Large-Eddy Simulation in typical industrial bends -...

03/03/2014

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Large-Eddy Simulation of typical industrial bends

In-plane and out-of-plane bend at Re =20’000 by V. Kumar, B. Kissling*, P. Panathansiou and F. Aydin

* Experimental data

Slide 1 V. Kumar

03/03/2014

E+H Flowtec AG

Endress+Hauser Flowtec is a world leader in industrial flow meters

Flow meters based on the principles

Thermal, magnetic-inductive, vortex, ultrasonic and Coriolis

Production centers in four continents

Large-Eddy Simulation of flows after typical industrial bends

Reinach-CH

Cernay-Fr

Europe

Asia

North America Asia

Greenwood / USA Suzhou / China

Aurangabad / India

Itatiba / Brazil

S. America

Slide 2 V. Kumar

03/03/2014

Product Portfolio

Line sizes from 1 mm to 3000 mm


4 Line Display

Touch Control

2 Line Display

Pushbutton

Prosonic Flow

Promass

Promag

Prowirl

t-mass

Slide 3 V. Kumar

03/03/2014

Where CFD is playing its role?

Optimizing the design of the flow meters

Flow meters can resolve effects of the order of 0.05% to 1%

highly accurate models and high quality grids are required

To investigate installation effects on the flow meters

how does the flow develops after a disturbance

Typical disturbances are bends, diffusors, reducers


→ It is very important for a turbulence model to accurately model the effects near

the wall

Slide 4 V. Kumar

03/03/2014

Bend Simulations


Slide 5 V. Kumar

03/03/2014

Bend configurations investigated

In-plane or 90° bend Out-of-plane bend

Fully-developed inlet generated by a periodic pipe simulation

Approx. 40D downstream length in the simulation

LES, Realizable k-eps two-layer, RSM two-layer and SST models tested

Measurements done using clamp-on ultrasonic sensors over the 0 to 360° at

different L/D’s downstream the bends.


Slide 6 V. Kumar

03/03/2014

Mesh

For the LES simulation:

Grid resolution 𝑟+ ≅ 15, 𝑧+ ≅ 30, 𝜃+ =15; ∆𝑦+< 1, 𝑆𝑟 < 1.2

Base size => 0.015 D

∆𝑦+ is estimated from 𝑅𝑒𝜏 = 0.199 𝑅𝑒7/8

Approx. 10 Million Cells for both the cases

→ Mesh variation and boundary layer variations were also carried


Slide 7 V. Kumar

03/03/2014

LES mesh size and effort requirement

Computational effort goes with 𝑵𝟏.𝟓 or 𝑹𝒆𝟑.𝟗

10-20 Million cells grids are computationally affordable for LES


Affordable for industry

ca. 2 days wall time with full

16 nodes, L/D~40

Slide 8 V. Kumar

03/03/2014

LES Methodology

Ratio of turbulent length scale and grid-size must be controlled

A RANS simulation carried out before starting an LES

𝑅𝐿 =∆

𝑙𝑡𝑢𝑟𝑏≤ 0.5, 𝑙𝑡𝑢𝑟𝑏 =

k3/2

ε

CFL <1 in 96-99% cells

Second order time- and space (BCD) discretization

WALE Sub-grid model with wall-limiter and Cw =0.544

Simulations are carried until the averaged mean flow does not change

anymore

100k time-steps with time-integration started after 20k steps.

→Synthetic turbulence at the inlet to avoid laminarization


Slide 9 V. Kumar

03/03/2014

In-Plane Bend

Velocity field downstream in-plane

bend

• Flow development using RKEPS

slowest among all

• SST shows artifacts close to the bend

• RSM is closest to LES

• Same grid for LES and RANS


Slide 10 V. Kumar

03/03/2014

Axial and radial velocity profiles

• All RANS models predict much slower flow development for the in-plane

bend


Slide 11 V. Kumar

03/03/2014

Comparison with measurements

• LDA Measurements by Kalpakli and Orlu, Int. J Heat and Fluid Flow 2013

at 0.67D Downstream the 90° bend

• Reasonably well agreement between two independent studies


Slide 12 V. Kumar

03/03/2014

Ultrasonic measurements vs Simulations

5D Downstream 30D Downstream

• Deviation from mean flow velocity is plotted

• LES shows a very good agreement throughout

• RSM the best among RANS


Slide 13 V. Kumar

03/03/2014

Out of plane bend at Re =20’000

• RSM gives artifacts

• SST results are similar to RSM

• Realizable k-epsilon model seems to be

best performing

• LES predicts different swirl decay than

all RANS models


Slide 14 V. Kumar

03/03/2014

Comparison with ultrasonic measurements-I

• At 3D downstream

• RKEPS-2L is underpredicting the flow distortion

• LES is very close to the measurements

• Both RSM and SST shows artificial effects

→ We performed transient RANS as well without much improvement


Slide 15 V. Kumar

03/03/2014

Comparison with ultrasonic measurements-II

• At 11 D downstream

• RSM model seems to recover further downstream

• In LES, swirl seems to be much faster, i.e. tangential stresses are under

predicted

→ We tested various mesh sizes and different subgrid models


Slide 16 V. Kumar

03/03/2014

Conclusions

In-plane bend:

• Both RSM and LES are well predicting the flow up to 30D downstream

• Realizable K-Epsilon model predicts slower decay of disturbances

• SST significantly worse than others

Out-of-plane bend:

• RANS are better predicting the rotational decay

• Close to the bend, both RSM and SST are not performing well

• LES is predicting very well close to the bend

• However further downstream, swirl decay much slower than as predicted by RANS

and in experiments

• LES models and grid-resolution to be thoroughly investigated for swirling flows


Slide 17 V. Kumar

03/03/2014

Thank you


Vortictiy field in 90° bend

Slide 18 V. Kumar

Large-Eddy Simulation in typical industrial bends -...

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