Numerical investigation of turbulent-driven secondary flow
- Author:
- Talebpour, Mahdad
- Published:
- [University Park, Pennsylvania] : Pennsylvania State University, 2016.
- Physical Description:
- 1 electronic document
- Additional Creators:
- Liu, Xiaofeng
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- Restrictions on Access:
- Open Access.
- Summary:
- Secondary flows of second type (also known as turbulent secondary flows) are one of the mostimportant mechanisms responsible for sediment transport processes in fluvial streams. A newtwo-equation Reynolds-Averaged Navier-Stokes (RANS) based model is investigated in depth inthis work, for modelling secondary flows of second type.This thesis incorporates a new komega model with nonlinear fourth-order closure terms for modellingReynolds stresses. The model has komega formulation which enables the model to solve for flowequations near the walls without the need for utilizing wall functions. Moreover, komega models arecapable of applying roughness on boundaries by imposing rough boundary turbulent attributesthrough omega functions. The model was tested in two main categories on five case-studies to observeits ability in simulating turbulent secondary flow in various configurations. The tests carried outcase scenarios identical to experimental case studies. First, the model was used in simulatingturbulent secondary current in a simple case study conducted inside a rectangular duct with smoothboundaries. The model performed well in this part, when simulated data such as secondary velocityprofiles, shear stresses, and secondary current vectors being compared with experimental data.In the second test, the model was investigated in case scenarios to explore the models capacityfor carrying out simulation of turbulent secondary currents over rough boundaries. While in case studies with uniform rough boundaries the model functioned well (velocity profiles, and shearstress distribution, being compared to experimental data), in cases with non-uniform roughnessdistribution the model needed noticeable tweaking, tuning, and calibration for roughness modelling.However, for validation purposes, the model with calibrated function parameter were tested againstother non-uniform distribution case scenarios, in which their results showed excellent agreementwith experimental data. The numerical simulations were able to produce secondary velocity profilesvery close to experimental studies which are difficult to capture. The proposed roughness heightvalues in roughness modelling function for secondary flows over beds, with nonuniformly distributedroughness, are critically discussed and assessed.During the tuning of the model, it was detected that the original approach for computing wall shearstresses, using law of the wall, provided dissimilar results compared to results which calculatedshear stresses directly from velocity gradients at the wall. This disagreement was investigated indepth, and it was concluded that the calculation of wall shear stress, using law of the wall, was notaccurate. Finally, providing accurate result along with computational efficiency (due to RANS-basedformulation), and applicability to rough case scenarios, this model is advantageous in investigationof turbulent secondary current.
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- Dissertation Note:
- M.S. Pennsylvania State University 2016.
- Reproduction Note:
- Library holds archival microfiches negative and service copy. 2 fiches. (Micrographics International, 2016)
- Technical Details:
- The full text of the dissertation is available as an Adobe Acrobat .pdf file ; Adobe Acrobat Reader required to view the file.
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