The main contributor to the high-cycle fatigue of compressor blades is the response to aerodynamic forcing functions generated by an upstream row of stators or inlet guide vanes. Resonant response to engine order excitation at certain rotor speeds is especially damaging. Studies have shown that flow control by trailing edge blowing (TEB) can reduce stator wake strength and the amplitude of the downstream rotor blade vibrations generated by the unsteady stator-rotor interaction. In the present study, the effectiveness of TEB to reduce forced blade vibrations was evaluated in a modern single-stage transonic compressor rig. A row of wake generator (WG) vanes with TEB capability was installed upstream of the fan blisk, the blades of which were instrumented with strain gages. Data was collected for varied TEB conditions over a range of rotor speed which included one fundamental and multiple harmonic resonance crossings. Sensitivity of resonant response amplitude to full-span TEB flowrate, as well as optimal TEB flowrates, are documented for multiple modes. Resonant response sensitivity was generally characterized by a robust region of substantial attenuation, such that less-than-optimal TEB flowrates could prove to be an appropriate design tradeoff. The fundamental crossing amplitude of the first torsion mode was reduced by as much as 85% with full-span TEB at 1.1% of the total rig inlet flow. Similar reductions were achieved for the various harmonic crossings, including as much as 94% reduction of the second leading edge bending mode resonant response using 0.74% of the rig flow for full-span TEB. At least 32% reduction was achieved for all modal crossings over the broad flow range of 0.5 to 0.9% of the rig flow. Thus the results demonstrate the modal- and flowrate-robustness of full-span TEB for reducing forced response in a modern, closely-spaced transonic compressor. Reduced spanwise TEB coverage was generally found to provide less peak reduction. Widely varying sensitivities of the vibration modes to the spanwise TEB distribution were also noted. While the second chordwise mode experienced roughly the same maximum response reduction of 80% for all of the spanwise TEB configurations, some other modes were amplified from the baseline case under part-span TEB conditions. Part-span TEB was thus found to be less modally-robust than full-span TEB. / Ph. D.

Traffic growth and limited roadway capacity decrease traveler mobility and increase traffic congestion and fuel consumption. Traffic managers employ various control techniques to mitigate the aforementioned problems. One well-known network-wide control strategy is perimeter control (or gating). Perimeter control is based on the Network Fundamental Diagram (NFD). NFD-based perimeter control techniques are used to solve congestion problems in transportation networks. One well-known method used in the literature is Proportional Integral Control (PIC). PIC solves the congestion problem, but suffers from sensitivity to parameter tuning and the need for model linearization. A weather-tuned perimeter control (WTPC) and a jam density-tuned perimeter controller (JTPC) were developed to cope with parameter sensitivity for different weather conditions and jam densities, respectively. In an attempt to overcome PIC problems, a sliding mode controller (SMC) was developed. SMC does not require model linearization and parameter tuning. It is also robust to varying demand patterns. SMC computes the flow that needs to enter a protected network and converts it to corresponding traffic signal timings to achieve the desired control strategies. Another approach to implementing the sliding mode controller is to control vehicle speeds on the links entering the protected network. Coupling speed harmonization (SH) with sliding mode control (SMC), an SMC-SH was developed and implemented in the INTEGRATION microscopic traffic simulator. The mentioned controllers are all tested on a mid-size grid network replicating downtown Washington DC. SMC-SH improved different performance metrics on the whole grid network compared to the no control case. Specifically, it improved average travel time, total delay, stopped delay, fuel consumption, CO2 emissions by 17.27%, 18.18%, 12.76%, 5.91%, and 7.04%, respectively. In order to test the SMC-SH on a real large-scale network, the downtown Los Angeles (LA) network is used. The LA network is known for its congested freeways, so a development of a Freeway-SMC-SH controller is performed and tested. It shows good results in improving the performance not only of freeways, but also the overall LA network performance. Particularly, the network-wide average travel time, total delay, stopped delay, fuel consumption and CO2 emissions improved with respect to the no control case by 12.17%, 20.67%, 39.58%, 2.6%, and 3.3%, respectively. An identification of a homogeneously congested area is needed to apply SMC-SH on LA roads (not freeways). The geographical self organizing maps (GeoSOM) clustering algorithm is applied and tested on the LA network. The clustering goal is to identify a geographically connected region with small density variance. GeoSOM is able to achieve that objective with better performance than the state-of-the-art Kmeans and DBSCAN clustering algorithms. The enhancements reached up to 15.15% for quantization error, 61.05% for spacial quantization error, and 43.96% for variance. Finally, the SMC-SH is tested on the protected region of the LA network identified by the GeoSOM algorithm. SMC-SH succeeds in improving network-wide vehicle travel time, total delay, stopped delay, fuel consumption and CO2 emissions by 6.25%, 9.4%, 16.47%, 1.7%, and 2.19%, respectively. / Doctor of Philosophy / Road congestion causes vehicular delays and increases travel time and fuel consumption. The goal of the research is to prevent or relieve traffic congestion in a network. That region that we attempt to address is termed the congested network or the protected network (PN). One way to solve the traffic jam problem is to set up gates on the PN borders so that the number of vehicles that enter the network is limited, and consequently traffic jams do not occur. However, the number of vehicles should not be limited too much to avoid overcrowding outside the PN. The developed controller calculates the right number of cars that should enter the network in order to improve the performance inside and outside the PN. The first way to apply the controller commands is to adjust traffic signal timings at the traffic signals located along the PN border. The second way (called SMC-SH) is to adjust the speed of the vehicles entering the network through these gates. In the first part of the work, all the controllers are implemented and tested in a mid-size grid network. In the second part of the work, the goal is to implement the controller on the real large-scale Los Angeles (LA) network. Since the LA network suffers from congestion on freeways, a freeway controller is developed and tested. It does not only succeed in reducing traffic jams on freeways, but also enhances the overall LA network traffic performance. In order to apply the SMC-SH controller on the LA network, we identify homogeneously congested regions. GeoSOM clustering is implemented to achieve this goal and compared to other clustering methods, and is shown to outperform them. Finally, the SMC-SH controller is tested on the congested region of LA, and succeeds in reducing travel time, total delay, and fuel consumption for the LA network.

The objective of this work is to study the basic mechanism of the active control of free shear flows and look for new concepts in actuation methodologies. The possibility of controlling the evolution of a triangular jet is discussed in Chapter 2. The piezoceramic actuators were mounted on the flat sides of the nozzle. The flow was fully sheared near the nozzle. Single mode excitation with frequency as the varying parameter was found to be ineffective for controlling the far field evolution. In contrast, excitation of the jet with non-integer and counter propagating azimuthal modes yielded marked changes in the jet evolution. A new method employing dynamic spatial modes to control the far field of a circular jet is examined in Chapter 3. The basic mechanism that governs the far field control was found to be the non-linear interaction of the instabilities of the standing waves. This observation agrees with conclusions of former investigators but with a new understanding that the non-linear interaction mechanism and the jet expansion are not to become effective until the potential core ends, after which the jet demonstrates large, directional expansion. It was shown in the experiment that this expansion could be easily predicted and controlled. These results point out a better control mechanism -- the dynamic mode control method. Three schemes were proposed: 1) the phase modulation, 2) the switching modulation, and 3) the spatial mode modulation, where the first two were implemented with great success in controlling the evolution of the jet flow. Finally, a triangular jet with a top hat initial velocity profile is examined in Chapter 4. The results of excited and unexcited jets were compared with those studies where the initial flow conditions were different. It was found that the initial flow condition affected the flow field in two ways: the axis switching and the jet expansion. The combination of an initial top-hat velocity profile and a non-symmetric nozzle geometry was proved to be the necessary condition to create axis switching. Proper combination of initial velocity profile, nozzle geometry and spatial mode could greatly enhance the jet expansion. / Ph. D.

Control of radiated acoustic noise is vital to the survivability and the detectability of submersible watercraft. Two primary sources of radiated fluid noise in submersible vessels are the boundary layer turbulence along the forebody and propulsor fluid-structure interaction. The propulsor contains several locations of such interaction, one of which was investigated in this research. Specifically, this research focused on experimentally investigating active flow control techniques to reduce rotor-stator interaction noise sources. Two of the three flow control configurations applied to the flow involved the application of active flow control to the leading edge of a single exit guide vane (EGV) mounted downstream of a seven-bladed rotor. The leading edge blowing configuration (LEB) consisted of a single jet expelled from the leading edge of the EGV against the oncoming flow. This interaction between the wake and jet should offset or disrupt the coherency of any incoming flow structures. The second active flow control method applied to the EGV involved a tangential blowing configuration (TB) where two symmetric tangential jets were used to create an insulating fluid layer that reduced the effect of passing flow structures on the EGV. The final flow control design was the implementation of trailing edge wake filling on a three bladed rotor. A rotor was designed to ingest lower velocity flow from the hub and pump the fluid out of a blowing slot at the blade trailing edge. The blowing slot was concentrated on the outer third of the blade span in order to maximize pumping effect. In order to quantify the effects of the active flow control techniques on rotor-stator interaction, the fluctuating lift force on the EGV was measured. Since this fluctuating force serves as a primary acoustic source, the effects of the active flow control on the radiated interaction sound can be estimated. These active flow control techniques were intended for reduction of blade passing frequency tonal sound radiation. The LEB configuration showed minor changes in overall spectral response; however, there was no significant reduction in forcing at the BPF measured. Similarly the TB configuration also yielded no measurable change in BPF tonal forcing. The first generation design of the self-pumping rotor also proved to have problems. Experiments showed that the application of the flow control on the self-pumping rotor did not generate the expected increase in torque demand or changes in the tonal forcing on the EGV. Field alterations to the rotor were unable to improve the performance; therefore, the conclusion became that the initial design was unable to pump fluid due to excessive pressure losses. Further design iterations are required to perfect the functionality of the self-pumping rotor. / Master of Science

Active pneumatic flow control methods as applied to aerospace applications have shown noteworthy improvements in lift compared to traditional means. The General Aviation Circulation Control (GACC) concept currently under investigation at NASA's Langley Research Center (LaRC) is an attempt at addressing some of the fundamental obstacles related to the successful development and implementation of such techniques. The primary focus of research in the field of high lift pneumatic devices is to investigate ways of obtaining significant improvements in the lift coefficient without resorting to moving surfaces. Though it has been demonstrated that the lift coefficient can be amplified in a variety of ways, the chosen method for the current work is via enhanced circulation stemming from a trailing edge Coanda jet. A secondary objective is to reduce the amount energy expenditure used in these pneumatic techniques by implementing time-variant flow. This paper describes experimental observations of the flow behavior at the trailing edge of a modified water tunnel based supercritical airfoil model that exploits both steady and pulsed Coanda driven circulation control. A total of 10 sets of data, excluding a baseline case of no Coanda jet, were sampled with five cases each for steady and pulsed flow, the latter at a reduced frequency, f+, of 1. Two cases of equal momentum coefficient but with varying forced frequencies were isolated for further study in an attempt to accurately compare the resultant flow dynamics of each method. All measurements were taken at a zero-lift angle of attack by means of a non-invasive time accurate flow visualization technique (DPIV). Vorticity behavior was investigated using Tecplot® and a MATLAB® program was developed to quantify the Strouhal Number of time-averaged velocity fluctuations moving aft of the Coanda surface for each case. / Master of Science

Microfluidics has been the focal point of research in various disciplines due to its advantages of portability and cost effectiveness, and the ability to perform complex tasks with precision. In the past two decades microfluidic technology has been used to cool integrated circuits, for exoplanetary chemical analysis, for mimicking cellular environments, and in the design of specialized organ-on-a-chip devices. While there have been considerable advances in the complexity and miniaturization of microfluidic devices, particularly with the advent of microfluidic large-scale integration (mLSI) and microfluidic very-large-scale-integration (mVLSI), in which there are hundreds of thousands of flow channels per square centimeter on a microfluidic chip, there remains an actuation overhead problem: these small, complex microfluidic devices are tethered to extensive off-chip actuation machinery that limit their portability and efficiency. Insects, in contrast, actively and efficiently handle their respiratory air flows in complex networks consisting of thousands of microscale tracheal pathways. This work analytically and experimentally investigates the viability of incorporating some of the essential kinematics and actuation strategies of insect respiratory systems in microfluidic devices. Mathematical models of simplified individual tracheal pathways were derived and analyzed, and insect-mimetic PDMS-based valveless microfluidic devices were fabricated and tested. It was found that not only are these devices are capable of pumping fluids very efficiently using insect-mimetic actuation techniques, but also that the fluid flow direction and magnitude could be controlled via the actuation frequency alone, a feature never before realized in microfluidic devices. These results suggest that insect-mimicry may be a promising direction for designing more efficient microfluidic devices. / Ph. D. / Microfluidics or the study of fluids at the microscale has gained a lot of interest in the recent past due to its various applications starting from electronic chip cooling to biomedical diagnostic devices and exoplanetary chemical analysis. Though there has been a lot of advancements in the functionality and portability of microfluidic devices, little has been achieved in the improvement of the peripheral machinery needed to operate these devices. On the other hand insects can expertly manipulate fluids, in their body, at the microscale with the help of their efficient respiratory capabilities. In the present study we mimic some essential features of the insect respiratory system by incorporating them in microfluidic devices. The feasibility of practical application of these techniques have been tested, at first, analytically by mathematically modeling the fluid flow in insect respiratory tract mimetic microchannels and tubes and then by fabricating, testing and analyzing the functionality of microfluidic devices. The mathematical models, using slip boundary conditions, showed that the volumetric fluid flow through a trachea mimetic tube decreased with the increase in the amount of slip. Apart from that it also revealed a fundamental difference between shear and pressure driven flow at the microscale. The microfluidic devices exhibited some unique characteristic features never seen before in valveless microfluidic devices and have the potential in reducing the actuation overhead. These devices can be used to simplify the operating procedure and subsequently decrease the production cost of microfluidic devices for various applications.

A high-turning compressor stator with a unique flow control design was developed and tested. Both boundary layer suction and trailing edge blowing developed from a single supplied motive pressure source are employed on the stator. Massflow removed through boundary layer suction is added to the motive massflow, and the resulting combined flow is used for trailing edge blowing to reduce the total pressure deficit generated by the stator wake. The effectiveness of the flow control design was investigated experimentally by measuring the reduction in the total pressure loss coefficient. The experiment was conducted in a linear transonic blowdown cascade wind tunnel. The inlet Mach number for all tests was 0.79, with a Reynolds number based on stator chordlength of 2,000,000. A range of inlet cascade angles was tested to identify the useful range of the flow control design. The effect of different supply massflows represented as a percentage of the passage throughflow was also documented. Significant reductions in the total pressure loss coefficient were accomplished with flow control at low cascade angles. A maximum reduction of 65% in the baseline (no flow control) loss coefficient was achieved by using a motive massflow of 1.6% of the passage throughflow, at cascade angle of 0°. The corresponding suction and blowing massflow ratio was approximately 1:3.6. Cascade angle results near 0° showed significant reductions in the loss coefficient, while increases in the cascade angle diminished the effects of flow control. Considerable suction side separation and the presence of a leading edge shock are noticeable as the cascade angle is increased, and contribute to the losses across the stator surface. Also identified was the estimated increase in wake turning due to flow control of up to 4.5°. / Master of Science

V této diplomové práci je provedena optimalizace profilu křídla vybaveného elastickou klapkou umístěnou na horní straně profilu. Optimalizační proces je proveden s vyžitím CFD prostředků, konkrétně URANS metody. V prvních kapitolách je popsána historie vývoje křídla vybaveného pohyblivými klapkami. Práce pokračuje popisem a zdůvodněním volby numerické metody. Vytvoření geometrie a výpočetní sítě je krátce popsáno. V práci je také prezentována validace a verifikace dané výpočetní metody. Případová studie je zaměřena na profil LS(1)-0417mod vybavený 20%, 30% a 40% dlouhou, pevnou kalpkou na různých úhlech náběhu. Aerodynamická účinnost společně s proudovým polem je analyzována. Je provedena nelineární pevnostní analýza s využitím MKP programu za účelem vyhodnocení ohybové tuhosti a deformovaného tvaru elastické klapky tak, aby byly splněný podmínky nutné pro automatické vychýlení.

Road vehicles are still largely a consumer product and as such the styling of a vehicle becomes a significant factor in how commercially successful a vehicle will become. The influence of styling combined with the numerous other factors to consider in a vehicle development programme means that the optimum aerodynamic package is not possible in real world applications. Aerodynamicists are continually looking for more discrete and innovative ways to reduce the drag of a vehicle. The current thesis adds to this work by investigating the influence of active flow control devices on the aerodynamic drag of square back style road vehicles. A number of different types of flow control are reviewed and the performance of synthetic jets and pulsed jets are investigated on a simple 2D cylinder flow case experimentally. A simplified ¼ scale vehicle model is equipped with active flow control actuators and their effects on the body drag investigated. The influence of the global wake size and the smaller scale in-wake structures on vehicle drag is investigated and discussed. Modification of a large vortex structure in the lower half of the wake is found to be a dominant mechanism by which model base pressure can be influenced. The total gains in power available are calculated and the potential for incorporating active flow control devices in current road vehicles is reviewed. Due to practicality limitations the active flow control devices are currently ruled out for implementation on a road vehicle. The knowledge gained about the vehicle model wake flow topology is later used to create drag reductions using a simple and discrete passive device. The passive modifications act to support claims made about the influence of in wake structures on the global base pressures and vehicle drag. The devices are also tested at full scale where modifications to the vehicle body forces were also observed.

<p>Many flow cases in fluid dynamics face undesirable flow separation due torising static pressure on wall boundaries. This occurs e.g. due to geometry as ina highly curved turbine inlet duct or e.g. on flow control surfaces such as wingtrailing edge flaps within a certain angle of attack range. Here, flow controldevices are often used in order to enhance the flow and delay or even totallyeliminate flow separation. Flow control can e.g. be achieved by using passiveor active vortex generators (VG) that enable momentum mixing in such flows.This thesis focusses on passive VGs, represented by VG vanes that are mountedupright on the surface in wall-bounded flows. They typically have an angle ofincidence to the mean flow and, by that, generate vortex structures that in turnallow for the desired momentum mixing in order to prevent flow separation.A statistical VG model approach, developed by KTH Stockholm and FOI,the Swedish Defence Research Agency, has been evaluated computationally.Such a statistical VG model approach removes the need to build fully resolvedthree-dimensional geometries of VGs in a computational fluid dynamics mesh.Usually, the generation of these fully resolved geometries is rather costly interms of preprocessing and computations. By applying this VG model, thecosts reduce to computations without VG effects included. Nevertheless, theVG model needs to be set up in order to define the modelled VG geometry inan easy and fast preprocessing step. The presented model has shown sensitivityfor parameter variations such as the modelled VG geometry and the VG modellocation in wall-bounded zero pressure gradient and adverse pressure gradientflows on a flat plate, in a diffuser, and on an airfoil with its high-lift systemextracted. It could be proven that the VG model qualitatively describes correcttrends and tendencies for these different applications.</p>