Browsing by Subject "flow control"
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Item Active flow control in an advanced serpentine jet engine inlet duct(2009-05-15) Kirk, Aaron MichaelAn experimental investigation was performed to understand the development and suppression of the secondary flow structures within a compact, serpentine jet engine inlet duct. By employing a variety of flow diagnostic techniques, the formation of a pair of counter-rotating vortices was revealed. A modular fluidic actuator system that would apply several different methods of flow control was then designed and manufactured to improve duct performance. At the two bends of the inlet, conformal flow control devices were installed to deliver varying degrees of boundary layer suction, suction and steady fluid injection, and suction and oscillatory injection. Testing showed that suction alone could delay flow separation and improve the pressure recovery of the duct by as much as 70%. However, this technique was not able to rid the duct completely of the nonuniformities that exist at the engine face plane. Suction with steady blowing, however, increased pressure recovery by 37% and reduced distortion by 41% at the engine face. Suction with pulsed injection had the least degree of success in suppressing the secondary flow structures, with improvements in pressure recovery of only 16.5% and a detrimental impact on distortion. The potential for gains in the aerodynamic efficiency of serpentine inlets by active flow control was demonstrated in this study.Item Flow control optimization in a jet engine serpentine inlet duct(2009-05-15) Kumar, AbhinavComputational investigations were carried out on an advanced serpentine jet engine inlet duct to understand the development and propagation of secondary flow structures. Computational analysis which went in tandem with experimental investigation was required to aid secondary flow control required for enhanced pressure recovery and decreased distortion at the engine face. In the wake of earlier attempts with modular fluidic actuators used for this study, efforts were directed towards optimizing the actuator configurations. Backed by both computational and experimental resources, many variations in the interaction of fluidic actuators with the mainstream flow were attempted in the hope of best controlling secondary flow formation. Over the length of the studies, better understanding of the flow physics governing flow control for 3D curved ducts was developed. Blowing tangentially, to the wall at the bends of the S-duct, proved extremely effective in enforcing active flow control. At practical jet momentum coefficients, significant improvements characterized by an improved pressure recove ry of 37% and a decrease in distortion close to 90% were seen.Item Flow control techniques for real-time media applications in best-effort networks using fluid models(Texas A&M University, 2004-11-15) Konstantinou, ApostolosQuality of Service (QoS) in real-time media applications is an area of current interest because of the increasing demand for audio/video, and generally multimedia applications, over best effort networks, such as the Internet. Media applications are transported using the User Datagram Protocol (UDP) and tend to use a disproportionate amount of network bandwidth as they do not perform congestion or flow control. Methods for application QoS control are desirable to enable users to perceive a consistent media quality. This can be accomplished by either modifying current protocols at the transport layer or by implementing new control algorithms at the application layer irrespective of the protocol used at the transport layer. The objective of this research is to improve the QoS delivered to end-users in real-time applications transported over best-effort packet-switched networks. This is accomplished using UDP at the transport layer, along with adaptive predictive and reactive control at the application layer. An end-to-end fluid model is used, including the source buffer, the network and the destination buffer. Traditional control techniques, along with more advanced adaptive predictive control methods, are considered in order to provide the desirable QoS and make a best-effort network an attractive channel for interactive multimedia applications. The effectiveness of the control methods, is examined using a Simulink-based fluid-level simulator in combination with trace files extracted from the well-known network simulator ns-2. The results show that improvement in real-time applications transported over best-effort networks using unreliable transport protocols, such as UDP, is feasible. The improvement in QoS is reflected in the reduction of flow loss at the expense of flow dead-time increase or playback disruptions or both.