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The Effect of Electromagnetic Stirring and Flow Control Devices on Eight-Strand Tundish PerformanceCendekia, Bintang Bergas January 2018 (has links)
The strand similarity and inclusion removal capability are two critical parameters to measure the performance of multi-strand tundish in clean steel production. In this work, the effect of two flow regulators, i.e., Flow Control Devices (FCD) and Electromagnetic Stirring (EMS) on eight-strand tundish performance have been investigated by establishing a water model and conducting numerical simulations of water model. The water model was focused on revealing the effect of stirring while the simulation was employed to investigate the effect of two FCDs, namely baffle wall and turbo-stopper. The analysis of strand similarity and inclusion removal were conducted by analyzing flow characteristics derived from Combined Model of Residence Time Distribution (RTD) curve and observing the flow movement in the tundish model. In addition, the tundish capability to remove inclusions was also studied by injecting inclusion particles using Discrete Phase Model (DPM) in ANSYS Fluent. Experiment results cause the Combined Model needs to be modified. This modification was employed when analyzing tundish configuration involving stirring. By using the modified Combined Model, the stirring can significantly increase the well-mix volume to almost 100% as it annihilates dead zone. The stirring also increases the similarity between strands and makes the RTD curve more similar to ideal mixing curve. However, the problem of short-circuiting flow need to be solved and care should be taken into consideration regarding the selection of stirring direction as well as bath surface condition when implementing EMS in reality. The simulation results show that the addition of baffle wall and turbo-stopper are beneficial to improve mixing as well as to avoid the short-circuiting flow. Furthermore, compared to individual FCD, the combination of baffle wall and turbo-stopper results in the best performance to remove inclusions by providing surface-directed flow and generating a higher plug flow.
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Influence on tip leakage flow in a compressor cascade with plasma actuationWang, Haotian January 2019 (has links)
As one of the key components of aero engines, compressor is required to endure higher pressure, possess higher efficiency and wider operating range. Intensive studies have been made on tip leakage flow and researchers find that by reasonably organizing tip leakage flow, aero engines are more likely to achieve better performance and reliability. Conventional flow controlling methods like casing treatment and micro jet could substantially modify tip leakage flow, unfortunately with a price of additional loss, not to mention the difficulty in manufacturing such structure. Whereas plasma actuation flow control method uses plasma actuators, such equipment is easy to build, responses fast and has a wide excitation bandwidth. This method has become a new trend in internal flow active control field. In this research, a phenomenological model is adopted to simulate DBD plasma actuation in the flow field inside a compressor cascade. The aim is to find out how plasma actuation will influence tip leakage flow. Meanwhile possible means to improve plasma actuation performance are discussed. First of all, numerical simulation of flow inside a compressor cascade without plasma actuation is conducted to validate accuracy of the numerical methodology adopted and then determine one numerical approach that satisfies specific needs sufficiently. Meanwhile, influence of casing movement on tip leakage flow as well as possible mechanism of tip leakage vortex core generation is investigated in detail. The results indicate: 1. Generating position of tip leakage vortex moves towards leading edge with increasing moving speed of shroud. 2. As shroud moving speed increases, trajectory of tip leakage vortex moves away from suction side of blade and closely towards shroud. 3. Casing movement tends to transform tip leakage vortex from circular to oval shape due to circumferential shearing. 4. Casing movement has little influence on total pressure field concerning absolute pressure value. While total pressure loss does reduce slightly with increasing moving speed of shroud. 5.Vorticity transport from tip clearance into passage may be contributing significantly to generation of tip leakage vortex inner core. Secondly, a simplified model of DBD plasma actuation based on literature [1] is derived and applied through UDF function of commercial software Fluent into the flow field. Different actuation positions, voltages and frequencies are applied in simulation and compared. After that casing movement is included. Main conclusions are as follow: 6. Plasma actuation shows significant suppressing effect on tip leakage vortex on both size, trajectory and strength. 7. The suppressing effect on tip leakage vortex grows stronger as actuator moves towards leading edge. 8. Increasing actuation voltage results in stronger suppressing effect on tip leakage vortex. 9. Plasma actuation can effectively improve total pressure loss situation near shroud region with increasing actuation power. 10. Increasing actuation frequency results in stronger suppressing effect on tip leakage vortex as well. Additionally, frequency performs slightly better than voltage. 11. Casing movement tends to weaken suppressing effect of tip leakage vortex by plasma actuation. More actuation power is needed to achieve sufficient suppressing effect in real compressors. / Som en av de viktigaste komponenterna i flygmotorer krävs det att kompressorn utsätts för högre tryck, har högre effektivitet och större driftsintervall. Intensiva studier har gjorts om skovlarnas toppspel läckageflöde och man anser att det är mer sannolikt att flygmotorer uppnår bättre prestanda och tillförlitlighet genom att på ett rimligt sätt reglera läckageflödet i toppspelet. Konventionella metoder för reglering av flödet, som behandling av “casing” och mikrojet, skulle kunna ändra läckageflödet avsevärt, men medför tyvärr ytterligare förlust, för att inte tala om svårigheten att tillverka en sådan struktur. Samtidig flödeskontroll med hjälp av plasma aktuatorer som är relativt lätta att bygga, reagerar snabbt och har en bred excitationsbandvid. Denna metod har blivit en ny trend inom det interna flödesaktiva kontrollområdet. I denna forskning antas en modell för att simulera plasmaaktivering av DBD i flödesfältet i en kompressorskaskad. Man försöker ta reda på hur plasmaaktivering påverkar läckageflödet. Möjliga sätt att förbättra effekten av plasmaaktivering diskuteras. För det första genomförs numerisk simulering av flödet i en kompressorskaskad utan plasmaaktivering för att validera noggrannheten i den numeriska metoden. Därefter undersöks i detalj vilken inverkan den relativa rörelsen av ”casing” har på läckageflödet genom toppspelet och mekanismen för toppspelsvirvel analyseras. Resultaten visar: 1. Startposition för läckagevirveln rör sig mot skovelns framkant när man introducerar och ökar den relativa hastigheten för ”casing”. 2. I takt med att den relativa hastigheten ökar, kretsbanan för läckage virveln rör sig bort från skovelns sugsida och närmare mot ”casing”. 3. Den relativa rörelsen tenderar att omvandla virveln från cirkulär till oval form på grund av skjuvkrafter. 4. Den relativa rörelsen av ”casing” påverkar inte det totala tryckfältet när det gäller det absoluta tryckvärdet. Samtidigt som den totala tryckförlusten minskar något med ökad hastighet. 5. Virveltransport från toppspelet till huvudkanalen kan på ett betydande sätt bidra till att skapa virvelns inre kärna. I senare delen av arbetet utvecklas och tillämpas en förenklad modell för plasmaaktivering av DBD baserad på litteratur [1], genom att använda UDF‐funktionen i kommersiell CFD programvara Fluent. Olika aktuatorläge, spänningar och frekvenser prövas i simuleringen och jämförs. De viktigaste slutsatserna är följande: 6. Aktuering av plasma visar en betydande dämpningseffekt på läckagevirveln i toppspelet både va det gäller dess storlek, bana och styrka. 7. Den dämpande effekten på läckagevirveln blir starkare när aktuator monteras närmare skovelns framkant. 8. Ökad aktuatorspänning leder till en starkare dämpande effekt på läckagevirveln. 9. Ökad aktuatorfrekvens leder till starkare dämpningseffekt på läckagevortex också.mDessutom fungerar frekvensen något bättre än spänningen. 10. Den relativa rörelsen av ”casing” försvagar effekten av plasmaaktuering. För att uppnå tillräcklig dämpningseffekt i riktiga kompressorer krävs mer effekt till aktuatorn.
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<strong>EXPERIMENTAL STUDY OF BOUNDARY LAYER SEPARATION IN A LOW-REYNOLDS, HIGH-DIFFUSION PASSAGE THROUGH INFRARED THERMOGRAPHY</strong>Luis Angel Zarate-Sanchez (14587421) 25 July 2023 (has links)
<p>Highly loaded airfoils in low-pressure turbines (LPTs) suffer from laminar flow separation from the suction side of the airfoils aft of the throat of the passages. This separation harms the performance of the engine by reducing the power extraction from the turning air and ultimately reduces the overall turbine efficiency. Flow control techniques have been investigated to eliminate flow separation in aerodynamic surfaces to abate the losses associated with it. This Master of Science Thesis investigates the design, implementation and testing of pulsated injection actuation in a low-Reynolds flow over a wall-mounted hump.</p>
<p>Furthermore, this Thesis expands on the existing expertise in the infrared (IR) thermography measurement technique at the Purdue Experimental Turbine Aerothermal Lab. This is done through an investigation of the factors affecting the IR measurement technique and the development of an optical instrument (borescope) to implement in an annular cascade wind tunnel. IR thermography is used on the wall-mounted hump blowdown tests to detect the separation point in the boundary layer using two techniques: by an investigation of the surface temperature distribution and an investigation of the heat transfer behavior at the surface. Finally, the borescope is commissioned through the first testing campaign of the LPT airfoils, and are processed to thermally investigate the passage.</p>
<p>This thesis succeeds in expanding the IR capabilities within PETAL, and at demonstrating pulsated injection as an effective method to eliminate flow separation. Furthermore, IR successfully detects flow separation on the wall-mounted hump through the two methods presented, as well as detecting the boundary layer reattachment caused by the flow control technique. The limitations of the thermal methodology, as well as those of the optical probe are addressed, and the uncertainties in the measurements are quantified. Finally, steps to continue the studies are suggested at the end of each methodology chapter, including the potential redesign of the IR borescope to improve the quality of measurements. </p>
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The Effects of Deployable Surface Topography Using Liquid Crystal Elastomers on Cylindrical Bodies In FlowSettle, Michael J., Jr 15 May 2023 (has links)
No description available.
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Analysis and control of boundary layer transition on a NACA 0008 wing profileSinha Roy, Arijit January 2018 (has links)
The main aim of this thesis was to understand the mechanism behind the classical transition scenario inside the boundary layer over an airfoil and eventually attempting to control this transition utilizing passive devices for transition delay. The initial objective of analyzing the transition phenomenon based on TS wave disturbance growth was conducted at 90 Hz using LDV and CTA measurement techniques at two different angles of attack. This was combined with the studies performed on two other frequencies of 100 and 110 Hz, in order to witness its impact on the neutral stability curve behavior. The challenges faced in the next phase of the thesis while trying to control the transition location, was to understand and encompass the effect of adverse pressure gradient before setting up the passive control devices, which in this case was miniature vortex generators. Consequently, several attempts were made to optimize the parameters of the miniature vortex generators depending upon the streak strength and stability. Finally, for 90 Hz a configuration of miniature vortex generators have been found to successfully stabilize the TS wave disturbances below a certain forcing amplitude, which also led to transition delay.
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On The Nature Of The Flow In A Separated Annular DiffuserDunn, Jason 01 January 2009 (has links)
The combustor-diffuser system remains one of the most studied sections of the turbomachine. Most of these investigations are due to the fact that quite a bit of flow diffusion is required in this section as the high speed flow exits the compressor and must be slowed down to enter the combustor. Like any diffusion process there is the chance for the development of an unfavorable adverse pressure gradient that can lead to flow separation; a cause of drastic losses within a turbine. There are two diffusion processes in the combustor-diffuser system: The flow first exits the compressor into a pre-diffuser, or compressor discharge diffuser. This diffuser is responsible for a majority of the pressure recovery. The flow then exits the pre-diffuser by a sudden expansion into the dump diffuser. The dump diffuser comprises the majority of the losses, but is necessary to reduce the fluid velocity within acceptable limits for combustion. The topic of active flow control is gaining interest in the industry because such a technique may be able to alleviate some of the requirements of the dump diffuser. If a wider angle pre-diffuser with separation control were used the fluid velocity would be slowed more within that region without significant losses. Experiments were performed on two annular diffusers to characterize the flow separation to create a foundation for future active flow control techniques. Both diffusers had the same fully developed inlet flow condition, however, the expansion of the two diffusers differed such that one diffuser replicated a typical compressor discharge diffuser found in a real machine while the other would create a naturally separated flow along the outer wall. Both diffusers were tested at two Reynolds numbers, 5x104 and 1x105, with and without a vertical wall downstream of the exit to replicate the dump diffuser that re-directs the flow from the pre-diffuser outlet to the combustor. Static pressure measurements were obtained along the OD and ID wall of the diffusers to determine the recovered pressure throughout the diffuser. In addition to these measurements, tufts were used to visualize the flow. A turbulent CFD model was also created to compare against experimental results. In the end, the results were validated against empirical data as well as the CFD model. It was shown that the location of the vertical wall was directly related to the amount of separation as well as the separation characteristics. These findings support previous work and help guide future work for active flow control in a separated annular diffuser both computationally and experimentally.
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Adaptive and model-based control in laminar boundary-layer flowsFabbiane, Nicolò January 2014 (has links)
In boundary-layer flows it is possible to reduce the friction drag by breaking the path from laminar to turbulent state. In low turbulence environments, the laminar-to-turbulent transition is dominated by local flow instabilities – Tollmien-Schlichting (TS) waves – that exponentially grows while being con- vected by the flow and, eventually, lead to transition. Hence, by attenuating these disturbances via localised forcing in the flow it is possible to delay farther downstream the onset of turbulence and reduce the friction drag. Reactive control techniques are widely investigated to this end. The aim of this work is to compare model-based and adaptive control techniques and show how the adaptivity is crucial to control TS-waves in real applications. The control design consists in (i) choosing sensors and actuators and (ii) designing the system responsible to process on-line the measurement signals in order to compute an appropriate forcing by the actuators. This system, called compen- sator, can be static or adaptive, depending on the possibility of self-adjusting its response to unmodelled flow dynamics. A Linear Quadratic Gaussian (LQG) regulator is chosen as representative of static controllers. Direct numerical simulations of the flow are performed to provide a model for the compensator design and test its performance. An adaptive Filtered-X Least-Mean-Squares (FXLMS) compensator is also designed for the same flow case and its per- formance is compared to the model-based compensator via simulations and experiments. Although the LQG regulator behaves better at design conditions, it lacks robustness to small flow variations. On the other hand, the FXLMS compensator proved to be able to adapt its response to overcome the varied conditions and perform an adequate control action. It is thus found that an adaptive control technique is more suitable to delay the laminar-to-turbulent transition in situations where an accurate model of the flow is not available. / I det tunna gränsskikt som uppstår en yta, kan friktionen minskas genom att förhindra omslag från ett laminärt till ett turbulent flöde. När turbulensnivån är låg i omgivningen, domineras till en början omslaget av lokala instabiliteter (Tollmien-Schlichting (TS) v ågor) som växer i en exponentiell takt samtidigt som de propagerar nedströms. Därför, kan man förskjuta omslaget genom att dämpa TS vågors tillväxt i ett gränsskikt och därmed minska friktionen.Med detta mål i sikte, tillämpas och jämförs två reglertekniska metoder, nämligen en adaptiv signalbaserad metod och en statiskt modellbaserad metod. Vi visar att adaptivitet är av avgörande betydelse för att kunna dämpa TS vågor i en verklig miljö. Den reglertekniska konstruktionen består av val av givare och aktuatorer samt att bestämma det system som behandlar mätsignaler (on- line) för beräkning av en lämplig signal till aktuatorer. Detta system, som kallas för en kompensator, kan vara antingen statisk eller adaptiv, beroende på om det har möjlighet till att anpassa sig till omgivningen. En så kallad linjär regulator (LQG), som representerar den statiska kompensator, har tagits fram med hjälp av numeriska simuleringar of strömningsfältet. Denna kompensator jämförs med en adaptiv regulator som kallas för Filtered-X Least-Mean-Squares (FXLMS) både experimentellt och numeriskt. Det visar sig att LQG regulatorn har en bättre prestanda än FXLMS för de parametrar som den var framtagen för, men brister i robusthet. FXLMS å andra sidan, anpassar sig till icke- modellerade störningar och variationer, och kan därmed hålla en god och jämn prestanda.Man kan därmed dra slutsaten att adaptiva regulatorer är mer lämpliga för att förhala omslaget fr ån laminär till turbulent strömning i situationer då en exakt modell av fysiken saknas. / <p>QC 20141020</p>
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Investigation of Three Dimensional Forcing of Cylinder Wake with Segmented Plasma Actuators and the Determination of the Optimum Wavelength of ForcingBhattacharya, Samik January 2013 (has links)
No description available.
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Understanding and Control of Coupling of Supersonic Twin Jets Using Localized Arc Filament Plasma ActuatorsCluts, Jordan Dean January 2018 (has links)
No description available.
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Surface Stress Sensors for Closed Loop Low Reynolds Number Separation ControlMarks, Christopher R. 18 July 2011 (has links)
No description available.
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