Date of Award

Fall 2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

Sushil K. Chaturvedi

Committee Member

Arthur C. Taylor III

Committee Member

Miltiadis Kotinis

Call Number for Print

Special Collections; LD4331.E56 M335 2010

Abstract

The present study involves performing simulations, using the commercially available CFD code Fluent, to obtain under-expanded jet flow structures for different values of nozzle pressure ratio (NPR). A fluid flow domain comprised of a converging nozzle attached to a plenum chamber is discretized, using triangular cells, in the pre-processing software Gambit, companion software to Fluent. The test of grid independence is carried out by performing simulations for NPR value of 10 using three discretized flow domains, referred to as a mesh or a grid, with varying cell numbers. Two models, namely the inviscid compressible flow model, employing Euler equations, and the viscous compressible model, using the Spalart-Allmaras (SA) method for modeling turbulence, are used to simulate the under-expanded jet structure. The two models are solved using the first-order numerical scheme in the solver, Fluent. The SA flow model is eventually chosen as it gives good results with stable far-field flow patterns. Although the inviscid flow model gives reasonable results for global parameters such as wavelength, stand-off distance etc. it displays oscillatory flow patterns in the far-field due to the absence of viscous effects. The SA flow model and the mesh, whose solutions are grid independent, are then used to simulate the under-expanded jet structures for the NPR values of 1.75, 3, 5, 7, 10 and 15. In order to validate the present approach, the results obtained from the present study are compared with the experimental results of Love et al. The results indicate the presence of different regimes of flow patterns for different ranges of NPR values. At low NPR values shock diamonds are observed, at intermediate NPR values Mach disks are observed and at high NPR values bow shocks are observed. Transition from one regime of flow to another is seen as the NPR value is increased. The simulation results also reveal the formation of cell-like structures within the under-expanded fluid jet and the number of cell-like structures formed within the under-expanded jet are governed by the NPR values.

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DOI

10.25777/vd0w-zf35

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