Paper Number
FI2                         My Program 

Session
Flow-Induced Instabilities and Non-Newtonian Fluids

Title
Asymptotic flow states in turbulent viscoelastic Taylor-Couette flow: The relationship between asymptotic drag states and large and small scale interactions

Presentation Date and Time
October 20, 2025 (Monday) 10:10

Track / Room
Track 7 / Sweeney Ballroom D

Authors (Click on name to view author profile)

1. Lin, Fenghui (University of Science and Technology of China, School of Engineering Scicence)
2. Lin, NanSheng (University of Science and Technology of China, School of Engineering Scicence)
3. Khomami, Bamin (University of Tennessee, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Fenghui Lin¹, NanSheng Lin¹ and Bamin Khomami^2
1School of Engineering Scicence, University of Science and Technology of China, Hefei,, Anhui 230027, China; ²Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37919

Speaker / Presenter 
Khomami, Bamin

Keywords
None

Text of Abstract
Adding a small amount of long-chain flexible polymer leads to intriguing drag modification (DM) in turbulent Taylor–Couette flows (TCF). Specifically, our earlier studies show the existence of asymptotic maximum drag enhance- ment/reduction (MDE/MDR) flow states in wide-/small-gap turbulent viscoelas- tic TCF. These intriguing asymptotic flow states emerge from the complex inter- action between turbulent vortices and microscale polymer dynamics. However, the connection between MDR and MDE in TCF remains to be explored. To that end, we performed extensive direct numerical simulations over a wide range of polymer concentrations (viscosity ratio ß = 0.99 ~ 0.90) at W i of O(100) with the FENE-P model in a wide gap TCF at Reynolds number 6000. For different ß, asymptotic flow states, including both MDR and MDE are achieved by gradually increasing W i. Interestingly, the transition from MDR to MDE occurs with decreasing ß (increasing polymer concentrations). That is, asymp- totic flow states with DM of -11. 7% and 34. 6% are present at ß = 0.99 and 0.90, respectively. By examining the driving forces, we demonstrate that different degrees of DM arise as a result of the competition between Reynolds stress reduction and polymer stress development. Moreover, the state transi- tion is accompanied by the transition in the flow structures, namely, MDR and MDE states are dominated by large- and small-scale flow structures, respec- tively. This is because decreasing ß leads to enhanced elastic instability, which facilitates the generation of elastic Gortler vortices. Finally, we elucidate these transitions through a detailed examination of the inner and outer scales. Overall, this study has provided a comprehensive mechanisticunderstanding of DM that arises from the interaction of polymers with small-and large-scale flow structures.