Experimental and computational investigations of fan/high-resistance medium flow interactions

Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical and Aerospace Engineering


Thong Q. Dang

Second Advisor

John Lagraff


Fan/high-resistance medium, Flow interactions, Turbomachinery

Subject Categories

Engineering | Mechanical Engineering


The fluid mechanics of the flow-interaction phenomena between an axial fan and a High-Resistance Medium (HRM) is thoroughly investigated through experimental efforts and 3D CFD simulations. The parameters considered in this study include the size of the HRM relative to the fan, the gap between the HRM and the fan, and the fan tip geometry. In the experimental effort, global parameters (fan power and back pressure) and detailed flow information (spanwise distribution of total pressure rise across the fan) are measured. Flow visualization studies using tufts are also performed to qualitatively examine the flowfield on the fan blade surface and near the fan trailing edge. Lastly, CFD calculations using the commercial software STAR-CD are employed to examine the complex 3D flowfield of the fan/HRM configuration. The most significant finding in this study is that fan performance (e.g. pressure rise and efficiency) can be significantly increased and the quality of the flowfield in the blade region can be considerably improved when the HRM is placed "close" to the fan. These improvements largely come from the reduction of leakage flow at the tip and flow separation at the hub, which results in lower and more uniform axial velocity at the fan trailing edge. The primary flow-interaction mechanism affecting fan performance is then identified as the radial shifting of streamlines as seen in the meridional plane. The other possible fan/HRM flow-interaction mechanism, the change in overall flow turning as seen in the blade-to-blade plane (or the so-called flow deviation angle ), is found to be weak for the fan studied here. Although the fully-shrouded fan has better performance than the partially-shrouded fan in a close-coupled fan/HRM configuration where the HRM diameter is larger than the fan diameter, system performance is poorer because the flow enters the HRM as a "jet" (hence larger pressure drop across the HRM). On the other hand, the open tip of the partially-shrouded fan allows the flow leaving the fan to rapidly spread out in the radial direction and to enter the HRM at a much lower axial-velocity magnitude (hence lower pressure drop across the HRM).


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