Thursday, June 18, 8:00 AM - 10:00 AM

Lecture

Session Chairs:
Oscar Kogenhop,
,

Presentations

Note: Presentations may start a few minutes before the time listed in the schedule.

John P. Clark
Aerodynamics Engineering Discipline Lead
KRATOS, Florida Turbine Technologies
Jupiter, FL
USA

Abstract: The ability to predict accurately the levels of unsteady forcing on turbine blades is critical to avoid high-cycle fatigue failures. Further, a demonstrated ability to make accurate predictions leads to the possibility of controlling levels of unsteadiness through aerodynamic design. There are several desiderata to achieve designs that experience reduced forcing functions. First, and quite simply, any such design is by definition grounded in the basic physics of the flow. Second, confidence in the fidelity of the design-level analyses used to predict the relevant flow physics is critical. This in turns means that design analyses are as well validated as possible and that both the viscous and geometric modeling of the turbine is appropriate to the problem. Additionally, it is critical that proper periodicity of the predicted flowfield is achieved during design-level analyses. An ability to judge this is in turn dependent on an understanding of basic concepts in digital signal processing that are also essential to the accurate calculation of unsteady forces on airfoils. Here, a method to assess the convergence of periodic flowfields is presented with reference to an experimental turbine designed at the Air Force Research Laboratory. Then, the physics of the flowfield in this turbine that gives rise to unsteady interactions is discussed with reference to available code-validation data. Then, several design techniques are considered either to reduce the magnitude or alter the phase of unsteady interactions within the turbine to mitigate forcing. These include the shaping of both the rotating and stationary airfoil profiles as well as a novel flow-control method that involves steady blowing from the pressure side of the downstream stationary airfoil row. In addition, the effects of downstream vane asymmetric spacing, vane-to-vane clocking, and downstream airfoil re-stagger are assessed. It is also shown that rapid-turnaround unsteady analysis is a useful tool for guiding the assembly of a turbine blade row to minimize forcing on a target airfoil. Finally, the efficacy of many of these methods to reduce unsteadiness is demonstrated through rotating turbine experiments.

Bio: Dr. John Clark is the Discipline Lead for Aerodynamics at Kratos, Florida Turbine Technologies. He joined Kratos in September of 2025 after more than 23 years with the Air Force Research Laboratory at Wright-Patterson Air Force Base, Dayton, OH. At AFRL he led the in-house research program in turbines for the Turbine Engine Division of the Aerospace Systems Directorate. He retired from the USAF as an AFRL Fellow, and he is a Fellow of the ASME. While at AFRL he was also named the AIAA Engineer of the Year in 2012. Prior to joining AFRL, he worked in the Turbine Aerodynamics group at Pratt & Whitney. He received his doctorate in Engineering Science from the University of Oxford where he was a student of the late Prof. Terry Jones.