Neste trabalho apresenta-se o estudo da transferência de massa (oxigênio) de bolhas de ar para a água, geradas por um difusor de ar, confeccionado com plástico microporoso e de fabricação nacional, em uma coluna de aeração. O processo de aeração conduziu à determinação do coeficiente volumétrico de transferência de massa, coeficiente volumétrico de transferência de massa global, e foi executado na coluna mencionada, construída em material transparente. Utilizou-se água de fonte, existente no abastecimento do Laboratório de Hidráulica Ambiental (SHS/CRHEA). Variou-se a vazão do ar no processo de aeração de 400 l/h a 2.000 l/h e o nível de água dentro da coluna de 0,50 m a 1,80 m. Optou-se pelo método químico para deaerar a água, utilizando sulfito de sódio anidro antes do início de cada ensaio. O aparelho WTW-323, um medidor de oxigênio do tipo membrana permeável, foi usado para determinar a evolução da concentração de oxigênio dissolvido na água durante todo o processo de aeração. Características hidrodinâmicas foram quantificadas, como os campos de velocidade ascensional das bolhas de ar, o diâmetro equivalente das bolhas e sua freqüência de ocorrência. Para essas quantificações utilizou-se equipamento Laser para velocimetria não-intrusiva. As características mencionadas são fundamentais para verificar as previsões para o coeficiente de transferência de massa encontradas na literatura. A coluna usada tem seção transversal quadrada de 0,19 m x 0,19 m, constante em toda sua extensão, e altura de 2,00 m. Através da determinação da eficiência de transferência de massa de oxigênio na água, variando a vazão de aeração e o nível de água na coluna, concluiu-se que a vazão entre 600 l/h e 800 l/h e nível de água de 1.80 m é que apresentou maior eficiência de transferência de massa. / The present work is a study of the oxygen mass transfer from air bubbles into water, generated by a diffuser of air, in a column of aeration. This diffuser was made of microporous plastic and produced in Brazil. The process of aeration in the column built with transparent material determined the volumetric coeficient of the mass transfer Kla. Water from the well located in the Environmental Hydraulic Laboratory (SHS/CRHEA) was used. The air flow in the process of aeration was changed from 400 l/h to 2000 l/h and the level of water, from 0,50 m to 1,80 m. The chemical method was chosen to deoxygenate water and sulfite of anhydrous sodium was used before starting each experiment. The equipment WTW-323, an oxygen gauge with permeable membrane, was used to determine the development of the oxygen concentration dissolved in water during the process of aeration. Several hydrodinamic characteristics were measured, such as the velocity range of the air bubbles, their diameter and their frequency, by using a laser equipment for non-intrusive velocimetry. These characteristics are fundamental to check the mass transfer coeficient that are in literature. The column used for the experiment had a square cross section of 0,19 m x 0,19 m in alI extension and height of 2 meters. After determination of the efficiency of the mass transfer of oxygen into water, changing the air flow rate and the level of water in the column, it was concluded that the air flow between 600 l/h and 800 l/h and the level of water of 1,80 m were the most efficient.

Wastewater treatment plants discharge effluents containing a number of constituents whose concentrations may negatively affect the receiving waters. Current research in mixing and transport between a point source discharge and the ambient environment attempts to reduce these effects through a better understanding of the physical processes involved and development of numerical models to better predict the fate of the effluents under different conditions. This thesis examined the mixing and transport of ammonia discharged from a multiport diffuser of a municipal wastewater treatment plant into the Ottawa River. The river reach was surveyed using an M9 acoustic Doppler current profiler to obtain spatially distributed measurements of depth and velocity. Water samples were collected at and downstream of the diffuser at multiple depths. The samples were analyzed for ammonia concentration and kinetics. The river reach was also simulated in the FLOW-3D model using available turbulence closure schemes. Comparisons were made between measured and modelled results, as well as some empirical and semi-empirical approximations. A combination of measured and modelled results helped describe (quantitatively and qualitatively) the mixing and transport between the discharged effluent and receiving river. Unionized ammonia was tested for regulatory compliance. Both measured and modelled results showed that although the regulatory end-of-pipe discharge concentrations were met, downstream regulations were not met.

No description available.

<p> Rising costs and volatility in aviation fuel and increased regulations resulting from climate change  concerns have driven gas turbine engine manufacturers to focus on reducing fuel consumption.  Implementing centrifugal compressors as the last stage in an axial engine architecture allows for  reduced core diameters and higher fuel efficiencies. However, a centrifugal compressor's  performance relies heavily on its stationary diffusion system. Furthermore, the highly unsteady  and turbulent flow field exhibited in the diffusion system often causes CFD models to fall short of  reality. Therefore, rapid validation is required to match the speed at which engineers can simulate  different diffuser designs utilizing CFD. One avenue for this is through the use of additive  manufacturing in centrifugal compressor experimental research. This study focused on implementing a new generation of the Centrifugal Stage for Aerodynamic  Research (CSTAR) at the Purdue Compressor Research Lab that utilizes an entirely additively  manufactured diffusion system. In addition, the new configuration was used to showcase the  benefits of additive manufacturing (AM) in evaluating diffusion components. Two diffusion  systems were manufactured and assessed. The Build 2 diffusion system introduced significant  modifications to the diffusion system compared to the Build 1 design. The modifications included changes to the diffuser vane geometry, endwall divergence, and increased deswirl pinch and vane  geometries. The Build 2 diffusion system showed performance reductions in total and static  pressure rise, flow range, and efficiencies. These results were primarily attributed to the changes  made to the Build 2 diffuser. The end wall divergence resulted in end wall separation that caused  increased losses. The changes to the diffuser vane resulted in increased throat blockage and lower  pressure rise and mass flow rate. In addition to the experimental portion of this study, a computational study was conducted to study  the design changes made to the Build 2 diffusion system. A speedline at 100% corrected rotational  speed was solved, and the results were compared to experimental data. The simulated data matched  the overall stage and diffusion system performance relatively well, but the internal flow fields of  the diffusion components, namely the diffuser, were not well predicted. This was attributed to  16 using the SST turbulence model over BSL EARSM. The BSL EARSM model more accurately  predicted the diffuser flow field to the SST model.  </p>

As modern gas turbines implement more and more complex geometry to increase life and efficiency, attention to unsteady aerodynamic behavior becomes more important. Computational optimization schemes are contributing to advanced geometries in order to reduce aerodynamic losses and increase the life of components. These advanced geometries are less representative of cylinder and backward facing steps which have been used as analogous geometries for most aerodynamic unsteadiness research. One region which contains a high degree of flow unsteadiness and a direct influence on engine performance is that of the MidFrame. The MidFrame (or combustor-diffuser system) is the region encompassing the main gas path from the exit of the compressor to the inlet of the first stage turbine. This region contains myriad flow scenarios including diffusion, bluff bodies, direct impingement, high degree of streamline curvature, separated flow, and recirculation. This represents the most complex and diverse flow field in the entire engine. The role of the MidFrame is to redirect the flow from the compressor into the combustion system with minimal pressure loss while supplying high pressure air to the secondary air system. Various casing geometries, compressor exit diffuser shapes, and flow conditioning equipment have been tested to reduce pressure loss and increase uniformity entering the combustors. Much of the current research in this area focuses on aero propulsion geometries with annular combustors or scaled models of the power generation geometries. Due to the complexity and size of the domain accessibility with physical probe measurements becomes challenging. The current work uses additional measurement techniques to measure flow unsteadiness in the domain. The methodology for identifying and quantifying the sources of unsteadiness are iv developed herein. Sensitivity of MidFrame unsteadiness to compressor exit conditions is shown for three different velocity profiles. The result is an extensive database of measurements which can serve as a benchmark for radical new designs to ensure that the unsteadiness levels do not supersede previous successful levels.

Highly integrated airframe-propulsion systems featuring ingestion of the airframe boundary layer offer reduced noise, emissions, and fuel consumption. Embedded engine systems are envisioned which require boundary layer ingesting (BLI) serpentine inlets to provide the needed air ow to the engine. These inlets produce distorted flow profiles that can cause aeromechanical, stability, and performance changes in embedded engines. Proper design of embedded engine systems requires understanding of the underlying fluid dynamics that occur within serpentine inlets. A serpentine inlet was tested in a specially designed wind tunnel that simulated boundary layer ingestion in a full-scale realistic environment. The measured total pressure proles at the inlet and exit planes of the duct, and the static pressure distributions along the walls provided useful data related to the flow in BLI serpentine inlet systems. A bleed ow control system was tested that utilized no more than 2% of the total inlet ow. Two bleed slots were employed, one near the first bend of the S-duct and one near second. The bleed system successfully reduced inlet distortions 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 determined flow transport within the serpentine inlet. Flow separation within the S-duct increased distortion at the engine inlet plane. Discussion of airframe/inlet/engine compatibility demonstrates that embedded engine systems require multi-disciplinary collaborative design efforts. An included fundamental analysis provides performance estimates and design guidelines. The ideal airframe performance improvement associated with wake-ingestion is estimated. / Master of Science

A computational study was performed on a vaned radial diffuser using the MEFP (The Moore Elliptic Flow Program) flow code. The vaned diffuser studied by Dalbert et al. was chosen as a test case for this thesis. The geometry and inlet conditions were established from this study. The performance of the computational diffuser was compared to the test case diffuser. The CFD analysis was able to demonstrate the 3D flow within the diffuser. An inlet conditions analysis was performed to establish the boundary conditions at the diffuser inlet. The given inlet flow angles were reduced in order to match the specified mass flow rate. The inlet static pressure was held constant over the height of the diffuser. The diffuser was broken down into its subcomponents to study the effects of each component on the overall performance of the diffuser. The diffuser inlet region, which comprises the vaneless and semi-vaneless spaces, contains the greatest losses, 56%, but the highest static pressure rise, 54%. The performance at the throat was also evaluated and the blockage and pressure recovery were calculated. The results show the static pressure comparison for the computational study and the test case. The overall pressure rise of the computational study was in good agreement with the measured pressure rise. The static pressure and total pressure loss distributions in the inlet region, at the throat, and in the exit region of the diffuser were also analyzed. The flow development was presented for the entire diffuser. The 3D flow calculations were able to illustrate a leading edge recirculation at the hub, caused by an inlet skew and high losses at the hub, and the secondary flows in the diffuser convected the high losses. The study presented in this thesis demonstrated the flow development in a vaned diffuser and its subcomponents. The performance was evaluated by calculating the static pressure rise, total pressure losses, and throat blockage. It also demonstrated current CFD capabilities for diffusers using steady 3D flow analysis. / Master of Science

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.

This work focuses on the issue of acoustic diffusers. The introductory chapter describes the necessary theory of the sound distribution through enclosed space. Acoustic fields are also described. A description of the different diffusion element types and theirs design methods follows. It focuses mainly on design, which uses pseudo-random mathematical sequences. The aim of the work is to produce several types of acoustic diffusors and to verify their diffusion properties by means of measurements. The work uses the AFMG Reflex to simulate the diffusion properties of the proposed elements. Further, the thesis contains a description of the diffusion properties measurement process by the boundary plane method and the process of evaluating the measured data using the Matlab program.

<p>  </p> <p>As aviation fuel costs and consumption have continued to rise over recent decades, gas turbine engine manufacturers have sought methods to reduce fuel burn. Manufacturers plan to achieve this by reducing the specific fuel consumption of the machine by increasing the bypass ratio through a reduction of the diameter of the engine core. This presents an opportunity for implementing a centrifugal compressor as the final stage of the high-pressure compressor. The vaned diffuser in a centrifugal compressor stage maintains an integral role in determining the extents of the operating range as well as conditioning the flow for the downstream combustor. Thus, it is critical to understand the aerodynamics and performance of the vaned diffuser across the entire compressor operating range.</p> <p>This investigation focused on seven compressor operating points at the stage’s design corrected speed, which ranged from choked flow to the minimum mass flow rate before rotating stall. Steady-state and unsteady performance data were acquired to study the aerodynamics at each operating point as well as the steady-state performance of the vaned diffuser. Laser Doppler velocimetry, high-frequency pressure transducers, and additive manufacturing techniques were all implemented to acquire data in the research compressor.</p> <p>Unsteady velocity measurements were acquired in the vaneless space and were used to quantify the change in diffuser inlet incidence as the stage mass flow rate changes. The impeller exit jet and wake were compared at each operating point to understand the effect of these flow structures on the spanwise incidence profile. Steady-state performance metrics for the vaned diffuser were compared with the change in incidence to assess the effect of incidence on performance. Maximum static pressure recovery and minimum total pressure loss occurred at the maximum incidence operating point. </p> <p>The chordwise static pressure distribution is critical for health monitoring of the polymer, additive manufactured diffuser vanes. Steady-state and unsteady pressure measurements were acquired along the diffuser vane surface to assess the change in the aerodynamic lift force across the compressor operating range as well as the static pressure differential across the vane leading edge. The maximum unsteady lift on the diffuser vanes was up to 34% greater than the steady-state lift force. Unsteady static pressure differentials across the diffuser vane leading edge were similar to the steady-state values, but they were marginally greater across the entire examined operating range. These unsteady pressure measurements were acquired with high-frequency response pressure transducers installed along the diffuser vane surfaces. These transducers were also used to study the rotating stall and surge behavior of the investigated centrifugal compressor stage. This centrifugal compressor stage exhibits a spike-type rotating stall pattern at the onset of stage instability, which rapidly evolves into full flow reversal with several surge cycles. During these surge cycles, the diffuser vane leading edges are subject to a 20 psid static pressure differential. </p> <p>A computational model was used to predict the compressor flow at three different operating points. This model utilized the BSL-EARSM turbulence model, and it included surface roughness and an experimentally measured shroud thermal profile. The model accurately predicted the diffuser inlet flow angles near the shroud, but it predicted more radial flow near midspan. The diffuser vane leading edge static pressure differential was predicted within 1 psid at higher aerodynamic loading conditions. The differences between the computationally predicted and experimentally measured flow are attributed to difficulties associated with modelling the rate of mixing within the flow.</p>