Search results

Title: Development of Powered Resonance-tube Actuators for Aircraft Flow Control Applications
Creator: Raman, G., Mills, A., Kibens, V.
Date: 2004-12
Publisher: American Inst Aeronaut Astronaut
Description: The present paper addresses both active-flow-control actuator technology development and the demonstration of the effectiveness of actuators...
Show moreThe present paper addresses both active-flow-control actuator technology development and the demonstration of the effectiveness of actuators that could be easily integrated into practical aircraft applications. The actuator used is an adaptation of the Hartmann oscillator. Demonstration experiments that illustrate the effectiveness of this actuator include cavity tone suppression at transonic speeds and the reduction of jet-impingement tones. The actuator concept is based on a high-speed jet aimed at the mouth of a cylindrical tube closed at the other end. The result is a high-amplitude self-sustaining fluctuating field accompanied by an intense narrowband tone, all in the region between the supply jet and the resonance tube. Using unsteady pressure sensors and flow visualization, we explored the effect of varying actuator parameters such as the spacing between the power jet and the resonance tube, supply pressure, resonance-tube depth, diameter, shape, and lateral spacing. By varying the depth of the tube, the frequency could be varied from about 1.6 kHz to over 10 kHz and amplitudes as high as 156 dB (microphone location dependent) were obtained in the vicinity of actuation. To integrate this concept into practical aircraft applications, two generations of a more complex version of this device known as the powered resonance-tube bank (PRTB) were developed and demonstrated. Results indicate that by using high-frequency excitation at 5-kHz suppression levels in excess of 20 dB were consistently obtained over a range of operating conditions in both cavity and impingement flow situations. Based on our results, we have grounds to believe that a properly designed PRTB has significant advantages over conventional actuators such as acoustic, piezo, and oscillatory microstructures.
Show less

Title: VIBRATIONAL STABILIZATION OF A CHEMICAL REACTOR - AN EXPERIMENTAL-STUDY
Creator: Cinar, A., Deng, J., Meerkov, S. M., Shu, X. S.
Date: 1987-04
Publisher: IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Description: Vibrational control is a method for modification of dynamic properties of linear and nonlinear systems by introduction of fast, zero-average...
Show moreVibrational control is a method for modification of dynamic properties of linear and nonlinear systems by introduction of fast, zero-average oscillations in a system's parameters. It has been previously shown that forced oscillations introduced in the reactant flow rates to a continuous stirred tank reactor (CSTR) cause a modification of theS- shaped steady-state curve. In the present note experimental evidence is given to show that this modification leads to the operation the CSTR at an asymptotically stable periodic regime located near an unstable steady-state of the reactor system having fixed flow rates. For a given average stabilized state, such a stabilizing mechanism results in a higher production rate or lower energy expenditure compared to a steady operation with shifted input conditions.
Endnote format citation
Show less

Title: ENHANCED MIXING OF MULTIPLE SUPERSONIC RECTANGULAR JETS BY SYNCHRONIZED SCREECH
Creator: Taghavi, R, Raman, G
Date: 1994-12
Publisher: AMER INST AERONAUT ASTRONAUT

Title: FLIP-FLOP JET NOZZLE EXTENDED TO SUPERSONIC FLOWS
Creator: Raman, G, Hailye, M, Rice, Ej
Date: 1993-06
Publisher: AMER INST AERONAUT ASTRONAUT
Description: An experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic...
Show moreAn experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic to supersonic. Unsteady velocity and pressure measurements were made using hot wires, piezoresistive pressure transducers, and pitot probes. In addition, smoke flow visualization using high-speed photography was used to document the oscillation of the jet. For the subsonic flip-flop jet, it was found that the apparent time-mean widening of the jet was not accompanied by an increase in the mass flux. Fluidically oscillated jets up to a Mach number of about 0.5 have been reported before, but to our knowledge there is no information on fluidically oscillated supersonic jets. It was found that it is possible to extend the operation of these devices to supersonic flows. The streamwise velocity perturbation levels produced by this device were much higher than the perturbation levels that could be produced using conventional excitation sources such as acoustic drivers. In view of this ability to produce high amplitudes, the potential for using a small-scale fluidically oscillated jet as an unsteady excitation source for the control of shear flows in full-scale practical applications seems promising.
Show less

Title: FORCED PERIODIC CONTROL OF AN EXOTHERMIC CSTR WITH MULTIPLE INPUT OSCILLATIONS
Creator: Rigopoulos, K., Shu, X. S., Cinar, A.
Date: 1988-12
Publisher: AMER INST CHEMICAL ENGINEERS
Description: Interaction among various oscillating inputs may result in significant modifications in the behavior of a system under forced periodic control...
Show moreInteraction among various oscillating inputs may result in significant modifications in the behavior of a system under forced periodic control. Forced oscillations in the input flow rate and input concentrations of an exothermic continuous stirred tank reactor enable the stabilized operation of the CSTR in the unstable steady state region. Reactor temperature oscillations under forced periodic control are similar to the oscillations resulting from proportional-integral feedback or nonlinear (push-pull) feedback control, and under some operating conditions the oscillation amplitude is significantly lower. Theoretical and experimental studies illustrate the effects of forcing frequency and phase shift on reactor behavior.
Endnote format citation
Show less

Title: Gerry-meandering: An Assessment of the Congressional District Model of Depository Allocation (preprint): AhrensGriffinfinalpreprint
Creator: Ahrens, Aric G., Griffin, Luke A.
Date: 2003-06
Description: The preprint of a published article dealing with the effect of allocating Federal Depositories by Congressional district. Conclusions drawn...
Show moreThe preprint of a published article dealing with the effect of allocating Federal Depositories by Congressional district. Conclusions drawn include the fact that due to redistricting that occurs after each decennial census, over time some districts may have within their boundaries a greater number than the two depositories that Congressional district allocation was intended to produce. Likewise, over time shifting boundaries of districts have created districts that have no depositories whatsoever.
Show less

Title: THE BIFURCATION BEHAVIOR OF AN AUTOTHERMAL PACKED-BED TUBULAR REACTOR
Creator: Adomaitis, R. A., Cinar, A.
Date: 1988
Publisher: PERGAMON-ELSEVIER SCIENCE LTD
Description: The analysis of a chemical reactor by numerical bifurcation techniques can completely define the multiplicity and stability of its equilibrium...
Show moreThe analysis of a chemical reactor by numerical bifurcation techniques can completely define the multiplicity and stability of its equilibrium states and can give insights into the reactor's parametric sensitivity and dynamical behavior in the neighborhood of the chosen operating points. In this paper, we will present some of the numerical bifurcation techniques used and developed in analyzing an autothermal packed bed tubular reactor. The bifurcation behavior found will be cataloged over the range of relevant reactant inlet conditions, and an explanation for the isolated solution branches characteristic of this reactor will also be presented.
Endnote format citation
Show less

Title: DISTURBANCE GROWTH TRIGGERED BY STEADY HEATING OF A JETS NOZZLE EXIT BOUNDARY-LAYER
Creator: Cornelius, D, Raman, G
Date: 1995-10
Publisher: AMER INST PHYSICS
Description: Experiments were conducted to investigate how heating only the nozzle exit boundary layer of an axisymmetric jet, with an unheated potential...
Show moreExperiments were conducted to investigate how heating only the nozzle exit boundary layer of an axisymmetric jet, with an unheated potential core, affects disturbance growth in the initial shear layer. The exit boundary layer had a minimum density ratio of 0.74, was laminar, and had a constant momentum thickness (theta) for all levels of nozzle heating used in this study. The fluctuating velocity (u') and temperature (t') in the exit boundary layer increased monotonically with increasing nozzle temperature. Low-amplitude acoustic excitation produced a more rapid growth of coherent velocity fluctuations for the heated case than for the unheated. (C) 1995 American Institute of Physics.
Show less

Title: A morphologically structured model for penicillin production
Creator: Birol, G., Undey, C., Parulekar, S. J., Cinar, A.
Date: 2002-03-05
Publisher: JOHN WILEY & SONS INC
Description: A morphologically structured model is proposed to describe penicillin production in fed-batch cultivations. The model accounts for the effects...
Show moreA morphologically structured model is proposed to describe penicillin production in fed-batch cultivations. The model accounts for the effects of dissolved oxygen on cell growth and penicillin production and variations in volume fractions of abiotic and biotic phases due to biomass formation. Penicillin production is considered to occur in the subapical hyphal cell compartment and to be affected by availability of glucose and oxygen. As it stands, the model provides a wide range of applicability in terms of operating conditions. The model has been tested for various conditions and has given satisfactory results. A series of glucose feeding profiles have been considered to demonstrate the capabilities of the proposed model. It is concluded that the model may be valuable for the interpretation of experimental data collected specifically for metabolic flux analysis during fed-batch cultivation because the elements of measured specific production rates are determined from measurements of the concentrations of the components and their mass balances. The proposed model may be further used for developing control strategies and model order reduction algorithms
Endnote format citation for DOI:10.1002/bit.10115
Show less

Title: Flow characteristics of a rectangular multielement supersonic mixer-ejector
Creator: Taghavi, R, Raman, G
Date: 1996-04
Publisher: SPRINGER VERLAG
Description: This study describes a technique that combines the benefits of focusing schlieren and phase conditioning. Focusing schlieren blurs and drops...
Show moreThis study describes a technique that combines the benefits of focusing schlieren and phase conditioning. Focusing schlieren blurs and drops contrast of non-critical features whereas phase conditioning emphasizes periodic flow features, and their combination produces unique results. The supersonic jets that we studied produced an intense tone referred to as screech. The measured screech tone signal was used as input to the phase conditioning circuit that adjusted the strobing light source to the vertical synchronization pulse of a CCD camera. The sharp video images obtained by this technique could either be frozen or continuously swept through one period of screech to acquire a slow motion video record of the jet unsteadiness. Two cases were visualized in this study: first, an underexpanded jet from a convergent rectangular nozzle at various fully expanded Mach numbers. Second, a supersonic jet emerging from a convergent-divergent rectangular nozzle at a design Mach number of 1.4, artificially excited by impingement tones. The results of this study illustrate the usefulness of this system in visualizing oscillatory flows.
Show less

Title: Intelligent process monitoring by interfacing knowledge-based systems and multivariate statistical monitoring
Creator: Norvilas, A., Negiz, A., Decicco, J., Cinar, A.
Date: 2000-08
Publisher: ELSEVIER SCI LTD
Description: An intelligent process monitoring and fault diagnosis environment has been developed by interfacing multivariate statistical process...
Show moreAn intelligent process monitoring and fault diagnosis environment has been developed by interfacing multivariate statistical process monitoring (MSPM) techniques and knowledge-based systems (KBS) for monitoring multivariable process operation. The real-time KBS developed in G2 is used with multivariate SPM methods based on canonical variate stare space (CVSS) process models. Fault detection is based on T-2 charts of state variables. Contribution plots in G2 are used for determining the process variables that have contributed to the out-of-control signal indicated by large T-2 values, and G2 Diagnostic Assistant (GDA) is used to diagnose the source causes of abnormal process behavior. The MSPM modules developed in Matlab are linked with G2. This intelligent monitoring and diagnosis system can be used to monitor multivariable processes with autocorrelated, cross-correlated, and collinear data. The structure of the integrated system is described and its performance is illustrated by simulation studies.
Endnote format citation
Show less

Title: Statistical process monitoring and disturbance diagnosis in multivariable continuous processes
Creator: Raich, A., Cinar, A.
Date: 1996-04
Publisher: AMER INST CHEMICAL ENGINEERS
Description: Detecting out-of-control status and diagnosing disturbances leading to the abnormal process operation early are crucial in minimizing product...
Show moreDetecting out-of-control status and diagnosing disturbances leading to the abnormal process operation early are crucial in minimizing product quality variations Multivariate statistical techniques are used to develop detection methodology for abnormal process behavior and diagnosis of disturbances causing poor process performance. Principal components and discriminant analysis ave applied to quantitatively describe and interpret step, ramp and random-variation disturbances. All disturbances require high-dimensional models for accurate description and cannot be discriminated by biplots. Diagnosis of simultaneous multiple faults is addressed by building quantitative measures of overlap between models of single faults and their combinations. These measures are used to identify the existence of secondary disturbances and distinguish their components. The methodology is illustrated by monitoring the Tennessee Eastman plant simulation benchmark problem subjected to different disturbances. Most of the disturbances can be diagnosed correctly, the success rate being higher for step and vamp disturbances than random-variation disturbances.
Endnote format citation
Show less

Title: Reversal in Spreading of a Tabbed Circular Jet Under Controlled Excitation
Creator: Zaman, Kbmq, Raman, G.
Date: 1997-12
Publisher: American Inst Physics
Description: Detailed flow field measurements have been carried out for a turbulent circular jet perturbed by tabs and artificial excitation. Two ''delta...
Show moreDetailed flow field measurements have been carried out for a turbulent circular jet perturbed by tabs and artificial excitation. Two ''delta tabs'' were placed at the nozzle exit at diametrically opposite locations. The excitation condition involved subharmonic resonance that manifested in a periodic vortex pairing in the near flow field. While the excitation and the tabs independently increased jet spreading, a combination of the two diminished the effect. The jet spreading was most pronounced with the tabs but was reduced when excitation was applied to the tabbed jet. The tabs generated streamwise vortex pairs that caused a lateral spreading of the jet in a direction perpendicular to the plane containing the tabs. The excitation, on the other hand, organized the azimuthal vorticity into coherent ring structures whose evolution and pairing also increased entrainment by the jet. In the tabbed case, the excitation produced coherent azimuthal structures that were distorted and asymmetric in shape. The self-induction of these structures produced an effect that opposed the tendency for the lateral spreading of the streamwise vortex pairs. The passage of the distorted vortices, and their pairing, also had a cancellation effect on the time-averaged streamwise vorticity field. These led to the reduction in jet spreading. [S1070-6631(97)03012-2].
Show less

Title: Fault detection and diagnosis in a food pasteurization process with hidden Markov models
Creator: Tokatli, F., Cinar, A.
Date: 2004-12
Publisher: CANADIAN SOC CHEMICAL ENGINEERING
Description: Hidden Markov Models (HMM) are used to detect abnormal operation of dynamic processes and diagnose sensor and actuator faults. The method is...
Show moreHidden Markov Models (HMM) are used to detect abnormal operation of dynamic processes and diagnose sensor and actuator faults. The method is illustrated by monitoring the operation of a pasteurization plant and diagnosing causes of abnormal operation. Process data collected under the influence of faults of different magnitude and duration in sensors and actuators are used to illustrate the use of HMM in the detection and diagnosis of process faults. Case studies with experimental data from a high-temperature-short-time pasteurization system showed that HMM can diagnose the faults with certain characteristics such as fault duration and magnitude.
Endnote format citation
Show less

Title: Pressure Sensitive Paint Demonstrates Relationship Between Ejector Wall Pressure and Aerodynamic Performance
Creator: Taghavi, R., Raman, G., Bencic, T.
Date: 1999-05
Publisher: Springer Verlag
Description: This paper provides an example of the application of Pressure Sensitive Paint (PSP) to complex internal suspersonic flows and demonstrates the...
Show moreThis paper provides an example of the application of Pressure Sensitive Paint (PSP) to complex internal suspersonic flows and demonstrates the relationship between ejector wall pressure and aerodynamic performance. Details of such jet mixer-ejector nozzles are relevant to jet noise reduction programs. Several ejector configurations with straight, convergent, and divergent side walls were used in our experiments. The side-wall that was painted with PSP was also instrumented with an array of 156 pressure taps connected to Electronically Scanned Pressure (ESP) modules, enabling simultaneous measurement of "true" reference pressures. The PSP results agreed very well with the "true" reference pressures and also provided a detailed map of the complicated pressure patterns that could not be detected using the pressure taps. Finally, we also demonstrated the direct relationship between ejector side-wall pressure distribution and ejector performance characteristics such as exit mean flow uniformity, pumping, and thrust augmentation.
Show less

Title: Aeroacoustic Characteristics of a Rectangular Multi-element Supersonic Jet Mixer-ejector Nozzle
Creator: Taghavi, R., Raman, G.
Date: 1997-10-23
Publisher: Academic Press Ltd
Description: This paper provides a unique, detailed evaluation of the acoustics and aerodynamics of a rectangular multi-element supersonic jet mixer...
Show moreThis paper provides a unique, detailed evaluation of the acoustics and aerodynamics of a rectangular multi-element supersonic jet mixer-ejector noise suppressor. The performance of such mixer-ejectors is important in aircraft engine applications for noise suppression and thrust augmentation. In contrast to most prior experimental studies on ejectors that reported either aerodynamic of acoustic data, the present work documents both types of data. Information on the mixing, pumping, ejector wall pressure distribution, thrust augmentation and noise suppression characteristics of four simple, multi-element, jet mixer-ejector configurations is presented. The four configurations included the effect of ejector area ratio (AR = ejector cross-sectional area/total primary nozzle area) and the effect of non-parallel ejector walls. The configuration that produced the best noise suppression characteristics has also been studied in detail. The present results show that ejector configurations that produced the maximum pumping (secondary (induced) flow normalized by the primary flow) also exhibited the lowest wall pressures in the inlet region, and the maximum thrust augmentation. When cases having the same total mass flow were compared, one found that noise suppression trends corresponded with those for pumping (per unit secondary area). Surprisingly, the mixing (quantified by the peak Mach number, and flow uniformity) at the ejector exit exhibited no relationship to the noise suppression at moderate primary jet fully expanded M-j (the Mach number that would have been attained under isentropic expansion). However, the noise suppression dependence on the mixing was apparent at M-j = 1.6. The above observations are justified by noting that the mixing at the ejector exit is not a strong factor in determining the radiated noise when noise produced internal to the ejector dominates the noise field outside the ejector. (C) 1997 Academic Press Limited.
Show less

Title: Measuring complexity in reactor networks with cubic autocatalytic reactions
Creator: Tatara, E., Birol, I., Cinar, A., Teymour, F.
Date: 2005-04-13
Publisher: AMER CHEMICAL SOC
Description: Systems with high steady-state multiplicity and rich dynamic behavior are difficult to investigate using conventional reductionist methods. A...
Show moreSystems with high steady-state multiplicity and rich dynamic behavior are difficult to investigate using conventional reductionist methods. A network of more than five reactors hosting cubic autocatalytic reactions may potentially have more than 101 steady states and many distinct dynamic regimes, all for the same parameter set. This paper discusses how the static complexity of such systems can be measured to give a holistic picture. To achieve this, stochastic simulations were performed to statistically determine the bifurcation structure of the system, and the gathered information is summarized using a measure akin to fractal dimension. With this measure, the growth of static complexity is investigated as a function of the network size.
Endnote format citation for DOI:10.1021/ie049246t
Show less

Title: Coupling of Twin Rectangular Supersonic Jets
Creator: Raman, G., Taghavi, R.
Date: 1998-01-10
Publisher: Cambridge Univ Press
Description: Twin jet plumes on aircraft can couple, producing dynamic pressures significant enough to cause structural fatigue. For closely spaced jets...
Show moreTwin jet plumes on aircraft can couple, producing dynamic pressures significant enough to cause structural fatigue. For closely spaced jets with a moderate aspect ratio (e.g. 5), previous work has established that two coupling modes (antisymmetric and symmetric) are kinematically permissible. However, the dynamics of twin-jet coupling have remained unexplored. In this paper a more fundamental assessment of the steady and unsteady aspects of twin-jet coupling is attempted. While we document and discuss the nozzle spacings and Mach numbers over which phase-locked coupling occurs, our concentration is much more on answering the following questions: (a) What mechanism causes the jets to couple in one mode or the other? (b) Why do the jets switch from one mode to another? (c) Are the two modes mutually exclusive or do they overlap at the transition point? Our results reveal, among many things, the following. (i) For very closely spaced twin jets in the side-by-side configuration phased feedback based on source to nozzle exit distance of adjacent jets does not fully explain the coupling modes. However, the 'null' phase regions surrounding the jets where the phase of an acoustic wavefront (arriving from downstream) does not vary appears to correlate well with the existence of the symmetric mode. When the 'null' regions of adjacent jets do not overlap antisymmetric coupling occurs and when they do overlap the jets couple symmetrically. We provide a simple correlation using a parameter (a) that can be used as a simple test to determine the mode of coupling. (ii) The switch from the antisymmetric to the symmetric mode of coupling appears to occur because of an abrupt shift in the effective screech source from the third to the fourth shock, which in turn causes the 'null' phase region surrounding the jets to grow abruptly and overlap. (iii) The two modes are mutually exclusive. Our results provide considerable insight into the twin-jet coupling problem and offer hope for designing twin-jet configurations that minimize damage to aircraft components.
Show less

Title: Modeling, monitoring and control strategies for high temperature short time pasteurization systems - 1. Empirical model development
Creator: Negiz, A., Ramanauskas, P., Cinar, A., Schlesser, J. E., Armstrong, D. J.
Date: 1998-02
Publisher: ELSEVIER SCI LTD
Description: Dynamic models of high temperature short time (HTST) pasteurization systems can be developed by using empirical model development paradigms...
Show moreDynamic models of high temperature short time (HTST) pasteurization systems can be developed by using empirical model development paradigms such as transfer functions and times series models. Properly designed experiments that excite all output variables provide good data that enable the development of accurate dynamic models. These models are used in feedback control and statistical process monitoring system design. The methodology for time series model development for HTST pasteurization processes is illustrated by using data collected from a pilot scale HTST pasteurization system.
Endnote format citation
Show less

Title: Innovative Actuators for Active Flow and Noise Control
Creator: Cain, A. B., Raman, G.
Date: 2002
Publisher: Professional Engineering Publishing Ltd
Description: Active flow control (AFC) has the potential to improve the efficiency of systems that involve both internal and external fluid flow. The...
Show moreActive flow control (AFC) has the potential to improve the efficiency of systems that involve both internal and external fluid flow. The primary driver in AFC is the expectation that the control will result in significant performance benefits at the system level with all trade-offs factored in. Successful application to aircraft systems can produce lighter, stealthier, agile aircraft with increased range, payload and a muffled acoustic signature. The design of an AFC system requires knowledge of flow phenomena and the selection of appropriate actuators, sensors and a control algorithm. The present overview focuses on actuators. Examples of flow and noise control presented here are restricted to open-loop systems. Various aspects of actuator utilization include actuator output characterization, exploiting resonances (plenum, structural or aeroacoustic) to enhance actuator amplitude and the different modes of actuation. A brief description of a high-bandwidth actuator is also provided, followed by a variety of application examples including edgetone suppression, cavity noise suppression, impingement noise suppression and jet mixing enhancement. The review concludes with a description of the successful application of AFC to the exhaust plume from an aircraft engine (JT8D).
Show less

repository.iit

Search the repository

Pages

Pages

Enabled Filters

Refine Results

Type

Date

Academic status of creator

Department

Subject

Creator

Part of