bluuebunny/crossref_metadata_2025 huggingface dataset:
Parental knowledge and attitudes towards pit and fissure sealants
Authors: Mafeni Jerome O. , Messer Louise Brearley
Published: May 2009

No survey of public knowledge and attitudes towards pit and fissure sealants has been carried out in Australia. This study assessed the knowledge and attitudes of parents of Melbourne school children attending five dental treatment centres, regarding sealants. Of 554 parents surveyed by questionnaire, 487 (88 per cent) provided codable responses which were analysed by the log‐likelihood ratio statistic and three‐way hierarchical log‐linear regression models. A total of 57.5 per cent respondents had heard of sealants; 46.4 per cent knew sealants prevent dental caries, and 45 per cent rated sealants important in caries prevention. Respondents attending private dentists or the Dental Therapy School were more knowledgeable about sealants than those attending other centres. Sealant awareness was related significantly to gender (p < 0.05), country of origin (p < 0.05), family income (p < 0.05), and frequency of dental visits of children (p < 0.001); the apparent association with country of origin, and annual family income, was explained by interactions between these variables and treatment centres. Dentists were the main source of dental health information including sealant awareness (p < 0.001). The most significant factors in sealant awareness were previous discussion of caries prevention by respondents with dentists; dentists as the main source of dental health information; and frequency of dental visits by the child(ren). These three factors confirm the importance of dentist‐patient interactions in disseminating oral health information.
Three‐year clinical evaluation of Tenure dentine bonding agent
Authors: Tyas Martin J.
Published: May 2009

Twenty cervical abrasion lesions in five patients of mean age 58 years were restored with Tenure dentine bonding agent and Silux composite, without enamel etching.

The cumulative loss rates of restorations were 5 per cent, 5 per cent, and 11 per cent after 1 year, 2 years and 3 years, respectively, and there was a slight increase of marginal staining. The results are in agreement with other authors.
Donovanosis of the oral cavity. Case report
Authors: Doddridge Miles , Muirhead Russell
Published: May 2009

Donovanosis (Granuloma inguinale) is an infectious disease, the effects of which are usually confined to the genital region. Various extragenital manifestations of the disease have been described. This report describes a case where the condition represented in the oral cavity some time after the apparently successful treatment of the genital lesion. Members of both the medical and dental profession serving the northern parts of Australia and adjacent tropical regions should be aware of the possibility of encountering this disease. Delay in its diagnosis may result in extensive tissue destruction and a potentially fatal outcome. Intensive antibiotic therapy followed by long‐term follow‐up is usually curative.
The effect of dentine conditioning with polyacrylic acid on the clinical performance of glass ionomer cement — 3‐year results
Authors: Tyas Martin J.
Published: May 2009

Forty cervical abrasion lesions were restored with a self‐cure Type 2A glass ionomer cement. Prior to placement of the restorations, 20 lesions were scrubbed for 15 seconds with 25 per cent polyacrylic acid and 20 lesions were cleaned with a pumice and water slurry on a rubber cup. After three years, there was negligible marginal staining, and one restoration from each group was partly lost. There was no evidence to suggest that polyacrylic acid was preferred to pumice and water in the restoration of cervical abrasion lesions with glass ionomer cement.
Screening for temporomandibular disorders in dental practice
Authors: Delcanho Robert
Published: May 2009

A simple screening procedure to determine evidence of a temporomandibular disorder (TMD) in a patient is presented. The current view is that dentists are responsible for the recognition and management of these disorders. The dentist should therefore perform a TMD screening examination on every patient and document the patient's functional status. If this is not known then it is impossible to discuss with the patient the possible implications of proposed dental treatment which could potentially worsen a pre‐existing TMD. Unless functional status is documented and informed consent obtained from the patient prior to proceeding with dental treatment, the dentist may be held liable should TMD problems develop during or after the treatment.
The effect of endodontic access cavity preparation and subsequent restorative procedures on incisor crown retention
Authors: Yu Yunxi Christine , Abbott Paul Vincent
Published: May 2009

Endodontic treatment often will require access through existing crowns. This study was undertaken to determine whether endodontic access cavity preparation affected the retention of crowns in anterior teeth and then to determine whether this retention can be regained by amalgam or post‐retained amalgam restorations. Twenty extracted human incisors were mounted in acrylic blocks and prepared for crowns. Metal copings were fabricated and cemented with zinc phosphate cement and the forces required to displace the copings after various procedures were measured with a tensile testing machine. Retention values for all stages were compared with the initial retentive value for each coping without an access cavity which was set at 100 per cent. Group one specimens had the following means: copings with access cavity, 85.64 ± 28.65 per cent of the initial values; amalgam flush with lingual dentine, 95.81 ± 36.2 per cent; amalgam flush with coping, 114.89 ± 34.5 per cent. Group two means were: copings with access cavity, 89.95 ± 21.42 per cent; posts and amalgam, 177.37 ± 77.5 percent. Statistical analysis with the two sample f test showed that retention with post‐retained amalgam restorations showed significantly higher values when compared with access cavities without restorations (p<0.05). Retention values for post‐retained restorations were significantly different from those just using amalgam. This study demonstrated that endodontic access cavities reduced the retention of the crowns, and subsequent restoration with amalgam or a post can regain the retention. Post‐retained restorations showed the highest retention when compared with the amalgam restorations, but the high standard deviation in the post group indicates that the amount of retention to be gained may be clinically unpredictable.
Australian Dental Research Fund Trebitsch Scholarship*: Immunohistological analysis of an in vivo Porphyromonas gingival is‐induced lesion in mice
Authors: Bowman J. J. D. , Gemmell E. , Bird P. S. , Seymour G. J.
Published: May 2009

Animal models have been used to study the pathogenic ability of putative periodontopathic bacteria. Injection of mice with live Porphyromonas gingivalis extracts has been shown to induce primary lesions which develop at the site of injection within one day and secondary lesions which develop at a distant site some 3–5 days later. These lesions are primarily polymorphonuclear cell (PMN) infiltrates. Recently, extensive data have shown that PMN activity may in part be controlled by T cells. Hence the aim of this report was to use the mouse model to determine the presence of T cells and macrophages in primary lesions in order to describe a baseline to be used for comparison in future studies.
Multiple canals in a mandibular first premolar. Case report
Authors: Yang Zu‐Pyn
Published: May 2009

It has been recorded that the occurrence rate of more than one canal in the mandibular first premolar varies between different races. This report presents the diagnosis and treatment of a mandibular first premolar with multiple root canals in a young male Asian. It is noted that knowledge of canal morphology, careful interpretation of the radiograph, and tactile sense during treatment constitute the major factors in achieving success with endodontic therapy in cases of complex root canal morphology.
Dynamic measurement of the torque‐speed characteristics of dental high speed air turbine handpieces*
Authors: Brockhurst P. J. , Shams Roya
Published: May 2009

The first requirement for adequate performance of an air turbine handpiece is sufficient power. Suppliers of such handpieces do not provide data on the power produced by their equipment. A method for determining the torque, speed and hence power during simulated operation is described. Forty‐one new and used handpieces were tested. Maximum speeds up to 500 000 rpm, maximum torques up to 2.33 N.mm and maximum power up to 29.6 watt were observed. The maximum power was produced at between 49 and 79 per cent of the free‐running speed. A relationship between maximum power and stall torque was noted. The maximum torque is at stall for ball‐bearing units. The stall torque can be easily determined by a simple stall torque test which is described. Using this test, the performance of handpieces can be easily checked in the clinic. The one air‐bearing handpiece tested performed in a manner similar to the others, except that stall occurred below 60 000 rpm.
Oral mucosal ulceration due to cytomegalovirus associated with human immunodeficiency virus infection. Case report and brief review
Authors: Firth Norman A. , Rich Alison M. , Reade Peter C.
Published: May 2009

Reports of oral lesions associated with cytomegalovirus (CMV) infection in human immunodeficiency virus (HIV) infected patients are uncommon1. In this article a case of CMV infection associated with oral mucosal ulceration and a brief review of the subject is presented. Establishing the cause of ulceration is important in determining a definitive diagnosis and prescribing appropriate therapy. It is important to recognize that CMV associated oral mucosal ulceration may be the initial manifestation of human immunodeficiency virus (HIV) infection.
Iatrogenic bismuth poisoning. Case report
Authors: Bridgeman Andrew M. , Smith Andrew C.
Published: May 2009

A case of bismuth intoxication following the intraoral use of BIPP‐impregnated gauze packs is presented. This report illustrates the need for caution when using potentially toxic compounds in the oral cavity where significant quantities can be absorbed to produce symptoms of poisoning.
Mechanical properties of some polymer materials used for tooth positioners
Authors: Collett Anthony R. , Cook Wayne D. , West Victor C.
Published: May 2009

The chemical composition, thermal behaviour and mechanical properties of three tooth positioner materials, Urethane P1 (P1), White Rubber (WR) and Elastocryl (EL) were investigated. Infra‐red spectrophotometry indicated the P1 polyurethane material to be of the polyether type, and EL to be a blend of poly(ethyl methacrylate) and poly(methyl methacrylate) while WR appeared to be filled cis‐poly (isoprene) (natural rubber). The glass transition temperature (Tg) for EL was determined as approximately 10deg;C, and for both P1 and WR the Tg was less than ‐50deg;C. The stress relaxation behaviour was assessed in compression by measuring the stress variation with time. The results for all three materials conformed to the superelastic theory of rubber elasticity. EL exhibited both a more rapid rate and higher degree of stress relaxation than did P1 and WR. Recovery from deformation was assessed by compressing cylinders for given periods of time and then measuring the level of reduced residual strain of the material with time. All three materials exhibited significant residual strain (ɛ(t)) over ‘clinically relevant’ time periods, and the reduced residual strain (ɛ (t)/ ɛ (0)) following deformation was greater for EL than P1 or WR. There was some indication that the three materials have some permanent set following deformation. It was concluded that, in considering desirable mechanical properties of tooth positioner materials, EL is the least suitable of the three examined, with none of the materials being ideal.
Plane of occlusion — a new concept
Authors: Mamootil J. A.
Published: May 2009

A new concept of the plane of occlusion based on anatomical landmarks has been developed. The posterior end of the plane is set by the centres of the retromolar pads, and the anterior end of the plane is at the upper lip line. These three points establish the plane of occlusion. An articulator has been developed to use this concept, which has been found to be clinically satisfactory for the construction of complete dentures.
Service‐mix provided to patients in Australian private practice
Authors: Spencer A. J. , Szuster F. S. P. , Brennan D. S.
Published: May 2009

Service‐mix can reflect changes in demographic factors, oral health, patient demand and treatment philosophies. The aim of this study was to compare service‐mix by patient age in 1988 with baseline data from 1983. A weighted, stratified random sample of dentists in Australia was surveyed by mailed questionnaire in 1983 and again in 1988. Service‐mix was dominated by restorative, diagnostic and preventive areas. Comparing 1988 with 1983, there were significant increases for diagnostic, preventive, advanced restorative, orthodontic and general areas. Patterns across patient age groups and between years indicated younger patients were being provided with increased preventive services (patients aged 5–11, 25–44 years) and decreased restorative services (patients aged 5–11, 12–17 years), while older patients were being provided with reduced prosthodontic services (patients aged 25–44, 45–64 years), but increased restorative services (patients aged 45–64, 65+ years) and advanced restorative services (patients aged 25–44, 45–64 years).These patterns of service‐mix have implications for dental education, research and service delivery.
Dental informatics for Australia
Authors: Hou Ann Y. S. C. , Barnard P. D.
Published: May 2009

Dentistry is undergoing significant changes with need for the dentist to manage a larger body of knowledge and information. There will be increasing reliance on electronic information systems in education, research, and dental practice. Dental informatics is concerned with computer and information science and technology and communications. Goals, that could be adopted for Australia, were proposed in the USA in 1989. Specific action steps that could meet those goals are proposed for Australia.
Growth and bone remodelling in a scorbutic rat model
Authors: Ellender G. , Gazelakis T.
Published: May 2009

This study used the scorbutic Osteogenic Disorder Shionogi rat model and a specific diet to reliably induce a state of sub‐scurvy scorbutus. Under these conditions overall somatic growth was assessed, as well as that of the caudal vertebrae, as an example of scorbutic bone growth. Tail loops were then used to mechanically stress mature caudal vertebrae under scorbutic conditions, and the vertebrae's adaptation to these applied forces was assessed, using measurements of bend deformation and histologic analysis of osteogenesis.

Scorbutic animals exhibited significant somatic growth retardation (p<0.05), and abnormal reductions in osteogenesis and periosteal responsiveness to growth. Scorbutic vertebrae also showed greater bend angles of deformation (p<0.05), and a marked reduction in cortical osseous remodelling and periosteal differentiation. It appeared that the sub‐scurvy scorbutic bones were smaller, weaker and less able to adapt to physical stresses: this pattern was reflected at the histologic level.
The effect of steam sterilization on the properties of set dental gypsum models
Authors: Whyte M. P. , Brockhurst P. J.
Published: May 2009

The aim of this study was to investigate the viability of autoclave sterilization of set dental gypsum models. The effects of autoclaving on the strength, surface hardness and dimensions of specimens of plaster, stone and diestone were investigated. In addition, sodium succinate was used to minimize any changes produced by autoclaving. It has been shown that dental gypsum casts can be successfully steam sterilized.

The results showed that for fully‐dried gypsum products, autoclaving at 132°C for 5 minutes rendered the casts unacceptable for use. Autoclaving at 121°C for 16 minutes had less effect although casts were still not satisfactory, with the main problems being excessive expansion for plaster and significant strength and surface hardness loss for stone and diestone.

The effect of three additional treatment procedures was examined and the least degradation was observed when the casts were soaked in 1 per cent sodium succinate solution and dried prior to autoclaving, then soaked in water immediately after. Using this procedure the averate change in properties for plaster, stone and diestone respectively were: loss of strength 36, 21 and 28 per cent, loss of surface hardness 34, 21 and 33 per cent, and linear expansion 0.05, 0.09 and 0.13 per cent. Further refinement may improve the procedure.
Recreating Political Order: The Somali Systems Today
Authors: Leonard David K.
Published: May 2009

The Somali pastoral system of production covers at least six political entities. Three of the formal ones are within the borders of the former Republic of Somalia and do not meet the full definition of states. Despite the warfare that has often engulfed the former Somalia, it is a mistake to think of the three political entities that occupy it as necessarily or wholly anarchic. Lineage institutions have survived from the colonial era and been resurrected to provide venues for negotiation, consensus‐building and the reduction of interpersonal violence, even if not the authoritative imposition of decisions upon groups of the unwilling. After 17 years of centrality to the continuity of Somali governance and the recreation of quasi‐state political authorities, however, these lineage institutions are showing signs of stress. As their great influence came to be recognised they were penetrated by patronage and used by warlords to prosecute sub‐clan warfare. They no longer are able to provide consensus representation even in the peaceful political systems of Somaliland and Puntland. Somalis therefore have experimented with new political institutions that could provide a greater basis for cross‐clan action and authoritative decision‐making – regional nationalism and democracy in Somaliland and Islamic sheria in all the territories but especially by the now‐deposed (but far from dead) Union of Islamic Courts. Indeed sheria now is a central, unifying ideology throughout the Somalis, even if there is conflict over its interpretation and the instrumentalities through which it will be enforced. Somali governmental processes thus are present, but weak in their ability to impose decisions and to project their authority into the rural areas. There are public goods that Somalis need which only states can provide. But the transformation of traditional order in the warlord conflicts of the last 17 years will make such states difficult to create.
Leading Edge Separation Bubbles on Turbomachine Blades
Authors: Walraevens R. E. , Cumpsty N. A.
Published: May 2009

Results are presented for separation bubbles of the type that can form near the leading edges of thin compressor or turbine blades. These often occur when the incidence is such that the stagnation point is not on the nose of the aerofoil. Tests were carried out at low speed on a single aerofoil to simulate the range of conditions found on compressor blades. Both circular and elliptic shapes of leading edge were tested. Results are presented for a range of incidence, Reynolds number, and turbulence intensity and scale. The principal quantitative measurements presented are the pressure distributions in the leading edge and bubble region, as well as the boundary layer properties at a fixed distance downstream, where most of the flows had reattached. Reynolds number was found to have a comparatively small influence, but a raised level of free-stream turbulence has a striking effect, shortening or eliminating the bubble and increasing the magnitude of the suction spike. Increased free-stream turbulence also reduces the boundary layer thickness and shape parameter after the bubble. Some explanations of the processes are outlined.
The Influence of Load Distribution on Secondary Flow in Straight Turbine Cascades
Authors: Weiss A. P. , Fottner L.
Published: May 2009

This paper describes an experimental study of the three-dimensional flow within two highly loaded turbine cascades subjected to the same overall load but different load distributions. Data were obtained using pneumatic probes, pressure tappings, and a surface flow visualization technique. It is found that the general nature of the flow is similar for both cascades. In the exit plane the cascades show different spanwise loss distributions. However, the averaged secondary loss is quite similar in this plane. Examining the measurements farther downstream and also by comparing the calculated mixed-out values, it becomes clear that a higher magnitude of secondary loss is generated by the front-loaded cascade.
Osborne Reynolds: Energy Methods in Transition and Loss Production: A Centennial Perspective
Authors: Moore J. , Moore J. G.
Published: May 2009

Osborne Reynolds’ developments of the concepts of Reynolds averaging, turbulence stresses, and equations for mean kinetic energy and turbulence energy are viewed in the light of 100 years of subsequent flow research. Attempts to use the Reynolds energy-balance method to calculate the lower critical Reynolds number for pipe and channel flows are reviewed. The modern use of turbulence-energy methods for boundary layer transition modeling is discussed, and a current European Working Group effort to evaluate and develop such methods is described. The possibility of applying these methods to calculate transition in pipe, channel, and sink flows is demonstrated using a one-equation, q-L, turbulence model. Recent work using the equation for the kinetic energy of mean motion to gain understanding of loss production mechanisms in three-dimensional turbulent flows is also discussed.
Bypass Transition in Boundary Layers Including Curvature and Favorable Pressure Gradient Effects
Authors: Volino R. J. , Simon T. W.
Published: May 2009

Recent experimental studies of two-dimensional boundary layers undergoing bypass transition have been reviewed to attempt to characterize the effects of free-stream turbulence level, acceleration, and wall curvature on bypass transition. Results from several studies were cast in terms of “local” boundary layer coordinates (momentum and enthalpy thickness Reynolds numbers) and compared. In unaccelerated flow on flat walls, skin friction coefficients were shown to match those from a laminar integral solution before transition and quickly adjusted to match those from a fully turbulent correlation after transition. Stanton number data also matched a correlation in the laminar region, but do not match correlation values so well in the turbulent region. The data showed that the relationship between skin friction coefficient and momentum thickness Reynolds number is unaffected by streamwise acceleration. Stanton numbers were strongly affected by acceleration, however, indicating a breakdown in Reynolds analogy. Concave curvature caused the formation of Go¨rtler vortices, which strongly influenced the skin friction. Convex curvature had an opposite, and lesser effect. The location and length of the transition region generally followed the expected trends as free-stream turbulence level, curvature, and acceleration were varied; the onset location and the transition length were extended by acceleration and convex curvature and reduced by concave curvature and enhanced turbulence. When individual cases were compared, some inconsistencies were observed. These inconsistencies indicate a need to characterize the flows to be compared more completely. Better spectral and length scale measurements of the free-stream disturbance would help in this regard. Within the transition region, the intermittency data from all the cases on flat walls (no curvature) were consistent with an intermittency distribution from the literature. Turbulent spot production rates were shown to be mostly dependent on free-stream turbulence, with a noted increase in spot production rate due to concave curvature and little effect of convex curvature. The acceleration effect on spot production rate was small for the cases studied.
Three-Dimensional Flow in a Highly Loaded Single-Stage Transonic Fan
Authors: Bryce J. D. , Cherrett M. A. , Lyes P. A.
Published: May 2009

Tests have been conducted at DRA Pyestock on a single-stage transonic fan with a very high level of aerodynamic loading at the hub. The objective of the tests was to survey the flow field in detail, with emphasis on studying the three-dimensional viscous aspects of the flow. The test module was highly instrumented. Detailed flow traversing was provided at rotor and stator exit, and replaceable stator cassettes allowed various types of on-blade instrumentation to be fitted. The test rig and instrumentation are described and detailed flow measurements, taken at peak efficiency operation on the design speed characteristic, are presented. These measurements, which are supplemented by flow visualization results, indicate the presence of a severe endwall corner stall in the stator hub flow field. The fan was modeled using the DRA S1-S2 method and these results are also discussed.
Control-Oriented High-Frequency Turbomachinery Modeling: Single-Stage Compression System One-Dimensional Model
Authors: Badmus O. O. , Chowdhury S. , Eveker K. M. , Nett C. N.
Published: May 2009

In this paper, a one-dimensional unsteady compressible viscous flow model of a generic compression system previously developed by the authors is applied to a multistage axial compressor experimental rig configured for single-stage operation. The required model parameters and maps are identified from experimental data. The resulting model is an explicit system of nine first-order ODEs. The model inputs are compressor speed, nozzle area, compressor discharge bleed area, plenum bleed area, inlet total pressure and entropy, and nozzle and bleed exit static pressures. The model and experimental data are compared with respect to both open-loop uncontrolled and closed-loop controlled behaviors. These comparisons focus on (i) forced transients and (ii) global nonlinear dynamics and bifurcations. In all cases the agreement between the model and experimental data is excellent. Of particular interest is the ability of the model, which does not include any hysteretic maps, to predict experimentally observed hysteresis with respect to the onset and cessation of surge. This predictive capability of the model manifests itself as the coexistence of a stable equilibrium (rotating stall) and a stable periodic solution (surge) in the model at a single fixed set of system input values. Also of interest is the fact that the controllers used for closed-loop comparisons were designed directly from the model with no a posteriori tuning of controller parameters. Thus, the excellent closed-loop comparisons between the model and experimental data provide strong evidence in support of the validity of the model for use in direct model based controller design. The excellent agreement between the model and experimental data summarized above is attributed in large part to the use of effective lengths within the model, as functions of axial Mach number and nondimensional compressor rotational speed, as prescribed by the modeling technique. The use of these effective lengths proved to be far superior to the use of physical lengths. The use of these effective lengths also provided substantial improvement over the use of physical lengths coupled with fixed first-order empirical lags, as proposed by other authors for the modeling of observed compressor dynamic lag. The overall success of this model is believed to represent a positive first step toward a complete experimental validation of the approach to control-oriented high-frequency turbomachinery modeling being developed by the authors.
Prestall Behavior of Several High-Speed Compressors
Authors: Tryfonidis M. , Etchevers O. , Paduano J. D. , Epstein A. H. , Hendricks G. J.
Published: May 2009

High-speed compressor data immediately prior to rotating stall inception are analyzed and compared to stability theory. New techniques for the detection of small-amplitude rotating waves in the presence of noise are detailed, and experimental and signal processing pitfalls discussed. In all nine compressors examined, rotating stall precedes surge. Prior to rotating stall inception, all the machines support small-amplitude (< 1 percent of fully developed stall) waves traveling about the circumference. Traveling wave strength and structure are shown to be a strong function of corrected speed. At low speeds, a ∼0.5 times shaft speed wave is present for hundreds of rotor revolutions prior to stall initiation. At 100 percent speed, a shaft speed rotating wave dominates, growing as stall initiation is approached (fully developed rotating stall occurs at about 1/2 of shaft speed). A new, two-dimensional, compressible hydrodynamic stability analysis is applied to the geometry of two of the compressors and gives results in agreement with data. The calculations show that, at low corrected speeds, these compressors behave predominantly as incompressible machines. The wave that first goes unstable is the 1/2 shaft frequency mode predicted by the incompressible Moore–Greitzer analysis and previously observed in low-speed compressors. Compressibility becomes important at high corrected speeds and adds axial structure to the rotating waves. At 100 percent corrected speed, one of these hitherto unrecognized compressible modes goes unstable first. The rotating frequency of this mode is constant and predicted to be approximately coincident with shaft speed at design. Thus, it is susceptible to excitation by geometric nonuniformities in the compressor. This new understanding of compressor dynamics is used to introduce the concept of traveling wave energy as a real time measure of compressor stability. Such a wave energy-based scheme is shown consistently to give an indication of low stability for significant periods (100–200 rotor revolutions) before stall initiation, even at 100 percent corrected speed.
Control of the Unsteady Flow in a Stator Blade Row Interacting With Upstream Moving Wakes
Authors: Valkov T. , Tan C. S.
Published: May 2009

A computational approach, based on a spectral-element Navier–Stokes solver, has been applied to the study of the unsteady flow arising from wake–stator interaction. Direct, as well as turbulence-model calculations, provide insight into the mechanics of the unsteady flow and demonstrate the potential for controlling its effects. The results show that the interaction between the wakes and the stator blades produces a characteristic pattern of vortical disturbances, which have been correlated to the pressure fluctuations. Within the stator passage, the wakes migrate toward the pressure surface where they evolve into counterrotating vortices. These vortices are the dominant source of disturbances over the pressure surface of the stator blade. Over the suction surface of the stator blade, the disturbances are due to the distortion and detachment of boundary layer fluid. They can be reduced by tailoring the blade loading or by applying nonuniform suction.
Turbomachinery Committee Best 1994 Paper Award: Dynamic Control of Rotating Stall in Axial Flow Compressors Using Aeromechanical Feedback
Authors: Gysling D. L. , Greitzer E. M.
Published: May 2009

Dynamic control of rotating stall in an axial flow compressor has been implemented using aeromechanical feedback. The control strategy developed used an array of wall jets, upstream of a single-stage compressor, which were regulated by locally reacting reed valves. These reed valves responded to the small-amplitude flow-field pressure perturbations that precede rotating stall. The valve design was such that the combined system, compressor plus reed valve controller, was stable under operating conditions that had been unstable without feedback. A 10 percent decrease in the stalling flow coefficient was obtained using the control strategy, and the extension of stable flow range was achieved with no measurable change in the steady-state performance of the compression system. The experiments demonstrate the first use of aeromechanical feedback to extend the stable operating range of an axial flow compressor, and the first use of local feedback and dynamic compensation techniques to suppress rotating stall. The design of the experiment was based on a two-dimensional stall inception model, which incorporated the effect of the aeromechanical feedback. The physical mechanism for rotating stall in axial flow compressors was examined with focus on the role of dynamic feedback in stabilizing compression system instability. As predicted and experimentally demonstrated, the effectiveness of the aeromechanical control strategy depends on a set of nondimensional control parameters that determine the interaction of the control strategy and the rotating stall dynamics.
Aircraft Engine Committee Best 1993 Paper Award: Control-Oriented High-Frequency Turbomachinery Modeling: General One-Dimensional Model Development
Authors: Badmus O. O. , Eveker K. M. , Nett C. N.
Published: May 2009

In this paper, an approach for control-oriented high-frequency turbomachinery modeling previously developed by the authors is applied to develop one-dimensional unsteady compressible viscous flow models for a generic turbojet engine and a generic compression system. We begin by developing models for various components commonly found in turbomachinery systems. These components include: ducting without combustion, blading, ducting with combustion, heat soak, blading with heat soak, inlet, nozzle, abrupt area change with incurred total pressure losses, flow splitting, bleed, mixing, and the spool. Once the component models have been developed, they are combined to form system models for a generic turbojet engine and a generic compression system. These models are developed so that they can be easily modified and used with appropriate maps to form a model for a specific rig. It is shown that these system models are explicit (i.e., can be solved with any standard ODE solver without iteration) due to the approach used in their development. Furthermore, since the nonlinear models are explicit, explicit analytical linear models can be derived from the nonlinear models. The procedure for developing these analytical linear models is discussed. An interesting feature of the models developed here is the use of effective lengths within the models, as functions of axial Mach number and nondimensional rotational speed, for rotating components. These effective lengths account for the helical path of the flow as it moves through a rotating component. Use of these effective lengths in the unsteady conservation equations introduces a nonlinear dynamic lag consistent with experimentally observed compressor lag and replaces less accurate linear first-order empirical lags proposed to account for this phenomenon. Models of the type developed here are expected to prove useful in the design and simulation of (integrated) surge control and rotating stall avoidance schemes.
The Structure of Tip Clearance Flow in Axial Flow Compressors
Authors: Lakshminarayana B. , Zaccaria M. , Marathe B.
Published: May 2009

Detailed measurements of the flow field in the tip region of an axial flow compressor rotor were carried out using a rotating five-hole probe. The axial, tangential, and radial components of relative velocity, as well as the static and stagnation pressures, were obtained at two axial locations, one at the rotor trailing edge, the other downstream of the rotor. The measurements were taken up to about 26 percent of the blade span from the blade tip. The data are interpreted to understand the complex nature of the flow in the tip region, which involves the interaction of the tip leakage flow, the annulus wall boundary layer and the blade wake. The experimental data show that the leakage jet does not roll up into a vortex. The leakage jet exiting from the tip gap is of high velocity and mixes quickly with the mainstream, producing intense shearing and flow separation. There are substantial differences in the structure of tip clearance observed in cascades and rotors.
Numerical Simulation of Tip Clearance Effects in Turbomachinery
Authors: Basson A. , Lakshminarayana B.
Published: May 2009

The numerical formulation developed here includes an efficient grid generation scheme, particularly suited to computational grids for the analysis of turbulent turbo-machinery flows and tip clearance flows, and a semi-implicit, pressure-based computational fluid dynamics scheme that directly includes artificial dissipation, and is applicable to both viscous and inviscid flows. The value of this artificial dissipation is optimized to achieve accuracy and convergency in the solution. The numerical model is used to investigate the structure of tip clearance flows in a turbine nozzle. The structure of leakage flow is captured accurately, including blade-to-blade variation of all three velocity components, pitch and yaw angles, losses and blade static pressures in the tip clearance region. The simulation also includes evaluation of such quantities as leakage mass flow, vortex strength, losses, dominant leakage flow regions, and the spanwise extent affected by the leakage flow. It is demonstrated, through optimization of grid size and artificial dissipation, that the tip clearance flow field can be captured accurately.
An Asymptotic Analysis of Mixing Loss
Authors: Fritsch G. , Giles M. B.
Published: May 2009

The objective of this paper is to establish, in a rigorous mathematical manner, a link between the dissipation of unsteadiness in a two-dimensional compressible flow and the resulting mixing loss. A novel asymptotic approach and a control-volume argument are central to the analysis. It represents the first work clearly identifying the separate contributions to the mixing loss from simultaneous linear disturbances, i.e., from unsteady entropy, vorticity, and pressure waves. The results of the analysis have important implications for numerical simulations of turbomachinery flows; the mixing loss at the stator/rotor interface in steady simulations and numerical smoothing are discussed in depth. For a transonic turbine, the entropy rise through the stage is compared for a steady and an unsteady viscous simulation. The larger interface mixing loss in the steady simulation is pointed out and its physical significance is discussed. The asymptotic approach is then applied to the first detailed analysis of interface mixing loss. Contributions from different wave types and wavelengths are quantified and discussed.
Measurement of Turbine Blade-Tip Rotordynamic Excitation Forces
Authors: Martinez-Sanchez M. , Jaroux B. , Song S. J. , Yoo S.
Published: May 2009

This paper presents results of a program to investigate the magnitude, origin, and parametric variations of destabilizing forces that arise in high power turbines due to blade-tip leakage effects. Five different unshrouded turbine configurations and one configuration shrouded with a labyrinth seal were tested with static offsets of the turbine shaft. The forces along and perpendicular to the offset were measured directly with a dynamometer, and were also inferred from velocity triangles and pressure distributions obtained from detailed flow surveys. These two routes yielded values in fair agreement in all cases. For unshrouded turbines, the cross-forces are seen to originate mainly (˜ 2/3) from the classical Alford mechanism (nonuniform work extraction due to varying blade efficiency with tip gap) and about 1/3 from a slightly skewed hub pressure pattern. The direct forces arise mainly (3/4) from this pressure pattern, with the rest due to a slight skewness of the Alford mechanism. The pressure nonuniformity (lower pressures near the widest gap) is seen to arise from a large-scale redistribution of the flow as it approaches the eccentric turbine. The cross-forces are found to increase substantially when the gap is reduced from 3.0 to 1.9 percent of blade height, probably due to viscous blade-tip effects. The forces also increase when the hub gap between stator and rotor decreases. The force coefficient decreases with operating flow coefficient. In the case of the shrouded turbine, most of the forces arise from nonuniform seal pressures. This includes about 80 percent of the transverse forces. The rest appears to come from uneven work extraction (Alford mechanism). Their level is about 50 percent higher than in the unshrouded cases.
Intermittent Flow and Thermal Structures of Accelerating Transitional Boundary Layers: Part 2—Fluctuation Quantities
Authors: Wang T. , Keller F. J.
Published: May 2009

The conditionally sampled fluctuation quantities of nonaccelerating and accelerating heated transitional boundary layers were analyzed. The results indicated that the values of u′, υ′, uv, and ut, in the turbulent part of the transitional flow were higher than those values in the fully developed turbulent flow. These higher values were believed to be manifestations of the vigorous activities involved in the transition process. The contributions to the unconditioned u′ by “mean-step” change due to the alternating behavior between turbulent and nonturbulent flows are about 20 percent in the near-wall region, but are negligible for Y+ > 30. The turbulent part uv values are higher than the fully turbulent and unconditioned values in the inner boundary layer but lower in the outer boundary layer. The mean-step change has negligible effect on unconditioned uv values. As acceleration increases, both u′ and t′ in the turbulent part are suppressed; however, turbulent part u′ is still higher than the unconditioned u′ Acceleration promotes streamwise Reynolds heat flux (ut) transport in both turbulent and nonturbulent parts. A second peak of the turbulent part ut occurs at around Y+ = 120 as acceleration increases. The turbulent part eddy viscosity values are much lower than those in the fully turbulent flow.
The Experimental Study of Matching Between Centrifugal Compressor Impeller and Diffuser
Authors: Tamaki H. , Nakao H. , Saito M.
Published: May 2009

The centrifugal compressor for a marine use turbocharger with its design pressure ratio of 3.2 was tested with a vaneless diffuser and various vaned diffusers. Vaned diffusers were chosen to cover impeller operating range as broad as possible. The analysis of the static pressure ratio in the impeller and the diffusing system, consisting of the diffuser and scroll, showed that there were four possible combinations of characteristics of impeller pressure ratio and diffusing system pressure ratio, The flow rate, QP, where the impeller achieved maximum static pressure ratio, was surge flow rate of the centrifugal compressor determined by the critical flow rate. In order to operate the compressor at a rate lower than QP, the diffusing system, whose pressure recovery factor was steep negative slope near QP, was needed. When the diffuser throat area was less than a certain value, the compressor efficiency deteriorated; however, the compressor stage pressure ratio was almost constant. In this study, by reducing the diffuser throat area, the compressor could be operated at a flow rate less than 40 percent of its design flow rate. Analysis of the pressure ratio in the impeller and diffusing systems at design and off-design speeds showed that the irregularities in surge line occurred when the component that controlled the negative slope on the compressor stage pressure ratio changed.
Numerical Flow Analysis in a Subsonic Vaned Radial Diffuser With Leading Edge Redesign
Authors: Casartelli E. , Saxer A. P. , Gyarmathy G.
Published: May 2009

The flow field in a subsonic vaned radial diffuser of a single-stage centrifugal compressor is numerically investigated using a three-dimensional Navier–Stokes solver (TASCflow) and a two-dimensional analysis and inverse-design software package (MISES). The vane geometry is modified in the leading edge area (two-dimensional blade shaping) using MISES, without changing the diffuser throughflow characteristics. An analysis of the two-dimensional and three-dimensional effects of two redesigns on the flow in each of the diffuser subcomponents is performed in terms of static pressure recovery, total pressure loss production, and secondary flow reduction. The computed characteristic lines are compared with measurements, which confirm the improvement obtained by the leading edge redesign in terms of increased pressure rise and operating range.
Automatic Genetic Optimization Approach to Two-Dimensional Blade Profile Design for Steam Turbines
Authors: Trigg M. A. , Tubby G. R. , Sheard A. G.
Published: May 2009

In this paper a systematic approach to the optimization of two-dimensional blade profiles is presented. A genetic optimizer has been developed that modifies the blade profile and calculates its profile loss. This process is automatic, producing profile designs significantly faster and with significantly lower loss than has previously been possible. The optimizer developed uses a genetic algorithm to optimize a two-dimensional profile, defined using 17 parameters, for minimum loss with a given flow condition. The optimizer works with a “population” of two-dimensional profiles with varied parameters. A CFD mesh is generated for each profile, and the result is analyzed using a two-dimensional blade-to-blade solver, written for steady viscous compressible flow, to determine profile loss. The loss is used as the measure of a profile’s “fitness” The optimizer uses this information to select the members of the next population, applying crossovers, mutations, and elitism in the process. Using this method, the optimizer tends toward the best values for the parameters defining the profile with minimum loss.
Nonlinear Separated Inviscid-Viscous Analysis of Oscillating Cascade Aerodynamics Using an Inverse Integral Method
Authors: Wolff J. M. , Fleeter S.
Published: May 2009

A mathematical model is developed to analyze the unsteady flow through an harmonically oscillating cascade of airfoils, including separated flow. The model incorporates an inverse integral boundary layer solution with the time-marching Euler analysis NPHASE. An embedded composite grid formulation is incorporated, specifically a deforming C-grid embedded in a Cartesian H-grid, thereby simplifying grid generation. To reduce computational requirements, Fourier series unsteady periodic boundary conditions are implemented. The integral turbulent boundary layer model is closed with steady correlations adopted in a quasi-steady manner. To couple the inviscid and viscous solutions, the viscous effect is modeled in the unsteady Euler solution in a quasi-steady manner by a transpiration boundary condition. An isolated airfoil is used to compare the steady interaction model with experimental data. Then a flat plate cascade is used to verify the unsteady flow solver with linear theory predictions. An experimental unsteady aerodynamics data set of a loaded cascade with separated meanflow executing torsional oscillations compared favorably with the analysis. The code is then utilized to study the effect of flow separation on the unsteady aerodynamics.