Existence and Analysis of a Rotating Stall Inception Continuum & Development of Concept Questions in Fluid Dynamics

Abstract

This thesis presents two projects, an analysis of rotating stall inception for axial compressors in turbomachinery, and a description of the creation of Concept Questions for a text on internal flows. The first part of this thesis identifies flow behavior that defines two routes to rotating stall, known as modal and spike type rotating stall inception. It continues previous studies by MIT and the University of Cambridge surrounding unification of these two stall types under a dynamical system framework. Calculations were carried out for an isolated rotor, with a high hub to tip radius ratio, using TBLOCK, a Reynolds Averaged Navier Stokes solver. The results show (i) the dependence of stall inception on the compressor axisymmetric pressure rise characteristic and the characterization of mode and spike stall inception as two paths, located at the ends of a continuum of possible paths to stall. (ii) the effect of blade passage accelerations and asymmetry in the onset process, and (iii) the divergence of stall inception from two-dimensionality as a function of the slope of the total-to-static compressor pressure rise characteristic. The calculations show that compressor pressure rise characteristic slopes, dψ/dϕ, less than 0.3 have a stall cell growth rate, σ, that agrees with two-dimensional theory. The divergence of stall inception from two-dimensionality is suggested as a distinguishing feature of spike type stall inception compared to modal type stall inception. The second part of this thesis encompasses the creation, editing and compilation of Concept Questions for seven book chapters in a new text that describes the use of Concept Questions in teaching (and learning) fluid mechanics. The composition and qualities of a good concept question are defined, and the process of generating and editing questions for the intended audience is discussed.