Advances in Granular Flow Research: A Three-Generation, Four Decade, Through-line Retrospective

Festschrifts can provide valuable vantage points for reflecting on a discipline’s evolution and future possibilities. This article honoring Devang Vipin Khakhar (DVK) offers such an opportunity─not through a comprehensive career review, but by examining one dimension of scholarly achievements through the lens of collaborative work spanning 40 years and three generations of researchers. Specifically, we review DVK’s contributions to our understanding of flowing granular materials across three domains: surface flows, mixing and segregation, and computational modeling. This retrospective traces the field’s evolution from early explorations of chaos and mixing in rotating tumblers to sophisticated analyses of flow kinematics and segregation in heaps. We use this opportunity to chart the emergence of granular mechanics as a predictive science. In addition, we look forward to identifying persistent challenges and emerging opportunities: modeling unconfined geometries with evolving boundaries, extending segregation theory across wide size-ratio regimes, addressing cohesive effects and particle breakage, and integrating multiscale computational approaches with machine learning.