The final report consists of an AIAA and an ASME paper. An experimental investigation was conducted to measure skin friction along the chamber walls of supersonic combustors. A direct force measurement device was used to simultaneously measure an axial and transverse component of the small tangential shear force passing over a non-intrusive floating element. Skin friction coefficients between 0.001-0.005 were measured dependent on the facility and measurement location.
The paper describes the design for manufacturability of a prototype product as part of a manufacturing engineering capstone course. The product chosen was a vertically launched unmanned aerial vehicle (UAV)-the "Flying Eye." The Flying Eye is an autonomous parafoil surveillance platform quipped with sensors, controllers, mechanical components, and software. Once the autonomous UAV is deployed, it is designed to follow a predetermined flight path down to the ground. The design effort of the prototype device took place over a three-year period as a collaborative effort between the Aerospace Engineering and Industrial and Manufacturing Engineering departments at California Polytechnic State University. This project proved to be an excellent tool for the "project-based learning environment," which is the focus of Cal Poly's hands-on engineering programs. Details of the Flying Eye project and lessons learned during the course of this educational experience are provided.
An experimental investigation was conducted to measure skin friction along the chamber walls of supersonic combustors. A direct force measurement device was used to measure simultaneously an axial and a transverse component of the small tangential shear force passing over a nonintrusive floating element. This measurement was made possible with a sensitive piezoresistive deflection sensing unit. The floating head is mounted to a stiff cantilever beam arrangement with deflection due to the flow on the order of 0.00254 mm (0.0001 in). This allowed the instrument to be a nonnulling type. A second gage was designed with active cooling of the floating sensor head to eliminate nonuniform temperature effects between the sensor head and the surrounding wall. The key to this device is the use of a quartz tube cantilever with piezoresistive strain gages bonded directly to its surface. A symmetric fluid flow was developed inside the quartz tube to provide cooling to the backside of the floating head. Tests showed that this flow did not influence the tangential force measurement. Measurements were made in three separate combustor test facilities. Tests at NASA Langley Research center consisted of a Mach 3.0 vitiated air flow with hydrogen fuel injection at Pt = 500 psia (3466 kPa) and Tt = 3000 R (1667 K). Two separate sets of tests were conducted at the General Applied Science Laboratory (GASL) in a scramjet combustor model with hydrogen fuel injection in vitiated air at Mach = 3.3, Pt = 800 psia (5510 kPa), and Tt = 4000 R (2222 K). Skin friction coefficients between 0.001–0.005 were measured dependent on the facility and measurement location. Analysis of the measurement uncertainties indicate an accuracy to within ± 10–15 percent of the streamwise component.
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