Jonathan Long

Date of Award

January 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical Engineering

First Advisor

Forrest Ames

Abstract

In the interest of reducing airport congestion in the near future, researchers at NASA Glenn Research Facility have envisioned a new civilian transport aircraft which takes off vertically and cruises horizontally at Mach 0.5 using tilt-rotor technology. The engine under development consists of a four stage low pressure (LP) turbine. Many challenges are presented as the engine transitions from 100% shaft speed at takeoff to 54% shaft speed at cruise. The blading in this engine must be designed to optimize fuel efficiency, especially at cruise. The flow conditions in the LP turbine will change significantly from a Reynolds number of about 500,000 with a nearly tenfold drop to 50,000. The low Reynolds number flow enhances the susceptibility of separation and introduces more aerodynamic losses which will act to reduce the overall efficiency of the blade design. The vastly changing shaft speeds will induce a large variation in the flow's incidence angle of about 60°. The changing Reynolds number and incidence angle increases the complexity of the flow and will have a significant effect on transition and separation phenomena along the blading.

Testing for this blade design was conducted in the University of North Dakota's high speed low Reynolds number facility. This facility is configured in a closed-circuit arrangement and allows for steady-state high speed testing at pressures well below atmospheric. The facility was configured to accommodate a six blade five full passage linear cascade to experimentally acquire aerodynamic data concerning the inlet boundary layers, blade load distributions and total pressure losses over a wide range of Reynolds numbers and incidence angles. The Reynolds numbers under investigation were based off exit conditions and true chord and range incrementally from 50,000 to 568,000. Eight discrete inlet nozzles were fabricated for this study based of the inlet angle measured from the axial direction: -17°, -12°, -2.6°, 8°, 18°, 28°, 34.2° and 40°. These inlet angles correspond to a range of incidence angles from -51.2° to 5.8°. In addition to the Reynolds number and incidence angle effect, the effects of low and moderate turbulence intensity were also investigated. The aerodynamic losses were measured via a five-hole stinger type cone probe. The key component of this study were the mass averaged total pressure loss buckets which encompassed the range of Reynolds numbers and incidence angles under low and moderate turbulence conditions.

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