Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 21 for “"stall margin"”.
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A Method to Control Turbofan Engine Starting by Varying Compressor Surge Valve Bleed
… while maintaining an adequate compressor stall margin during engine start by varying the surge valve bleed. Varying the surge valve bleed was also shown to reduce compressor and fan required torque. A new method of turbofan engine component characteristic map extrapolation was developed. …
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Stall inception in high stage loading low pressure ratio transonic fans
… space that is highly challenging in terms of stall. Stall inception of a modern, high stage loading, low pressure ratio transonic was investigated using single-passage steady and full annulus unsteady computational fluid dynamics. The computational method was validated using experimental data …
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L1 Adaptive Control of Uncertain Nonlinear Systems with Dynamic Constraints: As Applied to Commercial Aircraft Engines
… or even total engine failure. Additionally stall, also known as compressor surge, which occurs when the compressor is unable to work against incoming air resulting in flow reversal, must be avoided. To decrease the chances of entering into surge or stall, control systems are developed to …
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Computational study of the effects of protruding studs casing treatment on the performance of an axial transonic turbofan
… compressor stability and increase compressor stall margin, usually with some sacrifice of performance and efficiency. Active methods make use of external devices injecting and/or bleeding air from the compressor duct. Passive methods are primarily based on casing treatments, often involving …
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Two investigations of compressor stability : spike stall inception and transient heat transfer effects
… first is of the formation of spike-type rotating stall precursors. Recently, high fidelity computations have attributed pre-cursor formation to a leading-edge separation and consequent shedding of vorticity near the rotor tip due to high incidence. This hypothesis is assessed via experiments in a …
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Computational investigation of the effects of casing treatments on the performance of a turbofan
… of enhancing the performance and increasing the stall margin of a model turbofan stage in transonic operating conditions. The study is divided into three phases. During the first phase two types of casing treatments, inward protruding rings and circumferential grooves, were tested with relatively …
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Convection from manufactured ice roughness with varying flux boundary conditions.
… decreases lift coefficients, and reduces stall margin, which can lead to aircraft accidents. To predict the shape of these ice accretions, codes, such as the NASA LEWICE code, have been created that step through time and solve an energy balance for an iced airfoil. A critical part of this …
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Tip clearance flows in axial compressors: stall inception and stability enhancement
… compressor influences the loss levels and the stall onset point. The role of tip clearance flows in the stall inception process is still debated, though. The aim of this thesis is to improve the fundamental understanding of the tip clearance flow field and its role in the stall inception …
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An Experimental Characterization of Tip Leakage Flows and Corresponding Effects on Multistage Compressor Performance
… rise capability, isentropic efficiency, and stall margin. With modern engine designs trending toward decreased core sizes to increase propulsive efficiency (by increasing bypass ratio) or additional compression stages to increase thermal efficiency by increasing the overall pressure ratio, …
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Convection from ice roughness surfaces using scaled Reynolds numbers for larger NACA 0012 airfoils.
… weight and drag, while also decreasing lift and stall margin. Previous studies at Baylor University characterized the convective heat transfer for roughness surfaces exposed to accelerating flow similar to that experienced by a 21-in. NACA 0012 airfoil. The current study characterizes the …
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Evaluation of primary flight display enhancements for improving general aviation safety
… accident causes identified takeoff and climbout, stall, and spatial disorientation as potential root causes that could be addressed with enhancements to the Primary Flight Display of an integrated general aviation cockpit. To address these accident causes, four prototype enhancements were …
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Three-dimensional rotating stall inception and effects of rotating tip clearance asymmetry in axial compressors
The effects of two types of flow nonuniformity on stall inception behavior were assessed with linearized stability analyses of two compressor flow models. Response to rotating tip clearance asymmetries induced by a whirling rotor shaft or rotor height variations were investigated with a …
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Measurements of Flow in Boundary Layer Ingesting Serpentine Inlets
… by as much as 30%, implying improvements in stall margin and engine performance. Analysis of the wake shape entering the S-duct showed that the airframe and inlet duct are both important components of a wake-ingesting inlet/diffusion system. Shape effects and static pressure distributions …
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Modal Response of a Transonic Fan Blade to Periodic Inlet Pressure Distortion
… pressure rise, and a reduction in mass flow and stall margin. Long-term effects are a result of vibratory blade response that can ultimately lead to high cycle fatigue (HCF), which in turn can quickly cause partial damage to a single blade or complete destruction of an entire compressor blade …
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Reynolds number effects on the aerodynamics of compact axial compressors
… $Re= 6\times10^4$) and at a condition close to stall for a datum stage design, a stage with an improved stator design and two stators with compound lean. It was found that losses in the rotor were greater than the stator losses across the whole range of $Re$. As expected, the loss decreased with …
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Use of Nonlinear Volterra Theory in Predicting the Propagation of Non-uniform Flow Through an Axial Compressor
… aerodynamic operability through a reduction in stall margin, pressure rise and mass flow, and to loss of structural integrity through means of high cycle fatigue (HCF). HCF is a primary mechanism of blade failure caused by vibrations at levels exceeding material endurance limits. Previous …
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Numerical Investigation of Subsonic Axial-Flow Tandem Airfoils for a Core Compressor Rotor
… coefficient, polytropic efficiency and numerical stall margin. An examination of the tandem rotor fluid mechanics revealed that the forward blade acts in a similar manner to a conventional rotor. The aft blade is strongly dependent upon the flow it receives from the forward blade, and tends to be …
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Axial compressor stability enhancement
… times. One source of instability is compressor stall. Stall problems can be reduced by machining cavities into the compressor casing adjacent to the rotor blades. This ‘casing treatment’ is the focus of the present work. Two treatment configurations are tested: circumferential grooves cut into …
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Time-resolved measurements of a transonic compressor during surge and rotating stall
… (about 20:1), good efficiency and sufficient stall margin. The rotor was tested without the presence of a stator (or any of the following seven stages) at the NASA Lewis single-stage, high-speed, core-compressor test-rig. The measurements were obtained with a single circumferential, …
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Characterization of performance-limiting flow mechanisms in a centrifugal compressor stage
… diffuser configuration experiences enhanced stall margin over the baseline diffuser at the design speed. These differences are traced to reduced secondary flows influence and thus reduced separation extent for the higher aspect ratio truncated diffuser. It is hypothesized that the onset of …
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