GTREO Seminar: Dr. John Clark – AFRL

An Alternate Means to Form Non-Dimensional Products in Dimensional Analysis

ABSTRACT: Engineering students encounter dimensional analysis early in an undergraduate curriculum. A critical step in the process involves the selection of scaling parameters, but unfortunately this selection can seem mysterious and arbitrary.  However, an alternate technique called the “step-by-step” method exists.  Discussion of the technique is largely absent from standard textbooks This seminar is intended to present this method.  It requires no prior selection of scaling parameters, and it is amenable to easy implementation in a computer scripting language.  Accordingly, it encourages the student to explore the derivation of various non-dimensional formulations.  The method is briefly described, and examples of its application are presented for: the process of vortex shedding from a circular cylinder, the variation of the heat-transfer distribution along a flat plate, and the location of the onset of transition to turbulence in turbine flows.  The form of the latter was certainly unknown at the outset, and the history of transition model development might lead one to conclude that the search for suitable models in such complicated flows was futile.  Nevertheless, dimensional analysis was applied to the problem, and models were developed that enabled substantial increases in the capability of low-pressure turbine airfoils.  Finally, experimental data validating these design improvements is presented. 

BIOGRAPHY: Dr. John Clark is Principal Engineer and Lead for Turbine Research in the Turbomachinery Branch of the Turbine Engine Division, Aerospace Systems Directorate at the Air Force Research Laboratory. He received his doctorate in Engineering Science from the University of Oxford where he was a student of the late Prof. Terry Jones. He has industrial experience from the Turbine Aerodynamics group at Pratt & Whitney. In 2012 he was named the Engineer of the Year by the American Institute of Aeronautics and Astronautics. He is a Fellow of the American Society of Mechanical Engineers, and in October 2024 he was named a Fellow of the Air Force Research Laboratory.