There has been recent incentive for understanding the possible deleterious effects that manufacturing deviations can have on compressor blade performance. This is of particular importance in today's age, as compressor designs are pushing operating limits by employing fewer stages with higher loadings and are designed to operate at ever higher altitudes. Deviations in these advanced, as well as legacy designs, could negatively affect the performance and operation of a core compressor; thus, a numerical investigation to quantify manufacturing deviations and their effects is undertaken. Data from three radial sections of every compressor blade in a single row of a production compressor is used as the basis for this investigation. Deviations from the compressor blade design intent to the as-manufactured blades are quantified with a statistical method known as principle component analysis (PCA). MISES, an Euler solver coupled with integral boundary-layer calculations, is used to analyze the effects that the aforementioned deviations have on compressor blade performance when the inlet flow conditions produce a Mach number of approximately 0.7 and a Reynolds number of approximately 6.5e5. It was found that the majority of manufacturing deviations were within a range of plus or minus 4 percent of the design intent, and deviations at the leading edge had a critical effect on performance. Of particular interest is the fact that deviations at the leading edge not only degraded performance but significantly changed the boundary-layer behavior from that of the design case. / Master of Science

A stator cascade was developed to simulate the flow conditions within a close-stage-spacing transonic axial compressor. Experiments were conducted in a linear transonic blowdown cascade wind tunnel with an inlet Mach number of 0.65. The bow shock from the downstream rotor was simulated by a single moving normal shock generated with a shock tube. First, steady pressure data were gathered to ensure that the stator cascade operated properly without the presence of the shock. Next, the effects of the passing shock on the stator flow field were investigated using shadowgraph photography and Digital Particle Image Velocimetry (DPIV). Measurements were taken for three different shock strengths. In every case studied, a vortex formed near the stator trailing edge as the shock impacted the blade. The size of this vortex was shown to be directly related to the shock strength, and the vortex remained present in the trailing edge flow field throughout the cycle duration. Analysis of the DPIV data showed that the vortex acts as a flow blockage, with the extent of this blockage ranging from 2.9% of the passage for the weakest shock, to 14.3% of the passage for the strongest shock. The vortex was also shown to cause flow deviation up to 75° for the case with the strongest shock. Further analysis estimated that the total pressure losses due to shock-induced vorticity ranged from 46% to 113% of the steady wake losses. Finally, the total pressure loss purely due to the upstream-propagating normal shock was estimated to be roughly 0.22%. / Master of Science

A high-turning compressor stator with a unique flow control design was developed and tested. Both boundary layer suction and trailing edge blowing developed from a single supplied motive pressure source are employed on the stator. Massflow removed through boundary layer suction is added to the motive massflow, and the resulting combined flow is used for trailing edge blowing to reduce the total pressure deficit generated by the stator wake. The effectiveness of the flow control design was investigated experimentally by measuring the reduction in the total pressure loss coefficient. The experiment was conducted in a linear transonic blowdown cascade wind tunnel. The inlet Mach number for all tests was 0.79, with a Reynolds number based on stator chordlength of 2,000,000. A range of inlet cascade angles was tested to identify the useful range of the flow control design. The effect of different supply massflows represented as a percentage of the passage throughflow was also documented. Significant reductions in the total pressure loss coefficient were accomplished with flow control at low cascade angles. A maximum reduction of 65% in the baseline (no flow control) loss coefficient was achieved by using a motive massflow of 1.6% of the passage throughflow, at cascade angle of 0°. The corresponding suction and blowing massflow ratio was approximately 1:3.6. Cascade angle results near 0° showed significant reductions in the loss coefficient, while increases in the cascade angle diminished the effects of flow control. Considerable suction side separation and the presence of a leading edge shock are noticeable as the cascade angle is increased, and contribute to the losses across the stator surface. Also identified was the estimated increase in wake turning due to flow control of up to 4.5°. / Master of Science

This thesis presents the results of a study performed in the Virginia Tech low speed linear cascade wind tunnel operating at a Reynolds number of 382,000 designed to model an axial compressor rotor. To simulate the flow created by the junction of a set of inlet guide vanes and the compressor casing, vortex generators were glued to a moving end wall. In this investigation, the tip clearance was varied from 0.83% to 12.9% chord. Measurements of the midspan and the tip blade loading were made using static pressure taps. The tip loading shows that the minimum suction surface pressure coefficient increases in magnitude linearly up to a tip clearance of 7.9% chord. Unsteady pressure was measured on the pressure and suction surfaces at the tip of two cascade blades using an array of 23 microphones mounted subsurface. These measurements reveal that the unsteady pressure at the blade tip is a linear function of tip clearance height. The instantaneous pressure shows that the surface pressure at the blade tip has the same character regardless of whether or not the blade is disturbed by the inflow vortices. This suggests that the vortex generators simply stimulate and organize the existing response of the blade. Single sensor hot-wire measurements were made within the tip clearance on the suction side of the blade 1mm from the tip gap exit. These measurements show that the mass flux through the tip clearance is closely related to the pressure difference across the tip gap. / Master of Science

The centrifugal compressor is a central part of the turbocharger on a truck. It compresses the air which allows for a larger intake of gas into the cylinders. This raises the amount of oxygen available for combustion which increases the efficiency of the engine. However, the operating range of a compressor is limited. If the mass flow through the compressor gets too low, it can start to surge. The surging phenomenon for centrifugal compressors is characterized by axial oscillations in the mass flow which can cause a backflow of air through the compressor. This can result in structural damage on the compressor. It is therefore important to understand under which conditions surge occurs. When it comes to the development and design of compressors, Computational Fluid Dynamics (CFD) is a valuable tool. It enables us to simulate the performance of compressors without the costly process of building a prototype and testing it. Even simpler steady-state simulations can give valuable insight on the performance. However, since surge is a dynamic phenomenon, it is not readily accessible through one of these steady-state simulations, where the sought solution is a flow field constant in time. The aim of this thesis is to capture the surge phenomenon in a steady-state simulation and develop a method for predicting when the compressor surges. This is done by looking at oscillations in the solver for the total pressure at a cross-sectional plane upstream of the compressor wheel. We find that the amplitude of these oscillations increases when the compressor is approaching surge. From this we define a surge criterion and fit the model parameters to an experimentally determined surge line. We then predict the location of the surge line for the same compressor, now equipped with a ported shroud (a geometry feature with the intention of mitigating surge). With this ported shroud, we expect the compressor’s operating range to be widened, which is also what the model predicts. However, this prediction needs to be compared with real data in order to see if the method accurately captures the location of the surge line.

V posledních několika desetiletích se objevuje snaha o snížení firemních nákladů, stejně tak jako nákladů, které je nucen vynaložit zákazník, čímž se společnosti snaží získat výhodu vůči svým konkurentům na trhu. Spolu s tímto trendem jde i neustálá snaha snížit dopady na životní prostředí. Vývoj stávajících produktů se proto zdá být klíčovým prvkem. Tento dokument se zabývá vývojem pístového kompresoru na CO2 chladivo, který vyrábí společnost Emerson Climate Technologies. Cíl práce je zvýšit COP kompresoru při zachování stávající životnosti kompresoru. Diplomová práce je rozčleněna do několika kapitol, které se zabývají analýzou originálního designu kompresoru, návrhem a vyhodnocením designů nových. Nezbytné teoretické základy mohou být také shlédnuty v počátečních kapitolách. V poslední části dokumentu jsou sdělena možná další vylepšení a případné jiné konstrukce. Vývoj byl zaměřen na sestavu ventilové desky. Na základě několika předpokladů a výsledků analýzy původního designu kompresoru byly navrženy nové konstrukce, které byly dále testovány statickou strukturální analýzou. Pomoci modální analýzy byly také vypočteny vlastní frekvence a vlastní tvary sacího jazýčku. Mimo modální a statické strukturální analýzy byla provedena také CFD analýza. V posledním kroku byly testovány navržené prototypy a jejich výsledky byly porovnány s původním kompresorem. K správnému návrhu bylo zapotřebí programové podpory a to především v podobě MATLABu, ANSYSu WB a Microsoft Excelu. V práci jsou velmi často prezentovány obzvláště výsledky získané v programu ANSYS WB.

Air bearing radial turbo (also called centrifugal) compressors prevail in most mobile fuel cell air supply applications due to the small size and weight, the high efficiency and the oil- and maintenance free operation. An important aspect in mobile fuel cell applications is the vibration resistance of all system components, including the compressor, with vibration requirements up to 20 g in automotive applications. This paper gives the background of the air bearing vibration characteristics, depicting the dependencies of vibration resistance on inlet conditions and operating points. The critical operating conditions concerning vibration resistance are identified, and it is outlined how vibration requirements can be included in the design process of an air bearing turbo compressor. A visualization of vibration resistance in the commonly used compressor map is presented, allowing the fuel cell system integrator to take qualified decisions for the mechanical integration of the compressor concerning vibrations.

No description available.

Thesis (MScEng)--Stellenbosch University, 2006. / ENGLISH ABSTRACT: The Stellenbosch University Compressor Code (SUCC) has been developed for the purpose of predicting the performance of axial flow compressors by means of axisymmetric inviscid throughflow methods with boundary layer blockage and empirical blade row loss models. This thesis describes the process of the implementation and verification of a number of stall prediction criteria in the SUCC. In addition, it was considered desirable to determine how certain factors influence the accuracy of the stall prediction criteria, namely the nature of the computational grid, the choice of throughflow method used, and the use of a boundary layer blockage model and a radial mixing model. The stall prediction criteria implemented were the di®usion factor limit criterion, de Haller's criterion, Aungier's blade row criterion, Aungier's boundary layer separation criterion, Dunham's, Aungier's and the static-to-static stability criteria. The compressors used as test cases were the Rofanco 3-stage low speed compressor, the NACA 10-stage subsonic compressor, and the NACA 5-stage and 8-stage transonic compressors. Accurate boundary layer blockage modelling was found to be of great importance in the prediction of the onset of stall, and that the matrix throughflow Method provided slightly better accuracy than the streamline curvature method as implemented in the SUCC by the author. The ideal computational grid was found to have many streamlines and a small number of quasi-orthogonals which do not occur inside blade rows. Radial mixing modelling improved the stability of both the matrix throughflow and streamline curvature methods without significantly affecting the accuracy of the stall prediction criteria. De Haller's criterion was over-conservative in estimating the stall line for transonic conditions, but more useful in subsonic conditions. Aungier's blade row criterion provided accurate results on all but the Rofanco compressor. The diffusion factor criterion provided over- optimistic predictions on all machines, but was less inaccurate than de Haller's criterion on the NACA 5-stage transsonic machine near design conditions. The stability methods performed uniformly and equally badly, supporting the claims of other researchers that they are of limited usefulness with throughflow simulations. Aungier's boundary layer separation method failed to predict stall entirely, although this could reflect a shortcoming of the boundary layer blockage model. / AFRIKAANSE OPSOMMING: Die Stellenbosch University Compressor Code (SUCC) is ontwikkel om die prestasie van aksiaalvloei kompressors te voorspel met behulp van aksisimmetriese nie-viskeuse deurvloeimetodes met grenslaagblokkasie en empiriese modelle vir die verliese binne lemrye. Hierdie tesis beskryf die proses waarmee sekere staakvoorspellingsmetodes in die SUCC geïmplementeer en geverifieer is. Dit was ook nodig om die effek van sekere faktore, naamlik die vorm van die berekeningsrooster, die keuse van deurvloeimetode en die gebruik van `n grenslaagblokkasiemodel en radiale vloeivermengingsmodel op die akuraatheid van die staakvoorspellingsmetodes te bepaal. Die staakvoorspellingsmetodes wat geïmplementeer is, is die diffusie faktor beperking metode, de Haller se metode, Aungier se lemrymetode, Aungier se grenslaagmetode en die Dunham, Aungier en die statiese-tot-statiese stabiliteitsmetodes. Die kompressors wat gebruik is om die metodes te toets is die Rofanco 3-stadium lae-spoed kompressor, die NACA 10-stadium subsoniese kompressor en die NACA 5- en 8-stadium transsoniese kompressors. Daar is vasgestel dat akkurate grenslaagblokkasie modelle van groot belang was om `n akkurate aanduiding van die begin van staking te voorspel, en dat, vir die SUCC, die Matriks Deurvloei Metode oor die algemeen 'n bietjie meer akkuraat as die Stroomlyn Kromming Metode is. Daar is ook vasgestel dat die beste berekeningsrooster een is wat baie stroomlyne, en die kleinste moontlike getal quasi-ortogonale het, wat nie binne lemrye geplaas mag word nie. Die numeriese stabiliteit van beide die Matriks Deurvloei en die Stroomlyn Kromming Metode verbeter deur gebruik te maak van radiale vloeivermengingsmodelle, sonder om die akkuraatheid van voorspellings te benadeel. De Haller se metode was oorkonserwatief waar dit gebruik is om die staak-lyn vir transsoniese vloei toestande, maar meer nuttig in die subsoniese vloei gebied. Aungier se lemrymetode het akkurate resultate gelewer vir alle kompressors getoets, behalwe die Rofanco. Die diffusie faktor metode was oor die algemeen minder akuraat as Aungier se metode, maar meer akkuraat as de Haller se metode vir transsoniese toestande. Die stabiliteitsmetodes het almal ewe swak gevaar. Dit stem ooreen met die bevindings van vorige navorsing, wat bewys het dat hierdie metodes nie toepaslik is vir simulasies wat deurvloeimetodes gebruik nie. Aungier se grenslaagmetode het ook baie swak gevaar. Waarskynlik is dit as gevolg van tekortkomings in die grenslaagblokkasiemodel.

Approved for public release, distribution is unlimited / The flow around second-generation controlled-diffusion blades in cascade at stall was examined experimentally through the use of a two-component laser-Doppler velocimeter. Blade surface pressure measurements were also preformed at mid span on the blades at various Reynolds numbers. Flow visualization techniques were used to observe and record the flow on the surface of the blade. A correlation between the experimental results and computational fluid dynamic predictions was attempted in order to determine the exact nature of the flow as the blades approached stall, to further assist in the development of advanced blade design. The blade surface pressure measurements showed that the mid-span section of the blade was at a lower loading than previously measured at a smaller inlet flow angle. This indicated that the blade section was at stall. The flow visualization highlighted the extent of the three-dimensional flow over the blades. The LDV measurements documented the mid-span boundary layer and wake profiles. / Ensign, United States Navy