Charles F. Wisniewski

Spatially resolved infrared spectra of F109 turbofan exhaust

There is a strong interest in diagnosing engine performance problems and maintenance needs using optical techniques instead of expensive, time-consuming mechanical inspection. A Telops Hyper-Cam MWIR imaging Fourier-transform spectrometer collected spectrally-resolved images of jet exhaust from an F109 turbofan engine operating at 53%, 82%, and 88% of maximum RPM. This work attempts to discern what information content about the turbulent jet flow field is revealed in the measured spectra. The spectrum is examined and simulated, a radial and axial temperature mapping of the plume is presented, and a turbulent temporal and spatial analysis method is demonstrated. Spectral simulation of a pixel centered at nozzle exit finds volume mixing fractions of 3.3% H2O and 2.8% CO2 and an exhaust temperature of 560K with the engine at 82%. A single, high frequency turbulent feature is mapped and tracked over several frames. Velocity of this feature, based on the 2.86kHz camera frame rate and 0.067cm2 per pixel spatial resolution, is approximately 176m/s and compares favorably with an estimate based on the measured mass flow rate. This effort is a proof of concept and intended to justify qualitative analysis of a more controlled and characterized turbulent source in future work.

Experimental Evaluation of Open Propeller Aerodynamic Performance and Aero-acoustic Behavior

A topic of increasing importance in the Unmanned Aerial System (UAS) community is the design and performance of open propellers used in hand launched, small UASs. The performance of these small propellers directly influences the operational capabilities of the UAS. As such, the design and testing of these propellers is necessary to accurately predict UAS performance. This experimental investigation examined the relationship between diameter, pitch, and number of blades to aerodynamic efficiency and aero-acoustic sound pressure levels. Thrust, torque, propeller rotational speed, and sound pressure level were measured for twelve aero-nautCAMcarbon (ACC) folding propeller configurations currently being used on an operational UAS with diameters ranging from 12 to 15 inches, pitches from 6 to 13 inches and increasing from two to three propeller blades. Each configuration was tested at 44 ft/s tunnel velocity, the typical cruising velocity of a small UAS, while the propeller rotational speed was varied to determine the rotational speed needed to produce 2.5 lbf of thrust, a typical cruise thrust required for a small UAS. As expected, the rotational speed required to achieve the desired thrust decreased approximately 7.7% per inch increase in the propeller diameter. At the same time, the noise signature decreased by approximately 0.8 dB per inch increase and overall efficiency rose by 2.9% per inch increase. Similar results were found for increasing both the number of propeller blades and also increasing the pitch of the propeller. Increasing from two to three blades decreased the rotational speed by 9.1% with a 2.1 dB drop in sound pressure level and an increase in overall efficiency of 3.2%. Increasing the pitch generally decreased rotational speed by 4.6% per inch of pitch increase and decreased noise level by 0.7dB per inch of pitch increase. Overall efficiency slightly increased by 0.6% for an inch increase in pitch. For a given diameter propeller there seems to be an optimum pitch for minimum sound pressure level. For design, this indicates there is an optimum angle of attack for the propeller, which translates to an optimum beta twist angle to achieve minimum sound pressure level. Noise generation was found to be a strong function of propeller rotational speed. Lower rotational speed generally produced less noise.

Designing Small Propellers for Optimum Efficiency and Low Noise Footprint

Abstract : A topic of increasing importance in the Unmanned Aerial System (UAS) community is the design and performance of open propellers used in hand launched, small UASs. The design and testing of these propellers is necessary to accurately predict UAS operation. This paper describes the design methodology used by Baylor University and the USAF Academy to design propeller blades for optimum efficiency and low noise. Propeller blade design theories are discussed as well as an overview of several of the existing design codes. Included is a discussion on geometric angle of attack, the induced angle of attack, and their impact on propeller design. The design program BEARCONTROL was developed which incorporates the programs QMIL and QPROI). Supplemental codes were also developed to work with Bearcontrol to design a propeller with a constant chord and variable twist. This resulted in the angle of attack for L/Dmax being used from the propeller hub to the tip. BEARCONTROL is a program written in MATLAB that gives a user the ability to quickly design a propeller, predict its performance, and then create a 30 model in SolidWorks. The MATLAB GUl ultimately results in a mostly automated process that is simple to use for individuals who are unfamiliar with command prompt programs and SolidWorks modeling. Also incorporated into BEARCONTROL is the program NREL AirFoil Noise (NAFNOISE) developed by the National Renewable Energy Laboratory (NREL). This program predicts the noise of any airfoil shape and provides a comparison for optimizing/minimizing predicted noise for the propeller being designed. Construction methods and materials also have a direct impact on cost, durability and operability when using a rapid prototype process to fabricate propellers. An overview of materials and construction methods used in this research are discussed. Incorporation of a hub with interchangeable blades is also presented as a more efficient testing method.

Integrating Systems Engineering Into the USAF Academy Capstone Gas Turbine Engine Course

This paper is intended to serve as a template for incorporating technical management majors into a traditional engineering design course. In 2002, the Secretary of the Air Force encouraged the United States Air Force (USAF) Academy to initiate a new interdisciplinary academic major related to systems engineering. This direction was given in an effort to help meet the Air Force’s growing need for “systems” minded officers to manage the development and acquisition of its ever more complex weapons systems. The curriculum for the new systems engineering management (SEM) major is related to the “engineering of large, complex systems and the integration of the many subsystems that comprise the larger system” and differs in the level of technical content from the traditional engineering major. The program allows emphasis in specific cadet—selected engineering tracks with additional course work in human systems, operations research, and program management. Specifically, this paper documents how individual SEM majors have been integrated into aeronautical engineering design teams within a senior level capstone course to complete the preliminary design of a gas turbine engine. As the Aeronautical Engineering (AE) cadets performed the detailed engine design, the SEM cadets were responsible for tracking performance, cost, schedule, and technical risk. Internal and external student assessments indicate that this integration has been successful at exposing both the AE majors and the SEM majors to the benefits of “systems thinking” by giving all the opportunity to employ SE tools in the context of a realistic aircraft engine design project.

Integration of a Turbine Cascade Facility Into an Undergraduate Thermo-Propulsion Sequence

The Department of Aeronautics at the United States Air Force Academy utilizes a closed-loop, two-dimensional turbine cascade wind tunnel to reinforce a learning-focused undergraduate thermo-propulsion sequence. While previous work presented in the literature outlined the Academy thermo-propulsion sequence and the contextual framework for instruction, this current paper addresses how the Academy turbine cascade facility is integrated into the aeronautical engineering course sequence. Cadets who concentrate in propulsion are to some extent prepared for each successive course through their contact with the cascade, and ultimately they graduate with an exposure to experimental research that enhances their grasp of gas turbine engine fundamentals. Initially, the cascade is used to reinforce airfoil theory to all cadets in the Fundamentals of Aeronautics course. Aeronautical engineering majors take this course during the first semester of their sophomore year. The next semester all aeronautical engineering majors take Introduction to Aero-thermodynamics. In this course, the closed-loop aspect of the cascade facility is used to reinforce concepts of work addition to the flow. Heat transfer is also discussed, using the heat exchanger that regulates test section temperature. Exposure to the cascade also prepares cadets for the ensuing Introduction to Propulsion and Aeronautics Laboratory courses, taken in the junior and senior year, respectively. In the propulsion course, cadets connect thermodynamic principles to component analysis. In the laboratory course, cadets work in pairs on propulsion projects sponsored by the Air Force Research Laboratory, including projects in the cascade wind tunnel. Individual cadets are selected from the cascade research teams for summer internships, working at an Air Force Research Laboratory turbine cascade tunnel. Ultimately, cadet experiences with the Academy turbine cascade help lay the foundation for a two-part senior propulsion capstone sequence in which cadets design a gas turbine engine starting with the overall cycle selection leading to component-level design. The turbine cascade also serves to integrate propulsion principles and fluid mechanics through a senior elective Computational Fluid Dynamics course. In this course, cadets may select a computational project related to the cascade. Cadets who complete the thermo-propulsion sequence graduate with a thorough understanding of turbine engine fundamentals from both conceptual and applied perspectives. Their exposure to the cascade facility is an important part of the process. An assessment of cadet learning is presented to validate the effectiveness of this integrated research-classroom approach.Copyright