Session: 15-01: Internal Cooling Design Optimization

Paper Number: 152415

Fluidic Oscillators in Impingement Jet Cooling: a Novel Configuration for Realizing Sweeping Jets 

This study introduces an enhanced impingement cooling system for turbomachinery that integrates fluidic oscillators in a novel configuration to generate sweeping jets. The aim is to improve thermal boundary layer disruption, enhance heat transfer, and reduce cooling air requirements. Existing literature indicates that the addition of sweeping jets can improve heat transfer and cooling uniformity.

The geometry represents a generic impingement cooling configuration with a row of nine inline impingement jets. Each impingement jet hole has a diameter of 0.0152 m, a nozzle-to-plate distance (H/D) of 5, and a jet pitch (p/D) of 5. The jets impinge on a heated plate within a square channel that is closed on one end, operating at a global jet Reynolds number of 10,000, and subjected to a self-induced crossflow. Fluidic oscillators are passive devices that utilize flow separation and feedback mechanisms to create a sweeping jet of air. The oscillators are strategically incorporated immediately downstream of each the impingement jets to induce optimal oscillating behavior.

To investigate these behaviors both numerically and experimentally, Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations were performed using the DLR's in-house CFD code, TRACE. The SST turbulence model was employed, with turbulent scalar fluxes modeled using the Reynolds analogy for a constant turbulent Prandtl number. A sensitivity analysis of the time step and a grid convergence study ensured the accuracy of the simulations. Complementing the simulations, high-speed Particle Image Velocimetry (PIV) was utilized to capture time-resolved 2D-2C flow data across a field of view encompassing up to three jets simultaneously. Modal analysis using proper orthogonal decomposition (POD) and spectral proper orthogonal decomposition (SPOD) provided insights into the flow dynamics.

These combined approaches clarify the effects of the fluidic oscillators on jet stabilization, cooling uniformity, and the disruption of the thermal boundary layer. This investigation highlights the effects of fluidic oscillators arranged in a novel configuration, focusing on heat transfer efficiency, cooling uniformity, and pressure losses. The integration of high-speed PIV data and numerical simulations offers a comprehensive understanding of the system's behavior, providing key parameters for the effective incorporation of fluidic oscillators in gas turbine cooling applications.

Presenting Author: Robin Brakmann DLR

Presenting Author Biography: Dr. Robin Georg Brakmann
Scientist & Group Leader
German Aerospace Center (DLR), Göttingen, Germany

Dr. Robin Georg Brakmann is a seasoned scientist and group leader at the German Aerospace Center (DLR), where he has been contributing since 2017. He holds a Ph.D. from the University of Stuttgart (2017) and has completed thesis work at both McGill University, Montreal, and the University of Stuttgart (2010). Before joining DLR, he worked as a research engineer at the University of Stuttgart from 2011 to 2017.

His research focuses on experimental and numerical investigations of heat transfer, with special expertise in enhancing heat transfer, coolant passages, unsteady flow, secondary gas paths, and film cooling.

Authors:

Robin G. Brakmann DLR
Francisco Carvalho DLR
Marcel Matha DLR
Christian Morsbach DLR
Camille Pain DLR
Julien Pellé LAMIH UMR CNRS 8201 - Département Mécanique
Emilie Rairoux DLR
Michael Schroll DLR
Erik Techen DLR
Christian Willert DLR