bluuebunny/crossref_metadata_2025 huggingface dataset:
In vivo evaluation of the dentate gate theory in epilepsy
Authors: Krook‐Magnuson Esther , Armstrong Caren , Bui Anh , Lew Sean , Oijala Mikko , Soltesz Ivan
Published: March 2015

Key points

A key mechanistic concept in epilepsy is the dentate gate hypothesis, which argues that the dentate gyrus protects hippocampal circuits from overexcitation and that a breakdown of this gate leads to epilepsy.

Direct in vivo evidence for the dentate gate hypothesis is lacking and it is therefore unclear whether interventions selectively targeting the dentate gyrus would inhibit seizures.

We demonstrate that on‐demand optogenetic restoration of the dentate gate through selective inhibition of granule cells is sufficient to inhibit spontaneous seizures in a mouse model of temporal lobe epilepsy.

By contrast, activation of granule cells worsens spontaneous seizures and can even induce acute seizures in non‐epileptic animals.

These data provide direct evidence for the dentate gate hypothesis, indicate that the dentate gyrus is indeed a critical node in temporal lobe seizure circuitry, and illustrate that the dentate gyrus can be an effective target for seizure inhibition.

The dentate gyrus is a region subject to intense study in epilepsy because of its posited role as a ‘gate’, acting to inhibit overexcitation in the hippocampal circuitry through its unique synaptic, cellular and network properties that result in relatively low excitability. Numerous changes predicted to produce dentate hyperexcitability are seen in epileptic patients and animal models. However, recent findings question whether changes are causative or reactive, as well as the pathophysiological relevance of the dentate in epilepsy. Critically, direct in vivo modulation of dentate ‘gate’ function during spontaneous seizure activity has not been explored. Therefore, using a mouse model of temporal lobe epilepsy with hippocampal sclerosis, a closed‐loop system and selective optogenetic manipulation of granule cells during seizures, we directly tested the dentate ‘gate’ hypothesis in vivo. Consistent with the dentate gate theory, optogenetic gate restoration through granule cell hyperpolarization efficiently stopped spontaneous seizures. By contrast, optogenetic activation of granule cells exacerbated spontaneous seizures. Furthermore, activating granule cells in non‐epileptic animals evoked acute seizures of increasing severity. These data indicate that the dentate gyrus is a critical node in the temporal lobe seizure network, and provide the first in vivo support for the dentate ‘gate’ hypothesis.
Influence of Surface Heat Flux Ratio on Heat Transfer Augmentation in Square Channels With Parallel, Crossed and V-Shaped Angled Ribs
Authors: Han J. C. , Zhang Y. M. , Lee C. P.
Published: March 2015

The effect of wall heat flux ratio on the local heat transfer augmentation in a square channel with two opposite in-line ribbed walls was investigated for Reynolds numbers from 15,000 to 80,000. The square channel composed of ten isolated copper sections has a length-to-hydraulic diameter ratio (L/D) of 20. The rib height-to-hydraulic diameter ratio (e/D) is 0.0625 and the rib pitch-to-height ratio (P/e) equals 10. Six ribbed side to smooth side wall heat flux ratios (Case 1 - q″r1/q″s = q″r2/q″s = 1; Case 2 - q″r1/q″s = q″r2/q″s = 3; Case 3 - q″r1/q″s = q″r2/q″s = 6; Case 4 - q″r1/q″s = 6 and q″r2/q″s = 4; Case 5 - q″r1/q″s = q″r2/q″s = ∞ and Case 6 - q″r1/q″s = ∞ and q″r2/q″s = 0) were studied for four rib orientations (90° rib, 60° parallel rib, 60° crossed rib, and 60° ∨-shaped rib). The results show that the ribbed side wall heat transfer augmentation increases with increasing ribbed side to smooth side wall heat flux ratios, but the reverse is true for the smooth side wall heat transfer augmentation. The average heat transfer augmentation of the ribbed side and smooth side wall decreases slightly with increasing wall heat flux ratios. Two ribbed side wall heating (Case 5 - q″r1/q″s = q″r2/q″s = ∞) provides a higher ribbed-side-wall heat transfer augmentation than the four-wall uniform heating (Case 1 - q″r1/q″s = q″r2/q″s = 1). The effect of wall heat flux ratio reduces with increasing Reynolds numbers. The results also indicate that the 60° ∨-shaped rib and 60° parallel rib perform better than the 60° crossed rib and 90° rib, regardless of wall heat flux ratio and Reynolds number.
Computational Study of Stall Flutter in Linear Cascades
Authors: Abdel-Rahim A. , Sisto F. , Thangam S.
Published: March 2015

Aeroelastic interaction in turbomachinery is of prime interest to operators, designers and aeroelasticians. Operation at off-design conditions may promote blade stall; eventually the stall pattern will propagate around the blade annulus. The unsteady periodic nature of propagating stall will force blade vibration and blade flutter may occur if the stall propagation frequency is entrained by the blade natural frequency. In this work a computational scheme based on the vortex method is used to simulate the flow over a linear cascade of airfoils. The viscous effect is confined to a thin layer which determines the separation points on the airfoil surfaces. The preliminary structural model is a two-dimensional characteristic section with a single degree of freedom in either bending or torsion. A study of the relationship between the stall propagation frequency and the blade natural frequency has been conducted. The study shows that entrainment, or frequency synchronization, occurs resulting in pure torsional flutter over a certain interval of reduced frequency. A severe blade torsional amplitude (of order 20°) has been computed in the entrainment region reaching its largest value in the center of the interval. However, in practice, compressor blades will not sustain this vibration and blade failure may occur before reaching such a large amplitude. Outside the entrainment interval the stall propagation is shown to be independent of the blade natural frequency. In addition, computational results show that there is no entrainment in the pure bending mode. Rather “de-entrainment” occurs with similar flow conditions and similar stall frequencies, resulting in blade buffeting in pure bending.
Compressor Cleaning Effectiveness for Marine Gas Turbines
Authors: Abdelrazik A. , Cheney P.
Published: March 2015

In two decades of operating gas turbines at sea, the Canadian Navy has gained much experience of compressor fouling and cleaning. Methods of combatting the problems encountered have encouraged investigations aimed at understanding the process of compressor contamination and into the effectiveness of various cleaning methods. These investigations have been undertaken at the Navy’s land based test facility using data from the fleet, engines returned from service and facility equipment.

This paper reports the findings of the investigations and includes the current recommendations for washing procedures in the installations of the Canadian Navy. The direction of future work aimed at providing further improvements in contaminant removal is included.
High-Cycle Fatigue Design Evolution and Experience of Freestanding Combustion Turbine Blades
Authors: Scalzo A. J.
Published: March 2015

Combustion turbine blade design criteria can generally be classified as either temperature or fatigue related. Since less is usually known about the factors influencing the fatigue phenomenon, it is considered the more challenging. In addition, as analytical and experimental techniques became more sophisticated and more accurate, the natural tendency was to replace archaic “guidelines” or “rules” with less conservative approaches that at times led to the discovery of new high cycle fatigue “thresholds”. This paper presents the evolution of the combustion turbine blade high cycle fatigue design criteria for freestanding blades; and, also presents the analysis and corrective actions taken to resolve several unique combustion turbine blade fatigue problems, all encountered over a thirty-five year period while the author has been employed at Westinghouse Electric Corporation. Included are high-cycle fatigue problems due to cooling air leakage, seal pin friction, combustion temperature maldistribution, as well as flow-induced nonsynchronous vibration.
Developments in Magnesium Based Materials and Processes
Authors: Lyon P. , King J. F. , Fowler G. A.
Published: March 2015

Recent developments in Magnesium alloys, processing techniques and corrosion protection schemes are reviewed.

The casting alloy WE43 is detailed, data being presented which shows that it compares favourably with Aluminium based casting alloys on a strength to weight basis. In addition its intrinsic corrosion characteristics are shown to be similar to those of Aluminium base alloys.

A counter - gravity casting process, specifically designed to make higher quality, thin-walled Magnesium alloy components is described together with property data indicating the improvements obtained.

Also discussed are the ongoing developments in Metal Matrix Composites and Rapid Solidification technologies, showing the benefits offered by these processing routes.

Finally current corrosion protection schemes are reviewed and their overall cost effectiveness discussed.
An Attempt to Experimentally Uncouple the Effect of Coriolis and Buoyancy Forces on Heat Transfer in Smooth Circular Tubes Which Rotate in the Orthogonal Mode
Authors: Morris W. D. , Salemi R.
Published: March 2015

This paper reports the results of an experimental investigation of the combined effect of Coriolis and buoyancy forces on forced convection in a circular tube which rotates about an axis orthogonal to its centre line. The experiment has been deliberately designed to minimise the effect of circumferential conduction in the tube walls by using material of relatively low thermal conductivity. A new correlating parameter for uncoupling the effect of Coriolis forces from centripetal buoyancy is proposed for the trailing and leading edges of the tube. It is demonstrated that enhanced heat transfer on the trailing edge occurs as a result of rotation. On the leading edge significant reductions in heat transfer compared to the zero rotation case can occur but with possible recovery at high rotational speeds.
A Burner Rig Investigation of the Hot Corrosion Behavior of Several Wrought Superalloys and Intermetallics
Authors: Lai G. Y. , Barnes J. J. , Barnes J. E.
Published: March 2015

The hot corrosion behavior of wrought Ni- and Co-base superalloys and nickel aluminide intermetallics was studied in a burner rig at 900°C (1650°F) injected with 5 and 50 ppm sea salt. Nickel aluminides (IC-50 and IC-218) were found to be extremely susceptible to hot corrosion attack. Some state-of-the-art wrought superalloys, such as HAYNES alloys 230 and 188, on the other hand, were extremely resistant to hot corrosion. The behavior of different alloy systems, breakaway corrosion and corrosion morphology are discussed.
Stator Averaged, Rotor Blade-to-Blade Near Wall Flow in a Multistage Axial Compressor With Tip Clearance Variation
Authors: Moyle I. N. , Walker G. J. , Shreeve R. P.
Published: March 2015

This paper describes the effect of tip clearance changes on the pressure at the case wall of a second stage rotor. Wall shear distributions under the rotor tip are also presented. The results show low pressure areas extending along the rotor suction side but lying away from the blade. Pressure contours indicate the tangential loading at the tip is lower than predicted by two dimensional calculations, however, the predicted loading is observed between the lowest pressure’s path in the passage and the blade pressure side. The results suggest a viscous or shearing layer, due to blade-to-wall relative motion, is generated on the blade side of the tip gap which modifies the inviscid relative flow field and produces an unloading on the blade tip.
Surge Dynamics in a Free-Spool Centrifugal Compressor System
Authors: Fink D. A. , Cumpsty N. A. , Greitzer E. M.
Published: March 2015

Turbocharger surge has been investigated in a radial impeller-vaneless diffuser free-spool system. Several different aspects are addressed. First, two very different compression systems, one with a large downstream volume and one with the smallest possible downstream volume, are employed to examine stall initiation phenomena as well as the behavior of the compressor characteristics when operating in surge. The measurements show impeller stall at the inducer tips to be a key phenomena in initiating surge. The inducer stall is stationary and asymmetric, due to the presence of the volute, and is most severe near the volute tongue angular position. The compressor characteristic in the large volume system (which gave surge) is observed to be flatter and to lag that in the stabilized small volume system. The difference arises because of the slow development time and differing circumferential extent of the inducer stall present at a given mass flow.

A nonlinear simulation of the system is also presented. The model deviates from previous treatments of unsteady flow in compressor systems in that the assumption of constant rotor speed is relaxed. Including a time lag on the order of the compressor throughflow time, together with proper treatment of speed variations, is shown to dramatically improve agreement with the observed surge behavior.
Rim Sealing of Rotor-Stator Wheelspaces in the Absence of External Flow
Authors: Chew J. W. , Dadkhah S. , Turner A. B.
Published: March 2015

Sealing of the cavity formed between a rotating disc and a stator in the absence of a forced external flow is considered. In these circumstances the pumping action of the rotating disc may draw fluid into the cavity through the rim seal. Minimum cavity throughflow rates required to prevent such ingress are estimated experimentally and from a mathematical model. The results are compared with other workers’ measurements. Measurements for three different types of rim seal are reported for a range of seal clearances and for rotational Reynolds numbers up to 3 × 106. The mathematical model is found to correlate the experimental data reasonably well.
Thermal Barrier Coating Life Prediction Model Development
Authors: Meier Susan Manning , Nissley David M. , Sheffler Keith D. , Cruse Thomas A.
Published: March 2015

A thermal barrier coated (TBC) turbine component design system, including an accurate TBC life prediction model, is needed to realize the full potential of available TBC engine performance and/or durability benefits. The objective of this work, which was sponsored in part by NASA under the Hot Section Technology (HOST) Program (Contract NAS3-23944), was to generate a life prediction model for electron beam - physical vapor deposited (EB-PVD) zirconia TBC. Specific results include EB-PVD zirconia mechanical and physical properties, coating adherence strength measurements, interfacial oxide growth characteristics, quantitative cyclic thermal spallation life data, and a spallation life model.
Numerical Simulations of Low-Btu Coal Gas Combustion in a Gas Turbine Combustor
Authors: Agrawal Ajay K. , Yang Tah-Teh
Published: March 2015

A numerical model for turbulent reacting flow is described and applied for predictions in an industrial gas turbine combustor operating on low-Btu coal gas. The model, based on fast-reaction limit, used Favre averaged conservation equations with the standard k-ε model of turbulence. Effects of turbulent fluctuations on chemistry are described statistically in terms of the mean, variance and probability density function (assumed to be β-distribution) of the mixture fraction. Two types of geometric approximations, namely axisymmetric and three-dimensional, were used to model the combustor. Computations were performed with (a) no swirl (b) weak swirl and (c) strong swirl at the fuel and primary air inlets. Essentially, the same bulk mean temperature distributions were obtained for axisymmetric and three-dimensional calculations while the computed pattern factors and the liner wall temperatures for the two differed significantly. Complete combustion was predicted with strong swirl, a result supported by the available test data. The maximum liner wall temperature predicted for three-dimensional calculations compared favorably with the experimental data while the predicted maximum exhaust gas temperature differed by ≈120 K. The difference was attributed to measurement uncertainties, model assumptions and lack of accurate data at the inlets. The maximum flame temperature was below 1,850 K indicating that thermal NOx may be insignificant.
Three-Dimensional Flow Near the Blade/Endwall Junction of a Gas Turbine: Application of a Boundary Layer Fence
Authors: Chung J. T. , Simon T. W. , Buddhavarapu J.
Published: March 2015

A flow management technique designed to reduce some harmful effects of secondary flow in the endwall region of a turbine passage is introduced. A boundary layer fence in the gas turbine passage is shown to improve the likelihood of efficient film cooling on the suction surface near the endwall. The fence prevents the pressure side leg of the horseshoe vortex from crossing to the suction surface and impinging on the wall. The vortex is weakened and decreased in size after being deflected by the fence. Such diversion of the vortex will prevent it from removing the film cooling flow allowing the flow to perform its cooling function. Flow visualization on the suction surface and through the passage shows the behavior of the passage vortex with and without the fence. Laser Doppler velocimetry is employed to quantify these observations.
Field Performance Testing of an Uprated Gas Reinjection Compressor/Turbine Train
Authors: Klein John M. , Draughon Patrick A.
Published: March 2015

A Dresser Rand compressor and a General Electric Frame 5 turbine were uprated from 26,950 to 37,960 horsepower to increase injection capacity at Prudhoe Bay, Alaska. This paper discusses the user’s experience in field performance testing the machinery train to verify the operation and reliability of the uprate. Aerothermal performance was verified on both the gas turbine and compressor. Emissions testing conducted on the gas turbine demonstrated the equipment would be in compliance with Alaska regulations. To assess reliability, optical alignment, transient vibration checks and lubrication system heat balance analysis were also undertaken. Results from the testing verified the performance and reliability of the conversion, providing confidence to continue with the thirteen-machine, multi-year project.
Dynamic Analysis Technique of Rotating Centrifugal Impeller
Authors: Zhang Jin , Chen X. J. , Wang W. L.
Published: March 2015

A dynamic analysis technique which can be employed in rotating centrifugal impeller is presented in this paper. It shows that multi–component partition can be made in repetitive sector region of the centrifugal impeller. The basic repectivie sector region of the centrifugal impeller is divided into three substructures: the full blade, the short blade and the sectorial part of the disc. By using Benfield mode substitution combined with group transformation successfully, the Hermite generalized mass and stiffness matrices under the reduced coordinates are derived. From this, the natural frequencies and the corresponding modal shapes of the bladed disc coupled system can be solved.

The comparison of the analytical results obtained by using this method, other methods and the experimental data of models verifies the reliability, practicability and considerable economic benefits of the method presented in this paper.
Measurement and Prediction of Heat Transfer From Compressor Discs With a Radial Inflow of Cooling Air
Authors: Farthing P. R. , Long C. A. , Rogers R. H.
Published: March 2015

An integral theory is used to model the flow, and predict heat transfer rates, for corotating compressor discs with a superposed radial inflow of air. Measurements of heat transfer are also made, both in an experimental rig and in an engine.

The flow structure comprises source and sink regions, Ekman-type layers and an inviscid central core. Entrainment occurs in the source region, the fluid being distributed into the two nonentraining Ekman-type layers. Fluid leaves the cavity via the sink region.

The integral model is validated against the experimental data, although there are some uncertainties in modelling the exact thermal conditions of the experiment. The magnitude of the Nusselt numbers is affected by the rotational Reynolds number and dimensionless flowrate; the maximum value of Nu is found to occur near the edge of the source region.

The heat transfer measurements using the engine data show acceptable agreement with theory and experiment. This is very encouraging considering the large levels of uncertainty in the engine data.
Turbulence Modelling for Secondary Flow Prediction in a Turbine Cascade
Authors: Cleak J. G. E. , Gregory-Smith D. G.
Published: March 2015

Predictions of secondary flow in an axial turbine cascade have been made using three different turbulence models; mixing length, a one equation model and a k-epsilon/mixing length hybrid model. The results are compared with results from detailed measurements, not only by looking at mean flow velocities and total pressure loss, but also by assessing how well turbulence quantities are predicted. It is found that the turbulence model can have a big influence on the mean flow results, with the mixing length model giving generally the best mean flow. None of the models give good predictions of the turbulent shear stresses in the vortex region, although the k-epsilon model gives quite good turbulent kinetic energy values. The one equation model is the only one to contain a transition criterion. The importance of such a criterion is illustrated, but the present one needs development to give reliable predictions in the complex flow within a blade passage.
Effects of the Tip Clearance Flow Field on the Secondary Losses
Authors: Kaldellis J. K. , Katramatos D. T. , Ktenidis P. D.
Published: March 2015

In this paper an extension of our secondary flow calculation method is presented in order to estimate the influence of the tip clearance on the secondary flow field.

The impact of the tip clearance vortex is embodied in the method so that the secondary vorticity field, based on the complete form of the meridional vorticity transport equation is properly modified. In this way the changes of the secondary flow field quantities are predicted along with the resulting additional losses imposed by the existence of the tip clearance.

The estimated tip clearance losses, based on the flow field structure, are compared to results obtained from various semi-empirical loss correlations found in the literature.

Several cases encountered in axial flow compressor configurations are investigated and the calculated results are favourably compared to experimental data and results of previous calculations.

Additionally, in order to clarify the influence of the tip clearance structure upon the secondary flow field, cases with and without tip clearance are also examined.
Conceptual Engineering of a 300-MW CAES Plant: Part 1 — Cost Effectiveness Analysis
Authors: Nakhamkin M. , Swensen E. C. , Abitante P. A. , Whims M. , Weiner D. , Vadasz P. , Brokman S.
Published: March 2015

This paper presents the results of a project performed for the Israel Electric Corporation, Ltd. (IEC), with the objective of developing the most cost-effective and technically feasible 300-MW CAES-plant concept with underground storage in an aquiferous reservoir. Three conceptually different turbomachinery trains are analyzed, including one based on the use of state-of-the-art combustion turbine components with high firing temperatures. The results are reported for each turbomachinery train concept, optimized for the geological conditions of two alternative underground-storage sites. Along with other generic findings, the paper concludes with the selection of a turbomachinery train, its cycle parameters and configuration, and underground storage site to be used for further preliminary engineering and cost estimates. The results are generalized for use in future CAES projects.
Development of Injection-Molded Gas Turbine Components: Investigation Into Toughening GTE PY6 Si3N4
Authors: Sordelet D. , Neil J. , Mahoney M. , Hecker A.
Published: March 2015

GTE Laboratories has been supporting Allison Gas Turbine Division of General Motors under the current ATTAP program since early 1988. Injection-molding process development and component fabrication has been the emphasis of this effort, but material property enhancement studies have also been an important complement. Attempts to increase the resistance to foreign object damage have been made through parallel investigations of microstructural control and SiC whisker reinforcement. The research activities aimed at improving fracture toughness of GTE PY6 Si3N4 are discussed.
Investigation of Engine Thrust Correlation Methods for Enclosed Test Cells
Authors: Bird J. W. , MacLeod J. D. , Mulligan M. F.
Published: March 2015

A test cell correlation program was carried out by the General Electric Company (GE) to establish a relationship between the performance of a designated F404 gas turbine engine in the National Research Council of Canada (NRCC) test cell No.5 and the GE test cell 108 at Lynn, Massachusetts. General Electric reported on the test results and provided a test cell correlation method. The test data and methods have been subsequently analyzed. Simplified methods were examined to provide ready means of correlating other test facilities. Two correlation methods are proposed which compare well with the manufacturer’s results.
A Viscous Flow Study of Shock-Boundary Layer Interaction, Radial Transport, and Wake Development in a Transonic Compressor
Authors: Hah Chunill , Reid Lonnie
Published: March 2015

A numerical study based on the three-dimensional Reynolds-averaged Navier-Stokes equation has been conducted to investigate the detailed flow physics inside a transonic compressor. Three-dimensional shock structure, shock-boundary layer interaction, flow separation, radial mixing, and wake development are all investigated at design and off-design conditions. Experimental data based on laser anemometer measurements are used to assess the overall quality of the numerical solution. An additional experimental study to investigate endwall flow with a hot-film was conducted, and these results are compared with the numerical results.

Detailed comparison with experimental data indicates that the overall features of the three-dimensional shock structure, the shock-boundary layer interaction and the wake development are all calculated very well in the numerical solution. The numerical results are further analyzed to examine the radial mixing phenomena in the transonic compressor. A thin sheet of particles is injected in the numerical solution upstream of the compressor. The movement of particles is traced with a three-dimensional plotting package. This numerical survey of tracer concentration reveals the fundamental mechanisms of radial transport in this transonic compressor. Strong radially outward flow is observed inside a separated flow region and this outward flow accounts for about 80 percent of the total radial transport. The radially inward flow is mainly due to the traditional secondary flow.
Optimizing Instrumentation When Measuring Jet Engine Blade Vibration
Authors: Griffin J. H.
Published: March 2015

An analytical model of bladed disk vibration is used to calculate the statistical variations in blade amplitudes that can occur in mistuned turbomachinery blading. The results provide a basis for evaluating alternative strategies for instrumenting the stage. This approach is illustrated by applying it to an unshrouded fan stage. It is found for this stage that the best strategy is to instrument blades that have frequencies near the tuned system frequency. A procedure is proposed for establishing how gages should be allocated from stage to stage throughout the engine.
A Simple Frequency Expression for the In-Plane Vibrations of Rotating Rings
Authors: Koff B. L. , El-Aini Y. M.
Published: March 2015

An approximate but accurate expression for determining the reference in-plane flexural frequencies of rotating rings is presented. The ring reference frequencies are with respect to a co-ordinate system that rotates with the ring at the mean speed of the forward and backward traveling waves analogous to the standing wave approach for rotating disks. The formula is based on adapting the correction factor for shear, centrifugal stiffening, and centrifugal mass of prismatic bars to be applied to Hoppe’s “Classical” formula for stationary, slender, inextensible rings. The result is a closed form analytical solution applicable to arbitrary shaped rotating rings with distributed loading. The formula has been verified for a wide range of ring radial depths and nodal diameters by comparison to elaborate NASTRAN solid finite element models that account for shear, centrifugal stiffening, and centrifugal mass effects. Excellent correlations, within 1%, for all test cases were achieved. Forward and Backward traveling–wave frequencies are obtained by using the reference frequency expression into Bryan’s “Classical” formula for thin rotating rings. Centrifugal mass contribution was shown to be particularly important for thin rings vibrating at low nodal diameters.
An Improved Method for Aerodynamic Design of Centrifugal Impeller Blades
Authors: Wang Zhengming , Wu Bangxian , Zhang Wu
Published: March 2015

Based on the “General Theory of Three-Dimensional Flow in Turbomachines”, an improved method for designing centrifugal impeller blades has been developed. The design procedure is performed with the help of the combination of an S2 inverse problem code, a code for generating a profile on a revolution surface by a two-step series expansion and the codes of S1 direct and inverse problems. After the calculation of the inverse problem on the S2 stream surface is completed, a special series expansion method is used for obtaining a preliminary blade profile, then the relative flow field is predicted by the S1 direct code and is improved by the S1 inverse code. The method is favourable for smoothing the velocity distribution on the blade surface, eliminating the separation bubble and raising the efficiency of the impeller. The present method has been successfuly applied to improving the design of a centrifugal impeller.
Computation of 3D Flow Phenomena in Axial Flow Compressor Blade Rows
Authors: Janssen M. , Dohmen H.-J. , Grahl K. G.
Published: March 2015

The main subject of the present publication is the comparison of results achieved with a 3D-partially parabolic calculation procedure and experimental data for the three dimensional flow in stationary and rotating blade rows of axial flow compressors.

To set up the numerical solution procedure, the Navier-Stokes Equations are written in finite difference form by applying the control-volume approach. The turbulent flow effects are taken into account by using the standard k—ε model for the calculation of the turbulent viscosity. For precisely introducing the boundary conditions for arbitrary geometries, the differential equations are transformed to a body-fitted coordinate system by a very simple method. To construct the physical mesh, the nonorthogonal curvilinear coordinates are taken as solutions of a suitable elliptic boundary value problem.

The abilities of the developed computer program are shown by comparing experimental and numerical results for three applications. The first, most simple case deals with the flow development in an isolated, stationary blade row of cylindrical blades and uniform boundary conditions upstream of the blade row. A more complex flow is regarded by calculating the flow field through highly turned, custom tailored airfoils working in a multistage environment. The flow conditions upstream of the flow domain under consideration show a well developed end wall boundary layer at the hub, leading to a strongly skewed inflow due to the superimposed tangential velocity component of the rotor upstream. The third application regards the flow development in a rotating axial compressor blade row in which the complexity of the flow field increases by flow effects that are due to centrifugal and Coriolis forces.

The comparisons between experimental and numerical results show good agreements for all applications.
A Finite Element Inverse Method for the Design of Turbomachinery Blades
Authors: Nicoud Didier , Bloa Catherine Le , Jacquotte Olivier-Pierre
Published: March 2015

We present a quasi-3D inverse method for the design of turbomachinery blades corresponding to a velocity distribution given arbitrarily. The theoretical aspect of the problem is first investigated, then the equations governing the quasi three-dimensional potential model are reviewed. The inverse method consists of solving the potential equation with Dirichlet boundary conditions on the profile, then modifying the profile iteratively until there is no mass flux through its surface. The convergence of the process is guaranteed by the preliminary theoretical study. The method is implemented using a finite element discretization, which relies on a mixed variational formulation involving two fields of unknowns: the velocity potential and the normal displacement of the profile.

Several results are shown on subsonic and transonic compressor profiles. The modified profiles are then validated with direct calculations such as quasi three-dimensional Navier-Stokes computations. These results illustrate the behavior of the method, in particular its robustness and its effectiveness.

The method was adapted to calculations on turbine blade profiles. Preliminary results are shown that illustrate an industrial use of the method on a subsonic profile.
Stall Inception in Axial Flow Compressors
Authors: Day I. J.
Published: March 2015

Studies have been conducted on two laboratory test compressors to investigate the process leading to the formation of finite amplitude rotating stall cells. The measurements were obtained from circumferential arrays of hot-wires and were spatially and temporarily analysed to show that modal perturbations are not always present prior to stall, and when present, sometimes have little direct effect on the formation of the stall cells. The measurements lead to the conclusion that the occurrence of modal perturbations, and the formation of finite amplitude stall cells, are two separate phenomena; both occurring under roughly the same conditions at the peak of the pressure rise characteristic. The measurements also underline the hitherto unsuspected importance of short length scale disturbances in the process of stall inception. Examples are given of different ways in which stall cells can develop and the conclusions are backed up with a summary of current test data from various machines around the world.
Stability Analysis of Bridged Cracks in Brittle Matrix Composites
Authors: Ballarini Roberto , Muju Sandeep
Published: March 2015

The bridging of matrix cracks by fibers is an important toughening mechanism in fiber reinforced brittle matrix composites. This paper presents the results of a non-linear finite element analysis of the Mode-I propagation of a bridged matrix crack in a finite size specimen. The composite is modeled as an orthotropic continuum and the bridging due to the fibers is modeled as a distribution of tractions which resist crack opening. A critical stress intensity factor criterion is employed for matrix crack propagation while a critical crack opening condition is used for fiber failure. The structural response of the specimen (load-deflection curves) as well as the stress intensity factor of the propagating crack are calculated for various constituent properties and specimen configurations for both tensile and bending loading. By controlling the length of the bridged crack results are obtained which highlight the transition from stable to unstable behavior of the propagating crack.
Life Time Prediction for Ceramic Gas Turbine Components
Authors: Stürmer G. , Schulz A. , Wittig S.
Published: March 2015

At the Institute for Thermal Turbomachinery, University of Karlsruhe (ITS), theoretical and experimental investigations on ceramic gas turbine components are performed. For the reliability analysis by finite element calculations the computer code CERITS has been developed. This code is used to determine the fast fracture reliability of ceramic components subjected to polyaxial stress states with reference to volumetric flaws and was presented at the 1990 IGTI Gas Turbine Conference.

CERITS-L now includes subcritical crack growth. With the new code CERITS-L, failure probabilities of ceramic components can be calculated under given load situations versus time. In comparing these time dependent failure probabilities with a given permissible failure probability, the maximum operation time of a component can be determined. The considerable influence of the subcritical crack growth upon the life time of ceramic components is demonstrated at the flame tube segments of the ITS ceramic combustor.
Experimental Investigation of the Longitudinal-Vortex-Nature of Rotating Stall in Vaneless Diffusers of Centrifugal Compressors
Authors: Chen Y. N. , Haupt U. , Seidel U. , Rautenberg M.
Published: March 2015

Rotating stall in a vaneless diffuser of a centrifugal compressor has been found to be guided by Rossby waves, which are composed of branches of high and low pressures (Chen, Haupt and Rautenberg, 1990a). The branch of the high pressure leads the unstalled region and that of the low pressure leads the stalled region. The phase velocity of the Rossby waves is then the pattern speed of the stall cell.

We report here an additional experimental result, according to which the flow of rotating stall is composed of a longitudinal spiral vortex pair. The vorticity and the axis of the longitudinal vortex were measured by means of two pressure transducers fixed at a distance of 2 mm to the opposite walls of the diffuser downstream of its inlet.

The analysis of the experimental result of Tsurusaki, Imaichi and Miyake (1987) about the fields of the total and fluctuating velocities of rotating stall in the vaneless diffuser reveals furthermore that the longitudinal spiral vortex is centred on the through flow. The two vortices of the pair stay side by side in touch but without mixing because of their opposite rotational sense. The longitudinal vortices make about 1 1/4 turns from the inlet to the outlet of the diffuser under the guidance of the Rossby waves. The vorticity of the longitudinal vortex is determined from the experimental result.

Furthermore, the experimental result reveals that the fronts along the high pressure ridges and the low pressure troughs of the Rossby wave pattern are themselves longitudinal vortices. Then these fronts possess a behaviour of the jet stream, which is associated with the Rossby waves of the atmosphere in the midlatitude.

Finally, the origin of the vorticity of the longitudinal vortices along the through flow and the Rossby-wave front is derived based on the experimental results obtained by Hergt and Jaberg (1988), and Hide (1958).
Rotating Stall Flow and Dangerous Blade Excitation of Centrifugal Compressor Impeller: Part 2 — Case Study of Blade Failure
Authors: Hasemann H. , Haupt U. , Jin D. , Seidel U. , Chen J. , Rautenberg M.
Published: March 2015

Following a case of blade failure in running the test into unsteady rotating stall regime at 16000 rpm for a centrifugal compressor with backswept impeller, systematic unsteady flow investigation has been conducted, in order to clarify the cause of the failure, for the same compressor with a dublicated impeller. The doubled frequency of 2 cell rotating stall excitation, which is happened in the present case in the range of resonant frequencies, has been found to potentially impose the blade failure. Another source of dangerous excitation was found to be the excitation of large-number cell rotating stall. Some study has also been conducted to analyse the influencing parameters of the large-number stall cell phenomenon, which shows a trend of alleviating the dangerous excitation with increasing the diffuser inlet radius ratio or decreasing the diffuser vane inlet angle.
Combustion Characteristics of Multicomponent Fuels Under Cold Starting Conditions in a Gas Turbine
Authors: Gauthier J. E. D. , Bardon M. F. , Rao V. K.
Published: March 2015

This paper describes a theoretical study of combustion in mixtures of fuel vapour, droplets and air under conditions representative of cold starting in gas turbines. It combines two previously developed models — one for heterogeneous flame propagation and the other for describing the complex evaporative behaviour of real fuel blends. Both models have been validated against experimental data, and the combined model is used to investigate the effect of fuel properties and injection system performance on minimum ignition energy, blowout velocity, lean extinction limits and related aspects significant for cold starting. Conditions are identified when fuel volatility is important and single component approximations are unrepresentative of real fuel behaviour. Explicit equations are given which predict the vapour pressures of JP-4, Jet A1 and diesel fuel.
Impact Design Methods for Ceramic Components in Gas Turbine Engines
Authors: Song J. , Cuccio J. , Kington H.
Published: March 2015

Garrett Auxiliary Power Division of Allied-Signal Aerospace Company is developing methods to design ceramic turbine components with improved impact resistance. In an ongoing research effort under the DOE/NASA-funded Advanced Turbine Technology Applications Project (ATTAP), two different modes of impact damage have been identified and characterized: Local damage and structural damage.

Local impact damage to Si3N4 impacted by spherical projectiles usually takes the form of ring and/or radial cracks in the vicinity of the impact point. Baseline data from Si3N4 test bars impacted by 1.588 mm (0.0625 inch) diameter NC-132 projectiles indicates the critical velocity at which the probability of detecting surface cracks is 50 percent equalled 130 m/sec (426 ft/sec). A microphysics-based model that assumes damage to be in the form of microcracks has been developed to predict local impact damage. Local stress and strain determine microcrack nucleation and propagation, which in turn alter local stress and strain through modulus degradation. Material damage is quantified by a “damage parameter” related to the volume fraction of microcracks. The entire computation has been incorporated into the EPIC computer code. Model capability is being demonstrated by simulating instrumented plate impact and particle impact tests.

Structural impact damage usually occurs in the form of fast fracture caused by bending stresses that exceed the material strength. The EPIC code has been successfully used to predict radial and axial blade failures from impacts by various size particles. This method is also being used in conjunction with Taguchi experimental methods to investigate the effects of design parameters on turbine blade impact resistance. It has been shown that significant improvement in impact resistance can be achieved by using the configuration recommended by the Taguchi methods.
Fracture Mechanics Approach to Creep Crack Growth in Welded IN738LC Gas Turbine Blades
Authors: Foo Wan-P’ng , Castillo Rafael
Published: March 2015

Microcracks caused by hot cracking or strain age cracking mechanisms are very likely to be discovered in the weld repair zone of precision cast IN738LC gas turbine blades. The possibility of crack propagation under the operating conditions of the gas turbine thereby becomes a crucial issue for gas turbine designers. The creep crack growth rate in air of the hipped and fully heat treated IN738LC was measured at the service temperature experienced by the first stage turbine blade tip. The corresponding growth behaviour was also studied.

The creep crack growth rate, da/dt, versus crack tip stress intensity factor, K1, a relation which exhibits the typical primary, secondary and tertiary behaviour, supports the applicability of K1 as an appropriate correlating parameter for the creep crack growth of this Ni-based superalloy under the loading conditions used in this study. Microstructural examination illustrated that the creep crack growth of IN738LC principally takes place by the nucleation, growth, coalescence and link-up of grain boundary microvoids and microcracks.

An excellent approximation of the stress intensity factor under service loading conditions in the vicinity of the crack tip was obtained by using the Westinghouse WECAN finite element analysis. It is shown that the crack tip stress intensity factor under normal loading conditions will not be able to drive the transverse through-the-wall-thickness blade tip crack in this study.
Similarity Transformations for Compressor Blading
Authors: Zhu N. G. , Xu L. , Chen M. Z.
Published: March 2015

Improving the performance of high speed axial compressors through low speed model compressor testing has proved to be economical and effective (Wisler, 1984). The key to this technique is to design low speed blade profiles which are aerodynamically similar to their high speed counterparts. The conventional aerodynamic similarity transformation involves the small disturbance potential flow assumption therefore its application is severely limited and generally not used in practical design. In this paper, a set of higher order transformation rules are presented which can accommodate large disturbances at transonic speed and are therefore applicable to similar transformations between the high speed HP compressor and its low speed model. Local linearization is used in the non–linear equations and the transformation is obtained in an iterative process. The transformation gives the global blading parameters such as camber, incidence and solidity as well as the blade profile. Both numerical and experimental validations of the transformation show that the non–linear similarity transformations do retain satisfactory accuracy for highly loaded blades up to low transonic speeds. Further improvement can be made by only slightly modifing profiles numerically without altering the global similarity parameters.
Inviscid-Viscous Coupled Solution for Unsteady Flows Through Vibrating Blades: Part 1 — Description of the Method
Authors: He L. , Denton J. D.
Published: March 2015

An efficient coupled approach between inviscid Euler and integral boundary layer solutions has been developed for quasi 3-D unsteady flows induced by vibrating blades. For unsteady laminar and turbulent boundary layers, steady correlations are adopted in a quasi-steady way to close the integral boundary layer model. This quasi-steady adoption of the correlations is assessed by numerical test results using a direct solution of the unsteady momentum integral equation. To conduct the coupling between the inviscid and viscous solutions for strongly interactive flows, the unsteady Euler and integral boundary layer equations are simultaneously time-marched using a multi-step Runge-Kutta scheme, and the boundary layer displacement effect is accounted for by a first order transpiration model. This time-resolved coupling method converges at conditions with considerable boundary layer separation.
Gas-Generator With High-Temperature Path Ceramic Components
Authors: Sudarev A. V. , Dubershtein V. H. , Kovalevsky V. P. , Ginsburg A. E.
Published: March 2015

The results of design-theoretical investigations of ceramic components of gas generator high-temperature path for gas turbine plant to drive the stationary equipment are shown. Analysis of effectiveness and application of various ceramic components was conducted, and ceramic components design, including rotor, was improved.