Principal Fluid Dynamics

COMPANY OVERVIEW Grex Defense builds autonomous systems for air dominance. The character of conflict is changing, with autonomy, mass, and software now deciding outcomes. The advantage goes to whoever can field new capability first, and Grex Defense exists to provide rapid capability solutions for hard defense problems. JOB DESCRIPTION Grex Defense is seeking a Principal Computational Fluid Dynamicist to lead the development of aerodynamic analysis, CFD, aeroelasticity, and fluid-structure interaction capabilities for clean-sheet autonomous aircraft. This is a senior, hands-on technical leadership role in an early-stage environment. You will work directly with the engineering leadership team to take aircraft from blank-sheet concepts through preliminary and detailed design, simulation, test, and flight. You will be responsible for determining how aerodynamic problems should be solved, not simply running an established CFD process. You will help establish the tools, workflows, computational infrastructure, verification and validation practices, and aerodynamic databases required to rapidly develop new aircraft. This includes determining where hand calculations and low-order methods are appropriate, where high-fidelity CFD or fully coupled multiphysics simulation is required, and how these methods should work together throughout the design process. As an early member of the engineering organization, you will also help define make-versus-buy decisions, evaluate commercial and academic tools, select outside partners where appropriate, identify and hire key technical talent, and mentor engineers as the team grows. Startup life requires moving comfortably between deep technical analysis, rapid conceptual design, tool development, troubleshooting, test support, and longer-term capability building. WHAT YOU’LL DO — 30 / 60 First 30 Days — Establish the Approach Work with the vehicle design team on blank-sheet aircraft conceptual design, rapidly evaluating configurations using analytical, empirical, and low-order aerodynamic methods. Establish first-order estimates of aircraft performance, aerodynamic characteristics, static stability, control effectiveness, trim, and vehicle loads. Assess existing aerodynamic requirements, assumptions, geometry, mission constraints, and available test or simulation data. Define the initial CFD and aerodynamic analysis strategy, including the appropriate fidelity level at each stage of vehicle development. Evaluate and recommend commercial, open-source, and internally developed CFD, meshing, post-processing, aeroelasticity, and FSI tools. Determine initial make-versus-buy decisions for CFD software, meshing, HPC/cloud compute, aeroelastic tools, automation, and specialized analysis capabilities. Establish initial meshing, solver, convergence, verification, data-management, and post-processing standards. Identify critical aerodynamic technical risks and the analyses or tests required to retire them. First 60 Days — Build the Capability Establish repeatable and automated CFD workflows for external and internal aerodynamic analysis. Build the initial low-order-to-high-fidelity analysis toolchain, connecting conceptual design methods with CFD and downstream simulation. Begin generating aerodynamic data across angle of attack, sideslip, control positions, Reynolds number, Mach number, and relevant vehicle configurations. Develop methods for calculating static stability and control derivatives and establish strategies for predicting dynamic and rotary derivatives. Define approaches for modeling vehicle angular rates, forced motion, dynamic derivatives, and unsteady aerodynamic behavior. Establish the architecture and data standards for a 6-DOF aerodynamic database suitable for flight dynamics, GNC, simulation, performance, and loads analysis. Develop initial aeroelastic workflows using low-order methods such as ASWING or equivalent tools to understand flexible-aircraft behavior early in the design process. Establish interfaces between aerodynamics, structures, propulsion, thermal, GNC, simulation, and vehicle design teams. Identify and begin recruiting key aerodynamic, CFD, aeroelasticity, and supporting technical hires required to grow the capability. QUALIFICATIONS Required 15+ years of professional experience in computational fluid dynamics, aerodynamics, or closely related disciplines, with significant experience using both commercial and academic/research CFD codes. Expert knowledge of fluid mechanics, aircraft aerodynamics, numerical methods, and aerodynamic design. Expert knowledge spanning low-order through high-fidelity methods, including analytical/empirical approaches, lifting-line, vortex-lattice, panel/potential-flow, Euler, RANS, and URANS methods. Demonstrated ability to move between hand calculations, low-order models, and high-fidelity CFD and select the appropriate fidelity for the engineering decision being made. Extensive experience with external aerodynamics, including complete aircraft configurations, control surfaces, propulsion integration, and aerodynamic interference. Extensive experience with internal aerodynamics, including intakes, ducts, cooling flows, heat exchangers, pressure losses, and exhaust flows. Expert understanding of aircraft static stability, trim, control derivatives, and dynamic/rotary derivatives. Experience developing aerodynamic models for angular rates, maneuvering flight, prescribed motion, forced oscillation, or other unsteady vehicle behavior. Demonstrated experience developing multidimensional aerodynamic databases for flight dynamics, controls, performance, loads, or real-time simulation. Expert knowledge of modern CFD meshing techniques, including structured, unstructured, hybrid, boundary-layer, overset, Cartesian, and adaptive approaches. Strong understanding of CFD verification and validation, including grid convergence, time-step convergence, iterative convergence, numerical uncertainty, turbulence-model sensitivity, and correlation with physical testing. Expert understanding of HPC and modern compute architectures, including parallel CFD, CPU/GPU computing, solver scaling, and efficient execution of large analysis campaigns. Expert knowledge of aeroelasticity and fluid-structure interaction and their application to aircraft design. Strong understanding of static and dynamic aeroelastic phenomena, including load redistribution, divergence, control reversal, flutter, structural mode coupling, and dynamic response. Experience with low-order aeroelastic methods such as ASWING or equivalent tools for flexible-aircraft trim, loads, stability, and rapid configuration assessment. Experience with high-fidelity CFD/FEA coupling, including one-way and two-way FSI using tools such as ANSYS Fluent and ANSYS Mechanical or equivalent. Ability to determine when rigid CFD, low-order aeroelastic analysis, one-way FSI, or fully coupled transient FSI is appropriate. Strong understanding of thermal-fluid modeling and conjugate heat transfer, particularly as applied to aircraft cooling and propulsion integration. Understanding of multiphase and free-surface CFD, including fuel slosh and the resulting forces and moments acting on a vehicle. Experience with unsteady aerodynamic phenomena, including separated flows, vortex shedding, gust response, maneuvering flight, and other transient effects. Strong programming and workflow automation skills using Python, C/C++, Fortran, MATLAB, or equivalent languages. Demonstrated ability to establish technical processes and tools in a clean-sheet or early-stage vehicle development environment. Ability to work across aerodynamics, structures, propulsion, thermal, GNC, simulation, test, and vehicle design disciplines. Demonstrated ability to provide technical leadership and mentorship while remaining hands-on with engineering analysis and tool development. Preferred Advanced degree in Aerospace Engineering, Mechanical Engineering, Applied Mathematics, Computational Science, or a related technical field. Experience supporting multiple clean-sheet aircraft programs from conceptual design through build, ground test, and flight test. Experience developing or modifying academic, research, open-source, or proprietary CFD solvers, rather than exclusively operating commercial software. Experience with DES, LES, scale-resolving simulation, high-order numerical methods, or other advanced CFD techniques. Experience developing reduced-order aerodynamic and aeroelastic models for design optimization, simulation, controls, or real-time applications. Experience with Design of Experiments, surrogate modeling, response surfaces, machine learning, or other methods for efficiently constructing high-dimensional aerodynamic databases. Experience integrating CFD and aerodynamic data directly into 6-DOF simulation, GNC development, hardware/software-in-the-loop environments, or real-time simulation. Experience correlating CFD and aeroelastic models against wind-tunnel, ground-vibration, structural, propulsion, or flight-test data. Experience with propeller, rotor, powered-lift, or other strongly coupled propulsion-airframe aerodynamic interactions. Experience building automated CFD infrastructure using cloud computing, HPC clusters, containers, job schedulers, or GPU-accelerated solvers. Experience establishing a new CFD/aerodynamics capability, technical team, or computational workflow from the ground up. Experience working in a fast-paced aerospace startup, advanced development program, or similarly rapid clean-sheet engineering environment. SUMMARY OF BENEFITS Compensation: $150,000–$300,000 including salary, bonus, and benefits. Total compensation is based on, but not limited to, work experience, education, training, certifications, critical skills, and other business considerations. All offers are contingent on successful background and reference checks.