Identifier

etd-04092013-093002

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

Abstract Unforced and forced film cooling jets are investigated in view to develop a reduced order model of the velocity and temperature fields. First, a vertical jet in cross-flow, a configuration well documented at high blowing ratios, is investigated at low blowing ratios using experimental visualizations and large eddy simulations. The unforced study reveals that dominant structures at low blowing ratio can be significantly different from the ones formed at high blowing ratio and describes their evolution and transition as the blowing ratio is changed. The forced jet investigations extend the results of past numerical studies in terms of starting vortex classification to partly modulated jets, and evidence a quantitative mismatch in the transition blowing ratio threshold between experiments and simulations. Film cooling performance estimations show that, at fixed mass flow rate, unforced jets perform better than the forced jets while at fixed pressure supply, forced jets can bring some improvements over their unforced counterpart. A survey of a more application relevant inclined jet is carried out using comparable methods. The unforced study shows the attached inclined and vertical jet vortical structures have strong similarities yet one of them is absent from the former configuration therefore leading to smoother regime transitions. The forced inclined jet study reveals some common starting vortex regimes with the ones of the vertical jet, but also exhibits unique sets of structures not observed before. Film cooling performance of inclined jets is also assessed and compared to relevant vertical jet results. Derivations of reduced order models of two-dimensional systems for both velocity and temperature fields using the Proper Orthogonal Decomposition (POD) - Galerkin method are used to establish the numerical methods and potential caveats of the method. Then, POD of unforced and forced inclined jet is carried out as a statistical analysis tool to evidence the energetically dominant flow structures. Finally, reduced order models of the unforced jet are obtained in the attached and transitional regimes and reduced order models for the forced jet are derived in both instantaneous and phase averaged fields. Most of the derived models show reasonable agreement with the projected empirical data once stabilized using appropriate linear damping methods. The flow analysis, models and methods presented herein constitute an essential step towards the development of close-loop controlled film cooling system.

Date

2013

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Guo, Shengmin

Share

COinS