer Transition ◽  
Free Stream Turbulence ◽  
High Reynolds Numbers ◽  
High Turbulence ◽  
High Reynolds

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state. For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.

Numerical Investigation of Flow Interference Effects in Fixed and Vibrating Tandem Square Columns Using Hybrid RANS-LES Models

2015 ◽  
Author(s):  
Harish Gopalan ◽  
Dominic Denver John Chandar ◽  
Narasimha Rao Pillamarri ◽  
Guan Mengzhao ◽  
Rajeev K. Jaiman ◽  
...  
Keyword(s):  
Solid Wall ◽  
Computational Cost ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Arbitrary Lagrangian Eulerian ◽  
High Reynolds Numbers ◽  
Flow Past ◽  
Ale Methods ◽  
High Reynolds ◽  
Flow Interference

Investigation of flow past tandem and side-by-side circular and square columns is of interest in offshore engineering. Flow past fixed and vibrating circular columns has received a lot of focus in the literature. However, the studies focused on square columns, especially at high Reynolds numbers are very limited due to the computational cost of large eddy simulation (LES). Unsteady Reynolds-averaged Navier-Stokes (URANS) methods are limited by their accuracy, especially for tandem columns in the wake interference regime (spacing to diameter ratio: L=D ∼ 3:0). Hybrid URANS-LES models (URANS near the solid-wall and LES away from the wall) can overcome the drawbacks of the traditional URANS methods and can provide a reasonable prediction of the flow physics at a fraction of the cost of LES without significantly sacrificing numerical accuracy. Arbitrary Lagrangian-Eulerian (ALE) methods fails when vibrating tandem bodies are in close proximity to each other or vibrate at high reduced velocities. Remeshing the domain can be expensive, especially at high Reynolds numbers (Re). Alternate strategies are necessary to efficiently simulation this problems. This study proposes the use of a non-linear URANS-LES model, coupled with an overset mesh method (for vibrating columns), for studying flow past tandem square columns. Simulations are performed at sub-critical Re to match the experimental Re. The initial results are encouraging for further investigation of fixed and vibrating tandem square column flow interference at high Reynolds numbers.

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