University of Toronto Institute for Aerospace Studies (UTIAS)

Permanent URI for this communityhttps://hdl.handle.net/1807/69352

UTIAS is a graduate studies and research institute, forming part of the Faculty of Applied Science and Engineering at the University of Toronto .

The continuing involvement of the University of Toronto in the aerospace sciences since World War I eventually led to the establishment of this institute in 1949. Originally called the Institute of Aerophysics, it is now known as the Institute for Aerospace Studies.

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Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending. Part I: analytical models and minimum weight design
(Elsevier, 2004-04) Steeves, Craig A; Fleck, Norman A
Analytical predictions are made for the three-point bending collapse strength of sandwich beams with composite faces and polymer foam cores. Failure is by the competing modes of face sheet microbuckling, plastic shear of the core, and face sheet indentation beneath the loading rollers. Particular attention is paid to the development of an indentation model for elastic faces and an elastic-plastic core. Failure mechanism maps have been constructed to reveal the operative collapse mode as a function of geometry of sandwich beam, and minimum weight designs have been obtained as a function of an appropriate structural load index. It is shown that the optimal designs for composite-polymer foam sandwich beams are of comparable weight to sandwich beams with metallic faces and a metallic foam core.
Collapse mechanisms of sandwich beams with composite faces and a foam core, loaded in three-point bending. Part II: experimental investigation and numerical modelling
(Elsevier, 2004-04) Steeves, Craig A; Fleck, Norman A
This study focuses on the competing collapse mechanisms for simply supported sandwich beams with composite faces and a PVC foam core subjected to three point bending. The faces comprise Hexcel Fibredux 7781-914G woven glass fibre-epoxy prepreg, while the core comprises closed cell Divinycell PVC foam of relative density 6.6% and 13.3%. The mechanical properties of the face sheets and core are measured independently. Depending upon the geometry of the beam and the relative properties of the constituents, collapse is by core shear, face sheet microbuckling or by indentation beneath the middle loading roller. A systematic series of experiments and finite element simulations have been performed in order to assess the accuracy of simple analytic expressions for the strength. In general, the analytic expressions for peak load are adequate; however, simple beam theory becomes inappropriate and the analytic models are inaccurate for stubby beams with thick faces relative to the core thickness. A failure mechanism map is constructed to reveal the dependence of the dominant collapse mechanism upon the geometry of the beam.
Material selection in sandwich beam construction
(Elsevier, 2004-05) Steeves, Craig A; Fleck, Norman A
A systematic procedure is presented for comparing the relative performance of sandwich beams with various combinations of materials in three-point bending. Operative failure mechanisms are identified and failure maps are constructed. The geometry of sandwich beams is optimized to minimize the mass for a required load bearing capacity in three point bending.
In-plane properties of composite laminates with through-thickness pin reinforcement
(Elsevier, 2006-05) Steeves, Craig A; Fleck, Norman A
Laminated fibre reinforced composites can be reinforced by through-thickness pins to reduce their susceptibility to delamination. However, the presence of the pins creates resin pockets and disrupts the alignment of the fibres, and may thereby lead to a degradation of the in-plane strength of the composite. Experiments and numerical simulations show that the presence of through-thickness reinforcing pins decreases the tensile strength of the composite by 27%, and the compressive strength of the composite by at least 30%. It is also shown that the pattern in which the pins are inserted has a strong influence on the compressive strength. A pin pattern is identified in order to minimise fibre alignment disruption and thereby maximise the compressive strength.
Concepts for structurally robust materials that combine low thermal expansion with high stiffness
(Elsevier, 2007-09) Steeves, Craig A; dos Santos e Lucato, Sergio L; He, Ming; Antinucci, Emilio; Hutchinson, John W; Evans, Anthony G
A family of robust stretch-dominated bimaterial lattices is introduced which combines low (or zero) thermal expansion with high stiffness, structural robustness over wide temperature ranges and manufacturing facility. This combination of properties is unavailable through any other material solution. The concept uses two constituents configured as adjoining sub-lattices. It accommodates the thermal expansion through rotation of the members of one sub-lattice. Moreover, the lattice exhibits large stiffness to weight because it is fully triangulated and does not rely on rotational resistance at the joints for structural rigidity. A wide range of constituents can be used to build the new lattices enabling many desirable properties to be incorporated, especially high strength and toughness. Examples of both planar and volumetric lattices are presented, and their thermo-mechanical properties derived. The results are verified by conducting experiments and finite element simulations on a lattice fabricated using aluminium and titanium alloy constituents.
Mesh Movement for a Discrete-Adjoint Newton-Krylov Algorithm for Aerodynamic Optimization
(American Institute of Aeronautics and Astronautics, 2008-07-01) Truong, A. H.; Oldfield, C. A.; Zingg, D. W.
A grid movement algorithm based on the linear elasticity method with multiple increments is presented. The method is relatively computationally expensive but is exceptionally robust, producing high-quality elements even for large shape changes. It is integrated with an aerodynamic shape optimization algorithm that uses an augmented adjoint approach for gradient calculation. The discrete-adjoint equations are augmented to explicitly include the sensitivities of the mesh movement, resulting in an increase in efficiency and numerical accuracy. This gradient computation method requires less computational time than a function evaluation and leads to significant computational savings as dimensionality is increased. The results of the application of these techniques to several large deformation and optimization cases are presented.
Feasibility of Metallic Structural Heat Pipes as Sharp Leading Edges for Hypersonic Vehicles
(American Society of Mechanical Engineers, 2009) Steeves, Craig A; He, Ming Y; Kaen, Scott D; Valdevit, Lorenzo; Wadley, Haydn N G; Evans, Anthony G
Hypersonic flight with hydrocarbon-fueled airbreathing propulsion requires sharp leading edges. This generates high temperatures at the leading edge surface which cannot be sustained by most materials. By integrating a planar heat pipe into the structure of the leading edge, the heat can be conducted to large flat surfaces from which it can be radiated out to the environment, significantly reducing the temperatures at the leading edge and making metals feasible materials. This paper describes a method by which the leading edge thermal boundary conditions can be ascertained from standard hypersonic correlations, and then uses these boundary conditions along with a set of analytical approximations to predict the behaviour of a planar leading edge heat pipe. The analytical predictions of the thermostructural performance are verified by finite element calculations. Given the results of the analysis, possible heat pipe fluid systems are assessed, and their applicability to the relevant conditions determined. The results indicate that the niobium alloy Cb-752, with lithium as the working fluid, is a feasible combination for Mach 6 to 8 flight with a 3 mm leading edge radius.
Experimental Investigation of the Thermal Properties of Tailored Expansion Lattices
(Springer Nature, 2009-05) Steeves, Craig A; Mercer, Chris; Antinucci, Emilio; He, Ming Y; Evans, Anthony G
Composite bimaterial lattice structures which possess both low, tailorable thermal expansion and nearly optimal stiffness have been proposed for applications which require high structural stiffness in environments which include large temperature fluctuations, such as the surfaces of high-speed aerospace vehicles. An experimental validation of the thermal properties of these lattices when they are constructed of practical materials with easily manufactured bonded joints is contained herein. Bonded lattices, comprising aluminum and titanium alloys, have been manufactured with press-fit dovetail joints and tested in a variety of thermal environments. Results for equilibrium heating, rapid transient heating and thermal cycling leading to shakedown are presented and shown to be consistent with theoretically and numerically attained results.
Airfoil Optimization Using Practical Aerodynamic Design Requirements
(American Institute of Aeronautics and Astronautics, 2010-09-01) Buckley, Howard P.; Zhou, Beckett Y.; Zingg, David W.
Practical aerodynamic design problems must balance the goal of performance optimization over a range of on-design operating conditions with the need to meet design constraints at various off-design operating conditions. Such design problems can be cast as multipoint optimization problems where the on-design and off-design operating conditions are represented as design points with corresponding objective/constraint functions. Two methods are presented for obtaining optimal airfoil designs that satisfy all design objectives and constraints. The first method uses an unconstrained optimization algorithm where the optimal design is achieved by minimizing a weighted sum of the objective functions at each of the operating conditions. To address the competing design objectives between on-design and off-design operating conditions, an automated procedure is used to efficiently weight the off-design objective functions so as to limit their influence on the overall optimization while satisfying the design constraints. The second method uses the constrained optimization algorithm SNOPT, which allows the aerodynamic constraints imposed at the off-design operating conditions to be treated explicitly. Both methods are applied to the design of an airfoil for a hypothetical aircraft where the problem is formulated as an 18-point multipoint optimization.
Optimizing sandwich beams for strength and stiffness
(SAGE, 2012-09) Steeves, Craig A
This paper presents a method for minimising structural mass by optimising the geometry and core density of sandwich beams comprising composite face sheets and polymer foam cores, loaded in three-point bending. The optimisation is constrained by both strength and stiffness requirements. All possible locations in design space which might be global minima of mass are identified, and it is shown that, for a global minimum mass, at least two constraints must be simultaneously active. Calculations for a typical set of material properties are performed with the result that, for a wide range of typical materials, a minimum-mass sandwich beam satisfying both strength and stiffness requirements utilises low density foam and is constrained by stiffness and indentation strength.
Parametric study of vortex structures and their dynamics in swirl-stabilized combustion
(Elsevier, 2013) Steinberg, Adam M.; Arndt, Christoph M.; Meier, Wolfgang
The dynamics of major flow structures were studied in a gas turbine model combustor for perfectly premixed swirl-stabilized flames under a variety of reacting and non-reacting conditions using high-repetition-rate laser diagnostics. The studied combustor is a target case for the International Workshop on Advanced Measurement Techniques and Computational Methods for Premixed and Partially Premixed Combustion. Measurements were taken of the three-component velocity field, OH planar laser induced fluorescence, and OH∗ chemiluminescence at a rate of 10 kHz for nine different flow conditions, covering a range of thermal powers (Pth = 10–35 kW) and equivalence ratios (ϕ = 0.65–0.8). Under all non-reacting conditions, the dominant flow structure was a helical vortex core (HVC) that rotated around the burner at a frequency represented by a constant Strouhal number StH,NR = 0.78. However, igniting the burner significantly altered the flow structures. At most conditions, the strength and frequency of the HVC increased relative to the corresponding non-reacting case. The HVC frequency in such cases was once again represented by a constant Strouhal number of StH,R = 0.88, irrespective of the thermal power or equivalence ratio. The HVC frequency was considerably higher than the frequency of the self-excited thermo-acoustic oscillations exhibited by the burner. However, at other conditions, combustion prevented formation of the HVC. In such cases, the dominant flow structure dynamics were periodic shear layer oscillations and shedding of toroidal vortices at the thermo-acoustic frequency. Cases in which combustion prevented formation of the HVC included those at low thermal powers (Pth ⩽ 15 kW) and the highest equivalence ratio (ϕ = 0.8). A distinct relationship was found between the flow structure geometry and the pressure oscillation amplitude, with cases having an HVC resulting in higher pressure oscillations.
Autoignition of Hydrogen / Nitrogen Jets in Vitiated Air Crossflows at Different Pressures
(Elsevier, 2013) Steinberg, Adam M.; Fleck, Julia M.; Griebel, Peter; Arndt, Christoph M.; Naumann, Clemens; Aigner, Manfred
Autoignition of hydrogen/nitrogen jets in crossflows of vitiated air has been experimentally studied at conditions relevant for gas turbine combustor operation, including practical pressures (5, 10, 15 bar), crossflow temperatures (Tcf = 1185 K and 1143 K), crossflow velocities (ucf = 200 and 300 m/s), and jet momentum ranges. Experiments were performed in an optically accessible duct, in which the appearance of autoignition events was investigated using high-speed imaging. At the different crossflow parameters, the H2 mole fraction XH2 in the fuel jet was incrementally increased until autoignition created a stable flame. During this process, the autoignition kernel and subsequent flame dynamics were recorded at a rate of 30 kHz. In order to compare the experimental autoignition characteristics of the partially premixed, turbulent system to a homogeneous system, kinetic simulations of homogenous systems were conducted for pressures, temperatures, and vitiated air compositions corresponding to the experiments. The ignition delay times estimated from the experiment were considerably shorter than those from the kinetic simulations, and exhibited a different pressure dependency. These differences suggest that, in the current flow configuration, autoignition is strongly affected by turbulent mixing and flow field characteristics.
Structure and stabilization of hydrogen jet flames in cross-flows
(Elsevier, 2013) Steinberg, Adam M.; Sadanandanb, R.; Dem, Claudiu; Kutne, P.; Meier, Wolfgang
The structure and stabilization of heated hydrogen jet flames in heated cross-flows was experimentally investigated in a configuration that is analogous to terrestrial gas turbine components. Three flames, with jet velocities ranging from 100 to 200 m/s, were investigated using particle image velocimetry and OH planar laser induced fluorescence in a total of 11 x–y and y–z planes. Additionally, laser Raman scattering was performed in the 200 m/s jet to characterize the thermo-chemical state. In all cases, the flame along the jet centerline plane consisted of two branches, one stabilized in the jet lee and one lifted above the jet trajectory. The positional stability of the lee-stabilized branch was greater in the higher jet velocity cases due to the larger and stronger recirculation zones created downstream of the injection point. The lifted flame branch was much more dynamic, with measured flame base axial positions ranging from the jet near field to the flame tip. This flame branch instantaneously resided downstream of regions with high extensive principal strain-rate, and the strain-rate significantly affected the thermo-chemical state. The Raman measurements indicated that the base of the lifted flame branch existed in locations where both tribrachial and/or stratified premixed flame behaviors are expected, depending on the instantaneous flame location. Accurately modeling these complex flame structures and flow-flame interactions therefore is necessary to properly simulate jet flames in cross-flows.
Auto-Ignition and Flame Stabilization of Hydrogen / Natural Gas / Nitrogen Jets in a Vitiated Cross-Flow at Elevated Pressure
(Elsevier, 2013) Steinberg, Adam M.; Fleck, Julia M.; Griebel, Peter; Arndt, Christoph M.; Aigner, Manfred
The influence of natural gas (NG) on the auto-ignition behavior of hydrogen (H2)/nitrogen (N2) fuel jets injected into a vitiated cross-flow was studied at conditions relevant for practical combustion systems (p = 15 bar, Tcross-flow = 1173 K). In addition, the flame stabilization process following auto-ignition was investigated by means of high-speed luminosity and shadowgraph imaging. The experiments were carried out in an optically accessible jet-in-cross-flow (JICF) test section. In a H2/NG/N2 fuel mixture, the fraction of H2 was stepwise increased while keeping the N2 fraction approximately constant. Two different jet penetration depths, represented by two N2 fraction levels, were investigated. The results reveal that auto-ignition kernels occurred even for the lowest tested H2 fuel fraction (XH2/NG = XH2 / (XH2 + XNG) = 80%), but did not initiate a stable flame in the duct. Increasing XH2/NG decreased the distance between the initial position of the auto-ignition kernels and the fuel injector, finally leading to flame stabilization. The H2 fraction for which flame stabilization was initiated depended on jet penetration; flame stabilization occurred at lower H2 fractions for the higher jet penetration depth (XH2/NG = 91% compared to 96%), revealing the influence of different flow fields and mixing characteristics on the flame stabilization process. It is hypothesized that the flame stabilization process is related to kernels extending over the duct height and thus altering the upstream conditions due to considerable heat release. This enabled subsequent kernels to occur close to the fuel injector until they could finally stabilize in the recirculation zone of the jet lee.
Effect of B3+ - N3- on YAG:Dy Thermographic on YAG:Dy Thermographic Phosphor Luminescence
(Optical Society of America, 2014) Kwong, Wing Yin; Steinberg, Adam M.; Chin, Ya Huei
The use of thermographic phosphors for high-temperature (> 1000 K) thermometry currently is limited by loss of signal due to thermal quenching. This work demonstrates a new phosphor generated by substituting tetrahedral site Al3+-O2- in YAG:Dy with B3+-N3- to produce YABNG:Dy. Conventional YAG:Dy and YABNG:Dy phosphors were synthesized using identical sol-gel synthesis techniques. X-ray diffraction measurements showed that both had nearly pure crystalline phases, with a minor secondary yttrium-aluminum-monoclinic (YAM) phase present in the YABNG:Dy. The YABNG:Dy sample had a larger and more spherical primary grain than the YAG:Dy in scanning electron microscopy images. Tests of the thermal response showed that the YABNG:Dy had much stronger phosphorescence emissions than YAG:Dy, likely due to the morphological differences. Furthermore, the onset of thermal quenching was delayed by approximately 100 K for YABGN:Dy compared to YAG:Dy, and the rate of signal decrease with temperature was reduced. This resulted in greater signal-to-noise ratios and less uncertainty in the temperature measurements, particularly at high temperatures.
High-Speed Tomographic PIV and OH PLIF Measurements in Turbulent Reactive Flows
(Springer Verlag, 2014) Coriton, Bruno; Steinberg, Adam M.; Frank, Jonathan H.
High-speed tomographic particle image velocimetry (TPIV) is demonstrated in turbulent reactive flows at acquisition rates ranging from 10 kHz to 16 kHz. The 10 kHz TPIV measurements are combined with planar laser-induced fluorescence (PLIF) imaging of OH to mark the high-temperature reaction zone of the flame. Simultaneous TPIV/OH PLIF measurements are applied to the stabilization region of a weakly-turbulent lifted DME/air jet flame (ReD = 7,600) and the mixing layer of a turbulent partially-premixed DME/air jet flame (ReD = 29,000). In the lifted jet flame, vortical structures exhibit time-dependent morphological changes and eventually dissipate as they approach the flame. In the near field of the turbulent jet flame, dynamics of localized extinction are captured as coherent structures with high compressive strain rates interact with the reaction zone and subsequently break apart. The principal axis of compressive strain has a strong preferential orientation at 45 degrees with respect to the jet axis. The 3D velocity field measurements are used to evaluate biases in 2D measurements of compressive strain rates in a turbulent jet flame. The biases in the 2D measurements primarily stem from out-of-plane orientation of the principal axis of compressive strain. Comparisons with a constant density turbulent non-reactive jet (ReD = 22,600) show that the jet flame has larger coherent structures that are confined near the reaction zone. Data from the non-reactive jet are also used to evaluate effects of noise, bias, and spatial averaging on measurements of the velocity and velocity gradients.
Thermo-acoustic velocity coupling in a swirl stabilized gas turbine model combustor
(Elsevier, 2014-06-26) Caux-Brisebois, Vincent; Steinberg, Adam M.; Arndt, Christoph M.; Meier, Wolfgang
Limit-cycle thermo-acoustic velocity coupling mechanisms are studied in a perfectly-premixed swirl-stabilized combustor using data from 10 kHz repetition-rate stereoscopic particle image velocimetry (SPIV) and OH planar laser induced fluorescence (PLIF). Five cases over a range of thermal powers and equivalence ratios are investigated, each of which underwent di erent amplitude limit-cycle oscillations. Proper orthogonal decomposition (POD) of the velocity data shows that each case contained a dynamic helical vortex core (HVC) that rotated around the combustor and greatly a ffected the flame behavior. Flow and flame statistics are compiled as a function of both the phase in the thermo-acoustic cycle and a phase representing the azimuthal position of the HVC relative to the measurement plane. These data are used to determine the thermo-acoustic energy transfer field at each HVC azimuthal angle, as described by the Rayleigh integral. It is found that periodic deformations of the HVC caused large-scale flame motions, resulting in regions of positive and negative energy transfer. The deformation of the HVC was linked to a swirl number wave that propagates from the burner nozzle. While the mechanism of thermo-acoustic coupling was the same for all cases, the phase between heat release and pressure oscillations varied significantly. This phase relationship was determined by the interaction of the pressure field, swirl wave, HVC deformation, and flame response. It is shown that these can be described by the combination of a Helmholtz resonator and a convective disturbance.
Experimental Study of Turbulence-Chemistry Interactions in Perfectly and Partially Premixed Confined Swirl Flames
(De Gruyter, 2014-12) Dem, Claudiu; Stöhr, Michael; Arndt, Christoph M.; Steinberg, Adam M.; Meier, Wolfgang
A gas turbine model combustor (Turbomeca Burner) for premixed methane/air flames has been operated at atmospheric pressure in two different modes of premixing. In the partially premixed mode, fuel was injected into the air flow within the swirl generator shortly upstream of the combustion chamber while in the perfectly premixed mode fuel and air were mixed far upstream. The main objective of this work is the study of the influence of the mode of premixing on the combustion behavior. Stereoscopic particle image velocimetry has been applied for the measurement of the flow field, OH chemiluminescence imaging for the visualization of the flame shapes and single-shot laser Raman scattering for the determination of the joint probability density functions of major species concentrations, mixture fraction and temperature. The mixing and reaction progress and effects of turbulence-chemistry interactions are characterized by scatterplots showing the correlations between different quantities. To isolate effects of mixing from combustion instabilities that were frequently observed in this combustor, operating conditions without thermo-acoustic oscillations or coherent flow structures were chosen. While the mode of premixing had no major influence on the general flame behavior characteristic differences were observed with respect to flame anchoring, the flow field in the inner recirculation zone and the CO concentration level. The results further extend the data base of previous experimental and numerical investigations with this burne
Experimental analysis of thermo-acoustic instabilities in a generic gas turbine combustor by phase-correlated PIV, chemiluminescence, and laser Raman scattering measurements
(Springer Verlag, 2015) Arndt, Christoph M.; Severin, Michael; Dem, Claudiu; Stöhr, Michael; Steinberg, Adam M.; Meier, Wolfgang
A gas turbine model combustor for partially premixed swirl flames was equipped with an optical combustion chamber and operated with CH4 and air at atmospheric pressure. The burner consisted of two concentric nozzles for separately controlled air flows and a ring of holes 12 mm upstream of the nozzle exits for fuel injection. The flame described here had a thermal power of 25 kW, a global equivalence ratio of 0.7, and exhibited thermo-acoustic instabilities at a frequency of approximately 400 Hz. The phase-dependent variations in the flame shape and relative heat release rate were determined by OH* chemiluminescence imaging; the flow velocities by stereoscopic particle image velocimetry (PIV); and the major species concentrations, mixture fraction, and temperature by laser Raman scattering. The PIV measurements showed that the flow field performed a “pumping” mode with varying inflow velocities and extent of the inner recirculation zone, triggered by the pressure variations in the combustion chamber. The flow field oscillations were accompanied by variations in the mixture fraction in the inflow region and at the flame root, which in turn were mainly caused by the variations in the CH4 concentration. The mean phase-dependent changes in the fluxes of CH4 and N2 through cross-sectional planes of the combustion chamber at different heights above the nozzle were estimated by combining the PIV and Raman data. The results revealed a periodic variation in the CH4 flux by more than 150 % in relation to the mean value, due to the combined influence of the oscillating flow velocity, density variations, and CH4 concentration. Based on the experimental results, the feedback mechanism of the thermo-acoustic pulsations could be identified as a periodic fluctuation of the equivalence ratio and fuel mass flow together with a convective delay for the transport of fuel from the fuel injector to the flame zone. The combustor and the measured data are well suited for the validation of numerical combustion simulations.
Influence of combustion on principal strain-rate transport in turbulent premixed flames
(Elsevier, 2015) Steinberg, Adam M.; Coriton, B.; Frank, J. H.
The transport of principal strain-rates (sisi) was experimentally investigated using high-repetition-rate (10 kHz) tomographic particle image velocimetry (T-PIV) and OH planar laser induced fluorescence (PLIF) in a Rej=13,000Rej=13,000 turbulent premixed flame. These measurements allowed calculation of the source terms in the sisi transport equation associated with the strain-rate and vorticity fields. Furthermore, the Lagrangian derivatives of sisi could be calculated by tracking theoretical Lagrangian fluid particles through space and time using the T-PIV data. These Lagrangian derivatives and the resolved source terms allowed the combined effects of the unresolved source terms to be inferred, namely the pressure Hessian, viscous dissipation, density gradients, and viscosity gradients. Statistics conditioned on the location of the Lagrangian fluid particles relative to the flame showed slight reductions in the strain-rate and vorticity source terms in the flame, indicating that these aspects of the turbulence were attenuated by the flame. Comparing the difference between the inferred source terms in the vicinity of the flame to the non-reacting flow showed that attenuation of sisi arose due to the combined effects of density and pressure gradients in the flame. The effects of flame-induced dilatation were small relative to the turbulent strain-rate and no change was found in the relative alignment of vorticity and strain-rate in the flame.

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