The present study focuses on local heat transfer characteristics on the tip and near-tip regions of a turbine blade with a flat tip, tested under transonic conditions in a stationary, 2-D linear cascade consisting of seven blades, the three center blades having a variable tip clearance gap. The effects of tip clearance and exit Mach number on heat transfer distribution were investigated on the tip surface using a transient infrared thermography technique. In addition, thin film gages were used to study similar effects on the near-tip regions at 94% based on engine blade span of the pressure and suction sides. The experiments were conducted at the Virginia Tech transonic blow-down wind tunnel facility with a seven-blade linear cascade. Surface oil flow visualizations on the blade tip region were carried-out to shed some light on the leakage flow structure. Experiments were performed at three exit Mach numbers of 0.7, 0.85, and 1.05 for two different tip clearances of 0.9% and 1.8% based on engine blade span. The exit Mach numbers tested correspond to exit Reynolds numbers of 7.6 x 105, 9.0 x 105, and 1.1 x 106 based on blade true chord. The tests were performed with a freestream turbulence intensity of 12%. Results at 0.85 exit Mach showed that an increase in the tip gap clearance translates into a 12% increase in the heat transfer coefficients on the blade tip surface. Similarly, at 0.9% tip clearance, an increase in exit Mach number from 0.85 to 1.05 also led to a 24% increase in heat transfer on the tip. High heat transfer was obtained at the leading edge area of the blade tip, and an increase in the tip clearance gap and exit Mach number augmented this leading edge heat transfer. At 94% of engine blade span on the suction side near the tip, a peak in heat transfer was observed in all test cases at an s/C of 0.66 due to the onset of a downstream leakage vortex. At the design condition, this peak represents an increase of a factor of 2.5 from the immediate preceding s/C location. An increase in both the tip gap and exit Mach number resulted in an increase, followed by a decrease in the near-tip suction side heat transfer. On the near-tip pressure side, a slight increase in heat transfer was observed with increased tip gap and exit Mach number. In general, the suction side heat transfer is greater than the pressure side heat transfer as a result of the suction side leakage vortices. / Master of Science

Experimental heat transfer data has been collected at engine representative conditions in this work to use in future work to improve computational models. Tests were carried out in a transonic cascade wind tunnel with the data collected using thin film gages. All of the necessary development to use the thin film gages has been completed, including construction of electronics and analysis tools to reduce the data. Gage installation and calibration techniques have been successfully implemented for the current research facility and those procedures have been documented. Heat transfer tests were carried out at engine design speed as well as conditions both above and below design speed. The resulting effect of different Reynolds numbers on heat transfer has been studied and the data collected has been compared with computer predictions, analytical correlations, and data from other published literature to validate the results obtained. Finally, it has been shown that a transient analysis technique can be used to process the data for gages that do not exhibit steady results during the quasi-steady test run. This transient technique resulted in data that agrees well with published literature and analytical correlations. / Master of Science

There are many limitations to the current methods used to measure vibration on rotating structures. These limitations include physical flow blockages, relating the measurement spot to the structure rotation, data processing issues, and having to physically alter the engine. This work further describes aspects of a self-tracking laser vibrometry system that can be used to measure the vibrations of rotating structures. This method, if setup correctly, has the capability to overcome many of the limitations listed above. A study of all misalignment effects is presented in this thesis. The study consists of a parametric sensitivity analysis of misalignment variables, a parametric Monte Carlo analysis of misalignment variables, and a full interaction Monte Carlo analysis of misalignment variables. In addition, the results of the misalignment variable analyses were used to develop a self-tracker test rig for obtaining fan vibration from a Pratt and Whitney JT15D turbofan engine. A prototype this test rig was designed, built, and tested on the turbofan. It was found that in order to achieve acceptable amounts of position and velocity error using the self-tracker LDV system, very strict alignment of the optical equipment is necessary. Additionally, the alignment criteria can likely be achieved with the use of digitally controlled high precision linear motion equipment. / Master of Science

The interaction of an unsteady wake with a solid body can induce sizable loading of the structure, which has many detrimental side effects in both the structural and acoustic senses. These interactions are ubiquitous in nature and engineering. A flow control technique is sought to mitigate this interaction, thereby decreasing the level of structural vibration. This thesis investigates the effectiveness of steady leading-edge blowing (LEB) flow control for modifying the vortex induced vibrations on an airfoil in the wake of a circular cylinder. The airfoil was allowed to oscillate perpendicular to the fluid flow direction in response to the impinging Von-Karman vortex street. The flow field and airfoil vibrations were simultaneously captured using Digital Particle Image Velocimetry (DPIV) and accelerometer measurements in a time-resolved sense. The results indicate that LEB can significantly reduce the degree of unsteady loading due to the blade vortex interaction (BVI). In some cases, the LEB jet appears to break the coherency of a vortex incident on the airfoil, and in other cases the jet increase the mean stand-off distance of the vortex as it convects over the airfoil surface. It was also found that, for large circular cylinders, if the airfoil is within the mean closure point of the circular cylinder wake, the LEB can increase the level of BVI. The Proper Orthogonal Decomposition (POD) was also used to analyze the DPIV data. POD is mathematically superior for reducing a data rich field into fundamental modes; a suitable basis function for the reduction is chosen mathematically and it is not left to the researcher to pick the basis function. A comparison of the energy in these modes is useful in ascertaining the dynamics of the BVI. For one of the two cases examined with POD, it was found for no LEB the fundamental (i.e. most energetic) mode is given by the vortex shedding of the circular cylinder upstream. The addition of LEB reduces the energy contained in this fundamental mode. Thus the LEB jet has the effect of reducing the flow field coherency; the structure of the large vortices is broken up into smaller vortices. For the other case, the LEB jet has the opposite effect: the jet has the ability to organize the circular cylinder wake into coherent structures. This acts to increase the coherency of the circular cylinder wake and increases the level of BVI. / Master of Science

This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 x 105, 8 x 105, and 11 x 105, based upon true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively. / Master of Science

The performance of aircraft engines can be significantly affected by the variety of foreign particles that are mixed into the air while operating under miscellaneous conditions. In particular, aircraft engines that operate in sandy or dusty conditions may fail within minutes of exposure to particle-laden flow due to foreign particle deposition on hot section components or erosion occurring on the compressor and turbine blades. For these reasons, the effect of sand ingestion on erosion, which may occur in the turbine and compressor blades, was studied in this master's thesis. In this master's thesis, the effect of sand ingestion on erosion on the M250 turboshaft engine's compressor blades will be investigated with the aid of numerical methods. In this study, we used the OpenFOAM software to solve the multiphase flow problem from the standpoint of finite control methods and the Eulerian-Lagrangian framework. The initial sand distribution conditions were taken from the Ph.D. thesis written by Olshefski, K. T. (2023) [1]. The compressor blade was modeled as 2D, which has a NACA 6510 profile shape, with a chord length of 63 mm. The results show that the leading edge and the suction side of the compressor, i.e. the upper half of the compressor, eroded more compared to the trailing edge, and the pressure side. Results also show that as the sand particle distribution becomes non-uniform the most eroded region shifts toward the trailing edge. In addition, for varying angles of attack, the region where the erosion occurs alters periodically. We observed that as the angle of attack increases, the eroded region shifts toward the trailing edge, but when the angle of attack is kept increasing the eroded region shifts back to the leading edge again. In conclusion, the non-uniformity of sand particle loading has a strong effect on the determination of the eroded regions. Furthermore, the variation of the angle of attack has a huge role in both the determination of eroded regions and the amount of eroded material. / Master of Science / In this master's thesis, the effect of sand ingestion on compressor blade erosion was investigated with the help of numerical methods. The compressor is one of the vital parts of air-breathing engines such as turboshaft, turbofan, turbojet, and turboprop engines. Therefore, the erosion on the compressor blades may cause pressure surges, which could cause severe problems in the operation of aircraft or airplanes operating under dusty conditions. Historically, it is reported that a TransAmerican aircraft propelled by Alison T-56 engines lost two of its four engines after 3 to 4 minutes of exposure to volcanic ash while flying over Mt. St. Helens in 1980. Another example of the effects of sand ingestion is an MV-22 Osprey crash that happened during a training exercise in Hawaii, claiming the lives of two US Marines and injuring twenty other personnel in 2015. It was attributed that the cause of the fatal accident was the ingestion of dust that caused engine failure. Therefore, our intention in studying this field is to have an understanding of the regions of compressor blades that are vulnerable to erosion. In this master's thesis, numerical methods based on the finite volume method were used to obtain numerical solutions to estimate erosion on the compressor blade by utilizing OpenFOAM. We would like to recommend a nice OpenFOAM tutorial for those who are interested in applying numerical methods using OpenFOAM, taught by Jozsef Nagy accessible on YouTube, https://www.youtube.com/@OpenFOAMJozsefNagy. Also, for creating geometry and mesh generation of an airfoil for the use of OpenFOAM, we would like to recommend the tutorial presented by Ali Ikhsanul, accessible on YouTube via this link https://www.youtube.com/@aliikhsanul7982. These tutorial videos could help those who are interested in Openfoam but do not have much experience with Openfoam. The work in this master's thesis indicates that the leading edge of the compressor blade is more prone to be eroded than the trailing edge. In addition, it is shown that the eroded region distribution is highly dependent on the angle of attack of sand particles.

With the ever-growing demand for power generation to support the world economy and electric transportation needs, efficient gas turbine power cycles need to be investigated to match the anticipated high demands of the future. Decarbonization efforts around the world to achieve Net Carbon Zero by 2050 have also brought many new challenges for the development of these systems due to the unique constraints imposed by less carbon-intensive fuels. In this effort to increase the efficiency and performance of such gas turbine power cycles, pressure gain combustion (PGC) has gained significant interest. The potential for an increase in the thermodynamic efficiency over the constant-pressure Brayton Cycle has made detonation combustors, a type of PGC, an attractive alternative to traditional deflagration-type combustors. Since Rotating Detonation Combustors (RDC) can provide a quasi-steady mode of operation when compared to Pulse Detonation Combustors (PDC), research has been triggered to integrate RDC with power-generating gas turbines. However, the presence of subsonic and supersonic flow fields which are generated due to the shock waves that stem from the detonation wave front and the highly non-uniform temperature and velocity profiles may cause a depreciation in the turbine performance. The current study seeks to investigate the challenges of integrating the RDC with nozzle guide vanes (NGV) of an industrial, can-annular gas turbine and attempts to understand the major contributors that impact efficiency and identify the key areas of optimization that need to be considered for maximizing performance. In order to compare the results with an F class gas turbine engine condition, a geometric model of RDC developed by the Air Force Research Laboratory (AFRL) was scaled using a linear mass flow to area relationship, aiming to achieve a higher flow rate. The RDC was integrated with the NGVs through a non-optimized straight duct-type geometry with a diffuser cone. 3-Dimensional Numerical analyses were performed to investigate sources of total pressure loss and to understand the unsteady effects of RDC which contribute towards the deterioration of performance. The entropy generation at different regions of interest was calculated to identify the major irreversibility's in the system. Finally, total pressure and temperature distribution along the radial direction at the exit of the transitional duct is presented to understand the various constraints imposed by the RDC when integrating with an Industrial gas turbine engine NGV. / Master of Science / In recent years, power generation has become more challenging and complex due to the ever-growing demand for running a developed or developing economy. With electric transportation becoming more accessible and affordable for the general public, an increase in the demand for power generation is expected in the future. Coupled with this is the ambition of every nation to move toward NetCarbonZero by 2050, to reduce emissions as well as move towards a more sustainable future for the next generations. One of the primary sources of power generation in modern-day industry comes from industrial gas turbine engines, due to their reliability in providing electricity to ensure grid stability as well as maintaining near-zero emission levels. But after decades of research and advancements, the constant pressure deflagration combustion process occurring in the combustors of these gas turbine engines which follow a Brayton cycle has reached to the stage where only incremental gains can now be achieved. However, detonation combustion, which is thermodynamically more efficient because of the constant volume combustion process, modifying the Brayton cycle to a Humphery cycle. Coupled with the possibility of a pressure gain type of combustion system, investigation has been triggered in recent years by many researchers and industry for matching the increase in power generation demands with detonation combustion. In this study, a Rotating Detonations Combustor (RDC), a type of continuous detonation wave propagating system is numerically investigated using a Simcenter Star CCM+ commercial CFD solver. A scaling approach, which has been pervious implemented for can-type combustor systems was modified and used to scale an RDC geometry to match the industrial gas turbine operating condition. The scaled RDC geometry was modeled with a transitional duct and a pair of Nozzle Guide Vanes (NGV) and 3D reacting numerical analysis was conducted to understand the pressure loss mechanism at various regions. These results should help future designers and researchers in conducting several design studies as well as implementing optimization methods for increasing the performance of this novel combustor technology.

Modelling studies have shown that 1.5 and 3.0 MW wind turbines with blade sweep have an increased annual energy production (AEP) of approximately 5% when compared to straight-blade wind turbines. The objective of the research was to further increase below-rated, variable speed, power capture when using swept-blades. When operating in the variable speed region, the turbine’s torque is proportional to the square of the generator speed, and k is the proportionality constant (T = kΩ 2 ). Initial studies indicated that the value of k needed to be lowered from the original value to increase AEP. This proved to be slightly beneficial for the 3.0 MW turbine but not for the 1.5 MW turbine. The optimal tip speed ratio was too high for both turbines and limited the ability to increase AEP. Original swept-blade chords were designed to fit a linear pattern for manufacturing purposes, but it is believed this is no longer a necessary constraint. The blades were redesigned to have a non-linear chord distribution, which is based on the Betz optimal design method, and the resultant increase in solidity proved to be the solution for slowing down the blades’ rotational speed. The change in chord design proved to be beneficial for both 1.5 and 3.0 MW wind turbines and had immediate, measurable increases to AEP. An effort to further increase AEP was then conducted by using an alternative torque-speed controller, which used a different equation to relate speed and torque. This method only resulted in an increase of AEP for the 1.5 MW turbine. In conclusion, the highest recorded AEP increases from straight-blade values were 6.9% and 8.9% for the 1.5 and 3.0 MW turbines, respectively. The 1.5 MW turbine benefited from the custom controller and redesigned chords, whereas the 3.0 MW turbine only benefited from redesigned chords.

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-05-09T13:09:50Z No. of bitstreams: 1 Marcio Vieira da Cunha.pdf: 268054 bytes, checksum: 4c968c79527a31867d221fe52ae60458 (MD5) / Made available in DSpace on 2017-05-09T13:09:50Z (GMT). No. of bitstreams: 1 Marcio Vieira da Cunha.pdf: 268054 bytes, checksum: 4c968c79527a31867d221fe52ae60458 (MD5) Previous issue date: 2006-02-21 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The experiment was carried out at the IPA Experimental Station, Itambé-PE, located in the Forest Zone of Pernambuco. The objective was study structural and morphologic characteristics and evaluate factors related the grazing efficiency in five Pennisetum sp. genotypes (IRI-381, Venezuela, HV-241, Elephant B and Hexaploid) during the dry period of the year. Genotypes were managed under rotational stocking (44 days of resting period and four days of grazing period). The experimental design was complete randomized blocks in split plot (genotypes represented the plots; grazing cycles, the subplots) and four replications. Six replications were used for total, green and dry pre-grazing leaf blade mass. The others variables (green leaf blade accumulation and grazing efficiency) were analyzed using a complete randomizedblocks design with four repetitions. There was variation in the structural and morphologic characteristics of the Pennisetum sp. genotypes. The IRI-381 and Elephant B presented high density of green leaf blade, low percentage of dead material and high density of remaining basal tillers and new aerial tillers, with averages of 5.0 kg DM/ha/cm, 33%, 22 and 146 tillers/m2, respectively. The same genotypes presented greater total and green pre-grazing leaf blade mass, and green leaf blade accumulation and grazing efficiency, with averages of 1374 and 737 kg DM/ha, 654 kg DM/ha/44 days and 80% of the green leaf blade accumulation, respectively. The HV-241 presented high participation of died material in its aerial biomass (55.6%) due to the high tiller mortality (19 and 114 basal and aerial dead tillers/m2, respectively). This genotype stillpresented high grazing efficiency (100% of the green leaf blade accumulation), however low green leaf blade accumulation (155 kg of MS/ha/44 days). Lesser grazing efficiencies were observed in the Hexaploid and Venezuela (59 and 36% of the green leaf blade accumulation, respectively), possibly due to the high losses by grazing (30 and 31% of the pre-grazing total leaf blade mass, respectively). The alterations in the structural and morphologic characteristics of the Pennisetum sp. genotypes suggest that the animal stoking will have to be adjusted to each grazing cycle aiming at the maintenance of forage stand and the quality of the animal diet. The genotypes IRI-381 and Elephant B presented potential to be used under rotational stocking in dry period of the year. There were indications that interspecific hybrid HV-241 was more affected bythe effect of the dry period of the year. / O experimento foi realizado na Estação Experimental do IPA, em Itambé-PE,objetivando estudar características estruturais e morfológicas, assim como os fatores relacionados à eficiência de pastejo em cinco genótipos de Pennisetum sp. (IRI-381,Venezuela, HV-241, Elefante B e Hexaplóide) no período seco do ano, da Zona da Mata de Pernambuco. Os genótipos foram manejados sob lotação rotacionada (44 dias de descanso e quatro dias de permanência) ao longo de dois ciclos de pastejo. Utilizou-se delineamento experimental em blocos ao acaso com parcelas subdivididas (os genótipos representaram as parcelas; os ciclos de pastejo, as subparcelas) e quatro repetições. Para massa de lâmina foliar total, verde, e seca pré-pastejo foram utilizadas seis repetições. Para acúmulo de lâmina foliar verde e eficiência de pastejo foi utilizado delineamento em blocos casualizados com quatro repetições. Houve variação nas características estruturais e morfológicas de genótipos de Pennisetum sp. O IRI-381 e Elefante B apresentaram alta densidade de lâmina foliar verde, baixa porcentagem de material morto e alta densidade de perfilhos basais remanescentes e aéreos novos, com médias de 5,0 kg de MS/ha/cm, 33%, 22 e 146 perfilhos/m2, respectivamente. Estes mesmos genótipos apresentaram maior massa de lâmina foliar total, e verde pré-pastejo, acúmulo de lâmina foliar verde e eficiência de pastejo, com médias de 1374 e 737 kg de MS/ha, 654 kg de MS/ha/44 dias e 80% do acúmulo lâmina foliar verde, respectivamente. OHV-241 apresentou alta participação de material morto em sua biomassa aérea (55,6%) devido a alta mortalidade de perfilhos (19 e 114 perfilhos basais e aéreos mortos/m2,respectivamente). Este genótipo apresentou ainda alta eficiência de pastejo (100% do acúmulo lâmina foliar verde, porém baixo acúmulo de lâmina foliar verde (155 kg de MS/ha/44 dias). Menores eficiências de pastejo foram observadas no Hexaplóide e Venezuela (59 e 36% do acúmulo de lâmina foliar verde, respectivamente), possivelmente devido às altas perdas sob pastejo (30 e 31% da massa de lâmina foliar total pré-pastejo, respectivamente). As alterações nas características estruturais e morfológicas dos genótipos de Pennisetum sp. sugerem que a lotação animal deverá ser ajustada a cada ciclo de pastejo visando a manutenção do stand forrageiro e a qualidade da dieta animal. Os genótipos IRI-381 e Elefante B apresentam potencial para serem utilizados sob lotação rotacionada no período seco do ano. Houve indicações que o híbrido interespecífico HV-241 foi mais afetado pelos efeitos do estresse hídrico noperíodo seco do ano.

Highly-loaded turbomachine blades can stall under off-design conditions. In this regime, the flow can separate close to the leading edge of the blade in a periodic manner that can lead to blade vibrations, commonly referred to as stall flutter. Prior experimental studies on stall flutter have been at large Re (Re ~ 106). In the present work, motivated by applications in Unmanned Air Vehicles (UAV) and Micro Air Vehicles (MAV), we study experimentally the forces and flow fields around an oscillating blade at low Re (Re ~ 3 x 104). At these low Re, the flow even over the stationary blade can be quite different. We experimentally study the propensity of an isolated symmetric and cambered blade (with chord c) to undergo self-excited oscillations at high angles of attack and at low Reynolds numbers (Re ~ 30, 000). We force the blade, placed at large mean angle of attack, to undergo small amplitude pitch oscillations and measure the unsteady loads on the blade. From the measured loads, the direction and magnitude of energy transfer to/from the blade is calculated. Systematic measurements have been made for varying mean blade incidence angles and for different excitation amplitudes and frequencies (f). These measurements indicate that post stall there is a possibility of excitation of the blade over a range of Strouhal Numbers (St = fc/U) with the magnitude of the exciting energy varying with amplitude, frequency and mean incidence angles. In particular, the curves for the magnitude of the exciting energy against Strouhal number (St) are found to shift to higher St values as the mean angle of attack is increased. We perform the same set of experiments on two different blade shapes, namely NACA 0012 and a compressor blade profile, SC10. Both blade profiles show qualitatively similar phenomena. The flow around both the stationary and oscillating blades is studied through Particle Image Velocimetry (PIV). PIV measurements on the stationary blade show the gradual shift of the flow separation point towards the leading edge with increasing angle of attack, which occurs at these low Re. From PIV measurements on an oscillating blade near stall, we present the flow field around the blade at different phases of the blade oscillation. These show that the boundary layer separates from the leading edge forming a shear layer, which flaps with respect to the blade. As the Strouhal number is varied, the phase between the flapping shear layer and the blade appears to change. This is likely to be the reason for the observed change in the sign of the energy transfer between the flow and the blade that is responsible for stall flutter.