Zugl.: Cottbus, Techn. Univ., Habil.-Schr., 2009

<p>Examensarbetet undersöker huruvida en blisk kan förses med ett heltäckande tak över bladtopparna. En blisk är en skiva och blad som är tillverkat i ett stycke. Som referens under arbetet används en befintlig blisk från provkompressorn Hulda. Målsättningen med att förse blisken med ett tak är att taket ska stabilisera konstruktionen genom att förstyva bladen och höja frekvenserna för de lägsta egenfrekvenserna samt eliminera läckflödet över bladen. Under arbetet undersöks material, tillverkningsmetoder, tillverkningskostnader samt de risker som finns vid användning av den takförsedda blisken. Utvärderingen baseras på tre koncept som genererats och utvalts under ett tidigare projektarbete. Koncepten är: Koncept 1, blisk och tak tillverkat i ett stycke titan. Koncept 2, blisk med separat titanring som förspänns. Koncept 3, blisk med tak tillverkat i ett stycke titan med förspänd kompositring som förstärkning. Materialet i blisken är sedan tidigare bestämt att vara en titanlegering. Som material till kompositen väljs kolfiberarmerad epoxi. För titanblisken väljs tillverkningsmetoderna svarvning och fräsning. Kompositringen tillverkas genom fiberlindning. Inledande beräkningar antyder att en förstärkning med lättviktsmaterial som i koncept 3 är mest gynnsamt. Detta styrks av resultatet från de statiska analyserna av koncept 1 och 2, där båda koncepten fallerar. I koncept 1 kan eventuellt de spänningskoncentrationer som uppstår avhjälpas med en omkonstruktion av bladens infästningar mot taket. I den statiska analysen av koncept 3 uppstår problem med att modellera kompositmaterialets egenskaper. FE-modellen är inte verklighetstrogen. Därför krävs en förbättring av denna för att verifiera konceptet. En jämförande modalanalys genomförs mellan referensblisken och koncept 1. Resultatet bekräftar antagandet att införandet av ett tak på en blisk höjer egenfrekvenserna.</p>

Examensarbetet undersöker huruvida en blisk kan förses med ett heltäckande tak över bladtopparna. En blisk är en skiva och blad som är tillverkat i ett stycke. Som referens under arbetet används en befintlig blisk från provkompressorn Hulda. Målsättningen med att förse blisken med ett tak är att taket ska stabilisera konstruktionen genom att förstyva bladen och höja frekvenserna för de lägsta egenfrekvenserna samt eliminera läckflödet över bladen. Under arbetet undersöks material, tillverkningsmetoder, tillverkningskostnader samt de risker som finns vid användning av den takförsedda blisken. Utvärderingen baseras på tre koncept som genererats och utvalts under ett tidigare projektarbete. Koncepten är: Koncept 1, blisk och tak tillverkat i ett stycke titan. Koncept 2, blisk med separat titanring som förspänns. Koncept 3, blisk med tak tillverkat i ett stycke titan med förspänd kompositring som förstärkning. Materialet i blisken är sedan tidigare bestämt att vara en titanlegering. Som material till kompositen väljs kolfiberarmerad epoxi. För titanblisken väljs tillverkningsmetoderna svarvning och fräsning. Kompositringen tillverkas genom fiberlindning. Inledande beräkningar antyder att en förstärkning med lättviktsmaterial som i koncept 3 är mest gynnsamt. Detta styrks av resultatet från de statiska analyserna av koncept 1 och 2, där båda koncepten fallerar. I koncept 1 kan eventuellt de spänningskoncentrationer som uppstår avhjälpas med en omkonstruktion av bladens infästningar mot taket. I den statiska analysen av koncept 3 uppstår problem med att modellera kompositmaterialets egenskaper. FE-modellen är inte verklighetstrogen. Därför krävs en förbättring av denna för att verifiera konceptet. En jämförande modalanalys genomförs mellan referensblisken och koncept 1. Resultatet bekräftar antagandet att införandet av ett tak på en blisk höjer egenfrekvenserna.

Techn. Universiẗat, Diss.--Cottbus, 2007.

No description available.

Zugl.: Cottbus, Techn. Univ., Diss., 2007

Zugl.: Cottbus, Techn. Univ., Diss., 2009

The present thesis discusses the forced response of a rotor’s bladed-disk when excited by the periodic force produced by a wake generator, or Inlet Guide Vane (IGV),with 8 equally-spaced blades. These components are part of an axial transonic compressor rig, moreover the Transonic Compressor Darmstadt 1 (TCD1), located at the Technical University of Darmstadt. The investigation is within the ARIAS (Advanced Research Into Aeromechanical Solutions) project, that aims to improve the predictive capabilities of the design methods used in the aircraft propulsion engine’s industry to study aerodynamically induced blade vibrations. The methodology comprised a set of numerical analyses that were conducted using the software Ansys, addressing both the structural and the aerodynamics sides of the aeroelastic problem, in a co-dependent way. At first, steady-state CFD simulations were conducted to study the mesh convergence and to analyse the operation of the compressor at N80 speed, obtaining its compressor map and its peak efficiency operation point. From these, the aerodynamic static force being applied on theblade was obtained, allowing to determine the pre-stresses of the bladed-disk, orblisk. With a modal analysis, the natural modes of the rotor blisk at N80 speed were obtained and the resonance crossing M2 EO8 was identified, plotting the Campbell and ZZENF diagrams. From the modal displacements of the critical mode, a blade flutter analysis was conducted in order to compute the aerodynamic damping ratio of the rotor blisk. With a transient CFD analysis, the periodic forcing being applied onthe rotor blisk that arises from the IGV wake pattern was determined and exported as Fourier coefficients. Finally, a harmonic simulation was carried out to analyse the forced response of the blisk, introducing both the aerodynamic damping value and the unsteady forcing mapped onto the blade. As a result, the frequency response of both the blade maximum alternating deflections and equivalent stresses was obtained, as well as the respective spatial contour plots at the obtained resonance frequency. Some of the results of the conducted analyses were investigated in order to analyse the aerodynamic phenomena occurring, where it was possible to identify vortex shedding, leading shock, tip-clearance and horse-shoe vortex.  Afterwards, the numerical results were compared to the experimental data optained from rig tests conducted at the TCD1 by partners of the ARIAS projects. The numerical model management to predict well the compressor map, thus the steady-state of the flow, as well as the resonance frequency. The aerodynamic damping value was over- predicted when compared to the entire data set. When it came to the harmonic analysis results, the numerical model under-predicted by one order of magnitude the maximum deflection, and the equivalent stress is, as well, far below the experimental results. These results led to conclude that the model is under-predicting the aerodynamix unsteady forcing that results from the wake pattern generated by the IGV and excites the rotor blades.

<p>  </p> <p>High cycle fatigue, regarding turbine engines, is one of the main causes of rotating component failure. Specifically, the blades of the wheels in the fan, compressor, and turbine sub-assemblies. Traditionally strain gauges are employed as a means of measuring blade vibration during component or full engine development testing. For rotating machinery, strain gauges require the use of a slip ring or a telemetry package. This becomes increasingly complicated as the number of strain gauges increase, thus the need for a more non-intrusive measurement capability for discernment of blade stress responses. Non-Intrusive Stress Measurement Systems (NSMS) allow engineers to detect high cycle fatigue (HCF) issues prior to component failure. It is important for the turbine engine industry to monitor for high cycle fatigue issues to maintain a fleet readiness. When unexpected HCF causes component or system failure the potential consequences are grounded fleets, cancelled flights, monetary loss, and loss of life. Once these issues occur an investigation is initiated and could take a few weeks to several months or more to resolve. This time impacts the engine companies as well as the people dependent upon functional engines. HCF monitoring processes and techniques are crucial to preserving fleet maintenance. One of the ways to prevent premature HCF failure is by detecting cracks in the blades or the wheels of the rotor.</p> <p>It <a href="https://hammer.purdue.edu/account/home#_msocom_1" target="_blank">[NLK1]</a> is the subject of this thesis to determine whether the static deflection of the blade as it rotates will begin to grow independent of rotational changes experienced by the rotor for an internal crack in the wheel as opposed to the blade of a rotor. Should a crack in the wheel occur, the stiffness should decrease, which would manifest when testing the rotor’s natural frequencies as a decrease in the natural frequency compared to an un-cracked rotor. The experiment was conducted using analysis tools for predicting blade natural frequencies of the pre-cracked rotor as well as physical experiments to determine the natural frequencies of the post-cracked rotor. The spin facility set up, data acquisition, data reduction, experiment details and results are provided. Both strain gauges and NSMS techniques were used to measure the natural frequencies of the rotor, and detection of damage while mounted in the spin facility. This research effort concluded it is possible to detect a crack in the wheel of a rotor using the NSMS blade stack capability. It is necessary to have a baseline vibration survey to understand the pre-damaged static deflection of each blade. This research also concluded that a comparison of the pre-cracked and post-cracked natural frequencies manifested roughly a 5% decrease. With a crack in the wheel, the expected stiffness of the wheel would decrease, thus, causing a decrease in the natural frequency of the component. This is evident in the comparison of the pre-cracked ping test data and the post-crack bench test data. In summary, it is possible to detect an internal crack of a rotor and the natural frequencies of the blades can change with an internally cracked wheel. </p>

Because blades in jet engine compressors are subject to dynamic loads based on the engine's speed, it is essential that the blades are properly "tuned" to avoid resonance at those frequencies to ensure safe operation of the engine. The tuning process can be time consuming for designers because there are many parameters controlling the geometry of the blade and, therefore, its resonance frequencies. Humans cannot easily optimize design spaces consisting of multiple variables, but optimization algorithms can effectively optimize a design space with any number of design variables. Automated blade tuning can reduce design time while increasing the fidelity and robustness of the design. Using surrogate modeling techniques and gradient-free optimization algorithms, this thesis presents a method for automating the tuning process of an airfoil. Surrogate models are generated to relate airfoil geometry to the modal frequencies of the airfoil. These surrogates enable rapid exploration of the entire design space. The optimization algorithm uses a novel objective function that accounts for the contribution of every mode's value at a specific operating speed on a Campbell diagram. When the optimization converges on a solution, the new blade parameters are output to the designer for review. This optimization guarantees a feasible solution for tuning of a blade. With 21 geometric parameters controlling the shape of the blade, the geometry for an optimally tuned blade can be determined within 20 minutes.