Scalar transport on rough surfaces

 Personnel: Dr. Zvi Hantsis, Prof. Ugo Piomelli
Collaborators: Prof. Bettina Frohnapfel, Mr. Francesco Secchi 

Scalar transport over rough surfacces Contours of scalar concentration and velocity vectors in a streamwise-wall normal plane
Scalar transport and momentum transport are governed by similar equaitons; in flows over smooth surfaces this results in the fact that many statistical quantities (first and second moments, notably) match when the scalar is normalized properly (Reynolds analogy). Over rough surfaces the presence of recirculation zones behind roughness elements results in a breakdown of the Reynolds analogy.  Through numerical simulations our group has been able to shed light on the causes of this breakdown.
  1. Z. Hantsis and U. Piomelli. Roughness effects on scalar transport. Phys. Rev. Fluids, 5(114607):1–23, 2020. https://link.aps.org/doi/10.1103/PhysRevFluids.5.114607
  2. Z. Hantsis and U. Piomelli. Effects of roughness on the turbulent Prandtl number, time-scale ratio and dissipation of a passive scalar. Phys. Rev. Fluids, 7(124601):1–24, 2022. https://10.1103/PhysRevFluids.7.124601
  3. Z. Hantsis and U. Piomelli. Numerical simulations of scalar transport on rough surfaces. Fluids, 9(159):1–31, 2024. https://10.3390/fluids9070159
  4. F. Secchi, D. Gatti, U. Piomelli, and B. Frohnapfel. A framework for assessing the reynolds analogy in
    turbulent forced convection. J. Fluid Mech., accepted for publication, 2025.

 

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River bedform evolution

Personnel: Dr, Gianmarco D'Alessandro, Prof. Ugo Piomelli
Collaborator: Prof. Cristian Marchioli (Univ. Udine)

 bedforms

We examined the evolution of bedforms on a loose sediment bed under turbulent flow conditions using input parameters obtained from laboratory measurements. Over time, the bedforms become more three-dimensional and irregular in shape, leading to changes in the shear layer, crest angle, and separation patterns. The bedforms continue to evolve until a quasi-steady equilibrium is reached. Our simulation highlights the crucial role played by the small-scale bedforms, which significantly affect the flow dynamics: an increase in the total drag is observed, related to the form drag generated by the local recirculation and the increased size of the large-scale recirculation bubble.

  1. G. D’Alessandro, Z. Hantsis, C. Marchioli, and U. Piomelli. Accuracy of bed-load transport models in eddy-resolving simulations. Int. J. Multiphase Flow, 141:1–1–16, 2021. https://doi.org/10.1016%2Fj.ijmultiphaseflow.2021.103676
  2. G. D’Alessandro, C. Marchioli, and U. Piomelli. Large-eddy simulation of the flow over a realistic riverine geometry. J. Fluid Mech., Submitted, 2024.

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Populating the near-wall region, one eddy at a time

Personnel: Dr. Zvi Hantsis, Mr. Nam Hoang, Prof. Ugo Piomelli
Collaborators: Prof. Beverley McKeon (Stanford University), Mr. Miles Chan (California Institute of Technology)

 

 

 

Contours of wall stress in a channel at Re=5,200.
Top: Standard WMLS; Bottom: WMLES with resolvent modes

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Wall models for LES of non-equilibrium flows

Personnel: Dr. Teresa Salomone, Mr. Michael Kelly, Prof. Ugo Piomelli
Collaborators: Prof. Charles Meneveau (Johns Hopkins Univ, USA), Prof. Giuliano De Stefano (Univ. "Luigi Vanvitelli", Italy)

 

 

 

  1. T. Salomone, U. Piomelli, and G. De Stefano. Large-eddy simulations of the flow over roughness strips. Fluids, 8(10):1–16, 2023.  https://10.3390/fluids8010010
  2. T. Salomone, C. Meneveau, G. De Stefano, and U. Piomelli. Wall-modelled large-eddy simulations of non-equilibrium turbulent-boundary layer with roughness. J. Fluid Mech., Submitted, 202

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