Mustang Daily, May 24, 1989

Student newspaper of California Polytechnic State University, San Luis Obispo, CA.https://digitalcommons.calpoly.edu/studentnewspaper/5030/thumbnail.jp

Use of fibre-optic (FBG) sensors in the structural health monitoring of a battlefield helicopter rotor blade

As the use of fibre composite materials and components become more widely accepted, so does the inherent risks of sudden and possibly catastrophic failure. This creates a distinct need for sound, structural health monitoring (SHM) methods to be employed to both warn of, and prevent impending failure. For aviation related fibre composite components this is of paramount importance; however, a secondary but equally important consideration is that of service life. Any extension of a components service life is of great financial and operational benefit to both civil and military operators of aviation assets. This is particularly true of military helicopters which use fibre reinforced composite rotor blades, such as the Boeing CH-47 Chinook. Experience has shown that these highly exposed components are frequently damaged during combat operations and rapidly come into short supply as a result of often minor damage. This minor damage may necessitate blade replacement prior to the aircraft being authorised for further flight. This project seeks to use finite element analysis (FEA) methods and physical blade testing via the use of optical fibre Bragg grating (FBG) sensors to evaluate typical battlefield, ballistic penetration damage by small arms fire projectiles to a composite Boeing CH-47 Chinook rotor blade test section. Abaqus FEA software was used to create both a flat plate simulation and a Boeing-Vertol VR-7 Aerofoil assembly model. Physical testing was conducted on a blade by applying incremental load increases as well as incremental levels of simulated damage. Both FBG and strain gauge systems were used to assess the micro-strain levels at predetermined, critical locations. The data response from these systems was then validated as far as possible by FEA methods, with correlations able to be drawn between the strain systems and the FEA results. This research demonstrated that the use of FBG sensors on the surface of a complex composite component is an appropriate method for determining strains in the vicinity of damage, which was validated in specific areas by FEA methods. It also concluded that FEA methods alone are very difficult to use in a practical sense when assessing the significant size, type and random nature of ballistic damage to a complex composite structure. With further future development the possibility of the embedding FBG sensor systems at manufacture into a composite rotor blade for real time SHM or lifing assessment exists. This may in turn lead to enhanced service life management of such components by moving to an on-condition based lifing approach

Computational Fluid Dynamics 2020

This book presents a collection of works published in a recent Special Issue (SI) entitled “Computational Fluid Dynamics”. These works address the development and validation of existent numerical solvers for fluid flow problems and their related applications. They present complex nonlinear, non-Newtonian fluid flow problems that are (in some cases) coupled with heat transfer, phase change, nanofluidic, and magnetohydrodynamics (MHD) phenomena. The applications are wide and range from aerodynamic drag and pressure waves to geometrical blade modification on aerodynamics characteristics of high-pressure gas turbines, hydromagnetic flow arising in porous regions, optimal design of isothermal sloshing vessels to evaluation of (hybrid) nanofluid properties, their control using MHD, and their effect on different modes of heat transfer. Recent advances in numerical, theoretical, and experimental methodologies, as well as new physics, new methodological developments, and their limitations are presented within the current book. Among others, in the presented works, special attention is paid to validating and improving the accuracy of the presented methodologies. This book brings together a collection of inter/multidisciplinary works on many engineering applications in a coherent manner

Uncertainty quantification Of performance and stability of high-speed axial compressors

Geometrical uncertainties in a compressor (due to manufacturing tolerance and/or in-service degradation) often result in flow asymmetry around the annulus of a compressor that jeopardises compressor stability and performance. Usually, sensitivity of compressor stability and performance for any parametric variation is arrived at by considering all blades to have same dimension. In reality, an inherent blade-to-blade variation causes the blades to have a probability distribution. These blades can be redistributed circumferentially resulting in adjacent passage areas between different blades to be completely random and hence the performance variation. Surrogate model is preferred for quantifying the effects of parametric variation on compressor stability and performance given its quick turnaround time vis-a-vis CFD and experiments. In this thesis, uncertainties for three test cases were considered: each representative of fans on military aircraft engines, fans on civil aircraft engines and a 1-stage transonic compressor used in industrial gas turbine. This research establishes a rule of thumb to arrange blades of differing dimensions around the compressor to eke out maximum performance and stability margin. The parameters tip gap and stagger angle represent manufacturing tolerance while in-service degradation was represented by leading edge damage. For both random tip gap variation (0.15% to 0.94% span) and random leading edge damage (4% to 18% chord), the compressor performance and stability boundaries were found to be best with a zigzag pattern of blade arrangement and worst with a sinusoidal pattern of arrangement. The converse was found to be true for blades having random stagger angle variation (± 2.25% change in nominal stagger angle). The best/worst arrangement of blades with differing dimensions was ascertained using a mix of CFD and travelling salesman (TSP) analogy. The TSP analogy is handy for determining the best arrangement when two or more parameters vary simultaneously. Generalised surrogate model was developed to accurately predict the performance of compressors undergoing random tip gap and stagger angle variation. Due to its robustness, the surrogate model was combined with Monte Carlo technique to gauge the impact of parametric variation on quantities of interest (QoI). The mean absolute percentage error between CFD and surrogate models of stagger angle and tip gap (for different QoI) were found to be less than 0.14% and 1.5% respectively. This de novo analysis considers only the aerodynamic effect from geometric variations while neglecting the associated aeroelastic effects. Detailed analyses based on past experience and physical reasoning were used to validate the numerical simulations.Open Acces

Numerical simulations of rotating stall in axial flow compressors

Gas turbine compressor performance may encounter deterioration during service for various reasons such as damage by debris from the casing or foreign objects impacting on the blades, typically near the rotor's tip. Moreover, mal-schedule of Variable Stator Vanes (VSVs) during start-up may also result in performance deterioration and reduction in the surge margin. Ability to assess the effect of compressor deterioration using Computational Fluid Dynamics (CFD) is important at both design stage and in service. Compressor blade damage breaks the cyclic symmetry and the VSVs mal-schecule creates mis-match between stages together with geometric variations, thus computations are desirable to be performed using full annulus assemblies. Furthermore, downstream boundary conditions are also unknown during rotating stall or surge and simulations become difficult. This research presents unsteady time-accurate CFD analyses of compressor performance with tip curl blade damage in a single stage axial flow compressor and VSVs mal-schedule in a 3.5 stage axial flow compressor. Computations were per- formed near stall boundary to predict rotating stall characteristics. The primary objectives are to characterise the overall compressor performance and analyse the detailed flow behaviour. Computations for the nominal blade configurations were also performed for comparison purposes for both compressors. All unsteady simulations were performed at part speeds with a variable nozzle downstream representing an experimental throttle. For the blade damage study, two different degrees of damage for one blade and multiple damaged blades were investigated and compared with the results from the undamaged case. For the VSVs mal-schedule study, the first two stators were assumed to be variable and were used to create mal-schedule vane settings for the investigation. The effects of blade damage and VSVs mal-schedule on the aerodynamics performance and rotating stall characteristics for both compressor assemblies were investigated respectively and discussed in detail

Smart Sensor System for Structural Condition Monitoring of Wind Turbines: 30 May 2002--30 April 2006

This report describes the efforts of the University of Cincinnati, North Carolina A&T State University, and NREL to develop a structural neural system for structural health monitoring of wind turbine blades

High-Fidelity Computational Fluid Dynamics Analysis of In-Serviced Shrouded High-Pressure Turbine Rotor Blades

In-service deterioration can lead to undesired shape variations on high-pressure turbine rotor blades. This can have a significant impact on efficiency, power generation, and component life. Loss of power production from the high-pressure turbine rotor causes engine over-Throttling to compensate for the lower performance. This will in turn worsen the operating conditions and ultimately reduce the life of the component. The aim of this study is to provide a high-fidelity flow simulation of in-serviced shrouded high-pressure turbine (HPT) blades of a modern Jet Engine. Shape variation effects on the aerodynamic performance of several shrouded HPT blades with a different number of in-service hours have been investigated. In order to establish a digital model of the shape variation, a novel reverse-engineering procedure is carried out to come up with a parametrized definition of each blade's variations from nominal including any observable damage. The investigation is conducted by means of an in-house, full 3D steady-state Reynolds-Averaged Navier-Stokes (RANS) simulation of the flow around a series of damaged rotor blade geometries, which are obtained through high-resolution optical blue-light "Gesellschaft für Optische Messtechnik" (GOM) scans. The analysis shows that the aerodynamic performance of the HPT rotor blades under investigation is primarily sensitive to shroud damage, which is found to account for efficiency losses often greater than 3%, and for more than 80% of the total performance loss. A secondary role on efficiency is found to be played by the blade shape deviation. A highly linear correlation is found between HPT stage efficiency and a combination of shroud damage parameters