On the impact of injection schemes on transition in hypersonic boundary layers
Three geometries are explored for injecting CO_2 into the boundary layer of a sharp five degree half-angle cone. The impact of the injection geometry, namely discrete injection holes or a porous conical section, on tripping the boundary layer is examined, both with and without injected flow. The experiments are conducted at Caltech's T5 reflected shock tunnel. Two different air free-stream conditions are explored. For the discrete-hole injectors, the diameter for the injection holes is 0.75 mm nominally and the length to diameter ratio is about 30. One injector has a single row of holes and the other has four rows. With the 4-row geometry fully turbulent heat transfer values are measured within four centimeters of the last injection row for both free-stream conditions. The 1-row injector results on a reduction of 50% in the transition Reynolds number. The porous injector does not move the transition Reynolds number upstream by itself with no injection flow.
This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. The authors would like to thank Bahram Valiferdowsi for helping with the design of the injection pieces and with the maintenance of the facility. Financial support for this work was provided in part by the Air Force Office of Scientific Research, USAF, under grant/contract number F49620-IHOUSE07E0000. The program manager is Dr. John Schmisseur to whom the authors are grateful for his continued support throughout this project.
Published - AIAA-2009-7204.pdf