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Tricritical Directed Percolation Controls the Laminar-Turbulent Transition in Pipes with Body Forces

Published in Physical Review Letters, 2025

Transition to turbulence in shear flows has been established to be a non-equilibrium phase transition. Body forces can make the transition discontinuous. Observed phenomenology can be explained by a new tricritical point near transition, enriching the phase diagram of transitional turbulence.

Recommended citation: Guru K. Jayasingh and Nigel Goldenfeld, Tricritical directed percolation controls the laminar–turbulent transition in pipes with body forces, Phys. Rev. Lett. 135, 104001 (2025). doi:10.1103/PhysRevLett.135.104001 https://doi.org/10.1103/46g3-n7cx

Laminar-turbulent transition in pipes with body forces: continuous, discontinuous or both?

Published: March 17, 2025

The laminar-turbulent transition in straight pipes is believed to occur through a continuous non-equilibrium phase transition in the directed percolation universality class. However, in curved pipes or in the presence of body forces it is possible to observe a discontinuous transition and other phenomenology which seem inconsistent with the emerging consensus. Here, we consider the perturbing effects of body forces and incorporate them into a minimal Landau theory of the transition. We calculate the phase diagram as a function of Reynolds number and body force strength, and show that above a threshold strength of the latter, there is a tricritical point which accounts for the observed discontinuity behavior, including spatially heterogeneous states. Our results are consistent with recent experiments in centrifugal pipes and direct numerical simulations of heated flows.

Tricritical Directed Percolation and Transitional Turbulence

Published: October 18, 2025

This talk explores how body forces alter the canonical picture of the laminar–turbulent transition in pipe flow. By extending the standard framework of directed percolation to include external forcing, we identify a tricritical regime that interpolates between continuous and discontinuous transitions. The resulting phase diagram reveals how sufficiently strong body forces induce metastability, coexistence, and relaminarization—features observed in curved and centrifugal pipes. The analysis provides a unifying theoretical basis for diverse experimental and numerical observations of forced transitional turbulence.

At Indian Institute of Technology Bombay

Undergraduate + Graduate courses, In person and Online, 2019

During my time at IIT Bombay, I served as a Teaching Assistant across multiple core and advanced physics courses:

At University of San Diego California

Undergraduate and Graduate courses, UCSD, Dept. of Physics, 2022

At UC San Diego, I have contributed to the Department of Physics’ teaching mission by supporting both graduate and undergraduate courses. A few of the courses include: