<p>The primary objective of this research was to shed light on the changes in performance observed in a high-speed, centrifugal compressor that occur during the transition from subsonic to transonic operating conditions, using experimental data collected on a research compressor developed by Honeywell Aerospace, as well as results from a numerical model of the compressor.</p> <p> An understanding of the flow behavior in transonic centrifugal compressors is critical as the drive for higher stage pressure ratios while maintaining a compact size results in higher rotational speeds and increased aspect ratios in the inducer of the impeller. Both of these design trends result in higher relative Mach numbers near the impeller leading edge, resulting in the formation of shocks and an increasingly complex flow field. Since it is necessary to maintain high efficiency and adequate surge margin at these conditions—to ensure the compressor is stable across the full operating range—it is important to understand the effects of the transition from subsonic to supersonic flow on performance and stability. Due to the limited availability of research in the open literature regarding transonic centrifugal impellers, especially experimental studies, these behaviors are still not fully understood.</p> <p>Experimental data collected during steady state operation as well as during speed transients, showed a sudden decrease in the variance of the unsteady pressure field throughout the compressor, but most dramatically in the inducer shroud. Analysis of the performance also showed a significant increase in impeller efficiency of approximately 2 points as speed was increased from 80% to 90% of the design speed. Temperature measurements upstream of the impeller leading edge indicated a dramatic reduction in the degree of flow recirculation in the same speed range, indicating the increase in performance is related to a decrease in the blockage near the impeller leading edge. A low pressure region was also observed in the inducer passage, which disappeared upon transition to the transonic operating regime, this coupled with decreased inducer static pressure rise and relative diffusion at lower speeds, strongly indicates that increased loss in the inducer at lower speeds is responsible for the observed performance deficiency during subsonic operation.</p> <p>Analysis of the numerical results revealed that the low pressure region in the inducer may be attributable to the interaction between the inlet shroud boundary layer and the low momentum tip leakage flow in the impeller passage, which at lower speeds, results in the tip leakage flow forming a large recirculation region in the inducer passage. It was also determined that the step change in instability coincides with the inducer shock extending to the shroud and reducing the strength of the interaction between the low momentum regions in the inlet and impeller passage, thereby allowing the tip leakage flow to form into a vortex and preventing the development of the recirculation region in the inducer. </p> <p>This research provides a possible explanation for the observed instability in the compressor, which may allow for further testing of techniques to mitigate the instability caused by the blockage in the inducer, such as casing treatment, bleed, or flow injection into the inducer shroud.</p>

The implementation of a ported shroud casing treatment is often used to extend the operating range of a centrifugal compressor. This work utilizes the STAR-CCM+ CFD package to analyze steady-state, single-passage simulations of a centrifugal compressor with and without a ported shroud to better understand how a ported shroud affects compressor flow physics. Verification and validation of simulations were conducted by comparison of results with a time-accurate full-annulus simulation and experimental data. Four different ported shroud revisions were considered and modeled along the full range of their stable operation, with emphasis placed on the flow limits of choke and stall. A ported shroud is found to improve the choked mass flow limit by increasing the aerodynamic area of the compressor. Near-stall operation is improved through flow recirculation through the ported shroud. This flow, which is induced with a large component of tangential velocity from having passed the impeller blades' leading edge once, reduces the impeller incidence. The influence of a strut is found to restrict both limits of operation by reducing the aerodynamic area and obstruction of tangential velocity. The revisions considered demonstrate that facilitation of flow entering the ported shroud under either near-stall or choked conditions causes a noteworthy improvement in performance. Such alterations, in this application, demonstrate a 3.3% improvement in choked mass flow rate under choked conditions and an 1.3 degree reduction in impeller incidence under near-stall conditions, as compared to the initial ported shroud design. Understanding the effect that a ported shroud casing treatment has on compressor flow physics, especially near its limits of operation, suggests methods for improving centrifugal compressor design to increase its stable operating range.

Performance of vacuum cleaners are affected by factors such static pressure, airflow rate and efficiency. In this thesis work, attempt has been made to design a fan to meet the requirements of suction static pressure and air flow rate and in the process understand the fan design parameters that affect these performance parameters. Parametric study has been conducted for the same, by choosing six fan design parameters. Additionally, ways to increase the fan efficiency has been investigated during the parametric study. Computational Fluid Dynamics is used to visualize the flow inside the fan casing and further to simulate fan performance at an operational point. Steady state RANS and moving reference frames was used to model the turbulence in the fluid flow and rotation of the fan, respectively. Performance curve showing the relation between static suction pressure and mass flow rate is plotted for the base model is in proximity to the required performance. Parametric study was conducted on the six fan design parameters: Fan diameter, number of impeller blades, blade outlet angle, radius of the curve connecting inlet to outlet section of the fan, diffuser exit length and splitter blade length. The range for each parameter analysis was restricted so that static pressure values are around the required performance. Greater performance variation was found with design parameters: fan diameter, blade outlet angle, radius of the curve connecting inlet to outlet section of the fan and diffuser exit length. This variation at low mass flow rate can be majorly attributed to the randomness in the flow captured by entropy contours. At high mass flow rate, blockage in the flow visualized by pressure contours reasoned for the performance variation. Greater performance variation was not when design parameters such as number of blades and splitter blade length were varied. Larger variation of these parameters is required to see better variation.

<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>

[pt] Apresenta-se, neste estudo, quatro análises sobre bombas centrífugas radiais: a) Determinação de curvas características teóricas; b )Obtenção de curvas características de rotores usinados; c) Influência do estreitamento do rotos nas curvas características d) Efeitos da rugosidade do rotor nas curvas características experimentais. Utilizando-se de dois modelos de bombas Dancor, determinaram-se curvas características nos planos vazão-altura manométrica, vazão –potência efetiva e vazão-rendimento. Escolhendo-se os coeficientes, necessários ao calculo teórico de uma curva característica, dentro de critérios estabelecidos, consegue-se a aproximação entre as curvas teóricas e experimentais de uma bomba centrífuga radial. Ao usinar-se o rotor de uma bomba, as curvas características para o novo diêmetro deixam de obedecer às leis de semelhança, pois há variação do rendimento, principalmente na zona de trabalho de bomba. Determinou-se curvas com redução de 3,7 por cento e 11,1 por cento do diâmetro do rotor normal. Com o estreitamento do rotor há, na realidade, variações nos triângulos de velocidade, em virtude das perdas que acontecem na saída do rotor e, conseqüentemente, alterando as curvas características. Ensinando-se rotores com larguras 23 por cento menores do que o rotor normal. A rugosidade também altera as curvas características deslocando o ponto máximo rendimento para a esquerda (menor vazão e menor altura manométrica), num rotor 60 por cento mais rugoso do que o normal. / [en] The present work deals with theoretical and experimental considerations abount radial centrifugal pumps. Four analysis are made. They are: a) determination of theoretical characteristic curves; b) determination of characteristic curves of impellers with reduced diametes; c) influence of the narrowing of, impeller upon the characteristic experimental curves. Curves were determined in the capacity-head, capacity-effective power and capacity-efficiency the utilization of two models of Dancor pumps. Once the choice of the coeffcients needed for the theoretical calculation of a characteristic curve is made according to established of a characteristic curve is made according to establishe criteria, an approximation between the theorical and experimental curves a radical centrifugal pump is obtained. The determination of curves with cuts with 3.7 per cent and 11.1 per cent of the full impeller has been made. IT has been observed that when a pump impeller is cut the characteristic curves for the new diameter do not follow any more the laws of similarity because the is a variation in the efficiency mainly in the work zone of the pump. Assays have benn made with implellers that had widths 23 per cent less than the full ones. It has benn observed that with the narrowing of the impeller there are actually alterations in the triangles of velocity due to losses that occurin the exit of the impeller. On that acount. The characteristic are altered. Assays have also benn made with an impeller with 60 per cent more rugosity than a full one. It has benn shown is this study that the increase in rugosity causes alterations in the characteristic curves by shifting the best point of effciency to the left (lower capacity and lower head).

A miniature centrifugal compressor is a key component of a reverse Brayton cycle cryogenic cooling system. The system is commonly used to generate a low cryogenic temperature environment for electronics to increase their efficiency, or generate, store and transport cryogenic liquids, such as liquid hydrogen and oxygen, where space limit is also an issue. Because of space limitation, the compressor is composed of a radial inlet guide vane, a radial impeller and an axial-direction diffuser (which reduces the radial size because of smaller diameter). As a result of reduction in size, in order to obtain the required static pressure ratio/rise, the rotating speed of the impeller is as high as 313 KRPM, if Helium is used as the working fluid. Two main characteristics of the compressor – miniature and high-speed, make it distinct from conventional compressors. Higher compressor efficiency is required to obtain a higher COP (coefficient of performance) system. Even though miniature centrifugal compressors start to draw researchers' attention in recent years, understanding of the performance and loss mechanism is still lacking. Since current experimental techniques are not advanced enough to capture details of flow at miniature scale, numerical methods dominate miniature turbomachinery study. This work numerically studied a high speed miniature centrifugal compressor. The length and diameter are 7 cm and 6 cm, respectively. The study was done on the same physical compressor but with three different combinations of working fluid and operating speed combinations: air and 108 KRPM, helium and 313 KRPM, and neon and 141 KRPM. The overall performance of the compressor was predicted with consideration of interaction between blade rows by using a sliding mesh model. It was found that the specific heat ratio needs to be considered when similarity law is applied. But Reynolds number effect can be neglected. The maximum efficiency observed without any tip leakage was 70.2% for air 64.8% for helium 64.9% for neon. The loss mechanism of each component was analyzed. Loss due to turning bend was found to be significant in each component, even up to 30%. Tip leakage loss of small scale turbomachines has more impact on the impeller performance than that of large scale ones. Use of 10% tip gap was found to reduce impeller efficiency from 99% to 90%. Because the splitter was located downstream of the impeller leading edge, any incidence at the impeller leading edge leads to poorer splitter performance. Therefore, the impeller with twenty blades had higher isentropic efficiency than the impeller with ten blades and ten splitters. Based on numerical study, a four-row vaned diffuser was used to replace a two-row vaned diffuser. It was found that the four-row vaned diffuser had much higher pressure recovery coefficient than the two-row vaned diffuser. However, most of pressure is found to be recovered at the first two rows of diffuser vanes. Consequently, the following suggestions were given to further improve the performance of the miniature centrifugal compressor. 1. Redesign inlet guide vane based on the numerical simulation and experimental results. 2. Add de-swirl vanes in front of the diffuser and before the bend. 3. Replace the current impeller with a twenty-blade impeller. 4. Remove the last row of diffuser.

Much is known about the atomic/molecular theories that govern adhesion as well as the macroscopic aspects and properties of adhesion. However, adhesion in the microparticle regime is poorly characterized. We report on experiments that use centrifugal force to remove polystyrene (PS) particles from the surface of a high-speed titanium rotor operated in vacuum. This unique rotor can apply forces far greater than other centrifugal force methods or related techniques using atomic force spectroscopy. The mode of attachment, whether particles were located on the windward side versus leeward side of the spinning rotor, time spent in vacuum prior to experiments, and surface imperfections all showed an effect on adhesion. Our observations show initial agreement with published results from atomic force spectroscopy experiments. We conclude that the liquid used to help suspend and apply the PS particles greatly influences the total adhesive forces present in the system. This in turn provides valuable clues as to the nature of the adhesive interaction.

The phenomena of stall and surge in axial-centrifugal compressors is investigated through high-response measurements of both the pressure field and the flowfield throughout the surge cycle. A unique high-response forward-facing and aft-facing probe provides flow information. Several axial-centrifugal compressors are examined, both in compressor rigs and engines. Extensive discussion is presented on the differences in axial and centrifugal rotors and their effect on the system response characteristics. The loading parameters of both are examined and data is presented that shows the increased tolerance of the centrifugal stage to instability. The dynamics of the compressor blade response are shown to be related to the transport time of a fluid particle moving through a blade passage. The data presented provides new insight into the dynamic interactions that occur prior to and during stall and surge. In addition, the inception of rotating stall and the inception of surge are shown to be the same phenomena . An analytical dynamic model (DYNTECC) is applied to one of the compression systems and the results are compared to data. The results show that the model can capture the global effects of rotating stall and surge. The data presented, along with the analytical results, provide useful information for the design of active and passive stall control systems. / Ph. D.

The performance of a vapor compression system is known to be affected by the ingestion of liquid droplets in the compressor. In these multiphase flows, the liquid and the vapor phase are tightly coupled. Therefore the interphase heat, mass and momentum transfer as well as droplet dynamics including droplet breakup and droplet-wall interactions play a vital role in governing these flows. Only thermodynamic analyses or two-dimensional mean-line calculations are not sufficient to gain an in-depth understanding of the complex multiphase flow field within the compressor. The objective of this research was to extend the current understanding of the operation of a multistage centrifugal compressor under two-phase flow conditions, by performing three-dimensional computational analysis. In this work, two-phase flow of a single constituent (refrigerant R134a) through a two-stage, in-line centrifugal compressor was analyzed using CFD. The CFD model accounted for real gas behavior of the vapor phase. Novel user defined routines were implemented to ensure accurate calculations of interphase heat, mass and momentum transfer terms and to model droplet impact on the compressor surfaces. An erosion model was developed and implemented to locate the erosion "hot spots" and to estimate the amount of material eroded. To understand the effects of increasing liquid carryover, the mass flow rate of the liquid phase was increased from 1% to 5% of the vapor mass flow rate. The influence of droplet size on the compressor performance was assessed by varying the droplet diameter at the inlet from 100 microns to 400 microns. The results of the two-phase flow simulations were compared with the simulation involving only the vapor phase. Liquid carryover altered the flow field within the compressor, and as a result, both impellers were observed to operate at off-design conditions. This effect was more pronounced for the second impeller. The overall effects of liquid carryover were detrimental to the compressor performance. The erosion calculations showed maximum erosion potential on the blade and shroud of the first impeller. The results from this investigation provided new and useful information that can be used to support improved design solutions. / Ph. D.

No description available.