Date of Award
2026
Degree Type
Open Access Dissertation
Degree Name
Engineering and Industrial Applied Mathematics Joint PhD with California State University Long Beach, PhD
Program
Institute of Mathematical Sciences
Advisor/Supervisor/Committee Chair
Hamid Rahai
Dissertation or Thesis Committee Member
Marina Chugunova
Dissertation or Thesis Committee Member
Ali Nadim
Dissertation or Thesis Committee Member
Antonella Sciortino
Terms of Use & License Information
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 License.
Rights Information
© 2025 Komal Gada
Keywords
Flow modification devices, Jet, Passive flow control, Fundamental physics, Turbulators
Subject Categories
Mechanical Engineering
Abstract
This dissertation presents a comprehensive numerical study of coil-inserted elevated turbulent jets, aimed at advancing the understanding of passive flow control mechanisms and their effects on both free jet and jet in crossflow (JICF). It provides new insight into the fundamental physics of swirl-assisted mixing and offers a scalable framework for designing passive devices for jet flows. The study employs a pipe jet with a jet Reynolds number of 8500 based on the jet’s bulk velocity and the pipe internal diameter, with coil-inserts resulting in 1.44% of geometric blockage at the jet outlet. The methodology integrates detailed parametric analyses of coil geometry, specifically coil length (ℓ/D = 1, 5, and 10) and pitch (p/D = 0.5, 1, and 2), at various crossflow velocity ratios (R = Uj/Ucf = 0.5, 1, 2, 5and ∞). Both Reynolds-Averaged Navier–Stokes (RANS) and Large-Eddy Simulation (LES) are conducted using ANSYS Fluent solver at second order accuracy to quantify the influence of coil geometry on jet entrainment, mixing, and vortex dynamics. The mesh independent grids used range from 5 million to 24 million cell counts. This study attempts to provide a deep physical understanding of how coil insert geometry governs turbulent jet behavior through coupled axial, azimuthal, and radial vorticity interactions. The results demonstrated that coil inserts act as effective internal helical perturbation generators, imposing swirl and azimuthal asymmetry at the nozzle exit. In the free-jet configuration, coil-inserts induced perturbation accelerated the potential-core collapse, enhancing entrainment by up to 20%, and promoted earlier transition to turbulence. Short coil-insert (ℓ/D = 1) intensifies near-field mixing, and the flow fluctuations contain spectral energy distributed across a wide range of frequencies, indicating multi-scale turbulence with a range of eddy sizes. Whereas longer coil-inserts (ℓ/D ≥ 5) stabilize the exit flow, sustain coherent streamwise vortices, and extend turbulence production farther downstream. In the JICF, coil-inserts modified the counter-rotating vortex pair (CVP), jet trajectory, and mixing efficiency. The results revealed that short coil-inserts amplify shear layer roll-up and lateral entrainment, while longer coil-inserts promote deeper penetration and maintain CVP coherence over extended streamwise distances. The helical inserts also induce a mild internal pressure build-up, which strengthens the jet exit acceleration and enhances the upstream shear-layer interaction. From a design perspective, the findings clearly outline the potential of coil-inserts as a low-cost, low-maintenance, and energy-efficient solution for enhancing jet performance in both environmental and industrial applications. Short coil-inserts are optimal for environmental dispersion and pollutant dilution, where rapid near-field mixing, and fast decay of coherent structures are beneficial. Long coil inserts, on the other hand, are more suitable for combustion and thermal management systems that require sustained flow coherence and controlled entrainment for efficient energy conversion or cooling performance. The dual nature of the coil acting as both a flow exciter and conditioner establishes it as a tunable passive flow-control device, bridging the gap between geometric simplicity and functional adaptability.
ISBN
9798265476296
Recommended Citation
Gada, Komal. (2026). Numerical Investigations of a Pipe Jet With Coil Inserts With and Without Crossflow. CGU Theses & Dissertations, 1046. https://scholarship.claremont.edu/cgu_etd/1046.
