Purdue University
Purdue University has a long and distinguished history of research in gas turbine engines, with work performed primarily at the Thermal Sciences and Propulsion Center (TSPC). Historically, our roots are in combustion with early gas turbine efforts being a natural continuation of Prof. Maurice Zucrow's pioneering rocket research.
Starting in the early 80's, work in turbomachinery began with the arrival of Sandy Fleeter. The gas turbine combustion effort was expanded and atomization and sprays added to our research topics when Arthur Lefebvre moved to TSPC as Reilly Professor of Combustion Engineering. At about the same time, Norm Laurendeau began developing laser diagnostic techniques for the measurement of combustion species with a goal of reducing pollutants. In succession, Anil Bajaj, Paul Sojka, Satish Ramadhyani, Klod Kokini and Osita Nwokah joined the faculty and began vibrations, combustion modeling, heat transfer, materials, and gas turbine controls programs. More recently, Mike Plesniak and Jay Gore have added their talents and expertise in the area of fundamental fluid mechanics and flame radiation and soot formation. Our newest colleagues, Luc Mongeau, Pat Lawless and Steve Frankel, bring expertise in aeroacoustics, aeromechanics of rotating machinery and Direct Numerical Simulation of reacting flows.
There are now twelve faculty members and nearly fifty graduate students working on gas turbine related projects at Purdue. Topics that are currently being addresses, or have been considered in the past, include: thermomechanical fracture processes in and design of multi-layer ceramic coatings, functionally gradient materials, and ceramic/ceramic composites; analysis of existing engine performance data and construction of a database, including emissions and fuel effects; combustion chemistry and kinetics, especially that of pollutants; development of diagnostics for radiation, soot, species, particle sizes and velocities, plus temperature; atomization and sprays, including entrainment and the development of equations to predict injector performance; evaporation/vaporization; NO x , its formation chemistry and the relationship between its formation and mixing; active control; combustion chemistry-fluid mechanics interactions with the end application being Reynolds number influence on emissions via turbulent mixing; fundamental studies on turbulence, its transport and relationship to mixing; and turbomachinery, including the fundamental unsteady aerodynamics of turbomachines, and indication of how the forcing function influences machine performance, what instabilities result from unsteady forces, and how these instabilities can be suppressed for axial, radial, and mixed flow designs operating from subsonic to transonic flow regimes. Government funding has come from AFOSR, ARO, DOE/Morgantown, DOE/Pittsburgh, DOE/HQ, NASA, NIST, NSF, and ONR. Industrial sponsors include Allison Gas Turbines, Boeing, Delevan, Ex-Cell-O, Exxon, Garrett, General Electric Aircraft Engines, Mobil, Parker Hannifin, Pratt-Whitney, Solar Turbines, and Westinghouse Electric.
Our facilities for research in these areas are presented in the following sections. The scope is broad and reflects the interests and capabilities of the faculty. Facilities include those for research in applied and fundamental combustion, radiation and soot in turbulent flames, combustion chemistry and pollutants, heat transfer, materials, controls, plus turbomachinery and fundamental fluid mechanics.
The majority of the facilities are located at the Thermal Sciences and Propulsion Center (TSPC), a satellite laboratory of the School of Mechanical Engineering . They are maintained by a staff of four machinist/mechanical technicians plus one electronics technician.
Extensive computational facilities also exist at TPSC, including three SUN work stations, three HP1000 work stations, a total of seven 286 and 386 based DOS PC's, five 486 based DOS PC's, four Macintosh PC's, three IBM RISC6000 workstations, and direct linkage to all the resources of both Engineering Computer Network (ECN) and the Purdue University Computer Center (PUCC). ECN consists of ten super-mini-computers (Gould NP1 and VAX 11/780 class) networked with 69 SUN servers (3 and 4 series) and 500 SUN work stations. PUCC comprises three super-computers (two ETA 10's and one CDC Cyber 205) plus numerous smaller machines.
Acoustics and Noise Control
Purdue has a well established and reputable program in engineering acoustics and noise control. Research in sounds and vibration induces by unsteady turbomachinery flows and other unsteady and/or turbulent flows is conducted by Prof. Mongeau. Facilities available include a 7300 cubic ft reverberation chamber, a 12x12x12 ft fully anechoic chamber, and a large 41x27x18 ft semi-anechoic chamber. A low-speed quiet wind tunnel is currently under construction. This latter facility has a closed rectangular test section, 1.5x2 ft in size, with a maximum air speed of 120 mph. Instrumentation to support a wide variety of experimental needs is available, as well as computing facilities, data acquisition systems, and data processing and presentation equipment.
Combustion and Heat Transfer
A variety of combustion research related to gas turbines is performed at Purdue. It ranges from the applied work on ignition, stability and emissions through turbulent combustion and flame radiation studies to combustion chemistry investigations. Facilities for each type of research are discussed below.
Applied combustion research is performed by Profs. Gore and Sojka using one of four rigs. Two of the rigs can supply up to 6.5 lbm/s of unvitiated air at temperatures up to 1250 F and pressures of 15 atmospheres. They are used primarily for autoignition, flame radiation and pollutant formation studies. A third rig can supply up to 10 lbm/s of vitiated air at temperatures up to 1350 F against a back pressure of 4.5 psi (provisions exist for restoring the vitiated air's oxygen content to 21%). This rig is used primarily for flame stabilization work. The last rig can supply one half lbm/s of electrically heated air temperatures up to 1250 F. It is used exclusively for ignition delay and pre-mixing research.
The turbulent combustion research performed by Prof. Gore is applicable to gas turbine combustors, as well as to radiant tube and furnace flames used in manufacturing, jet and pool fire safety, and radiant heat loads from flames in all applications. Diagnostic capabilities include a laser Doppler velocimeter (LDV), a particle imaging velocimetry system (PIV), multi-wavelength emission-absorbing spectroscopy, gas chromatography, chemiluminescent NO x , analysis, exhaust CO, CO 2 , and unburned HC analysis, thin film pyrometry, Mie scattering from liquid fuel mists, Mie video imaging, radiation property measurements (absorption coefficient and single scattering albedo) using blackbody tube furnaces and radiometry, and spectrometry.
Experimental work is aimed at development of: (1) an enhanced understanding of NO x formation and emission from liquid gas fired premixed flames, as well as development of effective generic combustor components; (2) an improved understanding and performance of ceramic stabilized and impingement enhanced heat transfer flames, as well as the development of novel ceramic stabilized burners; and (3) a better understanding of entrainment into fires in order to develop predictive capabilities for flame size, product composition and compartment vitiation.
Theoretical work is aimed at developing novel models and methodology for predicting NO x formation, emission and control in turbulent flames including the effects of turbulence/chemistry interactions. A discrete probability function (DPF) method has been pioneered in this laboratory.
Research into combustion chemistry at Purdue is performed by Prof. Norm Laurendeau whose Flame Diagnostics Laboratory has played a major international role in the development of laser-based fluorescence methods for the measurement of species concentrations and temperature in reactive flows. Particular attention has been given to simple radical species such as OH and to pollutant species such as NO.
Research in this area is performed using a high-pressure flame facility that allows measurements on premixed and diffusion flames from subatmospheric (450 psi) pressures. Two Q-switched Nd:YAG/dye lasers are available for measurements requiring low sampling rates and high laser irradiances; two mode-locked Nd:YAG/dye lasers allow measurements needing high sampling rates and low laser irradiances. Additional equipment induces UV-sensitive imaging system two boxcar averagers, two lock-in amplifiers, several sampling oscilloscopes, two monochromators and associated minicomputer systems.
Computational work in turbulent combustion is performed by Prof. Frankel. This work involves Direct Numerical Simulation (DNS), Large Eddy Simulation (LES), Linear Eddy Modeling (LEM), and Probability Density Function (PDF) modeling to study turbulence-chemistry-radiation interactions. The work is being performed using recent additions to the computational facilities at TPSC, which include three IBM RISC6000 workstations. Computational time on the NCSA CRAY Y-MP and the Lawrence Livermore CRAY C-90 is currently being solicited for work involving both vector and parallel computational modeling and simulation of turbulent reacting flows.
Controls
Engine and component dynamics and control research at Purdue makes use of the extensive computational facilities available at the University. These include ME facilities, plus all the resources of both the Engineering Computer Network (ECN) and the Purdue University Computer Center (PUCC).
Extensive software exists for on-going/planned work in: (1) multivariable and distributed control of gas turbine engines; (2) aero-mechanics of bladed disk assemblies; (3) nonlinear dynamics of bladed disk assemblies; (4) active feedback control of compressor surge and rotating stall; (5) transient performance modeling using component matching; (6) condition monitoring and fault tolerant control. There has been continuing interest in the work from several DOD agencies including ARO, NASA, and AFOSR.
Although a large proportion of our previous experience has been with small and large high efficiency/high performance aircraft gas engines, most of the knowledge can easily be adapted for work on industrial type gas engines. Of particular relevance is how work in fault tolerance engine health monitoring translate directly from aircraft to industrial type gas turbines.
Heat Transfer
Professor Ramadhyani is involved in heat transfer and combustion research of interest to gas turbine manufacturers. In the heat transfer realm, he is studying the heat transfer capabilities of two-phase jet impingement and spray cooling techniques. His experimental results show that extremely high heat fluxes can be dissipated by promoting rapid evaporation of a thin layer of liquid on a heated surface. Evaporation is accomplished by impinging gas jets on the liquid film.
In the area of combustion, Prof. Ramadhyani has developed computational models capable of predicting mane of the details associated with a turbulent reacting flow. His models include procedures for calculating radiation from the combustion gases as well as formation of nitric oxide. The models have been validated against the experimental data obtained from actual gas turbine combustors.
Materials
The research facilities in this area of high temperature materials and ceramic coatings include two computer controlled, focused, high intensity infrared lamps which are used to apply a localized heat flux on the surface of specimens and simulate the effect of localized combustion processes. The specimen is cooled on the substrate side through a copper plate, thus providing two-dimensional temperature gradients. Computer control of the system permits the application of different thermal fatigue regimes to the specimen. The cracks formed as a result of the applied transient thermal loads are studied using an optical microscope.
A new 1.5 kW CO 2 laser is being acquired for studies of coatings subjected to high heat fluxes. This equipment will allow the application of very rapid temperature transients and very high surface temperatures, such as those encountered in stationary gas turbines and jet engines.
In addition, the lab is equipped with a high temperature furnace (1700 C) controlled by a programmable microprocessor. This allows automatic thermal cycling of specimens. The environment inside the furnace can be controlled by the addition of inert gases in order to perform studies on the effects of oxidizing versus inert environments. This furnace can also be used in conjunction with mechanical testing equipment to perform thermomechanical fatigue experiments.
Turbomachinery and Fluid Mechanics
Turbomachinery research is performed by Profs. Fleeter and Lawless. Six major research facilities are utilized for turbomachinery research under the direction of Prof. Fleeter: Multistage Axial Flow Research Compressor, Rotating Annular Cascade, Research Turbine, Large Scale Research Centrifugal Compressor, High Speed Axial Fan, and High Speed Centrifugal Compressor. Mini-computers with high speed A-D boards and work stations are utilized for digital data acquisition and analysis. In addition to steady performance measurements, instrumentation utilized in these facilities includes hot-wire anemometers, laser Doppler anemometry, particle image velocimetry, high response miniature transducers, microphones and heated film gauges, with on-rotor data acquisition accomplished by wetted mercury slip ring assemblies. Current research activities include flow induced vibrations, aerodynamic damping of compressor and turbine blades, blade row unsteady aerodynamic interactions, unsteady turbine noise generation and active control. The capabilities of each individual facility are discussed in the following paragraphs.
The Multistage Axial Flow Research Compressor models the fundamental turbomachinery unsteady aerodynamic multistage phenomena which include the incidence angle, the velocity and pressure variations, the aerodynamic forcing function waveforms, the reduced frequency, and the unsteady blade row interactions. The compressor is driven by a dc electric motor and each identical stage contains 43 rotor blades and 31 stator vanes, with the first stage rotor inlet flow field established by an inlet guide vane row of 36 airfoils.
The Rotating Annular Cascade is an open-loop draw-through type wind tunnel capable of test section velocities of 220 ft/sec. The conditioned inlet flow accelerates into the annular test section via a bellmouth inlet. The annular test section houses a rotor independently driven by an ac motor controlled by a variable frequency drive to create the desired unsteady flow field together with a downstream stator row. The separate drive motors on the rotor system and fan uncouple rotor speed from the through field velocity. The fundamentals of both compressor and turbine blade rows are considered utilizing this facility. Namely, the rotor steady loading, i.e., compressor or turbine, is varied by changing the angle-of-attack.
The Research Turbine is a two stage, low speed, 50% reaction axial flow turbine which reproduces the essential aspects of the steady and unsteady flow fields inherent in high speed turbines. The flow through the turbine is induced by a centrifugal blower powered by an electric motor, with the flow rate regulated by a remote controlled pre-spin inlet damper.
The Large Scale Research Centrifugal Compressor is a low speed, moderate scale turbomachine which features a mixed flow impeller with 23 backswept blades and a vaned radial diffuser. The shrouded impeller has an axial direction. Optical access to the impeller flow passages is accomplished with a Plexiglas shroud. A window provides optical access to the vaneless space and the vaned radial diffuser, covering three diffuser vane passages and to the impeller outlet.
The High Speed Axial Fan inlet flow is conditioned by honey-comb aluminum mounted upstream of a 16:1 contraction. The drive system consists of an ac motor driving a magnetic clutch. A variable speed output shaft from the magnetic clutch drives a gearbox which is coupled to the test section by a rotary torque transformer which measures total compressor power during testing. The facility features a 12 in. diameter, 1200 ft/sec 2/3 hub-tip ratio design compressor rotor which is integral with the shaft.
The High Speed Centrifugal Compressor facility consists of three main components: a turboshaft engines, a slave gearbox, and a research centrifugal compressor. The turboshaft gas turbine engine powers the research compressor while the slave gearbox is used to covert the engine output to the required for the research compressor. The research compressor, consisting of an impeller and a vaned radial diffuser, produces a flow of 5 lb/sec at a pressure ration of 5.0 at 100% speed. Because of the importance of the diffuser flow, optical access is provided to the diffuser section.
Fundamental Fluid Mechanics research aimed at gas turbine related problems is performed by Prof. Mike Plesniak. He uses the facilities discussed in the following three paragraphs.
A wind tunnel, in which film cooling experiments have been performed at Mach numbers up to 0.8, is supplied with high pressure air and has operated at flow rates of 5 lbm/s and temperatures of 300 to 500 F. The estimated maximum continuous mass flow rate is 10 lbm/s for 20 minutes. The test-section is 18 by 12 inches in cross-section and 140 inches in length. The facility is also capable of delivering hot and/or cold flow to the test-section. A combustor, burning methyl alcohol, can deliver heated air at a pressure of 125 psig, a temperature of 500 F, and a flow rate of 5 lbm/s. For cold air, a turboexpander is designed to expand pressurized air from a turbine inlet condition of 300 psia, 70 F to a turbine outlet condition of 40 psia, -100 F at a flow rate of 0.7 lbm/s.
A supersonic mixing layer test-section is currently being installed. It will allow study of turbulence transport and mixing. The high-speed, supersonic stream will flow at a Mach number of 4 to 5, with the low-speed stream being subsonic. A converging/diverging inlet with splitter plate will be used to form the mixing layer with access windows added to facilitate the optical diagnostic techniques that will be utilized to investigate the flow field. These techniques include, but are not limited to, focusing schlieren and laser Doppler velocimetry. It should be noted that the largest size of the test-section will minimize confinement effects, while the interior walls (which are ground smooth) will minimize disturbances emanating from the side walls.
A low-speed water channel is also being installed and consists of a test section that is 24 by 36 inches in cross-section and 144 inches long with a maximum operating velocity of 40 ft/min. The channel will be supplied from a gravity feed reservoir and equipped with turbulence management devices to the test section for optical diagnostic techniques and flow visualization. The channel will be equipped with a test surface consisting of interchangeable modules used to generate a variety of pressure- and shear-driven three-dimensional boundary layers. A streamwise pressure gradient adjustment will allow the examination of the complex interaction of three dimensionality with favorable and adverse pressure gradients. The physics of these interactions constitute important components in the endwall flows in turbomachinery that have important consequences on the heat transfer and, hence, cooling problems encountered in these regions. Curves test-sections may be fabricated and fitted to the facilities described above to investigate the role of streamwise curvature on turbulence transport, convective heat transfer, and mixing.
A dedicated Apple Quadra 900 microcomputer with data acquisition capability will be used to control the experiments and acquire velocity data. Velocity measurements are currently being made using a single component LDV system. Purchase of a TSI ColorLink fiber-optics-based 2-component LDV system with the IFA 750 high-speed digital burst correlator is currently being arranged. |