About

Andres Goza is an Assistant Professor in Aerospace Engineering at the University of Illinois Urbana-Champaign. He holds a Ph.D. in Mechanical Engineering from the California Institute of Technology, where his thesis focused on numerical methods for fluid-structure interaction and their application to flag flapping. His academic background also includes a Master's degree in Mechanical Engineering from Caltech and a Bachelor's degree in Mechanical Engineering with a minor in Computational and Applied Mathematics from Rice University. His research interests encompass unsteady aerodynamics, fluid-structure interaction, and computational fluid dynamics. He has contributed to the understanding of aeroelasticity, applied aerodynamics, and flow control, with a focus on phenomena such as flapping, resonance, and nonlinear fluid-structure interactions. Dr. Goza has held positions as an Affiliate Assistant Professor in Computational Science and Engineering and Mechanical Science and Engineering at Illinois since January 2019, and he completed postdoctoral research at Princeton University. His work involves developing and applying advanced simulation techniques to study complex aerodynamic systems, including unsteady flows, bio-inspired flow control devices, and phononic materials for aerodynamic applications.

Research topics

• Computer Science
• Mechanics
• Aerospace engineering
• Physics
• Engineering
• Marine engineering
• Structural engineering
• Geology
• Classical mechanics
• Mathematics

Selected publications

• A framework to systematically study the nonlinear fluid-structure interaction of phononic materials with aerodynamic flows

  Journal of Fluids and Structures · 2026-04-06

  articleOpen accessSenior author

  Phononic materials (PMs) are periodic media that exhibit novel elastodynamic responses. While PMs have made progress in vibration-mitigation applications, recent studies have demonstrated the potential of PMs to passively and adaptively modulate flow behavior through fluid-structure interaction (FSI). For example, PMs have been shown to delay laminar-to-turbulent transition and mitigate unsteadiness in shock-boundary layer interactions. However, a systematic framework to relate the effect of specific PM behaviors to the FSI dynamics is lacking. Such a framework is essential to systematically investigate the complex and nonlinear coupled dynamics of the FSI. Further, parameters that are not typically considered in PM models become critical, such as the vibration amplitude. This article addresses this gap by proposing FSI-relevant ``behavioral'' parameters, distinct from the structural parameters of the PM, but with a clear mapping provided to them. We use high-fidelity, strongly coupled simulations to quantify the FSI between a novel configuration of laminar flow past a flat plate, equipped with a PM. Our study proposes four critical PM behavioral parameters -- effective stiffness, truncation resonance frequency, a quantity representing the dynamic displacement amplitude, and unit cell mass -- that influence the spectral characteristics of the vortex-shedding process inherent to the flat plate system. Results show connections between each parameter and distinct behavior in the lift coefficient in FSI. While the focus of this work is on the PM-FSI dynamics in an aerodynamic flow, we argue that identifying these behavioral parameters is key to unlocking scientific study and design with phononic materials in fluid flows more broadly.

  PublisherDOI

• Beyond first-order accuracy in continuous-forcing immersed boundary methods, and their well-conditioned projection-based solution

  arXiv (Cornell University) · 2026-04-30

  preprintOpen accessSenior author

  We introduce a refined immersed boundary (IB) methodology that is better-than-first-order accurate in practice, while preserving key properties of "continuous-forcing" IB approaches that retain a singular source term in the governing equations. Our method leverages a smoothed indicator (Heaviside) function, following ideas from multiphase flow and immersed layers formulations, to recast the IB solution as a composite of distinct interior and exterior fields. We demonstrate that, when cast through this composite-solution lens, prior continuous-forcing IB methods can be seen as neglecting terms in the governing and constraint equations that restrict the solution to first-order accuracy. We incorporate these terms to systematically improve accuracy without the need for heuristic corrections. In canonical Poisson problems, we empirically demonstrate second-order convergence, and in incompressible Navier-Stokes simulations the method achieves slightly sub-second-order performance. While our present study focuses on these cases, the framework suggests a path towards second-order accuracy or higher, with further extensions. This perspective reframes accuracy limitations typically attributed to IB schemes. Although continuous-forcing IB methods are often reported to be only first-order accurate, we show that neither smoothing nor interface interpolation inherently restricts attainable order. Moreover, we naturally incorporate this higher-order formulation into a projection-based solution process. The resulting algorithm simultaneously mitigates the spurious surface stresses produced by ill-conditioned linear systems and reduces sensitivity to geometric resolution, addressing both conditioning and accuracy concerns within a unified approach.

  PublisherDOI

• Weakly coupled fluid-structure interaction between wall-bounded turbulent flows and defect-embedded phononic subsurfaces

  ArXiv.org · 2026-04-12

  articleOpen access

  We investigate the interaction between wall-bounded turbulence and defect-embedded phononic subsurface (D-Psub) using a weakly coupled fluid--structure framework, in which the flow and structure are advanced sequentially without sub-iterations. The D-Psub subsurface is modeled as a dynamic wall with a resonance introduced via a localized structural defect, driven by spatially averaged wall-pressure fluctuations from a turbulent channel flow. This configuration enables a controlled study of how a narrow-band structural response interacts with the broadband forcing of near-wall turbulence. Despite broadband turbulent forcing, the D-Psub exhibits a narrow-band response that modifies near-wall dynamics, with representative cases showing suppression of velocity fluctuations, increased coherence of streamwise streaks, and a measurable reduction in turbulent drag. Crucially, the coupled system displays behavior that cannot be replicated by prescribed wall motion: the dominant oscillation frequency shifts away from the designed resonance due to fluid--structure interaction. Additionally, the phase between panels is shown to be governed by the convection of turbulent structures. These results reveal a mechanism by which phononic subsurfaces filter and reorganize turbulent energy through frequency-selective coupling, distinct from conventional compliant or actively forced walls. The findings provide a physical basis for designing passive resonant surfaces that exploit turbulence-structure coupling for flow control.

  PublisherOA PDF

• A High-Fidelity Simulation Framework for Turbulent Flows with Complex (Metamaterial) Structures

  2026-01-08

  article

  We present a high-fidelity fluid–structure interaction framework based on a continuous-forcing immersed boundary method, integrated into a parallelized three-dimensional turbulent channel flow solver. The method is designed to handle a wide range of (sub)surface geometries, including complex metamaterial interfaces. We extend an existing strongly coupled IB-FSI formulation with new spatially discrete operators that enable information transfer between subsurface metamaterials and compliant IB patches. Several key modifications support this versatile functionality: a hybrid uniform–stretched grid to reduce the computational load, IB forcing to compute one-sided velocity gradients for accurate friction velocity, and parallelized IB operations aligned with the underlying flow solver’s domain decomposition. We demonstrate the method using five test cases: laminar cylindrical Couette flow; a parallel scaling test; and three turbulent channel flow configurations at a friction Reynolds number of 186, including a minimal flow unit with rigid walls, a channel with prescribed traveling wave–like wall deformations, and a channel with a compliant wall exhibiting rigid-body–like dynamics. The last test problem demonstrates the growing capability to handle arbitrary structures engaging in coupled dynamics with the flow, towards future investigations into fluid–metamaterial interaction.

  PublisherDOI

• Weakly coupled fluid-structure interaction between wall-bounded turbulent flows and defect-embedded phononic subsurfaces

  arXiv (Cornell University) · 2026-04-12

  preprintOpen access

  We investigate the interaction between wall-bounded turbulence and defect-embedded phononic subsurface (D-Psub) using a weakly coupled fluid--structure framework, in which the flow and structure are advanced sequentially without sub-iterations. The D-Psub subsurface is modeled as a dynamic wall with a resonance introduced via a localized structural defect, driven by spatially averaged wall-pressure fluctuations from a turbulent channel flow. This configuration enables a controlled study of how a narrow-band structural response interacts with the broadband forcing of near-wall turbulence. Despite broadband turbulent forcing, the D-Psub exhibits a narrow-band response that modifies near-wall dynamics, with representative cases showing suppression of velocity fluctuations, increased coherence of streamwise streaks, and a measurable reduction in turbulent drag. Crucially, the coupled system displays behavior that cannot be replicated by prescribed wall motion: the dominant oscillation frequency shifts away from the designed resonance due to fluid--structure interaction. Additionally, the phase between panels is shown to be governed by the convection of turbulent structures. These results reveal a mechanism by which phononic subsurfaces filter and reorganize turbulent energy through frequency-selective coupling, distinct from conventional compliant or actively forced walls. The findings provide a physical basis for designing passive resonant surfaces that exploit turbulence-structure coupling for flow control.

  PublisherDOI

• Dynamic Passive Control of Turbulent Drag via Subsurface Resonant Phononic Material

  2026-01-08

  article

  This work presents a passive turbulence-control strategy based on a resonant phononic material (RPM) embedded beneath the surface of a turbulent channel flow. The RPM is modeled as a mass–spring–damper chain tuned to a defect-induced resonance that interacts with near-wall turbulence. Using a weakly coupled fluid–metamaterial framework, we show that both the wall-pressure forcing and the RPM response collapse onto a narrow frequency band dictated by the designed resonance, and that within a moderate actuation-amplitude range the system produces measurable transient drag-reduction effects. Direct numerical simulations (DNS) further reveal a well-defined stable interval of RPM damping coefficients, with a sharp transition between underdamped (growing) and overdamped (bounded) response regimes. To enable rapid exploration of RPM configurations, we also develop a reduced-order weakly coupled model in which a linear wall-pressure approximation replaces the full pressure-Poisson solution; this simplified model accurately reproduces the key bifurcation behavior observed in DNS. Overall, the study clarifies the mechanisms governing RPM–flow coupling and informs the design of passive, energy-efficient compliant surfaces for aerodynamic applications.

  PublisherDOI

• Beyond first-order accuracy in continuous-forcing immersed boundary methods, and their well-conditioned projection-based solution

  ArXiv.org · 2026-04-30

  articleOpen accessSenior author

  We introduce a refined immersed boundary (IB) methodology that is better-than-first-order accurate in practice, while preserving key properties of "continuous-forcing" IB approaches that retain a singular source term in the governing equations. Our method leverages a smoothed indicator (Heaviside) function, following ideas from multiphase flow and immersed layers formulations, to recast the IB solution as a composite of distinct interior and exterior fields. We demonstrate that, when cast through this composite-solution lens, prior continuous-forcing IB methods can be seen as neglecting terms in the governing and constraint equations that restrict the solution to first-order accuracy. We incorporate these terms to systematically improve accuracy without the need for heuristic corrections. In canonical Poisson problems, we empirically demonstrate second-order convergence, and in incompressible Navier-Stokes simulations the method achieves slightly sub-second-order performance. While our present study focuses on these cases, the framework suggests a path towards second-order accuracy or higher, with further extensions. This perspective reframes accuracy limitations typically attributed to IB schemes. Although continuous-forcing IB methods are often reported to be only first-order accurate, we show that neither smoothing nor interface interpolation inherently restricts attainable order. Moreover, we naturally incorporate this higher-order formulation into a projection-based solution process. The resulting algorithm simultaneously mitigates the spurious surface stresses produced by ill-conditioned linear systems and reduces sensitivity to geometric resolution, addressing both conditioning and accuracy concerns within a unified approach.

  PublisherOA PDF

• Adjoint-based optimal actuation for separated flow past an airfoil

  Physics of Fluids · 2025-03-01

  articleSenior author

  This study determines the normal actuation on the surface of a NACA (National Advisory Committee for Aeronautics) 0012 airfoil for lift and drag benefits using numerical optimization. The airfoil is at an angle of attack of α=15° and a Reynolds number of Re=1000 and actuation is permissible on both the suction and pressure surfaces. This approach of optimal actuation along the full airfoil surface augments most other studies that have focused on parametrically varying control on the suction surface. The gradient-based optimization procedure requires the gradient of the cost functional with respect to the design variables, which is determined using the adjoint of the governing equations. The optimal actuation profiles for the two performance aims are compared. Where possible, similarities with commonly considered open-loop actuation in the form of backward traveling waves on the suction surface have been highlighted. In addition, the key spatial locations on the airfoil surface for the two control strategies have been compared to earlier works where actuation has been limited to a sub-domain of the airfoil surface. The flow features emerging from the optimal actuation variations and their consequent influence on the instantaneous aerodynamic coefficients have been analyzed. To complement our findings with normal actuation, we also provide in the Appendixes: results for a more general form of actuation with independent x and y components and for a different optimization window to assess the effect of this window parameter on the actuation profile and the flow features.

  PublisherDOI

• Intrinsic phase-based proper orthogonal decomposition (IPhaB POD): a method for physically interpretable modes in near-periodic systems

  Journal of Fluid Mechanics · 2025-01-09 · 3 citations

  articleOpen access

  Fluid dynamics systems driven by dominant, near-periodic dynamics are common across wakes, jets, rotating machinery and high-speed flows. Traditional modal decomposition techniques have been used to gain insight into these flows, but can require many modes to represent key physical processes. With the aim of generating modes that intuitively convey the underlying physical mechanisms, we propose an intrinsic phase-based proper orthogonal decomposition (IPhaB POD) method, which creates energetically ranked modes that evolve along a characteristic cycle of the dominant near-periodic dynamics. Our proposed formulation is set in the time domain, which is particularly useful in cases where the cyclical content is imperfectly periodic. We formally derive IPhaB POD within a POD framework that therefore inherits the energetically ranked decomposition and optimal low-rank representation inherent to POD. As part of this derivation, a dynamical systems representation is utilized, facilitating a definition of phase within the system's near-periodic cycle in the time domain. An expectation operator and inner product are also constructed relative to this definition of phase in a manner that allows for the various cycles within the data to demonstrate imperfect periodicity. The formulation is tested on two sample problems: a simple, low Reynolds number aerofoil wake, and a complex, high-speed pulsating shock wave problem. The method is compared to space-only POD, spectral POD (SPOD) and cyclostationary SPOD. The method is shown to better isolate the dominant, near-periodic global dynamics in a time-varying IPhaB mean, and isolate the tethered, local-in-phase dynamics in a series of time-varying modes.

  PublisherOA PDFDOI

• Towards an Immersed-Boundary Resolvent Analysis Framework for Wall-Bounded Flows With Various Surface Configurations

  2024-07-27

  articleSenior author

  New flow control paradigms for wall-bounded flows are leveraging increasingly sophisticated actuation strategies targeted near the wall surface including riblets, anisotropic porous and textured surfaces, and passively adaptive metamaterials. This new direction brings a growing need for predictive computational tools that can accurately and efficiently account for these complex surface effects, potentially involving fully coupled fluid-structure interactions (FSI). The resolvent analysis framework is a natural choice for these aims, as it provides a fast computational model rooted in an analysis of the true linearized operator for the wall-bounded flows of interest. Yet, while there are a number of resolvent-based strategies designed to incorporate surface effects, most are formulated for a specific configuration and cannot be readily extended to different setups. We present developments towards a more general formalism rooted in an immersed boundary (IB) treatment of the surface that we call IB resolvent. The proposed method inherits the benefits of versatile flow-surface treatment that high-fidelity IB methods have enjoyed for decades, formally incorporated into a spanwise-streamwise-temporal homogeneous resolvent framework that has become a workhorse for wall-bounded flow analysis and control design. We present the mathematical formulation for the case of turbulent channel flow with a static sinusoidal wall boundary condition and examine its performance. We also demonstrate that when the wall is equivalent to a flat surface, the IB resolvent results match those of the conventional resolvent analysis. While the results are focused on this canonical setting, the derivation is constructed to facilitate straightforward extensions to more complex configurations.

  PublisherDOI

Recent grants

• Bioinspired, Adaptive, and Self-Deploying Flaps for Distributed Aerodynamic Flow Control

  NSF · $475k · 2020–2023

Frequent coauthors

• Nirmal J. Nair

  University of Illinois Urbana-Champaign

  14 shared

• Tim Colonius

  11 shared

• Brent Houchens

  Sandia National Laboratories

  11 shared

• Sam Oke

  Rice University

  5 shared

• Kurt Kienast

  5 shared

• Rachel Jackson

  5 shared

• Juan Castilleja

  Boeing (Australia)

  5 shared

• Ernold Thompson

  5 shared

Labs

• Gas Dynamics LaboratoryPI

Education

• PhD, Mechanical and Civil Engineering

  California Institute of Technology

  2017

• BS, Mechanical Engineering

  Rice University

  2011

Awards & honors

• Alumni Award for Distinguished Service
• Distinguished Alumnus Award
• Harry H. Hilton Dedicated Service Award
• Outstanding Recent Alumni Award