Grant O. Musgrove

Computational Design of a Louver Particle Separator for Gas Turbine Engines

The extreme temperatures in a jet engine require the use of thermal barrier coatings and internal cooling channels to keep the components in the turbine section below their melting temperature. The presence of solid particles in the engine’s gas path can erode thermal coatings and clog cooling channels, thereby reducing part life and engine performance. This study uses computational fluid dynamics to design the geometry of a static, inertial particle separator to remove small particles, such as sand, from the engine flow. The concept for the inertial separator includes the usage of a multiple louver array followed by a particle collector. The results of the study show a louver design can separate particles while not incurring large pressure loss.Copyright

Validation and Rules-of-Thumb for Computational Predictions of Liquid Slosh Dynamics

During flight, the sloshing of liquid propellant onboard the vehicle can have significant effects on vehicle stability due to the large amount of propellant mass. Because of the stability effect, propellant sloshing is included in the guidance, navigation and control (GNC) analysis to account for the dynamics of the propellant sloshing motion. Typically, the sloshing propellant is simplified either as a mechanical system in the form of a swinging pendulum or as a spring-mass system. In either case, the important parameters governing the dynamics of the system are the mass, natural frequency, and damping ratio. The sloshing parameters of frequency and damping of the slosh system are dependent on the type of propellant, tank geometry, and the liquid level in the tank. The parameters are typically derived from the large amount of experimental data currently available for conventional tank shapes. Unconventional tank shapes, however, require either experimental or computational work to develop new sloshing parameters. Because of the cost of experimental slosh testing, it may be preferred to use computational fluid dynamics (CFD) solvers to predict sloshing dynamics. While previous studies have shown the applicability of CFD to predict sloshing parameters, a consistent methodology to conduct sloshing simulations has not yet been reported. Specifically, there is currently no guidance in the literature for selecting the necessary physics in the simulation, nor is there a suggestion for a starting point of the computational grid resolution. In this paper, the CFD solver FLOW-3D is used to simulate propellant sloshing in oblate spheroidal and cylindrical tanks. The slosh frequency and damping factor predicted with the simulations are validated with experimental data for a range of propellant fill levels and with and without tank baffles. The required physics for sloshing simulations are discussed and rules-of-thumb are presented to provide a starting point for defining the computational grid resolution.

EXPERIMENTAL EVALUATION OF COMPRESSOR BLADE FOULING

Fouling of compressor blades is an important mechanism leading to performance deterioration in gas turbines over time. Experimental and simulation data are available for the impact of specified amounts of fouling on performance, as well as the amount of foulants entering the engine for defined air filtration systems and ambient conditions.This study provides experimental data on the amount of foulants in the air that actually stick to a blade surface for different conditions of the blade surface. Quantitative results both indicate the amount of dust as well as the distribution of dust on the airfoil, for a dry airfoil, as well as airfoils that were wet from ingested water, as well as different types of oil. The retention patterns are correlated with the boundary layer shear stress. The tests show the higher dust retention from wet surfaces compared to dry surfaces. They also provide information about the behavior of the particles after they impact on the blade surface, showing that for a certain amount of wet film thickness, the shear forces actually wash the dust downstream, and off the airfoil. Further, the effect of particle agglomeration of particles to form larger clusters was observed, which would explain the disproportional impact of very small particles on boundary layer losses.Copyright

Overview of Important Considerations in Wet Gas Compression Testing and Analysis

During upstream production of natural gas fields, it is common that a gas-liquid mixture of product is brought to the surface. The mixture, termed wet gas, is generally made up of mostly gas with a small amount of liquid, typically up to 5% by volume of the mixture. Because of the difficulties of compressing wet gas, the practical approach has been to separate the liquid and gas phases before compression. However, large separation equipment is unfavorable for subsea installations because of the cost to place machinery on the sea floor. Instead, a compressor designed for wet gas operation is preferred because it eliminates the need for large separation equipment leading to plant simplification and cost reduction. To address this design need, researchers have been active in addressing the challenges with wet gas compression. As result, experimental work has been conducted to study the effects of wet gas on compressor aerodynamic and mechanical performance. This experimental research has presented many challenges in recreating wet gas conditions and quantifying the effect of the liquid on the compressor performance. The results from this testing have helped to characterize the performance effects. But so far each work has focused on a range of test variables without identifying those that have the largest effect on compressor performance. This paper aims to provide the reader with an overview of the completed wet gas research, the challenges associated with doing the experimental work, and a discussion of the resulting trends observed in most of the wet gas research. This will include an in-depth review of relevant literature on wet gas compression testing and performance, a discussion of the important

Performance Measurements of a Unique Louver Particle Separator for Gas Turbine Engines

Solid particles, such as sand, ingested into gas turbine engines, reduce the coolant flow in the turbine by blocking cooling channels in the secondary flow path. One method to remove solid particles from the secondary flow path is to use an inertial particle separator because of its ability to incur minimal pressure losses in high flow rate applications. In this paper, an inertial separator is presented that is made up of an array of louvers followed by a static collector. The performance of two inertial separator configurations was measured in a unique test facility. Performance measurements included pressure loss and collection efficiency for a range of Reynolds numbers and sand sizes. To complement the measurements, both two-dimensional and three-dimensional computational results are presented for comparison. Computational predictions of pressure loss agreed with measurements at high Reynolds numbers, whereas predictions of sand collection efficiency for a sand size range 0–200lm agreed within 10% of experimental measurements over the range of Reynolds numbers. Collection efficiency values were measured to be as high as 35%, and pressure loss measurements were equivalent to less than 1% pressure loss in an engine application. [DOI: 10.1115/1.4007568]

Gas Turbine Blade Stress and Temperature Sensitivity to Turbine Inlet Profile and Cooling Flow

Actual operating conditions in the hot section of a gas turbine vary from the design condition due to factors such as geographic location, component wear, and fuel composition. Turbine design practices typically use a conservative approach that requires checking the sensitivity of operating parameters such as turbine inlet profiles, cooling flows, and heat transfer correlations on component temperatures and stresses. In most cases, a sensitivity check is limited to analyzing the bounds of a range of values for only a few input parameters, whereby the inputs that produce the most conservative results are carried through the remainder of the analysis. For flow path components, however, multiple inputs must be evaluated over a range of values due to the interaction of the hot gas flow field and internal cooling systems. The study presented in this paper uses a probabilistic approach to develop surrogate models to evaluate the sensitivity of a set of operating parameters on the predicted blade temperatures and stresses. Commercially available software is utilized to predict blade temperatures and stresses for the first two stages of an industrial gas turbine. The operating parameters define the blade cooling flow and the shape and values of the turbine inlet profiles of total temperature and total pressure. The results of the study show the spatially resolved sensitivity of the operating parameters on blade temperature and stress distributions.Copyright

Design of a Small Scale Gas Turbine for a Hybrid Propulsion System

As part of the Great Horned Owl (GHO) program Southwest Research Institute© (SwRI©) has developed a small, lightweight gas-turbine generator to provide power for an electric or hybrid electric Unmanned Aerial Vehicle (UAV). This original design for a fuel-to-electricity component of a hybrid propulsion system was designed, built and tested at the SwRI facility in San Antonio, TX. The design is based on a patented SwRI gas-turbine configuration and went through five major design iterations leading to the final configuration. The design iterations of the gas generator were driven by aggressive targets for weight, size and performance that were part of program requirements. The design of the GHO machine evolved from the initial concept based on lessons learned from previous testing at SwRI and considerations to improve manufacturability and operability. Improvements to the design were also incorporated to meet performance goals and increase life of hot section parts.This machine is low-cost and simple to operate and in addition to the original design intent of fuel-to-electricity use in a hybrid propulsion system can be used as a technology demonstration platform. SwRI plans to use the GHO machine in projects such as instrumentation development, as a test bed for new technologies such as ceramic or additive manufactured parts and for use as a component in a hardware-in-the-loop system.Copyright

Measured Effects Of Liquid Distribution On Compressor Performance During Wet Gas Ingestion

Upstream production of natural gas is commonly a mixture of both liquid and gas hydrocarbons that is separated before boosting the gas or liquid flows to higher pressure for transport. The gas-liquid mixture is known to affect the compressor performance, but it is not known if the distribution of the liquid entering the compressor affects the maximum amount of liquid that the compressor can safely ingest. The work presented in this paper determines if liquid atomization affects the compressor operation or influences the amount of liquid that can be safely ingested by the compressor, compared to non-atomized liquid. To determine the effect of atomization on compressor performance, three injection methods are used to characterize the performance for atomized and non-atomized flow. Non-atomized flow is generated by injecting liquid far upstream of the compressor to allow a natural two-phase flow regime to develop before entering the compressor. Atomized flow is generated near the compressor suction flange using liquid pressure to generate large droplets on the order of 2,000 m and gas-assisted atomization to generate droplets at least an order of magnitude less than the large droplets (100 m). Results of the work are reported in this paper to include compressor performance measurements for two rotation speeds and a range of liquid and gas flow rates. In addition, the control of the compressor during wet gas ingestion is demonstrated through movement of the compressor on the flow map. Finally, high-speed flow images of the liquid entering the compressor are qualitatively shown to illustrate the difference in injection method.

Rotordynamic Force Prediction of an Unshrouded Radial Inflow Turbine Using Computational Fluid Dynamics

Cross-coupled forces due to bladed components, bearings and seals can contribute to destabilizing a rotor system and are an important input to the rotordynamic design of turbomachinery. Alford (1965) developed a simple formula for describing the cross-coupled mechanism of an unshrouded axial turbine stage. The high flow radial inflow turbine studied here can exhibit similar characteristics due to its long stage length. In this work, a transient computational solution is developed to predict cross-coupling stiffness of an unshrouded turbo-expander. The three-dimensional computational fluid dynamics (CFD) model includes the flow path from the inlet guide vanes (IGV’s) to the exit of the radial inflow turbine. A 360 degree model of the flow path is used to simulate the turbine centered at its axis of rotation while the shroud is displaced a small distance from the axis of rotation. This offset simulates the uneven blade tip clearance that is present in a whirling rotor. Unsteady effects are included using a time-transient simulation while time-averaged forces acting on the turbine are used to calculate the cross-coupling aerodynamic coefficients. The rotordynamic coefficients calculated using this method are compared to both the Alford equation and formulations used for shrouded centrifugal compressor impellers.Copyright

Calibration of Gas Turbine Blade Temperature Predictions Using Surrogate Models

Actual gas turbine performance and component life at specific engine installations is highly dependent on the actual operating conditions, since not all engines are operated in the same manner. Due to the variability in turbine operation, it may be prudent to evaluate the operation of hot section components for turbine inlet conditions that are specific to a single installation. However, determining the actual turbine inlet conditions can be a difficult and expensive process that is usually only done on test bed gas turbines. This paper presents a method to determine turbine inlet conditions using a model calibration approach. Two-stage CFD and thermal analyses are developed to predict blade temperature. By varying the model inputs, computational predictions of blade temperature are calibrated to blade interdiffusion zone thickness measurements. In order to speed up calculations, surrogate models are used in place of the full-scale analysis codes during the calibration analysis. The result of the study is a prediction of the turbine inlet profile necessary to obtain the best agreement between predicted and measured blade temperatures.Copyright