bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiobjective Optimization Approach to Turbomachinery Blades Design
Authors: Li Jun , Li Guojun , Feng Zhenping , Liu Lijun
Published: November 2008

This paper presents an automated optimization design methodology for turbomachinery blades using multiobjective evolutionary algorithms (MOEAs) and Navier-Stokes solver. The multi-branch Tournament selection and Pareto solution conception are used in the presented MOEAs. Elitist method and generation gap are adapted to ensure the optimization performance and decrease the computation expense. The Bezier-curves are utilized to parameterize the designed blade profile and corresponding control points are used as the designed variables. Reynolds-Averaged Navier-Stokes solver is applied to evaluate the aerodynamic performance of the designed candidates. Two design cases of the 2D and 3D compressor blade are used to demonstrate the presented methodology performance. A 2D axial compressor blade is optimized for maximization of the static pressure rise and minimization of the total pressure loss at the fixed flow condition. The Pareto solutions are obtained using the presented optimization algorithm. The detailed analysis between the certain Pareto solutions with the higher static pressure rise and the lower total pressure loss and the initial design are illustrated. A 3D centrifugal compressor impeller blade is optimized as the second case. The maximization of the pressure rise and blade load and minimization of the rotational total pressure loss at the given flow conditions are worked as the design targets. The present method obtains many reasonable Pareto optimal designs that outperform the original centrifugal impeller at the designed condition.
Redesign of a Multistage Axial Compressor for a Heavy Duty Industrial Gas Turbine (GT11NMC)
Authors: Savic Sasha M. , Micheli Marco A. , Bauer Andreas C.
Published: November 2008

Different approaches to compressor design exist in industrial practice. This paper describes two design philosophies that can be followed with compressor development (re-staggering and new airfoil design), and reports on field experience gained with an advanced compressor design using CDA (Controlled Diffusion Airfoils) profiles. The first philosophy described is based on incremental changes of compressor design, consisting of keeping the same blade profiles and re-staggering a number of rotor blades and/or stator vanes. The second philosophy described is to utilize advanced CDA profiles in compressor design, optimized for increased mass-flow and backpressure. The second philosophy was followed in the development of a compressor upgrade for ALSTOM’s GT11NM gas turbines, where a significant increase in GT power output (exceeding 10%) and improved overall engine efficiency (+0.4% additive) at unchanged surge margin were achieved. Power output and improved efficiency resulted solely from the advanced blade design, requiring no additional power augmentation techniques. These figures were measured on a natural gas-fired GT operating in an open-cycle power plant.
The Boundary Layer Over Turbine Blade Models With Realistic Rough Surfaces
Authors: McIlroy Hugh M. , Budwig Ralph S.
Published: November 2008

Results are presented of extensive boundary layer measurements taken over a flat, smooth plate model of the front one-third of a turbine blade and over the model with an embedded strip of realistic rough surface. The turbine blade model also included elevated freestream turbulence and an accelerating freestream in order to simulate conditions on the suction side of a high-pressure turbine blade. The realistic rough surface was developed by scaling actual turbine blade surface data provided by U. S. Air Force Research Laboratory. The rough patch can be considered to be an idealized area of distributed spalls with realistic surface roughness. The results indicate that bypass transition occurred very early in the flow over the model and that the boundary layer remained unstable (transitional) throughout the entire length of the test plate. Results from the rough patch study indicate the boundary layer thickness and momentum thickness Reynolds numbers increased over the rough patch and the shape factor increased over the rough patch but then decreased downstream of the patch. It was also found that flow downstream of the patch experienced a gradual re-transition to laminar-like behavior but in less time and distance than in the smooth plate case. Additionally, the rough patch caused a significant increase in streamwise turbulence intensity and normal turbulence intensity over the rough patch and downstream of the patch. Also, the skin friction coefficient over the rough patch increased by nearly 2.5 times the smooth plate value. Finally, the rough patch caused the Reynolds shear stresses to increase in the region close the plate surface.
Film-Cooling Effectiveness on Squealer Rim Walls and Squealer Cavity Floor of a Gas Turbine Blade Tip Using Pressure Sensitive Paint
Authors: Mhetras Shantanu , Yang Huitao , Gao Zhihong , Han Je-Chin
Published: November 2008

Effects of shaped holes on the tip pressure side, coolant jet impingement on the pressure side squealer rim from tip holes and varying blowing ratios for a squealer blade tip were examined on film-cooling effectiveness. The film-cooling effectiveness distributions were measured on the blade tip, near tip pressure side and the inner pressure side rim wall using Pressure Sensitive Paint technique. Air and nitrogen gas were used as the film cooling gases and the oxygen concentration distribution for each case was measured. The film cooling effectiveness information was obtained from the difference of the oxygen concentration between air and nitrogen gas cases by applying the mass transfer analogy. The internal coolant-supply passages of the squealer tipped blade were modeled similar to those in the GE-E3 rotor blade with two separate serpentine loops supplying coolant to the film cooling holes. A row of compound angled cylindrical film cooling holes was arranged along the camber line on the tip and another row of compound angled shaped film cooling holes was arranged along the span of the pressure side just below the tip. The average blowing ratio of the cooling gas was controlled to be 0.5, 1.0 and 2.0. Tests were conducted in a five-bladed linear cascade in a blow down facility with a tip gap clearance of 1.5%. The free stream Reynolds number, based on the axial chord length and the exit velocity, was 1,138,000 and the inlet and the exit Mach number were 0.25 and 0.6, respectively. Turbulence intensity level at the cascade inlet was 9.7%. Numerical predictions were also performed using Fluent to simulate the experiment at the same inlet flow conditions. Predictions for film cooling are presented. Results show a good correlation between experimental and predicted data. The shape and location of the film cooling holes along with varying blowing ratios can have significant effects on film-cooling performance.
A Numerical Investigation of Boundary Layer Suction in Compound Lean Compressor Cascades
Authors: Song Yanping , Chen Fu , Yang Jun , Wang Zhongqi
Published: November 2008

This paper is focused on the numerical investigation of boundary layer suction (BLS) via a slot on the suction surfaces of two compound lean compressor cascades with large camber angles as well as a conventional straight compressor cascade for comparison. The objective of the investigation is to study the influence of boundary layer suction on the performance of compound lean compressor cascades, thus to discuss the possibility of the application of boundary layer suction to improve their performance. An extensive numerical study has been carried out under different spanwise lengths and different axial positions of the slots, and different suction flow rates. The results show that the total loss of all three cascades is reduced significantly by boundary layer suction, and the largest reduction occurs at the highest suction flow rate. The axial locations of the slot have little effect on the total loss of the three cascades, which means the slots are opened within the optimal axial range in this case. The slot opened along the full span is the best one to obtain the largest reduction in total loss for all three cascades due to the alleviation of flow separation in the corner between the endwall and the suction surface. Moreover, the flow turning is increased, and pressure rise at the rear of the passage is recovered along the whole blade height via boundary layer suction along the full span, enhancing the working range of the highly loaded compressor cascades.
The Influence of Compressor Blade Row Interaction Modeling on Performance Estimates From Time-Accurate, Multi-Stage, Navier-Stokes Simulations
Authors: Van Zante Dale , Chen Jenping , Hathaway Michael , Chriss Randall
Published: November 2008

The time-accurate, multi-stage, Navier-Stokes, turbomachinery solver TURBO was used to calculate the aero performance of a 2 1/2 stage, highly-loaded, high-speed, axial compressor. The goals of the research project were to demonstrate completion times for multi-stage, time-accurate simulations that are consistent with inclusion in the design process, and to assess the influence of differing approaches to modeling the effects of blade row interactions on aero performance estimates. Three different simulation setups were used to model blade row interactions: 1.) single passage per blade row with phase lag boundaries, 2.) multiple passages per blade row with phase lag boundaries, and 3.) a periodic sector (1/2 annulus sector). The simulations used identical inlet and exit boundary conditions and identical meshes. To add more blade passages to the domain, the single passage meshes were copied and rotated. This removed any issues of differing mesh topology or mesh density from the following results. The 1/2 annulus simulation utilizing periodic boundary conditions required an order of magnitude less iterations to converge when all three simulations were converged to the same level as assessed by monitoring changes in overall adiabatic efficiency. When using phase lag boundary conditions the need to converge the time history information necessitates more iterations to obtain the same convergence level. In addition to convergence differences, the three simulations gave different overall performance estimates where the 1/2 annulus case was 1.0 point lower in adiabatic efficiency than the single passage phase lag case. The interaction between blade rows in the same frame of reference set up spatial variations of properties in the circumferential direction which are stationary in that reference frame. The phase lag boundary condition formulation will not capture this effect because the blade rows are not moving relative to each other. Thus for simulations of more than two blade rows and strong interactions, a periodic simulation is necessary to estimate the correct aero performance.
An Investigation of the Application of Roughness Elements to Enhance Heat Transfer in an Impingement Cooling System
Authors: Son Changmin , Dailey Geoffery , Ireland Peter , Gillespie David
Published: November 2008

The inclusion of roughness elements on the target surface of a turbine aerofoil impingement cooling system is an attractive means of heat transfer enhancement. In such a system, it is important to minimise additional pressure loss caused by the roughness elements and thus their shape, size and position need to be optimised. The research showed how heat transfer enhancement is normally achieved at the expense of extra pressure loss. A hexagonal roughness element designed by the authors showed up to 10% heat transfer enhancement with minimal extra pressure loss. The present work includes shear pattern visualisation on the target surface, pressure loss measurements and heat transfer coefficient measurements for an impingement cooling system with simply shaped roughness elements-specifically cylindrical & diamond pimples. Flow visualisation results and pressure loss measurements for the above configurations provided criteria for selecting the shape, size and position of the roughness elements. The detailed heat transfer measurements on the target surface and over the roughness elements were used to explain the heat transfer enhancement mechanisms. It was found that the largest contribution to heat transfer is the impingement stagnation point and the developing wall jet regions. However, the research showed that the low heat transfer coefficient region could be made to contribute more by using strategically located roughness elements. A hexagonal rim was designed to cover the complete low heat transfer coefficient region midway between neighbouring jets. The effect of the height, cross sectional shape and wall angle of the hexagonal rim were studied using a series of heat transfer and pressure loss experiments. The transient heat transfer tests were conducted using a triple thermochromic liquid crystal technique and the thermal transient was produced by a fine wire mesh heater. The heat transfer coefficient over the pimples was measured using a hybrid transient method that analysed the thermal transient of the copper pimple. The detailed heat transfer coefficient distributions over the complete area of the target surface provided comprehensive understanding of the performance of the hexagonal rim. Tests were conducted at three different mass flow rates for each configuration. The average and local jet Reynolds numbers varied between 21500 and 31500, and 17000 and 41000 respectively.
Improvement of a Film-Cooled Blade by Application of the Conjugate Calculation Technique
Authors: Kusterer Karsten , Hagedorn Torsten , Bohn Dieter , Sugimoto Takao , Tanaka Ryozo
Published: November 2008

The conjugate calculation technique has been used for the three-dimensional thermal load prediction of a film-cooled test blade of a modern gas turbine. Thus, it becomes possible to take into account the interaction of internal flows, external flow, and heat transfer without the prescription of heat transfer coefficients. The numerical models consist of all internal flow passages and cooling hole rows including shaped holes. Based on the results, deficiencies of the test configuration close to the leading edge region and in the blade tip region have been detected, which lead to hot spots and surface areas of high thermal load. These regions of high thermal load have been confirmed by thermal index paint measurements in good agreement to the conjugate calculation results. Based on the experimental and numerical results, recommendations for the improvement of the blade cooling were derived and an improved blade cooling configuration has been designed. The conjugate calculation results as well as new measurement data show that the changes in the cooling design have been successful with respect to cooling performance. Regions of high thermal load have vanished and effective cooling is reached for all critical parts of the test blade.
Experiments on the Physical Mechanism of Heat Transfer Augmentation by Freestream Turbulence at a Cylinder Stagnation Point
Authors: Nix A. C. , Diller T. E.
Published: November 2008

Detailed time records of velocity and heat flux were measured near the stagnation point of a cylinder in low-speed air flow. The freestream turbulence was controlled using five different grids positioned to match the characteristics from previous heat flux experiments at NASA Glenn using the same wind tunnel. A hot wire was used to measure the cross-flow velocity at a range of positions in front of the stagnation point. This gave the average velocity and fluctuating component including the turbulence intensity and integral length scale. The heat flux was measured with a Heat Flux Microsensor located on the stagnation line underneath the hot-wire probe. This gave the average heat flux and the fluctuating component simultaneous with the velocity signal, including the heat flux turbulence intensity and the coherence with the velocity. The coherence between the signals allowed identification of the crucial positions for measurement of the integral length scale and turbulence intensity for prediction of the time average surface heat flux. The frequencies corresponded to the most energetic frequencies of the turbulence, indicating the importance of the penetration of the turbulent eddies from the freestream through the boundary layer to the surface. The distance from the surface was slightly less than the local value of length scale, indicating the crucial role of the turbulence in augmenting the heat flux. The resulting predictions of the analytical model matched well with the measured heat transfer augmentation.
Flow and Heat Transfer Characteristics of an Impinging Jet in Crossflow at Low Nozzle-to-Plate Spacings
Authors: Cheong Brian C. Y. , Ireland Peter T. , Ling John P. C. W. , Ashforth-Frost Shirley
Published: November 2008

The research reported in this paper has measured in detail the near wall hydrodynamic and thermal characteristics of a confined single impinging jet in crossflow. To the authors’ knowledge, the work is unique in that the flow and thermal fields have been linked to the local surface heat transfer coefficients, which were measured at high resolution. The near wall velocity, turbulence, temperature and temperature fluctuation distributions of the jet were measured using hotwire anemometry and cold-wire thermometry. The target surface heat transfer coefficients were determined using the transient liquid crystal method. The multiple colour play coating enabled both the heat transfer coefficient and the adiabatic wall temperature distributions to be measured. The turbulent jet discharged with uniform exit velocity and temperature profiles at a Reynolds numbers of 20 000 and 40 000. The jet was subject to a crossflow at jet-to-crossflow velocity ratios of 1, 2, 3, 4 and 5. Two nozzle-to-plate spacings of 1.5d and 3d were examined. The results show that impinging jets in crossflow at z/d = 1.5 are significantly more intact at the target surface than jets with z/d = 3. As a result, the surface heat transfer rates beneath a jet in crossflow at the closer spacing are consistently higher. The results would provide excellent test cases for CFD works of similar flow configurations. The results are compared to related data in the literature. In addition, the driving gas temperature measured with the liquid crystals is compared to the near wall thermal field measured with the cold-wire.
Experimental and Numerical Investigations on a High Pressure Ratio Centrifugal Compressor
Authors: Choi Jae Ho , Sung Ok Suck , Chen Seung-Bae , Lim Jin Shik
Published: November 2008

An aerodynamic design, flow analysis and performance test of a pressure ratio 4:1 centrifugal compressor are presented in this paper. The compressor is made up of a centrifugal impeller, a two-stage diffuser consisted of radial and axial types. The impeller has a 45 degree backswept angle and the design running tip clearance is 5% of impeller exit height. Two types of diffusers are designed for this compressor. Three-dimensional numerical analysis is performed to analyze the flows in the impeller, diffuser and deswirler considering the impeller tip clearance. A test module and rig facilities for the compressor stage performance test are designed and fabricated. The overall compressor stage performances as well as the static pressure fields on the impeller and diffuser are measured. Two diffusers of wedge and airfoil types are tested with an impeller. The calculation and test results show the airfoil diffuser has the better aerodynamic characteristics than those of wedge diffuser in the studied models.
Numerical Investigation of Endwall Boundary Layer Removal on Highly-Loaded Axial Compressor Blade Rows
Authors: Gu¨mmer V. , Goller M. , Swoboda M.
Published: November 2008

This paper presents results of numerical investigations carried out to explore the benefit of endwall boundary layer removal from critical regions of highly-loaded axial compressor blade rows. At the loading level of modern aero-engine compressors the performance is primarily determined by three-dimensional flow phenomena occuring in the endwall regions. 3DNS simulations were conducted on both a rotor and a stator test case in order to evaluate basic effects and the practical value of bleeding air from specific locations at the casing endwall. The results of the numerical survey demonstrated substantial benefits of relatively small bleed rates to the local flow field and to the performance of the two blade rows. On the rotor, boundary layer fluid was removed from the main flow path through an axisymmetric slot in the casing over the rotor tip. This proved to give some control over the tip leakage vortex flow and the associated loss generation. On the stator, boundary layer fluid was taken from the flow path through a single bleed hole within the passage. Two alternative off-take configurations were evaluated, revealing a large impact of the bleed hole shape and location on the cross-passage flow and the suction side corner separation. On both blade rows investigated, rotor and stator, boundary layer removal resulted in a reduction of local reverse flow, blockage and losses in the respective near-casing region. This paper gives insight into changes occuring in the 3D passage flow field near the casing and summarises the effects on the radial matching and pitchwise-averaged performance parameters, namely loss and deviation of the rotor and stator when suction is active. Primary focus is put on the aerodynamics in the blade rows in the main flow path; details of the internal flow structure within the bleed off-take cavities/ports are not discussed here.
Numerical Investigation of the Secondary Flow of a Transonic Turbine Stage Using Various Turbulence Closures
Authors: Pecnik Rene , Pieringer Paul , Sanz Wolfgang
Published: November 2008

The accurate numerical simulation of the flow through turbine stages strongly depends on the proper prediction of turbulence phenomena. Especially investigations of heat transfer, skin friction, flow separation and secondary flow effects demand a reliable simulation of the turbulence respectively laminar to turbulent boundary layer transition. This paper presents a steady state three-dimensional numerical investigation of a transonic turbine guide vane at flow conditions similar to modern highly loaded gas turbines. At the Institute for Thermal Turbomachinery and Machine Dynamics extensive experimental investigations of the three dimensional flow trough this turbine stage were done to gain a better understanding of the flow physics and to verify computational results. The applied numerical code, which was developed at the institute, solves the Reynolds-averaged Navier-Stokes equations using a time-iterative finite volume method. Turbulence is modeled with the one equation model of Spalart and Allmaras, the two equation SST k-ω model of Menter and the V2F model of Durbin, the latter model is also able to capture boundary layer transition to turbulence. The objective of this paper is to compare the numerical results with experimental data and to figure out the impact of the different turbulence models on secondary flow effects.
Detailed Study of Pulsating Flow Performance in a Mixed Flow Turbocharger Turbine
Authors: Costall Aaron , Martinez-Botas Ricardo F. , Palfreyman Dean
Published: November 2008

Automotive turbocharger turbines experience a highly unsteady and pulsating flow field due to the abrupt operation of the exhaust valves in a reciprocating internal combustion engine. Previous work has demonstrated and validated against experiment a computational model of a turbine stage under such conditions. The same model is used in the present paper to examine in greater detail the complex flow characteristics observed. The pulsating inlet condition results in a highly disturbed flow field in the turbine stage, the main features of which have already been identified. The effect of the passing of the blades at the volute tongue is observed, and the fluctuating velocity field in the blade passages is seen to lead to poor flow direction control at the turbine inlet and exit. The turbine geometry, calculated for steady flow, is forced to operate away from design conditions for most of the pulse period. Through a detailed analysis of the intricate flow field features at varying instants during the pulse period, this paper highlights areas of the blade geometry and periods in the pulse profile that should be investigated further, such that the integrated performance across the entire pulse cycle can be improved.
Experimental Evaluation of Active Flow Control Mixed-Flow Turbine for Automotive Turbocharger Application
Authors: Pesiridis Apostolos , Martinez-Botas Ricardo F.
Published: November 2008

The current paper introduces a new concept in turbocharger development, namely, that of active turbocharger flow control. In the Active (Flow) Control Turbocharger (ACT) the nozzle is able to alter the inlet area at the throat of the turbine inlet casing in phase and at the same frequency as that of the incoming exhaust stream pulses. Actuated by an electrodynamic shaker the nozzle can adapt according to the engine exhaust gas pulse pressure variation, thus taking advantage of the lower energy levels existent before and after each pulse pressure peak, which the current systems do not take advantage of. Thus, ACT makes better use of the exhaust gas energy of the engine than a conventional VGT. The numerical simulation and experimental work concentrates on the potential gain in turbine expansion ratio and eventual power output as well as the corresponding effects on efficiency.
Evaluation of the Volume of Fluid Modelling Approach for Simulation of Oil/Air System Flows
Authors: Young Colin , Chew John W.
Published: November 2008

In recent years, improvements in computing hardware and numerical methods have provided the means for aero-engine manufacturers to use CFD to undertake air system analyses in ever-increasing detail. The main benefit of this work is that it has provided both qualitative and quantitative insights into air system performance and design practices that were not previously accessible by other means. With continued improvements in computing technology virtually assured to the end of the decade, it is logical to expect that the technological advances made in air systems analysis will be extended into the more complex two-phase applications — such as those found in the oil systems of aero-engines. In the present work a number of two-phase volume of fluid (VOF) applications are presented, in situations likely to be encountered in an aero-engine oil system. Some of these applications represent generic test cases, whilst others are direct applications to actual engine components. It is evident from the results presented that considerable understanding and insight can be gained from the application of CFD techniques in these two-phase regimes and that with care these methods can be used to guide two-phase design methods.
Computational Investigation of the Airflow Through a Shrouded Bevel Gear
Authors: Farrall Mark , Simmons Kathy , Hibberd Stephen , Young Colin
Published: November 2008

Bevel gear systems are used in aero-engines to transmit power from the main drive shaft to the auxiliary systems. Friction between the rotating gear and the surrounding air increases turbulence and heat generation, and has been reported to account for as much as 10% of the total losses in a gear system. Potential savings in losses may result from enclosing the gear with a shroud, or restricting the flow through the teeth using an inlet dam. Numerical simulations of the airflow around a crown bevel gear running in isolation are presented for a shaft speed of 15000 rpm. The results are used to gain an insight into the flow patterns that exist and the changes that occur with the introduction of an inlet dam or shroud. Three face clearances are studied for the shroud with the results indicating that, decreasing the face clearance decreases the windage loss towards an optimal value. Smaller face clearances than this optimum result in increased windage loss.
Effects of Upstream Platform Geometry on the Endwall Flows of a Turbine Cascade
Authors: de la Rosa Blanco Elena , Hodson H. P. , Va´zquez R.
Published: November 2008

This paper describes the effect that the endwall geometry has on the endwall flows in the vicinity of the blade platform in a low-pressure turbine. The aim of this work is to assess the effect on blade performance of a step in hub diameter just ahead of the blade row. The blade profile under consideration is of high aspect ratio and characterized by a large pressure surface separation bubble. The tests are conducted on a linear cascade and the experimental results are supported by numerical simulations. Two different steps are employed, i.e., forward facing and backward facing steps. Furthermore, the size of the step and the thickness of the inlet endwall boundary layer are also varied. It was found that the presence of the step ahead of the blade row can significantly alter the structure and the strength of the endwall flows. A backward facing step gives rise to lower losses when compared with a flat endwall. However, the effect is found to be dependent on the step height and the thickness of the approaching boundary layer. A forward facing step, on the other hand, produces higher losses than a flat endwall.
CFD Application in Design of GT Structural Components
Authors: Vassiliev V. , Kostege V. , Pirscher A. , Chernyshev S.
Published: November 2008

Currently CFD is extensively used in turbine and compressor blading design and analysis with numerous examples of CFD applications to be found in literature. At the same time, there are no reports about CFD simulation of secondary flows inside the turbomachine (e.g. cooling air transit, purge, etc). One probable reason is that the amount of air/gas involved in these flows is typically too small to have a direct impact on the engine performance. However, these secondary flows have a big impact on the heat transfer in cavities between structural components, and as a result have an impact on the thermal state, life of structural components, and clearances in the main flowpath. Therefore, the proper prediction of the flow between structural components is also an important part of the design procedure. In spite of the recent progress in computational hardware and software development, CFD simulation of flow between structural components remains still a challenging task due to very complex geometries, 3D turbulent flow structure with separations, reattachments and vortices. In addition to this, to be applied in design practice, the CFD code should satisfy certain important requirements, for instance the ability to automate the calculations in order to execute the analysis within a reasonable time and cost. Only recently has it become possible to satisfy this requirement, and now CFD starts to penetrate into design practices. This paper presents the experience accumulated within ALSTOM during the last few years in CFD simulation of flow between different structural components using commercial and in-house software. The following issues are presented: • Validation of numerical models; • Automation of numerical calculation; • Application examples (the flow in different cavities between casings and in rotor cavity).
Designing Low-Pressure Turbine Blades With Integrated Flow Control
Authors: Bons Jeffrey P. , Hansen Laura C. , Clark John P. , Koch Peter J. , Sondergaard Rolf
Published: November 2008

A low pressure turbine blade was designed to produce a 17% increase in blade loading over an industry-standard airfoil using integrated flow control to prevent separation. The design was accomplished using two-dimensional CFD predictions of blade performance coupled with insight gleaned from recently published work in transition modeling and from previous experiments with flow control using vortex generator jets (VGJs). In order to mitigate the Reynolds number lapse in efficiency associated with LPT airfoils, a mid-loaded blade was selected. Also, separation predictions from the computations were used to guide the placement of control actuators on the blade suction surface. Three blades were fabricated using the new design and installed in a two-passage linear cascade facility. Flow velocity and surface pressure measurements taken without activating the VGJs indicate a large separation bubble centered at 68% axial chord on the suction surface. The size of the separation and its growth with decreasing Reynolds number agree well with CFD predictions. The separation bubble reattaches to the blade over a wide range of inlet Reynolds numbers from 150,000 down to below 20,000. This represents a marked improvement in separation resistance compared to the original blade profile which separates without reattachment below a Reynolds number of 40,000. This enhanced performance is achieved by increasing the blade spacing while simultaneously adjusting the blade shape to make it less aft-loaded but with a higher peak cp. This reduces the severity of the adverse pressure gradient in the uncovered portion of the modified blade passage. With the use of pulsed VGJs, the design blade loading was achieved while providing attached flow over the entire range of Re. Detailed phase-locked flow measurements using three-component PIV show the trajectory of the jet and its interaction with the unsteady separation bubble. Results illustrate the importance of integrating flow control into the turbine blade design process and the potential for enhanced turbine performance.
The Measurement of Shaft Power in a Fully Scaled Transient Turbine Test Facility
Authors: Atkins Nicholas R. , Ainsworth Roger W.
Published: November 2008

Transient test facilities offer the potential for the simultaneous study of turbine aerodynamic performance, unsteady flow phenomena and the heat transfer characteristics of a turbine stage. This paper describes the accurate measurement of the shaft power generated by the turbine in the Oxford Rotor Facility (ORF), one of the key requirements for aerodynamic performance testing. A high resolution encoder system has been developed for the accurate measurement of the turbine speed and acceleration. The desired accuracy and frequency response specifications of the system are outlined. The method that has been developed to characterise the error signature of the encoder disc and the signal processing used to remove it are also outlined. The measurement of the losses due to disc windage and bearing friction are also described.
Net Heat Flux Reduction and Overall Effectiveness for a Turbine Blade Leading Edge
Authors: Mouzon Brian D. , Terrell Elon J. , Albert Jason E. , Bogard David G.
Published: November 2008

The external cooling performance of a film cooled turbine airfoil can be quantified as a net reduction in heat transfer relative to the turbine airfoil without film cooling. This quantification is generally accomplished by using measurements of the adiabatic effectiveness and the change in heat transfer coefficients (hf/h0) for the film cooled surface to determine the net heat flux reduction (Δqr). Although measurement of Δqr for laboratory models give an indication of the ultimate film cooling performance, this does not show how much the surface temperature of the airfoil is reduced by film cooling. Measurement of scaled surface temperatures can be accomplished by using laboratory models constructed so that the Biot number is matched with that of the actual airfoil. These measurements provide a scaled temperature distribution on the airfoil that is referred to as the overall effectiveness, φ. For the current study, measurements of Δqr and φ have been made for a simulated turbine blade leading edge. The simulated leading edge incorporated shaped coolant holes, and had three rows of coolant holes. Improvements due to the shaped holes were determined by comparisons with previously measured round hole configurations. Spatially distributed hf/h0 show increases of 5% to 15% for M = 1.0 and 10% to 30% for M = 2.0. Results show that local variation in Δqr much greater than variation in φ, but laterally averaged Δqr distributions are reasonable predictors of the laterally averaged φ distributions.
Convective Heat Transfer Through Film Cooling Holes of a Gas Turbine Blade Leading Edge
Authors: Terrell Elon J. , Mouzon Brian D. , Bogard David G.
Published: November 2008

Studies of film cooling performance for a turbine airfoil predominately focus on the reduction of heat transfer to the external surface of the airfoil. However, convective cooling of the airfoil due to coolant flow through the film cooling holes is potentially a major contributor to the overall cooling of the airfoil. This study used experimental and computational methods to examine the convective heat transfer to the coolant as it traveled through the film cooling holes of a gas turbine blade leading edge. Experimental measurements were conducted on a model gas turbine blade leading edge composed of alumina ceramic which approximately matched the Biot number of an engine airfoil leading edge. The temperature rise in the coolant from the entrance to the exit of the film cooling holes was measured using a series of internal thermocouples and an external traversing thermocouple probe. A CFD simulation of the model of the leading edge was also done in order to facilitate the processing of the experimental data and provide a comparison for the experimental coolant hole heat transfer. Without impingement cooling, the coolant hole heat transfer was found to account for 50 to 80 percent of the airfoil internal cooling, i.e. the dominating cooling mechanism.
Miller Cycle Analysis Using EGM
Authors: Ribeiro Bernardo , Martins Jorge
Published: November 2008

The Entropy Generation Minimization (EGM) method is based on the analysis by three sciences (thermodynamics, fluid flow and heat transfer) of the different processes that may occur in a system or in an equipment. Herein the EGM method is applied to internal combustion engines to determine the entropy generation caused by different processes. A model incorporating entropy generation calculations is used to assess various engines configurations. Otto cycle was tested and Variable Valve Timing (VVT) and Variable Compression Ratio (VCR) were applied so thermodynamic benefits could be tested and evaluated. With the referred model, the Miller cycle variables are analyzed in order to establish the best working conditions of an engine under a certain load. The intake and exhaust valve timing, combustion start, compression ratio adjustment and heat transfer are the variables for which a best working condition is determined based on the minimization of the entropy generation of the several engine processes.
A Stand-Alone Multi-Zone Model for Combustion in HCCI Engines
Authors: Kongsereeparp Paitoon , Kashani Behzad , Checkel M. David
Published: November 2008

Because they have the potential for ultra low NOx emissions and high efficiency, Homogeneous Charge Compression Ignition (HCCI) engines have the potential to develop a significant niche. However, a narrow operating range, (bracketed by severe knock and misfire problems), presents a formidable obstacle to developing usable HCCI combustion systems. HCCI combustion is influenced by a complex array of operating variables including fuel octane quality, intake preheating temperature, compression ratio, equivalence ratio, exhaust gas recirculation and engine component temperature. These variables affect the two critical combustion parameters: ignition timing and combustion duration. If these two parameters can be controlled by appropriate settings of the operating variables, a good HCCI combustion scheme could be achieved. Therefore, the theoretical prediction of these two combustion parameters as a function of the key operating variables is necessary for development of HCCI combustion. This paper describes a stand-alone, single-zone and multi-zone combustion model which have been developed for the specific purpose of investigating HCCI combustion control. In the multi-zone model, temperature and composition in each zone were adjusted in order to study the effect of in-homogeneity which is critical to understanding ignition timing and combustion duration in real HCCI engines. The models simulated HCCI combustion using two fuels: hydrogen, (11 species, 23 reactions- from CHEMKIN library), and natural gas, (53 species, 325 reactions- from GRI mech). The capabilities of the two models to predict ignition timing, combustion duration and peak pressure were verified against experimental and simulation results of Fiveland et al [2, 11]. The models were then used to study the effect of different in-homogeneity levels of equivalence ratio, intake temperature and residual fraction. The single zone model could only predict ignition timing while the multi-zone model shows the capability to mimic realistic HCCI combustion phenomena. The study showed that some degree of in-homogeneity is critical to predicting performance of the homogeneous charge compression ignition engine. Further, stratification of equivalence ratio was relatively ineffective at changing combustion while stratification of mixture temperature was very effective. Stratification of the residual fraction proved to be the most promising method of controlling combustion parameters and the mechanism was primarily thermal.
Effect of Hydrogen Content in Hydrogen Natural-Gas Fuel Mixtures on Emissions in a Lean-Burn IC Engine
Authors: Salanki Paul A. , Wallace James S.
Published: November 2008

The influence of hydrogen content in hydrogen-natural gas fuel mixtures on the emissions of a lean-burn spark ignition engine has been examined under representative operating conditions, a mid load and a high load. The hydrogen content in the fuel gas mixtures was varied from 0 to 30% with the balance made up of natural gas. The primary effect on emissions was to influence the tradeoff between NOx and hydrocarbon emissions. At the mid-load condition, increasing the hydrogen content from 0 to 15% at constant equivalence ratio reduced the HC emissions by 80% with little change in NOx emissions. Increasing from 15 to 30% hydrogen content reduced the HC emissions a further 50% but increased the NOx emissions by 16%. At the high load condition, the overall result of increasing the hydrogen content was to increase the NOx emissions substantially without significantly reducing the HC emissions. The impact of increasing hydrogen content on engine efficiency is similar to the impact on hydrocarbon emissions. At the mid-load condition, engine efficiency was increased by increasing hydrogen content, but with diminishing returns. An increase from 0 to 5% hydrogen content provides a significant benefit under marginal combustion conditions but further increases in hydrogen content are less effective.
A Study on the Calculation of Heat Release Rate to Compensate the Error Due to Single Zone Assumption in Diesel Engine
Authors: Ryu Seung Hyup , Kim Ki Doo , Yoon Wook Hyeon , Ha Ji Soo
Published: November 2008

Accurate heat release analysis based on the cylinder pressure trace is important for evaluating combustion process of diesel engines. However, traditional single-zone heat release models (SZM) have significant limitations due mainly to their simplified assumptions of uniform charge and homogeneity while neglecting local temperature distribution inside cylinder during combustion process. In this study, a heat release analysis based on single-zone model has been evaluated by comparison with computational analysis result using Fire-code, which is based on multi-dimensional model (MDM). The limitations of the single-zone assumption have been estimated. To overcome these limitations, an improved model that includes the effects of spatial non-uniformity has been applied. From this improved single-zone heat release model (Improved-SZM), two effective values of specific heats ratios, denoted by γV and γH in this study, have been introduced. These values are formulated as the function of charge temperature changing rate and overall equivalence ratio by matching the results of the single-zone analysis to those of computational analysis using Fire-code about medium speed marine diesel engine. Also, it is applied that each equation of γV and γH has respectively different slopes according to several meaningful regions such as the start of injection, the end of injection, the maximum cylinder temperature, and the exhaust valve open. This calculation method based on improved single-zone model gives a good agreement with Fire-code results over the whole range of operating conditions.
Enhancement of Coolant Side Heat Transfer in Water Cooled Engines by Using Finned Cylinder Heads
Authors: Selim Mohamed Y. E. , Elfeky S. M. S. , Helali A.
Published: November 2008

An experimental investigation has been carried out for almost the first time to examine the heat transfer by forced convection and subcooled boiling from a finned water-cooled engine cylinder head using steady state technique. Cast iron and cast steel specimens with and without fins have been used in the present work. The effects of flow velocity, coolant bulk temperature, fin length, fin number and fin material have been examined. It has been found that the use of finned cylinder head surface greatly improves the forced convection heat transfer coefficient and subcooled boiling heat flux as the fin length and number influenced the heat transfer process. The cast iron specimen exhibited better heat transfer characteristics over the cast steel one. The effects of bulk flow velocity and temperature for flat and finned specimens have been evaluated for forced convection and subcooled boiling. A correlation has been developed to relate the Nusselt number with Reynolds’ number, Prandtl number, viscosity ratio and fin length ratio, for forced convection from the cast iron specimen, which read: Nu=0.023Re0.697Pr0.33μr0.14(1+A)0.623
Laser Ignition: A New Concept to Use and Increase the Potentials of Gas Engines
Authors: Herdin Gu¨nther , Klausner Johann , Wintner Ernst , Weinrotter Martin , Graf Josef , Iskra Kurt
Published: November 2008

Due to market demands aimed at increasing the efficiency and the power density of gas engines, existing ignition systems are rapidly approaching their limits. To avoid this, gas engine manufacturers are seeking new technologies. From the viewpoint of gas engine R&D engineers, ignition of the fuel/air mixture by means of a laser has great potential. Especially the thermodynamic requirements of a high compression ratio and a high power density are fulfilled well by laser ignition. Results of measurements on the test bench confirm the high expectations — with a BMEP of 1.8 MPa it was possible to verify NOx values of a non-optimized system of 30 ppm (70 mg/Nm3 @ 5 % O2) with very high combustion stability. Despite this, considerable developmental steps are still necessary to adapt the laser ignition concept fully to desired objectives (especially costs).
Effect of Multiple Injections on Fuel-Air Mixing and Soot Formation in Diesel Combustion Using Direct Flame Visualization and CFD Techniques
Authors: Chryssakis Christos A. , Assanis Dennis N. , Kook Sanghoon , Bae Choongsik
Published: November 2008

The main objective of this study is to investigate the effect of pilot-, post- and multiple-fuel injection strategies on fuel-air mixing and emissions formation in diesel combustion, using a combination of experimental observations and Computational Fluid Dynamics (CFD) analysis. The experimental study was carried out on a single-cylinder optical direct-injection diesel engine equipped with a high pressure common rail fuel injection system. The experimental work was supported by CFD simulations on the single-cylinder engine in order to investigate the effect of multiple injections on mixture formation. The limitations of the soot formation model were identified through direct comparisons with experimental flame visualization.