About

Rajat Mittal is a professor of mechanical engineering at Johns Hopkins University, specializing in computational fluid dynamics. His research group, the Flow Physics and Computation Lab, develops and employs computational methods to model various flows, with a focus on immersed boundary methods, vortex dominated flows, biomedical fluid dynamics, biological and bioinspired locomotion such as swimming and flying, bioacoustics, active flow control, fluid-structure interaction, and high-performance computing. Due to the cross-disciplinary nature of his work, he collaborates extensively with researchers from zoology, cardiology, robotics, biomechanics, and dynamics, making significant contributions to the fields of computational fluid mechanics and biomechanics.

Research topics

• Artificial Intelligence
• Medicine
• Physics
• Computer Science
• Simulation
• Mechanics
• Risk analysis (engineering)
• Telecommunications
• Virology
• Ecology
• Mathematics

Selected publications

• Flow-induced dorso-ventral deformation enhances propulsive efficiency in flexible caudal fins

  Bioinspiration & Biomimetics · 2026-01-16

  articleOpen accessSenior author

  Fish swim with flexible fins that stand in stark contrast to the rigid propulsors of engineered vehicles. Using numerical simulations of the dynamics of flow-structure interaction, we have found that dorso-ventral deformation in flexible caudal fins results in a 70% increase in efficiency of caudal fin swimmers compared to a rigid fin generating the same amount of thrust. By correlating fin deformation to the flow physics, we find that the greater power requirements of rigid fins can be largely attributed to their propensity to generate high-magnitude lateral forces. In contrast, flexible fins achieve high efficiency local-redirection of force where deformations orient pressure forces on the fin in fore-aft and dorso-ventral directions to reduce the power demand of generating thrust forces. These deformations occur at phases in the tail-beat cycle where the fin experiences large lateral velocities and pressure differentials and this reduces the net power expended by the flexible fins. In this way, the flexibility of a caudal fin offers a simple and elegant solution for efficient locomotion which does not require sensing, computation and control that might otherwise be provided by the nervous system of a fish or a computer within a underwater vehicle. These flow-induced dorso-ventral fin deformations therefore imbue a mechanical intelligence in these fins that provides propulsive advantages to caudal fin swimmers and they also offer solutions for efficient propulsion in engineered systems.

  PublisherDOI

• Scaling laws for caudal fin swimmers incorporating hydrodynamics, kinematics, morphology and scale effects

  Journal of Fluid Mechanics · 2026-03-02 · 2 citations

  articleOpen accessSenior author

  Many species of fish, as well as biorobotic underwater vehicles (BUVs), employ body–caudal fin (BCF) propulsion, in which a wave-like body motion culminates in high-amplitude caudal fin oscillations to generate thrust. This study uses high-fidelity simulations of a mackerel-inspired caudal fin swimmer across a wide range of Reynolds and Strouhal numbers to analyse the relationship between swimming kinematics and hydrodynamic forces. Central to this work is the derivation and use of a model for the leading-edge vortex (LEV) on the caudal fin. This vortex dominates the thrust production from the fin and the LEV model forms the basis for the derivation of scaling laws grounded in flow physics. Scaling laws are derived for thrust, power, efficiency, cost-of-transport and swimming speed, and are parametrised using data from high-fidelity simulations. These laws are validated against published simulation and experimental data, revealing several new kinematic and morphometric parameters that critically influence hydrodynamic performance. The results provide a mechanistic framework for understanding thrust generation, optimising swimming performance, and assessing the effects of scale and morphology in aquatic locomotion of both fish and BUVs.

  PublisherDOI

• Duodenogastric reflux in health and disease: insights from a computational fluid dynamics model of the stomach

  American Journal of Physiology-Gastrointestinal and Liver Physiology · 2025-01-28 · 5 citations

  articleOpen accessSenior authorCorresponding

  An in silico model of the stomach is presented to study the phenomenon of duodenogastric reflux. We use the model to investigate the role of pyloric incompetence, food properties, and gastroparesis on reflux. This first-ever in silico study of duodenogastric reflux provides new insights into the mechanisms and factors implicated in this reflux and the sequelae of conditions that result from the exposure of the stomach lumen to bile.

  PublisherDOI

• From vortices to forces – a data-driven framework for unsteady lift generation in three-dimensional vortex-dominated flows

  Journal of Fluid Mechanics · 2025-10-01 · 1 citations

  articleOpen accessSenior authorCorresponding

  Time-varying flow-induced forces on bodies immersed in fluid flows play a key role across a range of natural and engineered systems, from biological locomotion to propulsion and energy-harvesting devices. These transient forces often arise from complex, dynamic vortex interactions and can either enhance or degrade system performance. However, establishing a clear causal link between vortex structures and force transients remains challenging, especially in high-Reynolds-number nominally three-dimensional flows. In this study, we investigate the unsteady lift generation on a rotor blade that is impulsively started with a span-based Reynolds number of 25 500. The lift history from this direct-numerical simulation reveals distinct early-time extrema associated with rapidly evolving flow structures, including the formation, evolution and breakdown of leading-edge and tip vortices. To quantify the influence of these vortical structures on the lift transients, we apply the force partitioning method (FPM) that quantifies the surface pressure forces induced by vortex-associated effects. Two metrics – $Q$ -strength and vortex proximity – are derived from FPM to provide a quantitative assessment of the influence of vortices on the lift force. This analysis confirms and extends qualitative insights from prior studies, and offers a simple-to-apply data-enabled framework for attributing unsteady forces to specific flow features, with potential applications in the design and control of systems where unsteady aerodynamic forces play a central role.

  PublisherOA PDFDOI

• Computational modelling and analysis of the coupled aero-structural dynamics in bat-inspired wings

  Journal of Fluid Mechanics · 2025-05-09 · 10 citations

  articleOpen accessSenior author

  We employ a novel computational modelling framework to perform high-fidelity direct numerical simulations of aero-structural interactions in bat-inspired membrane wings. The wing of a bat consists of an elastic membrane supported by a highly articulated skeleton, enabling localised control over wing movement and deformation during flight. By modelling these complex deformations, along with realistic wing movements and interactions with the surrounding airflow, we expect to gain new insights into the performance of these unique wings. Our model achieves a high degree of realism by incorporating experimental measurements of the skeleton’s joint movements to guide the fluid–structure interaction simulations. The simulations reveal that different segments of the wing undergo distinct aeroelastic deformations, impacting the flow dynamics and aerodynamic loads. Specifically, the simulations show significant variations in the effectiveness of the wing in generating lift, drag and thrust forces across different segments and regions of the wing. We employ a force partitioning method to analyse the causality of pressure loads over the wing, demonstrating that vortex-induced pressure forces are dominant while added-mass contributions to aerodynamic loads are minimal. This approach also elucidates the role of various flow structures in shaping pressure distributions. Finally, we compare the fully articulated, flexible bat wing with equivalent stiff wings derived from the same kinematics, demonstrating the critical impact of wing articulation and deformation on aerodynamic efficiency.

  PublisherDOI

• Hydrodynamically Beneficial School Configurations in Carangiform Swimmers: Insights from a Flow-Physics Informed Model

  ArXiv.org · 2025-01-16

  preprintOpen accessSenior author

  Researchers have long debated which spatial arrangements and swimming synchronizations are beneficial for the hydrodynamic performance of fish in schools. In our previous work (Seo and Mittal, Bioinsp. Biomim., Vol. 17, 066020, 2022), we demonstrated using direct numerical simulations that hydrodynamic interactions with the wake of a leading body-caudal fin carangiform swimmer could significantly enhance the swimming performance of a trailing swimmer by augmenting the leading-edge vortex (LEV) on its caudal fin. In this study, we develop a model based on the phenomenology of LEV enhancement, which utilizes wake velocity data from direct numerical simulations of a leading fish to predict the trailing swimmer's hydrodynamic performance without additional simulations. This approach enables a comprehensive analysis of the effects of relative positioning, phase difference, flapping amplitude, Reynolds number, and the number of swimmers in the school on thrust enhancement. The results offer several insights regarding the effect of these parameters that have implications for fish schools as well as for bio-inspired underwater vehicle applications.

  PublisherOA PDFDOI

• Hydrodynamically beneficial school configurations in carangiform swimmers: insights from a flow-physics informed model

  Journal of Fluid Mechanics · 2025-07-07 · 8 citations

  articleOpen accessSenior authorCorresponding

  Researchers have long debated which spatial arrangements and swimming synchronisations are beneficial for the hydrodynamic performance of fish in schools. In our previous work (Seo and Mittal, Bioinsp. Biomim. , Vol. 17, 066020, 2022), we demonstrated using direct numerical simulations that hydrodynamic interactions with the wake of a leading body -caudal fin carangiform swimmer could significantly enhance the swimming performance of a trailing swimmer by augmenting the leading-edge vortex (LEV) on its caudal fin. In this study, we develop a model based on the phenomenology of LEV enhancement, which utilises wake velocity data from direct numerical simulations of a leading fish to predict the trailing swimmer’s hydrodynamic performance without additional simulations. For instance, the model predicts locations where direct simulations confirm up to 20 % enhancement of thrust. This approach enables a comprehensive analysis of the effects of relative positioning, phase difference, flapping amplitude, Reynolds number and the number of swimmers in the school on thrust enhancement. The results offer several insights regarding the effect of these parameters that have implications for fish schools as well as for bio-inspired underwater vehicle applications.

  PublisherOA PDFDOI

• Harnessing leading-edge vortices for improved thrust performance of wave-induced flapping foil propulsors

  Physical Review Fluids · 2025-07-22

  articleSenior author
  PublisherDOI

• <i>In silico</i> study of the dynamics of solid food particles in the stomach during gastric digestion

  Journal of The Royal Society Interface · 2025-08-01 · 1 citations

  articleOpen accessSenior authorCorresponding

  In recent years, there has been growing interest in computational fluid dynamics models of the gastric phase of the digestion process. While several models address the digestion and emptying of liquid meals, none incorporate large solid food particles. This omission is significant, as a food bolus typically contains solid particles of varying sizes, with those exceeding 1-2 mm unable to pass through the pylorus. The current study integrates large spherical particles into an imaging-based stomach model to examine the action of hydrodynamic and contact forces on these particles. The model captures particle shuttling dynamics and quantifies the forces that drive trituration in a healthy and a hypomotile stomach at different viscosities of the surrounding liquid contents. The results show that the presence of solid foods can reduce the gastric emptying rate of liquids while also significantly influencing the flow inside the antrum. Hypomotile stomachs were ineffective in trapping the solids next to the pylorus, with many food particles never even making it to the terminal antrum, unlike the healthy case. The pressure, shear stresses and contact forces acting on the solid particles were also lower for the hypomotile case.

  PublisherDOI

• Aerodynamics and Aeroacoustics of da Vinci's Aerial Screw

  ArXiv.org · 2025-06-11

  preprintOpen accessSenior author

  Leonardo da Vinci's aerial screw, conceived in the 15th century, represents one of the earliest conceptualizations of lift-generating rotary flight. Despite its historical significance, the aerodynamic and aeroacoustic performance of this rotor has received limited scientific attention. In this study, we employ direct numerical simulations to analyze the aerodynamic forces and acoustic emissions of a modernized da Vinci aerial screw design across a range of Reynolds numbers (2000, 4000, 8000, and 16000). These results are compared against those from a canonical two-bladed rotor producing similar lift. The aerial screw demonstrates 42.2% lower mechanical power consumption and 72.3% lower acoustic intensity per unit lift, primarily due to its larger wetted area and correspondingly lower rotational speed. Although the aerial screw exhibits a lower lift coefficient and much of its surface contributes minimally to lift generation, the net performance under iso-lift conditions highlights its efficiency and reduced noise signature. The continuous spiral geometry of the aerial screw also helps suppress blade-vortex interaction noise common in multi-bladed systems. These findings support previous scaling analyses and point toward unconventional rotor designs as viable options for low-noise aerial platforms.

  PublisherOA PDFDOI

Recent grants

• UNS: Coupled Flow-Chemistry Modeling of Thrombogensis in Human Ventricles

  NSF · $290k · 2015–2020

• SCH: INT: Mapping the Cardiac Acousteome: Biosensing and Computational Modeling Applied to Smart Diagnosis and Monitoring of Heart Conditions

  NSF · $2.0M · 2013–2018

• Collaborative Research: Effective Face Masks to Mitigate COVID-19 Transmission: Insights from Multimodal Quantitative Analysis

  NSF · $336k · 2020–2025

• Multiphase Chemo-Fluid Dynamics in the Stomach: Computational Models with Applications to Gastric Digestion in Health and Disease

  NSF · $470k · 2020–2025

• Effect of Wing Deformation and Flexibility on the Aerodynamics of Insect Flight

  NSF · $208k · 2009–2011

Frequent coauthors

• Jung-Hee Seo

  Johns Hopkins University

  91 shared

• Louis N. Cattafesta

  39 shared

• Jung Hee Seo

  Johns Hopkins University

  36 shared

• Charles Meneveau

  32 shared

• Meliha Bozkurttas

  28 shared

• H. S. Udaykumar

  25 shared

• Fady Najjar

  Lawrence Livermore National Laboratory

  25 shared

• Donghyun You

  Pohang University of Science and Technology

  24 shared

Education

• PhD, Theoretical and Applied Mechanics

  University of Illinois System

  1995

• M.S., Aerospace Engineering

  University of Florida

  1991

Awards & honors

• 2025 American Institute for Medical and Biological Engineeri…
• 1996 Francois Frenkiel Award from the Division of Fluid Dyna…
• 2022 Stanley Corrsin Award from the Division of Fluid Dynami…
• 2006 Lewis Moody Award from the American Society of Mechanic…
• 2021 Freeman Scholar Award from the American Society of Mech…