Converging-diverging nozzle simulations at varying nozzle pressure ratios
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Authors
Martinus, Tyler
Issue Date
2025-05
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Aeronautical engineering
Alternative Title
Abstract
Compressible converging-diverging nozzles have a wide range of applications, including aerospacepropulsion, flow control and microfluidic flows commonly found in deposition, coating and
cooling techniques. When the ambient pressure is low, the continuum assumption does not
hold. With this aim in mind, compressible flow simulations near the continuum-rarefied
boundary are modeled using open-source software to increase the efficiency of converging-
diverging nozzles. This thesis employs OpenFOAM’s density-based solver, rhoCentralFoam,
to simulate nozzle flow dynamics under a range of operating conditions. Close comparisons
were made with the existing experimental and numerical data in the literature. Furthermore,
a comparative study is conducted between a unsteady Reynolds-Averaged Navier-Stokes
(URANS) based k − ω SST model and a Large Eddy Simulation (LES) k-equation model
to evaluate their accuracy in capturing turbulent structures and shock phenomena. Simu-
lations cover both free jet and impinging jet scenarios over a nozzle pressure ratio (NPR)
range of 8.78 to 296. For the impinging jet simulations, multiple distances from the wall
were simulated, specifically at 2.08 and 3.08 X/D. A grid convergence study was conducted
for the k − ω SST and k-equation model geometries to demonstrate mesh independence.
A time convergence study was performed for the k − ω SST model geometry and a batch
convergence study was performed for the k equation model geometry to verify temporal ac-
curacy. Experimental data from previous studies using an identical nozzle geometry validate
the numerical results, highlighting features such as mach disks, expansion plumes, and shock
structures across the continuum regime and near the continuum-rarefied boundary. The
findings provide insights into the benefits and limitations of each turbulence model, offering
guidelines for their application in high-performance nozzle design and aeroacoustics. Future
work on simulating impinging supersonic underexpanded jets can yield novel results on the
shock tones and aeroacoustic features present in unsteady impinging jets especially within
the rarefied regime.
Description
May2025
School of Engineering
School of Engineering
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY