Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.
Abstract
The primary purpose of this study was to develop an understanding of the stability of laminar
flow through bluff body arrays, and investigate the nature of the unsteady vortex shedding regime
that follows. The flow was numerically investigated using a specially developed multi-domain
spectral element solver. Important criteria in the solver development were flexibility, efficiency, and
accuracy. Flexibility was critical to the functionality of the code, as arrays of varying geometry
were investigated. Efficiency with a high degree of accuracy was also of primary importance, with
the code implemented to run efficiently on today's massively parallel architectures.
Numerical two-dimensional stability analysis of the flow in several configurations of inline and
staggered array geometries was performed. The growth rate, eigenfunction, and frequency of the
disturbances were determined. The critical Reynolds number for flow transition in each case was
identified and compared to that of flow over a single body. Based on the solutions of the laminar
flow, a one-dimensional analytical analysis was performed on selected velocity profiles in the wake
region. The results of this analysis were used to guide the interpretation of the two dimensional
results and formulate a general theory of stability of inline and staggered bluff body arrays. The
nature of the flow in the unsteady regime following the onset of instability was examined for an
inline and a staggered arrangement. Particular attention was focused on the vortex shedding which
was visualized and quantified through computation of the flow swirl, a quantity which identifies
regions of rotary motion. The conditions required for the generation of leading edge vortex shedding
were identified and discussed. Finally, a third geometry related to the inline and staggered arrays
was considered. Flow solution data for this geometry is presented and its suitability as a model for
louvered arrays was discussed.Air Conditioning and Refrigeration Project 11
