bluuebunny/crossref_metadata_2025 huggingface dataset:
OPTIMIZATION OF DECENTRALIZED PI/PID CONTROLLERS BASED ON GENETIC ALGORITHM
Authors: Li Donghai , Gao Furong , Xue Yali , Lu Chongde
Published: September 2010

In this paper, an optimization method of tuning decentralized PI/PID controllers based on genetic algorithms is presented. First, the existence of decentralized PI controllers with integrity is examined. Then, stable regions of each PI/PID controller parameters are calculated as the feasible area to be exploited, and the optimal PI/PID controllers are obtained by using a real‐coded genetic algorithm with elitist strategy, to meet the design specifications for the whole control system. The proposed method is applied to six examples from literature. Simulation results demonstrate that the proposed decentralized PI control is compatible to the referenced method while the decentralized PID control is better than the referenced method, and the proposed method is feasible for more complicated control systems optimizations.
SLIDING MODE PREDICTION TRACKING CONTROL DESIGN FOR UNCERTAIN SYSTEMS
Authors: Xiao Lingfei , Su Hongye , Chu Jian
Published: September 2010

In this paper, a tracking control algorithm based on sliding mode prediction for a class of discrete‐time uncertain systems is presented. By creating a special model to predict the future sliding mode function value and by combining feedback correction and receding horizon optimization approaches, which are extensively applied in predictive control strategy, a discrete‐time sliding mode control law for tracking problem is constructed. With the designed control law, closed‐loop systems have strong robustness to matched or unmatched uncertainties as they eliminate chattering. Besides, in the robustness analysis, the boundary condition for uncertainties, which is a universal presupposition in sliding mode control method, is not required. Numerical simulation and cart‐pendulum experiment results illustrate the validity of the proposed algorithm.
ROBUST OBSERVER DESIGN FOR THERMOACOUSTIC DYNAMICS WITH DISTRIBUTED‐DELAY HEAT INPUT
Authors: Hong Boe‐Shong , Lin Tsu‐Yu
Published: September 2010

This paper develops a strategy for the design of robust observers upon thermoacoustic dynamics with both spatial and temporal dimension‐infiniteness, model‐truncation error and exogenous disturbance. It helps the identification of their assumed flame dynamics that is feedback‐interconnected with the thermoacoustic dynamics in a combustion chamber and is usually to‐be‐identified. This paper formulates the proceedings to the proposed strategy and performs numerical tests for such a strategy.
SLIDING SURFACE MATCHED CONDITION IN SLIDING MODE CONTROL
Authors: Xiang Ji , Su Hongye , Chu Jian , Wei Wei
Published: September 2010

In this paper, the recently developed sliding surface matching condition (SSMC) is viewed from a new point that the mismatched uncertain term should satisfy the minimum‐phase condition for the nominal system. With this new viewpoint, SSMC is extended to a more general class of system with nonlinear uncertainties. Finally, a numerical example demonstrates the developed results.
ROBUST H∞ CONTROL AND QUADRATIC STABILIZATION OF DISCRETE‐TIME SWITCHED SYSTEMS WITH NORM‐BOUNDED TIME‐VARYING UNCERTAINTIES
Authors: Ji Zhijian , Guo Xiaoxia , Wang Long , Xie Guangming
Published: September 2010

We focus on robust H∞ control analysis and synthesis for discretetime switched systems with norm‐bounded time‐varying uncertainties. Sufficient conditions are derived to guarantee quadratic stability along with a prescribed H∞‐norm bound. Each of them can be dealt with as a linear matrix inequality (LMI) which can be tested with efficient algorithms. All the switching rules are constructively designed, and do not rely on any uncertainties.
ABSOLUTE STABILITY AND APPLICATION TO DESIGN OF OBSERVER‐BASED CONTROLLER FOR NONLINEAR TIME‐DELAY SYSTEMS
Authors: Hamed Bassem Ben , Abdallah Abdallah Ben , Chaabane Mohamed
Published: September 2010

In this paper we present a new sufficient condition for absolute stability of delay Lure system. This condition improves the one given in [1]. We use this new criterion to construct an observer‐based control for a class of nonlinear time‐delay systems. Some examples are given to illustrate the results of this paper.
STRONG STABILIZATION OF MIMO SYSTEMS: A PROJECTION APPROACH
Authors: Saif Abdul‐Wahid A.
Published: September 2010

In this paper, the strong stabilization problem of multivariable linear time‐invariant systems is considered. The approach is based on state‐space stable projection. The formulation is reduced to find a full rank constant output feedback. The computations involved are simpler than other methods.
UNKNOWN INPUTS OBSERVERS DESIGN FOR DELAY SYSTEMS
Authors: Darouach M.
Published: September 2010

This paper concerns the design of functional, reduced and full order observers for linear time delay systems with unknown inputs. A new method generalizing those existing in the literature is presented for systems with unknown inputs, these unknown inputs are present in both the state and the measurement equations. Conditions for the existence of these observers are given and sufficient conditions for the stability independent of delays are derived using linear matrix‐inequality (LMI) formulation. The independent of internal delay and independent of delay cases are also presented. A numerical example is presented to illustrate our approach.
MULTI‐HOPPING INDUCED GAIN SCHEDULING FOR WIRELESS NETWORKED CONTROLLED SYSTEMS
Authors: Nikolakopoulos George , Panousopoulou Athanasia , Tzes Anthony , Lygeros John
Published: September 2010

A multi‐hopping induced gain scheduler for Wireless Networked Controlled Systems (WiNCS) is proposed. The control scheme is based on a client‐server architecture. The data packets are assumed to be carried over a network composed of wireless sensor nodes running the 802.11b protocol. The number of hops necessary for packets to reach their destinations is variable and depends on current traffic conditions. Changes in the number of hops induces changes in the latency times introduced by the communication network in the feedback loop. To deal with these changes an LQR‐output feedback scheme is introduced, whose parameters are adjusted according to the number of the hops. The weights of the LQR controllers are subsequently tuned using LMIs to ensure a prescribed stability margin despite the variable latency times. The overall scheme resembles a gain scheduled controller with the number of hops playing the role of the scheduling parameter. Simulation results on the NS‐2 simulator are provided to highlight the efficacy of the proposed scheme.
DESIGN OF REDUCED‐ORDER STATE/UNKNOWN INPUT OBSERVERS BASED ON A DESCRIPTOR SYSTEM APPROACH
Authors: Fernando T. , Trinh H.
Published: September 2010

This paper solves the problem of estimating simultaneously a linear function of the state and unknown input of linear systems with unknown inputs. Here, the problem is conveniently solved by using the descriptor system approach. The observers proposed in this paper are of low‐order and do not include derivatives of the outputs. Conditions for the existence of reduced‐order observers are derived. Based on the newly derived existence conditions, a step‐by‐step design procedure is given. A numerical example is given to illustrate the attractiveness and simplicity of the design procedure.
PID TUNING FOR DOMINANT POLES AND PHASE MARGIN
Authors: Tang Wei , Wang Qing‐Guo , Ye Zhen , Zhang Zhiping
Published: September 2010

A simple PID tuning method for dominant pole placement and phase margin specification is proposed in this paper. Time domain specifications as settling time and percentage overshoot are represented by a pair of dominant poles, which is combined with phase margin specification to achieve closed‐loop stability and robustness. A graphical method is developed to determine PID settings to meet these specifications simultaneously. An example is given for illustration.
ROBUST OUTPUT FEEDBACK GUARANTEED COST CONTROL FOR 2‐D UNCERTAIN STATE‐DELAYED SYSTEMS
Authors: Peng Dan , Guan Xinping , Long Chengnian
Published: September 2010

This paper considers the robust guaranteed cost control problem of two‐dimensional (2‐D) state‐delayed systems. First, the definition of guaranteed cost matrix is proposed and an upper bound of the cost function is given. Then, the guaranteed cost control problem is resolved. Furthermore, the minimum upper bound of the closed‐loop cost function is obtained by solving an optimization problem with LMIs' constraints. A numerical example demonstrates the effectiveness of our results.
VOLTAGE REGULATION OF A BUCK BOOST CONVERTER—A HYBRID CONTROL APPROACH
Authors: Sreekumar C. , Agarwal Vivek
Published: September 2010

In this paper, the output voltage regulation problem in a buck boost converter is defined as a hybrid control problem. For control design, the mutually interacting continuous and discrete dynamics are modeled as a hybrid automaton. Thus, the control problem is defined as a guard selection problem of the hybrid automaton. The system trajectory is switched between different modes based on the guards to achieve the required voltage regulation. The guards defined are fixed surfaces represented in terms of the state variables for a given operating condition. The logic‐based switching in the state plane is stable in terms of the chaotic and bifurcation behavior. The effectiveness of the control scheme for buck and boost operation under line and load disturbances is demonstrated by simulation in the MATLAB‐SIMULINK environment and the results are presented.
COMPARISON OF FLIGHT CONTROL SYSTEM DESIGN METHODS IN LANDING
Authors: Sadati S. H. , Parvar M. Sabzeh , Menhaj M. B.
Published: September 2010

Intelligent control theory usually involves the subjects of neural control and fuzzy logic control. The great potential of intelligent control in control designs has recently been realized in the literature. In this survey paper, we attempt to employ this subject and provide the reader with an overview of related topics, such as conventional, fuzzy logic‐based, neural net‐based adaptive control techniques. Practical control schemes realistically applicable in the area of control system design are introduced. The control laws are demonstrated on a three‐degree‐of‐freedom simulation with linearized aerodynamic and engine models. This paper deals the issue of aircraft landing maneuvers. Generally this part of flight needs to be strongly assisted by human pilot.
Autophagy protects against human islet amyloid polypeptide‐associated apoptosis
Authors: Morita Shuhei , Sakagashira Setsuya , Shimajiri Yoshinori , Eberhardt Norman L , Kondo Toshikazu , Kondo Tomoyoshi , Sanke Tokio
Published: September 2010

Aims/Introduction:  Islets in type 2 diabetes are characterized by deposition of islet amyloid polypeptide (IAPP) as well as β‐cell dysfunction. The unique amyloidogenic character of human (h)IAPP is associated with cytotoxicity. Autophagy is a ubiquitous system of cellular recycling that contributes to cell survival. Thus, we examined whether autophagy could ameliorate hIAPP‐associated cytotoxicity.

Materials and Methods:  First, we used a COS‐1 cell model, lacking endogenous IAPP that might affect cytotoxicity related to exogenous hIAPP. Next, we used the mouse β‐cell line, MIN‐6 cells. Both cells were transfected with hIAPP or rat (r)IAPP expression constructs, or transfected with bicistronic vectors expressing green fluorescent protein (GFP) and either hIAPP or rIAPP for flow cytometry analysis. Cell viability and apoptosis markers were studied in relation to chemical or genetic modulation of autophagy.

Results:  The viability of cells expressing hIAPP was significantly decreased as compared with those expressing rIAPP and the cleavage of pro‐caspase‐3 was elevated in hIAPP‐transfected cells. The formation of autophagosomes and the conversion of microtubule‐associated protein light chain 3B I to II were elevated in hIAPP‐expressing cells. The viability of hIAPP‐expressing cells was increased after treatment with rapamycin, an inducer of autophagy, and decreased after treatment with 3‐methyladenine, an inhibitor of autophagy. In MIN‐6 cells, annexin positive cells were increased by 3‐methyladenine and decreased by rapamycin using flow cytometry. Knocking down of the autophagy protein 5 gene decreased hIAPP‐transfected cell viability.

Conclusions:  Autophagy is co‐localized with hIAPP expression and it plays a protective role in hIAPP‐associated apoptosis. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00065.x, 2010)
Replacement of neutral protamine Hagedorn insulin with the long‐acting insulin analogue, detemir, improves glycemic control without weight gain in basal–bolus insulin therapy in Japanese patients with type 1 diabetes
Authors: Hayakawa Taro , Ishii Michiyo , Watanabe Megumi , Iwase Hiroya , Nishimura Asako , Monden Takako , Kamiuchi Kenji , Isono Motohide , Shibata Nobuhito
Published: September 2010

Aims/Introduction:  The aim of the present study was to evaluate the efficacy of replacing neutral protamine Hagedorn insulin (NPH) with the long‐acting insulin analogue, detemir, in clinical practice.

Materials and Methods:  We carried out a retrospective study to compare the effects of replacing NPH with detemir in basal–bolus insulin therapy in Japanese patients with type 1 diabetes. A total of 19 patients were enrolled in the study, and changes in hemoglobin A1c (HbA1c), insulin dose, bodyweight, fasting blood glucose levels (FBG), within‐patient variability in FBG and prevalence in hypoglycemia were monitored for 12 weeks before replacement and during three periods after replacement; 1–12 weeks (period 1), 13–24 weeks (period 2) and 25–36 weeks (period 3).

Results:  HbA1c values improved significantly in periods 2 and 3. Despite the total insulin dose remaining unchanged throughout the study, the basal insulin dose increased from 0.24 to 0.27 IU/kg/day in period 2 and 0.28 IU/kg/day in period 3. Bodyweight decreased from 61.8 to 60.8 kg in period 1, whereas FBG improved throughout the study. Within‐patient variability in FBG was lower with detemir treatment than with NPH, despite the number of hypoglycemic episodes increasing significantly after replacement.

Conclusions:  These findings show that the weight loss observed in patients was independent of the reduction in calorie intake resulting from less frequent hypoglycemic attacks. In Japanese patients with diabetes who received NPH, replacing NPH with detemir led to improvements in glycemic control without any weight gain. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00066.x, 2010)
Hydranencephaly in a foal
Authors: Baiker K. , Saunders N. , Summers B. A. , Piercy R. J. , Smith K.
Published: September 2010

Hydranencephaly is well recognised in several domestic animals, especially ruminants, but is virtually unknown in the horse. This case report describes a premature filly foal that on the day of delivery was found with a severe neurological disorder that initially improved but then progressively worsened. The foal was subjected to euthanasia on humane grounds andpost mortemexamination revealed somewhat asymmetric but bilateral destruction of the telencephalon identified as hydranencephaly. The possible causes of hydranencephaly in foals are discussed.
Stromatoxin‐sensitive, heteromultimeric Kv2.1/Kv9.3 channels contribute to myogenic control of cerebral arterial diameter
Authors: Zhong Xi Zoë , Abd‐Elrahman Khaled S. , Liao Chiu‐Hsiang , El‐Yazbi Ahmed F. , Walsh Emma J. , Walsh Michael P. , Cole William C.
Published: September 2010

Cerebral vascular smooth muscle contractility plays a crucial role in controlling arterial diameter and, thereby, blood flow regulation in the brain. A number of K+ channels have been suggested to contribute to the regulation of diameter by controlling smooth muscle membrane potential (Em) and Ca2+ influx. Previous studies indicate that stromatoxin (ScTx1)‐sensitive, Kv2‐containing channels contribute to the control of cerebral arterial diameter at 80 mmHg, but their precise role and molecular composition were not determined. Here, we tested if Kv2 subunits associate with ‘silent’ subunits from the Kv5, Kv6, Kv8 or Kv9 subfamilies to form heterotetrameric channels that contribute to control of diameter of rat middle cerebral arteries (RMCAs) over a range of intraluminal pressure from 10 to 100 mmHg. The predominant mRNAs expressed by RMCAs encode Kv2.1 and Kv9.3 subunits. Co‐localization of Kv2.1 and Kv9.3 proteins at the plasma membrane of dissociated single RMCA myocytes was detected by proximity ligation assay. ScTx1‐sensitive native current of RMCA myocytes and Kv2.1/Kv9.3 currents exhibited functional identity based on the similarity of their deactivation kinetics and voltage dependence of activation that were distinct from those of homomultimeric Kv2.1 channels. ScTx1 treatment enhanced the myogenic response of pressurized RMCAs between 40 and 100 mmHg, but this toxin also caused constriction between 10 and 40 mmHg that was not previously observed following inhibition of large conductance Ca2+‐activated K+ (BKCa) and Kv1 channels. Taken together, this study defines the molecular basis of Kv2‐containing channels and contributes to our understanding of the functional significance of their expression in cerebral vasculature. Specifically, our findings provide the first evidence of heteromultimeric Kv2.1/Kv9.3 channel expression in RMCA myocytes and their distinct contribution to control of cerebral arterial diameter over a wider range of Em and transmural pressure than Kv1 or BKCa channels owing to their negative range of voltage‐dependent activation.
Monosynaptic excitatory inputs to spinal lamina I anterolateral‐tract‐projecting neurons from neighbouring lamina I neurons
Authors: Luz Liliana L. , Szucs Peter , Pinho Raquel , Safronov Boris V.
Published: September 2010

Spinal lamina I receives nociceptive primary afferent input to project through diverse ascending pathways, including the anterolateral tract (ALT). Large projection neurons (PNs) form only a few per cent of the cell population in this layer, and little is known about their local input from other lamina I neurons. We combined single‐cell imaging in the isolated spinal cord, paired recordings, 3‐D reconstructions of biocytin‐labelled neurons and computer simulations to study the monosynaptic input to large ALT‐PNs from neighbouring (somata separated by less than 80 μm) large lamina I neurons. All 11 connections identified were excitatory. We have found that an axon of a presynaptic neuron forms multiple synapses on an ALT‐PN, and both Ca2+‐permeable and Ca2+‐impermeable AMPA receptors are involved in transmission. The monosynaptic EPSC latencies (1–12 ms) are determined by both post‐ and presynaptic factors. The postsynaptic delay, resulting from the electrotonic EPSC propagation in the dendrites of an ALT‐PN, could be 4 ms at most. The presynaptic delay, caused by the spike propagation in a narrow highly branched axon of a local‐circuit neuron, can be about 10 ms for neighbouring ALT‐PNs and longer for more distant neurons. In many cases, the EPSPs evoked by release from a lamina I neuron were sufficient to elicit a spike in an ALT‐PN. Our data show that ALT‐PNs can receive input from both lamina I local‐circuit neurons and other ALT‐PNs. We suggest that lamina I is a functionally interconnected layer. The intralaminar network described here can amplify the overall output from the principal spinal nociceptive projection area.
Attenuated exercise induced hyperaemia with age: mechanistic insight from passive limb movement
Authors: McDaniel John , Hayman Melissa A. , Ives Steve , Fjeldstad Anette S. , Trinity Joel D. , Wray D. Walter , Richardson Russell S.
Published: September 2010

The influence of age on the central and peripheral contributors to exercise‐induced hyperaemia is unclear. Utilizing a reductionist approach, we compared the peripheral and central haemodynamic responses to passive limb movement (exercise without an increase in metabolism) in 11 old (71 ± 9 years of age s.d.) and 11 young (24 ± 2 years of age) healthy subjects. Cardiac output (CO), heart rate (HR), stroke volume (SV), mean arterial pressure (MAP), and femoral blood flow of the passively moved and control legs were evaluated second‐by‐second during 2 min of passive knee extension at a rate of 1 Hz. Compared to the young, the old group exhibited a significantly attenuated increase in HR (7 ± 4%vs. 13 ± 7%s.d.), CO (10 ± 6%vs. 18 ± 8%) and femoral blood flow in the passively moved (123 ± 55%vs. 194 ± 57%) and control legs (47 ± 43%vs. 77 ± 96%). In addition, the change in vascular conductance in the passively moving limb was also significantly attenuated in the old (2.4 ± 1.2 ml min−1 mmHg−1) compared to the young (4.3 ± 1.7 ml min−1 mmHg−1). In both groups all main central and peripheral changes that occurred at the onset of passive knee extension were transient, lasting only 45 s. In a paradigm where metabolism does not play a role, these data reveal that both central and peripheral haemodynamic mechanisms are likely to be responsible for the 30% reduction in exercise‐induced hyperaemia with age.
Heat Transfer From Low Aspect Ratio Pin Fins
Authors: Lyall Michael E. , Thrift Alan A. , Thole Karen A. , Kohli Atul
Published: September 2010

The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Heat transfer augmentation in internal flows is commonly achieved through the use of pin fins, which increase both surface area and turbulence. The present research is focused on internal cooling of turbine airfoils using a single row of circular pin fins that is oriented perpendicular to the flow. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. A number of spanwise spacings were investigated for a Reynolds number range between 5000 and 30,000. Both pressure drop and spatially resolved heat transfer measurements were taken. The heat transfer measurements were made on the endwall of the pin fin array using infrared thermography and on the pin surface using discrete thermocouples. The results show that the heat transfer augmentation relative to open channel flow is the highest for smallest spanwise spacings and lowest Reynolds numbers. The results also indicate that the pin fin heat transfer is higher than the endwall heat transfer.
Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor—Part II: Numerical Results
Authors: Schnell R. , Voges M. , Mönig R. , Müller M. W. , Zscherp C.
Published: September 2010

A single stage transonic axial compressor was equipped with a casing treatment consisting of 3.5 axial slots per rotor pitch in order to investigate its influence on stall margin characteristics, as well as on the rotor near tip flow field, both numerically and experimentally. Contrary to most other studies, a generic casing treatment (CT) was designed to provide optimal optical access in the immediate vicinity of the CT, rather than for maximum benefit in terms of stall margin extension. The second part of this two-part paper deals with the numerical developments and their validation, carried out in order to efficiently perform time-accurate casing treatment simulations. The numerical developments focus on the extension of an existing coupling algorithm in order to carry out unsteady calculations with any exterior geometry coupled to the main flow passage (in this case a single slot), having an arbitrary pitch. This extension is done by incorporating frequency domain, phase-lagged boundary conditions into this coupling procedure. Whereas the phase lag approach itself is well established and validated for standard rotor-stator calculations, its application to casing treatment simulations is new. Its capabilities and validation will be demonstrated on the given compressor configuration, making extensive use of the detailed particle image velocimetry flow field measurements near the rotor tip. Instantaneous data at all measurement planes will be compared for different rotor positions with respect to the stationary slots in order to evaluate the time-dependent interaction between the rotor and the casing treatment.
Effects of Syngas Ash Particle Size on Deposition and Erosion of a Film Cooled Leading Edge
Authors: Rozati Ali , Tafti Danesh K. , Sreedharan Sai Shrinivas
Published: September 2010

The paper investigates the deposition and erosion caused by Syngas ash particles in a film cooled leading edge region of a representative turbine vane. The carrier phase is predicted using large eddy simulation for three blowing ratios of 0.4, 0.8, and 1.2. Ash particle sizes of 1 μm, 3 μm, 5 μm, 7 μm, and 10 μm are investigated using Lagrangian dynamics. The 1 μm particles with momentum Stokes number, Stp=0.03 (based on approach velocity and leading edge diameter), follow the flow streamlines around the leading edge and few particles reach the blade surface. The 10 μm particles, on the other hand with a high momentum Stokes number, Stp=0.03, directly impinge on the surface, with blowing ratio having a minimal effect. The 3 μm, 5 μm, and 7 μm particles with Stp=0.03, 0.8 and 1.4, respectively, show some receptivity to coolant flow and blowing ratio. On a number basis, 85–90% of the 10 μm particles, 70–65% of 7 μm particles, 40–50% of 5 μm particles, 15% of 3 μm particles, and less than 1% of 1 μm particles deposit on the surface. Overall there is a slight decrease in percentage of particles deposited with increase in blowing ratio. On the other hand, the potential for erosive wear is highest in the coolant hole and is mostly attributed to 5 μm and 7 μm particles. It is only at BR=1.2 that 10 μm particles contribute to erosive wear in the coolant hole.
An Integrated System for the Aerodynamic Design of Compression Systems—Part I: Development
Authors: Ghisu Tiziano , Parks Geoffrey T. , Jarrett Jerome P. , Clarkson P. John
Published: September 2010

The design of gas turbine engines is a complex problem. This complexity has led to the adoption of a modular design approach, in which a conceptual design phase fixes the values for some global parameters and dimensions in order to facilitate the subdivision of the overall task into a number of simpler subproblems. This approach, while making a complex problem more tractable, necessarily has to rely on designer experience and simple evaluations to specify these process-intrinsic constraints at a point in the design process where very little knowledge about the final design exists. Later phases of the design process, using higher-fidelity tools but acting on a limited region of the design space, can only refine an already established design. While substantial improvements in performance have been possible with the current approach, further gains are becoming increasingly hard to achieve. A gas turbine is a complex multidisciplinary system: a more integrated design approach can facilitate a better exploitation of the trade-offs between different modules and disciplines, postponing the setting of these critical interface parameters (such as flow areas, radii, etc.) to a point where more information exists, reducing their impact on the final design. In the resulting large, possibly multimodal, highly constrained design space, and with a large number of objectives to be considered simultaneously, finding an optimal solution by simple trial-and-error can prove extremely difficult. A more intelligent search approach, in which a numerical optimizer takes the place of the human designer in seeking optimal designs, can enable the design space to be explored significantly more effectively, while also yielding a substantial reduction in development times thanks to the automation of the design process. This paper describes the development of a system for the integrated design and optimization of gas turbine engines, linking a metaheuristic optimizer to a geometry modeler and to evaluation tools with different levels of fidelity. In recognition of the substantial increase in design space size required by the integrated approach, an improved parameterization based on the concept of principal components’ analysis was implemented, allowing a rotation of the design space along its most significant directions and a reduction in its dimensionality, proving essential for a faster and more effective exploration of the design space.
An Integrated System for the Aerodynamic Design of Compression Systems—Part II: Application
Authors: Ghisu Tiziano , Parks Geoffrey T. , Jarrett Jerome P. , Clarkson P. John
Published: September 2010

The complexity of modern gas turbine engines has led to the adoption of a modular design approach, in which a conceptual design phase fixes the values for a number of parameters and dimensions in order to facilitate the subdivision of the overall task into a number of simpler design problems. While making the overall problem more tractable, the introduction of these process-intrinsic constraints (such as flow areas and radii between adjacent stages) at a very early phase of the design process can limit the level of performance achievable, neglecting important regions of the design space and concealing important trade-offs between different modules or disciplines. While this approach has worked satisfactorily in the past, the continuous increase in components’ efficiencies and performance makes further advances more difficult to achieve. Part I of this paper described the development of a system for the integrated design optimization of gas turbine engines: postponing the setting of the interface constraints to a point where more information is available facilitates better exploration of the available design space and better exploitation of the trade-offs between different disciplines and modules. In this second part of the paper, the proposed approach is applied to several test cases from the design of a three-spool gas turbine engine core compression system, demonstrating the risks associated with a modular design approach and the consistent gains achievable through the proposed integrated optimization approach.
The Influence of Blade Lean on Straight and Annular Turbine Cascade Flow Field
Authors: D’Ippolito Gabriele , Dossena Vincenzo , Mora Alessandro
Published: September 2010

The work proposes a detailed description of the flow field throughout leaned turbine nozzles and reports a sensitivity analysis with respect to the lean angle. A phenomenological approach focuses the attention on pressure contours distribution on both inside and outside the passage. The study involves both straight and annular cascades mounting a typical intermediate reaction degree section, designed for steam turbines. Blades are built by stacking the same 2D profile along different linear axes, characterized by different angles with respect to the normal or radial direction: α=0 deg for prismatic blade and α=10 deg, 15 deg, and 20 deg for the leaned ones are considered. Experimental and numerical tests were performed at the nominal inlet flow angle in order to avoid any effect related to blade sweep. Experimental tests were carried out at the design outlet Mach number of 0.65; measurements were performed at the Laboratorio di Fluidodinamica delle Macchine of Politecnico di Milano. Only linear cascades with prismatic and 20 deg leaned blades were experimentally tested, providing data both downstream and inside the blade passage by means of pressure probe traversing, endwall pressure taps, and oil flow visualization. Experimental results were also used to validate the numerical setup, which provided a detailed computational picture of the flow field throughout the channel. The influence of the pressure contours’ shape on secondary vorticity activity downstream of the passage is highlighted and discussed, focusing the attention on secondary structures and loss distribution in this region. The resulting description of the flow field, based on the representation of pressure contours, supports the sensitivity analysis with respect to the blade lean angle, identifying the mechanism that leads the secondary vorticity to grow in regions where secondary losses and blade loading decrease.
Effect of Wake-Disturbed Flow on Heat (Mass) Transfer to a Turbine Blade
Authors: Olson S. , Sanitjai S. , Ghosh K. , Goldstein R. J.
Published: September 2010

This study investigates the effect of wakes in the presence of varying levels of background freestream turbulence on the heat (mass) transfer from gas turbine blades. Measurements using the naphthalene sublimation technique provide local values of the mass transfer coefficient on the pressure and suction surfaces of a simulated turbine blade in a linear cascade. Experimental parameters studied include the pitch of the wake-generating blades (vanes), blade-row separation, Reynolds number, and the freestream turbulence level. The disturbed flow strongly affects the mass transfer Stanton number on both sides of the blade, particularly along the suction surface. An earlier transition to a turbulent boundary layer occurs with increased background turbulence, higher Reynolds number, and from wakes shed from vanes placed upstream of the linear cascade. Note that once the effects on mass transfer are known, similar variation on heat transfer can be inferred from the heat/mass transfer analogy.
Reduction of Fan and Compressor Wake Defect Using Plasma Actuation for Tonal Noise Reduction
Authors: Lemire Sébastien , Vo Huu Duc
Published: September 2010

This paper proposes a new technique to reduce the noise generated by rotor-stator interaction (tonal noise) in fans and compressors. The method involves the use of single dielectric barrier discharge (plasma) actuators near the blade trailing edge to reduce blade wakes. Plasma actuators are a new and simple type of active flow control device consisting of two parallel and offset electrodes separated by a layer of dielectric material. The application of a high ac voltage at high frequency to the electrodes generates a body force on the flow in the vicinity of the electrodes to inject momentum without mass addition. A preliminary assessment of the proposed concept is performed with a computational study on modern low-speed compressor rotor geometry. A plasma actuator model is implemented in an established turbomachinery CFD code. Simulations are carried out to evaluate the effect of the actuator strength, location, and actuation method (continuous versus pulsed) on the rotor wake. Results show that plasma actuators operated in continuous mode near the trailing edge can significantly influence the wake of the rotor with relatively little power consumption. The effectiveness of the actuation is proportional to actuator strength (induced body force). The exact position of the actuator in the trailing edge region has little effect on the effectiveness of the actuation. The results from simulations with pulsed actuation show very low time-averaged influence on the wake and are not fully conclusive, due possibly to the frequencies simulated and the limitations of the RANS CFD tool.
Experimental and Numerical Analysis of Gas Turbine Blades With Different Internal Cooling Geometries
Authors: Eifel M. , Caspary V. , Hönen H. , Jeschke P.
Published: September 2010

This paper presents the effects of major geometrical modifications to the interior of a convection cooled gas turbine rotor blade. The analysis of the flow is performed experimentally with flow visualization via paint injection into water, whereas the flow and the heat transfer are investigated numerically with ANSYS CFX, utilizing the SST turbulence model. Two sets of calculations are carried out: one under the same conditions as the experiments and another according to realistic hot gas conditions with conjugate heat transfer. The aim is to identify flow phenomena altering the heat transfer in the blade and to manipulate them in order to reduce the thermal load of the material. The operating point of the geometric base configuration is set to Re=50,000 at the inlet while for the modified geometries, the pressure ratio is held constant compared with the base. Flow structures and heat transfer conditions are evaluated and are linked to specific geometric features. Among several investigated configurations one could be identified that leads to a cooling effectiveness 15% larger compared with the base.
Heat Transfer for a Turbine Blade With Nonaxisymmetric Endwall Contouring
Authors: Lynch Stephen P. , Sundaram Narayan , Thole Karen A. , Kohli Atul , Lehane Christopher
Published: September 2010

Complex vortical secondary flows that are present near the endwall of an axial gas turbine blade are responsible for high heat transfer rates and high aerodynamic losses. The application of nonaxisymmetric, three-dimensional contouring to the endwall surface has been shown to reduce the strength of the vortical flows and decrease total pressure losses when compared with a flat endwall. The reduction in secondary flow strength with nonaxisymmetric contouring might also be expected to reduce endwall heat transfer. In this study, measurements of endwall heat transfer were taken for a low-pressure turbine blade geometry with both flat and three-dimensional contoured endwalls. Endwall oil flow visualization indicated a reduction in the passage vortex strength for the contoured endwall geometry. Heat transfer levels were reduced by 20% in regions of high heat transfer with the contoured endwall, as compared with the flat endwall. The heat transfer benefit of the endwall contour was not affected by changes in the cascade Reynolds number.
Film Cooling Performance of Converging-Slot Holes With Different Exit-Entry Area Ratios
Authors: Liu Cun-liang , Zhu Hui-ren , Bai Jiang-tao , Xu Du-chun
Published: September 2010

Film cooling performances of two kinds of converging-slot-hole (console) with different exit-entry area ratios have been measured using a new transient liquid crystal measurement technique, which can process the nonuniform initial wall temperature. Four momentum ratios are tested. The film cooling effectiveness distribution features are similar for the two consoles under all the momentum ratios. Consoles with smaller exit-entry area ratio produce higher cooling effectiveness. And the laterally averaged cooling effectiveness results show that the best momentum ratio for both consoles’ film cooling effectiveness distribution is around 2. For both consoles, the heat transfer in the midspan region is stronger than that in the hole centerline region in the upstream but gradually becomes weaker as flowing downstream. With the momentum ratio increasing, the normalized heat transfer coefficient h∕h0 of both consoles increases. In the upstream, the heat transfer coefficient of console with small exit-entry area ratio is higher. But in the downstream, the jets’ turbulence and the couple vortices play notable elevating effect on the heat transfer coefficient for large exit-entry area ratio case, especially under small momentum ratios. Consoles with smaller exit-entry area ratio provide better thermal protection because of higher cooling effectiveness. And the distributions of heat flux ratio are similar with those of cooling effectiveness because the influence of η on q∕q0 is larger. For the consoles, smaller exit-entry area ratios produce lower discharge coefficients when the pressure variation caused by the hole shape is regarded as flow resistance.
Concurrent Blade Aerodynamic-Aero-elastic Design Optimization Using Adjoint Method
Authors: He L. , Wang D. X.
Published: September 2010

Increasing aerothermal and aero-elastic performance requirements and constraints are closely linked in modern blading designs. There is thus a need for more concurrent interaction between the disciplines at earlier stages of a design process. Presented in this paper are the development, validation, and demonstration of the adjoint approach to concurrent blading aerodynamic and aero-elastic design optimizations. A nonlinear harmonic phase solution method is adopted to solve the unsteady Reynolds-averaged Navier–Stokes equations. The flow field response in terms of both the mean aerothermal performance and aero-elastic stability to a geometrical perturbation can be obtained by three “steadylike” flow solutions at three distinctive temporal phases. This unsteady flow solution method is computationally very efficient and provides a convenient and consistent base for formulating the corresponding adjoint equations. The adjoint system for the unsteady flow solver is solved effectively by a relatively simple extension of the method and techniques previously developed for a steady flow adjoint solver. As a result, the sensitivities of both the steady (time-mean) flow loss and the aerodynamic damping/forcing to detailed blade geometry changes can be very efficiently obtained by solving equivalently three steadylike adjoint equations. Several case studies are presented to illustrate the validity and effectiveness of this new concurrent approach.
A Study of Mesh-Fed Slot Film Cooling
Authors: Bunker R. S.
Published: September 2010

This investigation demonstrates the potential improvement in adiabatic film effectiveness that can be achieved through the use of mesh-fed surface slot film cooling. Mesh, or in-wall network, cooling is composed of fairly compact arrays of pedestals sized to fit within the limited wall thickness of a turbine airfoil. When the coolant discharge from such a mesh is along a shallow ramp to the airfoil aerodynamic surface (i.e., like an angled film hole), the resulting film effectiveness from this combined geometry can be very high. The in-wall mesh network acts as the structural means for obtaining the slot geometry. In this study, flat plate warm wind tunnel testing has been conducted on two mesh-fed film geometries and compared against data for a row of axial round film holes, as well as a row of shaped diffuser film holes. The mesh-fed geometries are composed of pedestal arrays with height-to-diameter ratios of 0.2 exiting onto 20-deg inclines to the surface. The mesh slot exit film blowing ratios tested ranged from M=0.1 to M=0.7, while round and shaped film hole conditions covered 0.5 to 1.2. The mesh-fed film effectiveness results indicate a performance greater than that of shaped diffuser holes, but less than that of a more idealistic two-dimensional slot film geometry. The mesh-fed film effectiveness was as much as 25% higher than that for shaped holes in the near-hole region of x/Ms<50, and up to 100% greater in the downstream region of x/Ms>50.
Analysis of Rotor-Stator-Interaction and Blade-to-Blade Measurements in a Two Stage Axial Flow Compressor
Authors: Ernst Marco , Michel Armin , Jeschke Peter
Published: September 2010

In order to improve unsteady CFD analysis for turbomachinery applications, there is still the need for high quality experimental data for validation. The first aim of this paper is to represent a unique work in providing unsteady data for the purpose of a CFD test case. Second, a detailed analysis of rotor-stator-interaction in a multistage compressor is performed by means of accompanying frequency analysis of the blading and the tip leakage flow for different indexing positions. The transonic two stage axial flow compressor is equipped with integrally bladed rotors and vanes with hub and tip shrouds with regard to a modern high pressure jet engine compressor. For detailed flow measurements both intrusive and nonintrusive measurement techniques were used. Beside pressure probes mounted with a semiconductor and microstrain gauges applied to the blades and vanes, a three component Doppler laser-two-focus velocimeter was used. The results of the time resolved pressure traverse measurements in the axial gaps as well as the analysis of the tip leakage flow show the propagation of the wakes and the potential upstream influence, which can be clearly detected by the blade passing frequencies as well. Additionally, the results of the blade-to-blade measurements impart an idea of the intrarotor-transport of the fluid and the flow phenomena within the rotor. Beside the detailed flow analysis, the preferential aim of this paper is to establish a method for the detection of flow phenomena due to the blade-row-interaction by means of a frequency analysis. This paper shows that a correlation of the fast Fourier transform results of strain gauges and semiconductor probes in the axial gaps and tip leakage flow region is a very promising starting point, especially for the analysis of forced response operating points.
Experimental and Numerical Investigation of Convective Heat Transfer in a Gas Turbine Can Combustor
Authors: Patil Sunil , Abraham Santosh , Tafti Danesh , Ekkad Srinath , Kim Yong , Dutta Partha , Moon Hee-Koo , Srinivasan Ram
Published: September 2010

Experiments and numerical computations are performed to investigate the convective heat transfer characteristics of a gas turbine can combustor under cold flow conditions in a Reynolds number range between 50,000 and 500,000 with a characteristic swirl number of 0.7. It is observed that the flow field in the combustor is characterized by an expanding swirling flow, which impinges on the liner wall close to the inlet of the combustor. The impinging shear layer is responsible for the peak location of heat transfer augmentation. It is observed that as Reynolds number increases from 50,000 to 500,000, the peak heat transfer augmentation ratio (compared with fully developed pipe flow) reduces from 10.5 to 2.75. This is attributed to the reduction in normalized turbulent kinetic energy in the impinging shear layer, which is strongly dependent on the swirl number that remains constant at 0.7 with Reynolds number. Additionally, the peak location does not change with Reynolds number since the flow structure in the combustor is also a function of the swirl number. The size of the corner recirculation zone near the combustor liner remains the same for all Reynolds numbers and hence the location of shear layer impingement and peak augmentation does not change.
A New Alternative for Reduction in Secondary Flows in Low Pressure Turbines
Authors: Torre Diego , Vázquez Raúl , de la Rosa Blanco Elena , Hodson Howard P.
Published: September 2010

This paper describes a new flow mechanism for the reduction in secondary flows in low pressure turbines using the benefit of contoured endwalls. The extensive application of contoured endwalls in recent years has provided a deeper understanding of the physical phenomenon that governs the reduction in secondary flows. Based on this understanding, the endwall geometry of a linear cascade of solid-thin profiles typical of low pressure turbines has been redesigned. Experimental data are presented for the validation of this new solution. Based on these data, a reduction of 72% in the secondary kinetic energy helicity (SKEH) and 20% in the mixed-out endwall losses can be obtained. Computational fluid dynamics simulations are also presented to illustrate the effect of the new endwall on the secondary flows. Furthermore, an explanation of the flow mechanism that governs the reduction in the SKEH, and the losses is given.