Gas turbine blades are subjected to complex mechanical loading coupled with extreme thermal loading conditions which range from room temperature to over 1000°C. Nickel-base superalloys exhibit high strength, good resistance to corrosion and oxidation, long fatigue life and is capable of withstanding high temperatures for extended periods of time. Consequently, Ni-base superalloys (NBSAs) are highly suitable as blading materials. The cyclic strains due to mechanical as well as thermal cycling leads to Thermomechanical fatigue (TMF). Damage from TMF takes the form of microstructural material cracking which consequently lead to the failure of the component. In order to increase the service life and reliability and reduce operating costs, development of simulations that accurately predict the material behavior for TMF is highly desirable. To support the mechanical design process, a framework consisting of theoretical mechanics, experimental analysis and numerical simulations must be used. Capturing the effects of thermomechanical fatigue is extremely important in the prediction of the material behavior and life expectation. Single crystal (SX) Ni-base superalloys exhibit anisotropic behavior. A modeling framework which is capable of simulating the physical attributes of the material microstructure is essential. Crystallographic slip along the slip planes controls the microstructural evolution of the material Crystal Visco-Plasticity (CVP) theory captures anisotropic behavior as well as the slip along the slip planes. CVP constitutive models can capture rate-, temperature, and history-dependence of these materials under a variety of conditions. Typical CVP formulations consist of a flow rule, internal state variables, and parameters. The model presented in the current study includes the inelastic mechanism of kinematic hardening and isotropic hardening which are captured by the back stress and drag stress, respectively. Crystallographic slip is accounted for by the incorporation of twelve octahedral six cubic slip systems. An implicit integration scheme which uses Newton-Raphson iteration method is used to solve the required solutions. The CVP model is implemented through a general-purpose finite element analysis software (i.e., ANSYS) as a User-Defined Material (USERMAT). A small batch of uniaxial experiments were conducted in key orientations (i.e., [001], [011], and [111] to assess the level of elastic and inelastic anisotropy. Modeling parameters are expressed as temperature-dependent to allow for simulation under non-isothermal conditions. An optimization scheme based in MATLAB utilizes this experimental data to calibrate the CVP modeling constants. The CVP model has the capability to simulate material behavior for monotonic and cyclic loading coupled with in phase and out phase temperature cycling for a variety of material orientations, strain rates, strain and temperature ranges. A CVP model that predicts SX behavior across various rates, orientations, temperatures and load levels have not been presented before now.

A major technical challenge for modern aero engines is the development of designs which reduce noise and emission whilst increasing aerodynamic efficiency and ensuring aeroelastic stability of low-temperature engine components such as fans and low-pressure compressors. Composites are used in aviation due to their excellent stiffness and strength properties, which also enable additional flexibility in the design process. The weight reduction of the turbomachine components, due to composite materials and lighter engines, is especially relevant for the design and developments of hybrid-electric or distributed propulsion systems [1]. To accomplish this, a representative volume element (RVE) of a glass-fiber reinforced polymer is created, describing the geometrical arrangement of the textile reinforcement structure within the polymer matrix. For both phases, realistic linear elastic properties are assumed. This RVE will be investigated with the finite element method under various loading conditions to assess its anisotropic elastic properties and also its damping behaviour for elastic waves. To study the influence of delamination on the mechanical properties, small defects will be introduced into the model at the interface between reinforcement and matrix. Based on this micromechanical approach, a constitutive model for the composite will be formulated that describes the anisotropic properties as well as the damping behaviour. This constitutive model is then used to describe the material response in a macro-mechanical model, which serves as the basis for an aeroelastic analysis of a 1/3-scaled high-speed fan using a conventional (Ti-6Al-4V) and fiber composite material.

Components in the hot section of a gas turbine engine experience extended high temperature dwells and cycles composed of multiple starts, changes in load, and variable duration. These loading profiles can lead to damage from cyclic viscoplasticity which is heavily path dependent as dwell stress, yield strength, and stress range change constantly during operation. Since an accurate prediction of accumulated damage is critical to managing an engine, reduced order methods for tracking material behavior over complex operation cycles are necessary tools to help avoid unplanned down time and optimize cost over the operational period. One method for tracking the material behavior during path dependent cyclic viscoplasticity requires the use of reference stress. Reference stress is a bulk representative stress that can be used in conjunction with various lifing methodologies to determine component durability. Previous papers provided a method for calculating reference stress for isotropic materials using limit load estimation. The goal of this paper is to extend these methodologies to a reference stress estimation method for anisotropic materials to estimate life for single crystal turbine blades. Derived equations will be shown and results from simple Finite Element (FE) test cases will be discussed to demonstrate the accuracy of the anisotropic reference stress estimation. Once reference stress is obtained, the long term forward creep stress of a component can be estimated for any given initial stress state. This approach can be used to calculate damage during shakedown resulting from redistribution and relaxation due to plasticity and creep, which can be critical for accurately predicting remaining useful life and optimizing engine management.

The nonlinear breathing crack behaviors and anisotropy of the bearing are important sources of severe vibration of rotor systems. However, the rotor system considering both of these factors has not gained sufficient attention in the existing studies. In this paper, the nonlinear dynamics of such anisotropic breathing cracked rotor system is investigated based on three-dimensional finite element model (FEM). Firstly, the equations of motion of the rotor system are established in the rotating frame to facilitate the modeling of the breathing crack. The fixed-interface component mode synthesis (CMS) is used to reduce the system’s degrees of freedom (DOFs). Then, in the process of solving the equations by harmonic balance method (HBM) and Newton-Raphson method, an original method for fast calculating tangent stiffness matrix is proposed. Finally, the effects of the crack depth, the anisotropy of bearing and relative angle between bearings on the nonlinear dynamics of the system are studied. The results show that the breathing behavior will complicate the vibration and introduce additional transverse stiffness. The increase of crack depth will deteriorate the vibration. The anisotropy and relative angle of bearing will lead to the splitting and merging of the resonant peaks, respectively.

The trailing edge slot is a canonical representation of the pressure-side bleed flow encountered in high pressure turbines. Predicting the flow and temperature downstream of the slot exit remains challenging for RANS and URANS, with both significantly overpredicting the adiabatic wall-effectiveness. This over-prediction is attributable to the incorrect mixing prediction in cases where the vortex shedding is present. In case of RANS the modelling error is rooted in not properly accounting for the shedding scales while in URANS the closures account for the shedding scales twice, once by resolving the shedding and twice with the model for all the scales. Here, we present an approach which models only the stochastic scales that contribute to turbulence while resolving the scales that do not, i.e. scales considered as contributing to deterministic unsteadiness. The model for the stochastic scales is obtained through a data-driven machine learning algorithm, which produces a bespoke turbulence closure model from a high-fidelity dataset. We use the best closure (blowing ratio of 1.26) for the anisotropy obtained in the a priori study of Lav, Philip & Sandberg [A New Data-Driven Turbulence Model Framework for Unsteady Flows Applied to Wall-Jet and Wall-Wake Flows, 2019] and conduct compressible URANS calculations. In the first stage, the energy equation is solved utilising the standard gradient diffusion hypothesis for the heat-flux closure. In the second stage, we develop a bespoke heat-flux closure using the machine-learning approach for the stochastic heat-flux components only. Subsequently, calculations are performed using the machine-learnt closures for the heat-flux and the anisotropy together. Finally, the generalisability of the developed closures is evaluated by testing them on additional blowing ratios of 0.86 and 1.07. The machine-learnt closures developed specifically for URANS calculations show significantly improved predictions for the adiabatic wall-effectiveness across the different cases.

The tip leakage flow in turbine and compressor blade rows is responsible for a relevant fraction of the total loss. It contributes to unsteadiness, and have an important impact on the operability range of compressor stages. Experimental investigations and, more recently, scale-resolving CFD approaches have helped in clarifying the flow mechanism determining the dynamics of the tip leakage vortex. Due to their continuing fundamental role in design verifications, it is important to establish whether RANS/URANS approaches are able to reproduce the effects of such a flow feature, in order to correctly drive the design of the next generation of turbomachinery. Base studies are needed in order to accomplish this goal. In the present work the tip leakage flow in axial compressor rotor blade cascade have been studied. The cascade was tested experimentally in Virginia Tech Low Speed Cascade Wind Tunnel in both stationary and moving endwall configurations. Numerical analyses were performed using the TRAF code, a state-of-the-art in-house-developed 3D RANS/URANS flow solver. The impact of the numerical framework was investigated selecting different advection schemes including a central scheme with artificial dissipation and a high-resolution upwind strategy. In addition, two turbulence models have been used, the Wilcox linear k–ω model and a non-linear eddy viscosity model (Realizable Quadratic Eddy Viscosity Model), which accounts for turbulence anisotropy. The numerical results are scrutinized using the available measurements. A detailed discussion of the vortex evolution inside the blade passage and downstream of the blade trailing edge is presented in terms of streamwise velocity, streamwise vorticity, and turbulent kinetic energy contours. The purpose is to identify guidelines for obtaining the best representation of the vortex dynamics, with the methodologies usually employed in routine design iterations and, at the same time, evidence their weak aspects that need further modelling efforts.

In the industrial simulation of flow phenomena, turbulence modeling is of prime importance. Due to their low computational cost, Reynolds-averaged methods (RANS) are predominantly used for this purpose. However, eddy viscosity RANS models are often unable to adequately capture important flow physics, specifically when strongly anisotropic turbulence and vortex structures are present. In such cases the more costly 7-equation Reynolds stress models often lead to significantly better results. Unfortunately, these models are not widely used in the industry. The reason for this is not mainly the increased computational cost, but the stability and convergence issues such models usually exhibit. In this paper we present a robust implementation of a Reynolds stress model that is solved in a coupled manner, increasing stability and convergence speed significantly compared to segregated implementations. In addition, the decoupling of the velocity and Reynolds stress fields is addressed for the coupled equation formulation. A special wall function is presented that conserves the anisotropic properties of the model near the walls on coarser meshes. The presented Reynolds stress model is validated on a series of semi-academic test cases and then applied to two industrially relevant situations, namely the tip vortex of a NACA0012 profile and the Aachen Radiver radial compressor case.

Leading edge instrumentation used in compressor and turbine blades for jet-engine test rigs can cause significant obstruction and lead to a marked increase in downstream pressure loss. Typical instrumentation used in such a scenario could be a Kiel-shrouded probe with either a thermocouple or pitot-static tube for temperature/pressure measurement. High fidelity analysis of a coupled blade and probe requires the generation of a high quality mesh which can take a significant amount of an engineers time. The application of Immersed Boundary Method (IBM) and Large Eddy Simulation is shown in this paper to enable the use of an extremely simple mesh to observe the primary flow features generated due to the blade and probe interaction effects, as well as quantify downstream pressure loss to within a high level of accuracy. IBM is utilised to approximately model the probe, while fully resolving the blade itself through a series of LES simulations. This method has shown to be able to capture downstream loss profiles as well as integral quantities compared to both experiment and fully wall-resolved LES without the need to spend a significant amount of time generating the ideal mesh. Additionally, it is also able to capture the turbulence anisotropy surrounding the probe and blade regions.

This study strives to provide a critical review and evaluation of influential constituent components in the two-equation k-ε turbulence model class, which are often employed in large full-fidelity gas turbine simulations in industry. All conjectures made, regarding the turbulence model behavior, will be compared to in-house experimental film effectiveness data from a novel film cooling array configuration. This experimental data set is comprised of high resolution adiabatic film cooling effectiveness measurements throughout two film cooling arrays comprised of diffused film holes of modern shape (streamwise inclination of α = 30°, expansion of Φ 1,2,3 = 10°, AR = 3.4, and β = 0° relative to the crossflow direction). The difference between each film cooling array is only a staggered verses inline pattern for the film holes, whereby each has a uniform spacing of X/D = P/D = 8. Local coverage, laterally averaged film cooling effectiveness, and superposition analysis was quantified over a variety of testing conditions (M = 0.5, 0.75, 1.0, 1.5, 2.0, 2.5 at DR = 0.9). First, rendered quantifications of the anisotropic nature of the turbulence are shown throughout the near-field injection region, by leveraging the Reynolds stresses to form anisotropic-invariant maps. Next, results from k-ε models using a linear, a cubic, and a quadratic constitutive relation are compared. Furthermore, effective and conservative scaling of the production and destruction terms in the turbulent transport equations was performed, within reasonable bounds, and the resulting impact on the adiabatic film effectiveness was quantified. This scaling encompasses the C ε2 coefficient, as well as the Durbin realizibility coefficient used in the turbulent viscosity definition. Finally, various formulations of the turbulent Prandtl number were compared, with the resulting adiabatic film effectiveness observed.

Pin fin arrays are common features in the trailing edge region of turbine blades, and provide both structural integrity and increases in heat removal rates. Aforementioned pins act as fins by increasing the flow-wetted area, while also introducing complex flow structures such as von Kármán vortex shedding and horseshoe vortex systems; both directly affecting the global and local heat transfer characteristics over the endwall. The present study utilizes a wind tunnel to investigate the row to row interactions throughout a pin fin array comprised of four staggered rows, with spanwise and streamwise pitches of 2.5 pin diameters with a focus on the flow field downstream of the first row. The channel height to pin diameter ratio of 2. The Reynolds numbers tested based on pin diameter and local maximum velocity are 10,000 and 30,000. PIV is used as the experimental method of choice for acquiring quantitative flow data to study the flow field and derive high fidelity turbulence data and vortex structures with respect to the effects of the upstream rows on the pin fins downstream; this describes the underlying flow physics that drive the local Nusselt Number distribution on the cooled surface. Also, it was found that the wake structure varies over the two Reynolds Numbers significantly due to increased flow instabilities which promote shear layer separation and vortex formation. Flow acceleration due to neighboring pins confines the vortex formation in spanwise direction. The distribution of turbulent kinetic energy and the contribution of all Reynolds Stress Tensor components is reported. The turbulent scheme in the wake region is particularly anisotropic. The test section pressure drop is in agreement with literature for 30,000 Reynolds Number, but larger for smaller Reynolds Numbers. A thorough RANS simulation of the baseline case was conducted by carefully adjusting the turbulence model parameters to accurately reflect this particular experimental setup. The numerical results are in good agreement with heat transfer results and thus are utilized to further understand the underlying flow physics. However, the shear layer breakdown is underpredicted in numerical results resulting in shielded regions in the wake of the pin with artificially low heat transfer. The findings of the study contribute to better understanding of the underlying flow physics in a pin fin cooled airfoil and assist design engineers in making better internal cooling geometries.

Additive manufacturing represents a new frontier in the design and production of rotor machines. This technology drives the engineering research framework to new possibilities of design and testing of new prototypes, reducing costs and time. On the other hand, the fast additive manufacturing implies the use of plastic and light materials (as PLA or ABS), often including a certain level of anisotropy due to the layered deposition. These two aspects are critical, because the aero-elastic coupling and flow induced vibrations are not negligible for high aspect ratio rotors. In this work, we investigate the aeroelastic response of a small sample fan blade, printed using PLA material. Scope of the work is to study both the structure and flow field dynamics, where strong coupling is considered on the simulation. We test the blade in two operating points, to see the aero-mechanical dynamics of the system in stall and normal operating condition. The computational fluid-structure interaction (FSI) technique is applied to simulate the coupled dynamics. The FSI solver is developed on the base of the finite element stabilized formulations proposed by Tezduyar et al. We use the ALE formulation of RBVMS-SUPS equations for the aerodynamics, the non-linear elasticity is solved with the Updated Lagrangian formulation of the equations of motion for the elastic solid. The strong coupling is made with a block-iterative algorithm, including the Jacobian based stiffness method for the mesh motion.

Ceramics matrix composites (CMCs) have higher heat resistance and specific strength than conventional metal. These effects can contribute to not only reducing cooling air and parts weight, but also increasing turbine inlet temperature (TIT). As a result, CMCs have potential to improve aero-engine performance and reducing emission. CMCs also have complicated material characteristics to apply aero engine turbine parts. Stress-strain curve shows not only non-liner behavior in higher stress level but also anisotropy. The behavior and fracture toughness show the anisotropy because of material internal structure. Material strengths indicate anisotropy as well. Low cycle fatigue (LCF) strength indicates dependency of stress gradient. Thus, conventional design methods using linear elastic analysis model and peak stress assessment are too conservative to design CMC parts. IHI is developing SiC-SiC 3D woven fabric which is used for aero engine turbine vane and also building up a fracture prediction model to design the CMC turbine vane. Fracture prediction model is composed of structural analysis model to estimate deformation and fracture evaluation model to predict strength. The material model is assumed as a homogeneous substance and this material model constitutive equation is constructed from the theory of continuum damage mechanics (TCDM). In fracture model, that strength parameter is calculated with averaging stress fields. Multi-axial stress fields are evaluated by engineering equations referred to Hashin’s criteria. To validate our fracture prediction model, specific structural feature test were conducted. Sub-component tests were based on the building block approach that was general to validate structural reliability of composite material parts. Static tests and low cycle and high cycle fatigue tests were carried out at room temperature and high temperature. The validation test results showed good agreement with prediction. Finally we have made sure the validation of this fracture prediction model.

Components in gas turbines, specifically turbine blades are subjected to extreme loading conditions such as high temperatures and stresses over extended periods of time; therefore, predicting material behavior and life expectancy at these loading conditions are extremely important. The development of simulations that accurately predict monotonic response for these materials are highly desirable. Single crystal Ni-base superalloys used in the design of gas turbine blades exhibit anisotropic behavior resulting from texture development and dislocation substructures. A Crystal Visco-plastic (CVP) model has the capability of capturing both phenomena to accurately predict the deformation response of the material. The rate dependent crystal visco-plastic model consists of a flow rule and internal state variables. This model considers the inelastic mechanism of kinematic hardening which is captured using the Back stress. Crystal graphic slip is taken in to account by the incorporation of 12 Octahedral slip systems. An implicit integration structure that uses Newton Raphson iteration scheme is used to solve the desired solutions. The MATLAB model is developed in two parts, including a routine for the CVP constitutive model along with a separate routine which functions as an emulator. The emulator replicates a finite element analysis model and provides the initial calculations needed for the CVP. A significant advantage of the MATLAB model is its capability to optimize the modelling constants to increase accuracy. The CVP model has the capability to display material behavior for monotonic loading for a variety of material orientations and temperatures.

High-pressure turbines of modern gas-turbine engines use single crystal blades that exhibit material anisotropy. Due to manufacturing tolerances, each blade in the bladed disk will have different crystal anisotropy axis orientation, thereby creating mistuning in the structure. In this paper, the blade anisotropy angles are considered as uncertain design parameters to study the variation in forced response of a mistuned bladed disk. For realistic, high fidelity model of a bladed disk, linear bonded contact conditions at blade roots and shrouds are considered. The following two kinds of analysis are performed: (a) statistical analysis using polynomial chaos expansion and (b) global sensitivity analysis using Sobol indices. An effective strategy based on gradient information is used to minimize the computational cost involved in statistical and sensitivity analysis. For the first time, the possibility of introducing intentional blade material anisotropy mistuning to reduce the amplification of forced response is investigated.

A new method has been developed for the analysis of nonlinear forced response of bladed disks mistuned by blade anisotropy scatter and for the forced response sensitivity to blade material anisotropy orientations. The approach allows for the calculation of bladed disks with nonlinear friction contact interfaces using the multi-harmonic balance method. The method uses efficient high-accuracy model reduction method for the minimization of the computational effort while providing required accuracy. The capabilities of the developed methods are validated and demonstrated using a two-blade model. A thorough study of the influence of the material anisotropy mistuning and its sensitivity on the characteristics of the forced response is carried out using finite element modes of anisotropy mistuned realistic bladed disk with nonlinear friction joints of blade roots and shroud contacts. The dependency of the nonlinear forced response on excitation level and contact pressure values has been carried out for anisotropy mistuned bladed disks.

Blade life in the hot section of the gas turbine is most affected by the high operating temperatures, constant centripetal loading, and thermally induced stresses during startup and shutdown. High temperatures and constant loading result in material creep that limits the blade operating duration under steady conditions. Transient operation of the gas turbine, such as start-up and shut-down cycles result in thermally induced stresses in the blades that can cause local plastic yielding while also contributing to material creep. In conducting a detailed transient or steady-state analysis of a gas turbine blade, an accurate representation of the blade material is required to estimate creep strain and transient strains that contribute to thermo-mechanical fatigue (TMF) life. Custom material models are typically defined for the greatest accuracy of blade material models. However, these models are expensive and time-consuming to generate. As an alternative, the material models currently available in commercial codes can be calibrated to produce the measured material response. In this paper, a methodology is provided to calibrate complex material models in a commercial finite element (FE) code for single-crystal (SX) and directionally solidified (DS) alloys. The material model calibration relies on available test data in the literature and is used to define the material elasticity, plasticity, creep, and yield strength. Because the materials are anisotropic, the material properties are defined using orthotropic material definitions that define different material responses in the global coordinate directions. To demonstrate the accuracy of the material models, the predicted material TMF response is compared directly to test data.

Despite significant advancements in computational power and various numerical modeling in past decades, flow simulation of a multi-stage axial-flow compressor is still one of the most active areas of research, for it is the critical component in engine performance and operability, and there are so many elements that need to be looked into to predicting correct matching of the stages and accurate flow distribution inside the machine. Modeling unsteadiness, both deterministic and random types, and real geometries are among the most important features to be considered in such prediction. The authors have conducted in their previous studies a series of unsteady RANS (URANS) simulations of a 6.5-stage high-speed highly-loaded axial-flow compressor, and explored many unsteady effects as well as effects of real geometries such as Variable Stator Vane (VSV) clearance and inter-stage seal leakage flow on the compressor performance. However, all the analyses failed to predict correct stage matching, total pressure and temperature radial profiles, or mass-flow with adequate accuracies. In the present study, an Improved Delayed Detached Eddy Simulation (IDDES) with SST k-omega model is applied to the simulation of the same compressor configuration at aerodynamic design point. Fifth-order WENO scheme is employed for improved spatial accuracy to suppress significant increase in mesh size. Total number of mesh points are over 400 million for 1/10th sector model. Computations are ensemble averaged for 20 sector passage. Computed overall performance and flow field are compared with the compressor rig test data. The predictions of inter-stage total temperature radial profiles are noticeably improved over the URANS with the same mesh, discretization scheme and eddy turbulence model. Good comparison with the rig data indicates the current simulation is properly capturing the span-wise mixing phenomena. Unsteady flow field are compared between IDDES and URANS to locate the cause for the enhanced mixing. It is shown that components of Reynolds stress responsible for radial diffusion and anisotropic features are intensified in the tip leakage vortex at the rotor exit for the IDDES.

A blade row which is located downstream of a combustor has an extremely high turbulence intensity at inlet, typically above 10%. The peak turbulent length scale is also high, at around 20% of the chord of the downstream blade row. In a combustor, the turbulence is created by impinging jets in cross flow. This may result in the turbulence being anisotropic in nature. The aim of this paper is to investigate the effect of combustor turbulence on the loss mechanisms which occur in a turbine blade row. The paper has a number of important findings. The combustor turbulence is characterized and is shown to be isotropic in nature. It shows that, when no pressure gradient is present, combustor turbulence increases the loss of a turbulent boundary layer by 22%. The mechanism responsible for this change is shown to be a deep penetration of the turbulence into the boundary layer. It shows that the presence of combustor turbulence increases the profile loss and endwall loss in the turbine cascade studied by 37% and 47%, respectively. The presence of combustor turbulence also introduces a freestream loss resulting in the total loss of the turbine cascade rising by 47%. When these loss mechanisms were applied to the vane alone, of an engine representative high pressure turbine, it was found to result in a 1.3% reduction in stage efficiency.

Multiple, interacting flames in DLE systems can increase flame surface area and promote mixing of hot-products into the reactants — leading to an efficient usage of combustion volume and improved injector performance. An optically-accessible, confined, linear array of five swirl nozzles was recently built [1] to investigate flame dynamics and validate computational strategies. The present work focuses on modeling a dataset representative of lean gas turbine conditions, using a flamelet approach. A preheated (500K), premixed fuel-air mixture (ϕ = 0.55, T flame = 1732K) at atmospheric pressure was injected through the swirlers at 40 m/s into a rectangular chamber. High-speed laser measurements of the flow (3 component velocity field from 10 kHz stereoscopic particle image velocimetry (S-PIV)) and flame (planar laser induced fluorescence of the hydroxyl radical (OH-PLIF)) were used for model validation. The objectives of this work: (1) Evaluate a flamelet-progress variable method based on flamelet-generated manifolds (FGM) and examine its sensitivity to models for micro (scalar dissipation) and large scale mixing (anisotropic RANS vs LES) and (2) Obtain insight into the velocity field and flame stabilization in an interacting system. Computations indicate that high-swirl nozzles produce bluff-body flames anchored to shear-layer vortices due to an arrested flow expansion. The anisotropic RANS turbulence model under-predicts the recirculation zone strength but predicts flow development and Reynolds stress profiles fairly well. While LES is more accurate overall, both models over-predict flow fluctuations in the transitional flow at the end of the recirculation bubble where flow becomes axially positive. The flamelet approach predicts the flame-shape and length correctly but over-predicts the reaction rate in-between swirlers. The effect of including a reactive SDR model is to significantly increase flame-flow interaction (higher scalar variance) but does not appear to influence the overall shape or location of the flame.

In this research, a micro-plasma system was investigated for its capability in additive manufacturing (AM). Micro-plasma AM system has the advantage of lower cost and higher deposition rate over laser based AM systems, and generates leaner and cleaner weld deposit than other arc based AM systems. However, the micro-plasma system is complex and involves a large number of process variables. In this study, the feasibility of using a micro-plasma system for additive manufacturing was assessed based on surface features, mechanical properties and microstructure. In addition, two arc and wire feed modes were examined to understand the effects of these two variables. Each was used to produce IN 718 superalloy samples for macro- and microstructure evaluation, hardness, wear, and tensile tests along both long and transverse directions. Preliminary results showed that crack free samples, measured up to 100 mm × 40 mm, can be generated without measurable distortion. Some surface discoloration was observed, ranging from light straw to a purple tint. After heat treatment, the hardness of the samples varies from 403 to 440 HV, with the transverse surface showing slightly lower hardness values. Pin-on-disk wear test yielded consistent wear volume for three sets of the samples produced using different process parameters; however, samples produced with no modifications to the current and wire feed mode showed marginally higher wear rate. Microstructural analysis with SEM and EDS revealed presence of small pinholes, measured from submicron up to 22 μm in diameter, and no indication of any cracks or boundary layers between passes. SEM analysis revealed the presence of high contrast Nb/Mo rich carbides along with γ″-Ni 3 Nb in the γ matrix. Finally, tensile test was carried out to understand the anisotropic behavior; the results showed that transverse direction had lower tensile strength and ductility. Samples produced with pulsed current and wire feed mode had lower yield/tensile strength but higher ductility than that without current and wire feed mode modification.