Gas Turbine Combustor: Modelling and Optimization

Present work is concerned with the flow field analysis inside an annular gas turbine combustor both under non-reacting and reacting conditions. Three-dimensional gas turbine combustor of 20-degree sector has been modeled using the pre-processor GAMBIT. Flow through the combustor has been simulated using FLUENT code by solving the appropriate governing equations viz., conservation of mass, momentum and energy. RNG κ-ε turbulence model is used for physical modeling. Initially prediffuser optimization has been carried out with respect to angle, length and contours. Flow through holes is modeled using porous jump boundary condition as well as modeling real holes themselves to study the efficacy of real hole modeling. Total pressure loss has been calculated to evaluate the cold flow as well as hot flow losses. Combustion has been modeled using the Probability Density Function (PDF) approach. Temperature and species concentrations are predicted.

Reducing Occupant Injury in Frontal Crashes for a Low-Floor City Bus

In this research, the effect of beam buckling in a predefined direction is used to reduce occupant injuries in frontal crashes of an ultra-low-floor (ULF) city bus. In ULF buses, the floor structure consists of several longitudinal long beams, which in case of a frontal crash may buckle due to the axial impact. The direction of rotational acceleration of the driver seat due to buckling is highly affected by the position of the driver seat. A finite element model of an ULF bus was developed using LS-Dyna. The driver model, a Hybrid III 50th male dummy with deformable jacket and abdomen, was restrained to the seat with a 3-point belt. An Elastic-Plastic material model was used for the bus structure to investigate the buckling behavior of the beam elements. Using diagonal beams to guide the buckling in a desired direction, rewarding results were achieved in reducing the occupant injuries. For example, with an extra diagonal beam under the seat, the driver’s HIC15 was reduced from 739 to 415.7 and HIC36 from 791 to 700.6.

Flow Investigations in an Aero Gas Turbine Engine Afterburner

This paper is concerned with the prediction of flow and flame characteristics behind complex flame stabilizer used in aero gas turbine afterburners. The numerical calculation is performed using SIMPLE algorithm with unstructured grid arrangement in which time averaged transport equation for mass, momentum, turbulence and energy are solved using finite volume method. The turbulence effects are simulated using RNG κ-ε model. Flow analysis has been carried out for the non-reacting and reacting conditions. Meshing of the flow domain is done in GAMBIT. A detailed analysis of non-reacting flow in a 60°sector afterburner from inlet to exit of the afterburner is carried out in FLUENT solver code. The various thermodynamic properties are analyzed and presented along the length of the afterburner. Three different combustion models viz. prePDF, eddy dissipation and finite rate/eddy dissipation model are used in order to predict the reacting flow. An experimental investigation of the three-dimensional confined flow fields behind a “V” shaped complex flame stabilizer in an isothermal model of an afterburner is carried out to validate the CFD code. From the present study it is concluded that the prediction procedure adopted especially for non-reacting flow can be used with confidence in the development of an afterburner at a lower cost. Since measurements were not possible under reacting conditions no attempt has been made for reacting flow validation.

Quick Evaluation of Crashworthiness for Nonlinear Damped Systems by Using an Analytical Linearization Method

The ability to predict crashworthiness is helpful for the cushion design. This is to minimize the impact loading on packaged products, such as drop impact loading occurring during shipment or transportation. In addition, the nonlinear characteristic of cushion system would affect the crashworthiness of the packaged goods. Therefore, an accurate analysis for the nonlinear cushion system is crucial in reliability design. However if nonlinear analysis is performed, a large computation load is required for numerical approaches; on the other hand, there is a need to include higher transcendent functions within the analytical approaches. In this paper, an analytical linearization method is applied to obtain quantitative solution in the nonlinear analysis. This method is not a numerical method, meanwhile, no high transcendent functions are considered. Therefore, the crashworthiness for nonlinear drop-impact systems can be quickly evaluated. In practical application, this method also shows good efficiency and good agreement with the experimental results.

Engine Testing of Advanced Materials for Hypersonic Applications

This paper describes the use of a ground based gaseous hydrogen/oxygen rocket engine to test advanced materials for rocket engine and hypersonic propulsion applications. The types of materials that have been tested include ceramic composites, metallic alloys and ceramic and metallic foams. There are various configurations in which these materials can be tested. A “square” engine is used for testing flat rectangular panels by placing the panel downstream of the rocket nozzle in the exhaust path. A more traditional “round” rocket engine is used to test axisymmetric engine components such as nozzle inserts and combustion chambers that are fabricated from either ceramic composites or metal alloys. Besides hydrogen, other engine fuels such as methane are being evaluated in order to expose test materials to a hydrocarbon environment. Various organizations from industry, academia and other government agencies have used this test cell to facilitate the development of advanced materials for use in both rocket engine and hypersonic propulsion applications.

High-Speed Biaxial Tissue Properties of the Human Cadaver Aorta

Traumatic rupture of the aorta (TRA) is one of the leading causes of mortality in automobile crashes. Finite element (FE) modeling, used in conjunction with laboratory experiments, has emerged as increasingly important tool to understand the mechanisms of TRA. Appropriate material modeling of the aorta is a key aspect of such efforts. The current study focuses on obtaining biaxial mechanical properties of aorta tissue at strain rates typically experienced during automotive crashes. Five descending thoracic aorta samples from human cadavers were harvested in a cruciate shape. The samples were subjected to equibiaxial stretch at a strain rate of 44 s−1 using a new biaxial tissue-testing device. Inertially compensated loads were measured. High-speed videography was used to track ink dots marked on the center of each sample to obtain strain. The aorta tissue exhibited anisotropic and nonlinear behavior. The tissue was stiffer in the circumferential direction with a modulus of 10.64 MPa compared to 7.94 MPa in longitudinal direction. The peak stresses along the circumferential and longitudinal directions were found to be 1.89 MPa and 1.76 MPa, respectively. The tissue behavior can be used to develop a better constitutive representation of the aorta, which can be incorporated into FE models of the aorta.

Simulation and Active Control of Surge Instability in Axial Flow Compressors

A one-dimensional unsteady model capable of analyzing various arrangements of turbomachinery components has been developed. Surge disturbance propagation has been captured within a turbojet engine. It is demonstrated that these instabilities can be stabilized by the use of active control strategies such as air bleeding and air injection. The effect of variable area diffuser is also studied. Two types of active control systems are considered: steady and unsteady. In steady case, mass is removed at a fixed rate from the diffuser or interstage, or mass is injected at a fixed rate into the first stage of compressor. In unsteady control, the rate of bleeding or injection is linked to the amplitude and frequency of the upstream pressure disturbances. Results show that both steady and unsteady strategies eliminate surge disturbance and suppress the instabilities. Therefore, they extend the stable operating range of compressor. It is observed that injection can reduce the amount of bleeding air. It is also shown that smaller amount of compressed air need to be removed with the unsteady control, as compared to steady case. Variable area diffuser is shown to be able of suppressing surge instabilities. Perturbations of inlet total pressure or temperature may lead the compressor to stall. Active control of instabilities caused by sinusoidal perturbations of inlet total pressure is also investigated in the present study.

An Improved Streamline Curvature Approach for Off-Design Analysis of Transonic Compressors

Streamline curvature is still a powerful method in predicting the performance of turbomachines whose results will be more realistic if a good combination of losses and deviation is incorporated in the calculations. A streamline curvature through flow numerical approach is modified to better approximate the flow field and performance of a single stage transonic compressor by incorporating shock and profile losses using previous correlations. Deviation is estimated on the basis of several correlations and results are then compared with the present experimental data. Looking at the effect of above mentioned methods on design and off-design performance of compression system, it is possible to recommend that a suitable combination of these methods be incorporated in the solution procedure.

Finite Element Modeling of Aortic Tissue Using High Speed Experimental Data

Traumatic rupture of the aorta (TRA) is responsible for 10% to 20% of motor vehicle fatalities [1]. Both finite element (FE) modeling and experimental investigations have enhanced our understanding of the injury mechanisms associated with TRA. Because accurate material properties are essential for the development of correct and authoritative FE model predictions, the objective of the current study was to identify a suitable material model and model parameters for aorta tissue that can be incorporated into FE aorta models for studying TRA. An Ogden rubber material (Type 77B in LS-DYNA 970) was used to simulate a series of high speed uniaxial experiments reported by Mohan [2] using a dumbbell shaped FE model representing human aortic tissue. Material constants were obtained by fitting model simulation results against experimentally obtained corridors. The sensitivity of the Ogden rubber material model was examined by altering constants G and alpha (α) and monitoring model behavior. One single set of material constants (α = 25.3, G = 0.02 GPa, and μ = 0.6000E-06 GPa) was found to fit uniaxial data at strain rates of approximately 100 s−1 for both younger and older aortic tissue specimens. Until a better material model is derived and other experimental data are obtained, it is recommended that the Ogden material model and associated constants derived from the current study be used to represent aorta tissue properties when using FE methods to investigate mechanisms of TRA.

Numerical Investigation of Injury Biomechanics of the Thorax and Lower Extremities Under Different Restraint Systems Using Wayne State University Human Model

Although newer vehicles are equipped with airbags and there is a high percentage of vehicular occupants who are wearing seatbelts, injuries to the thorax and lower extremities accounted for 33% of all occupant injuries. Moreover, when considering the frequency of injuries with a severity on the Abbreviated Injury Scale (AIS) of 3 to 6 (heretofore referred to as AIS 3+), injuries to the chest and lower extremities accounted for a total of approximately 43% of all occupants with these injuries. Consequently, a more detailed study of injury risks to these two body regions is called for. A series of numerical studies has been conducted to simulate a frontal crash using a three-dimensional (3D) finite element (FE) whole body human model representing a 50th percentile male to estimate the injury risks to the thorax and lower extremities. Three different combinations of restraint systems were simulated along with the no restraint condition. Results indicate that injury risks to the thorax were much higher in an unrestrained driver compared to those of a driver restrained by either the airbag only, three-point belt only, or combined airbag and three-point belt condition. On the other hand, injury risks to the lower extremities in occupants without any restraint or airbag only were greater than those restrained by three-point belt only or combined airbag and three-point belt. The combined airbag and three-point belt system simulated in this study showed the lowest injury risks to the thorax and lower extremities.