bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction of a Project-Based-Course in Turbine Stage Design for Undergraduate Students at Graz University of Technology
Authors: Marn Andreas , Schönleitner Florian , Peterleithner Johannes , Woisetschläger Jakob , Heitmeir Franz
Published: September 2016

This 5 day-course is offered to undergraduate students at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. Goal of the course is to give students an holistic education and to train a “understanding of systems function as wholes”. Within this course students are designing an axial turbine stage from the very beginning and apply all the theory learned in separate courses before. At first the students design the annulus and the blades. They determine the inlet and outlet velocity triangles for several channel heights and define the camber line of the profile before a thickness distribution is superimposed. Secondly, a 3d CAD model including a disk design is created to get a realistic blade root. Then the students perform a finite element analysis (FEA) of the rotor blade and evaluate mechanical stresses in distinct sections of the blade. Also, natural frequencies are determined and a Campbell diagram is calculated. If the students have proven that there design is free from mechanical problems a steady state simulation of the flow through one passage is performed. Due to the fact that there is one numerical simulation platform for FEA as well as for CFD, a coupling of the fluid structure interaction (FSI) can be realised as final step. In a 1 way FSI analysis the students evaluate basic aeroelastic characteristics. After finishing that theoretical part an experimental part follows in which the students measure the static wall pressure distribution on the suction and pressure surface of that particular mid span profile in a subsonic wind tunnel. Natural frequencies are also experimentally determined using laser vibrometers. At the end of the course students will “produce” their own rotor blade with a 3d-printer. The blade can be kept as a souvenir. This paper describes the content of the course in detail and presents some results of last year’s class and reports the feedback of the students.
Novel Designs of Turbine Blades for Additive Manufacturing
Authors: Magerramova Liubov , Vasilyev Boris , Kinzburskiy Vladimir
Published: September 2016

Improving engine performance requires creating new materials and improving design and manufacturing. Additive Manufacturing (AM) is advancing rapidly and allows us to produce details of complex shapes that cannot be produced by traditional methods. The goal of this study was to demonstrate the possibility of using AM for the manufacture of turbine blades with a complex geometry, including those with advanced cooling systems, which cannot be manufactured by conventional methods.

This paper presents the results of the design and calculations of high-pressure turbine (HPT) cooled blades, as well as a low-pressure turbine (LPT) uncooled blade that was designed using topology optimization (TO). Several blades were manufactured using AM. 3D tomography test results for those blades confirm the possibility of AM application in production of blades with complex geometry.
Ultra Low Emission Technology Innovations for Mid-Century Aircraft Turbine Engines
Authors: Grönstedt Tomas , Xisto Carlos , Sethi Vishal , Rolt Andrew , García Rosa Nicolás , Seitz Arne , Yakinthos Kyros , Donnerhack Stefan , Newton Paul , Tantot Nicolas , Schmitz Oliver , Lundbladh Anders
Published: September 2016

Commercial transport fuel efficiency has improved dramatically since the early 1950s. In the coming decades the ubiquitous turbofan powered tube and wing aircraft configuration will be challenged by diminishing returns on investment with regards to fuel efficiency. From the engine perspective two routes to radically improved fuel efficiency are being explored; ultra-efficient low pressure systems and ultra-efficient core concepts. The first route is characterized by the development of geared and open rotor engine architectures but also configurations where potential synergies between engine and aircraft installations are exploited. For the second route, disruptive technologies such as intercooling, intercooling and recuperation, constant volume combustion as well as novel high temperature materials for ultra-high pressure ratio engines are being considered. This paper describes a recently launched European research effort to explore and develop synergistic combinations of radical technologies to TRL 2. The combinations are integrated into optimized engine concepts promising to deliver ultra-low emission engines. The paper discusses a structured technique to combine disruptive technologies and proposes a simple means to quantitatively screen engine concepts at an early stage of analysis. An evaluation platform for multidisciplinary optimization and scenario evaluation of radical engine concepts is outlined.
Computational and Experimental Studies of Midpassage Gap Leakage and Misalignment for a Non-Axisymmetric Contoured Turbine Blade Endwall
Authors: Lange Eric , Lynch Stephen , Lewis Scott
Published: September 2016

Turbine vanes and blades are generally manufactured as single or double airfoil sections that must each be installed onto a turbine disk. Between each section, a gap at the endwalls through the blade passage is present, through which high pressure coolant is leaked. Furthermore, sections can become misaligned due to thermal expansion or centrifugal forces. Flow and heat transfer around the gap is complicated due to the interaction of the mainstream and the leakage flow. An experimental and computational study was undertaken to determine the physics of the leakage flow interaction for a realistic turbine blade endwall, and assess whether steady RANS CFD, commonly used for non-axisymmetric endwall design, can be used to accurately model this interaction. Computational models were compared against experimental observations of endwall heat transfer on a contoured endwall with a midpassage gap. Endwall heat transfer coefficients were determined experimentally by using infrared thermography to capture spatially-resolved surface temperatures on a uniform heat flux surface (heater) attached to the endwall. Predictions and measurements both indicated an increase in endwall heat transfer with increasing gap leakage flow, although the distribution of heat transfer coefficients along the gap was not well captured by CFD. A misalignment of the blade endwall causing a forward-facing step for the near-endwall flow resulted in a large highly turbulent recirculation region downstream of the step and high local heat transfer that was overpredicted by CFD. Conversely, a backward-facing step reduced turbulence and local heat transfer. The misprediction of local heat transfer around the gap is thought to be caused by unsteady interaction of the passage secondary flow and gap leakage flow, which cannot be well-captured by a steady RANS approach.
Research on the Matching Relationship Between HPT and LPT of One and One-Half Vaneless Contra-Rotating Turbines
Authors: Xu Xiao , Zhao Qingjun , Luo Weiwei , Tang Fei , Sun Xiaolei
Published: September 2016

The vaneless contra-rotating turbine (VCRT) has the potential to improve the thrust-to-weight ratio for future high performance propulsion systems. Without the inter-stage vane, the variation of the high pressure turbine (HPT) exit swirl, under off-design conditions, can introduce more significant effects on the operation of the low pressure turbine (LPT). This study performed both analytical and numerical work investigating the matching relationship between the two stages of one and one-half stage (1+1/2) VCRTs. The significant difference of 1+1/2 VCRTs from conventional turbines, under choking geometry-fixed conditions, was found the flow capacity at the station between HPT and LPT is not invariant. The matching relationship between HPT and LPT is indeed how the flow capacity at the station between the two stages varies for different matching conditions. Influenced by the variation of the flow capacity, both the total pressure ratio of HPT and the corrected mass flow rate at the inlet of LPT are confined by the matching relationship. The corrected rotational speeds of the two stages define different matching conditions. A correlation, defining the matching conditions that LPT can work with constant incidence, was also derived. With aid of the correlation, the matching conditions can be controlled assuring LPT work with stable high efficiency. In the end, an application of incorporating the matching relationship into the investigation of engine performances is demonstrated, in which, a turbojet performance cycle analysis was performed. This paper has established a framework guiding how to obtain the matching relationship between the two stages of 1+1/2 VCRTs and incorporate it into the investigation of engine performances.
A Method to Evaluate the Heat Exchanger Retrofit for Industrial Gas Turbines Based on Technical and Economic Perspective
Authors: Al-Busaidi Waleed , Pilidis Pericles
Published: September 2016

One way to enhance the thermal efficiency of simple gas turbines cycle is by using recuperation to recover some of the exhaust heat. Therefore, this study aims to introduce a new integrated approach to evaluate the techno-economic value of recuperator retrofit on existing industrial gas turbines. The original engines are designed for combined cycles so that the pressure ratios are moderate to secure suitable exhaust temperatures. The developed model is described and implemented for two gas turbines, and the obtained characteristics are evaluated against the actual data. This approach will help the users to select the suitable gas turbine models with favorable recuperator characteristics based on a technical and economic perspective. Besides, the performance results are used to select the optimum thermodynamic and geometrical characteristics of TEMA tubular heat exchanger so that the generated design alternatives are optimized using multi-decision process principle in order to ensure the highest techno-economic value. One of the unique features of the new method is that it depends only on the velocity of recuperator streams to derive the rest of the heat exchanger design and performance characteristics. Moreover, this paper includes a sensitivity study to investigate the effects of power setting, utilization factor and operation availability on the selected recuperator features.
High Pressure Gas Fired Intercooled Semi-Closed Recuperated Cycle
Authors: Wettstein Hans E.
Published: September 2016

A promising semi-closed recuperated cycle (SCRC) has been suggested earlier by the author. For assessing the polytropic changes of state within this cycle ideal gas assumptions have been used as usual in gas turbine cycle analysis. But this leads finally to approximations which prevent an accurate extrapolation to a pressure level considerably above critical. The SCRC concept allows easy access to very high pressure and this has not yet been explored due to the lack of an appropriate method.

In two papers an incremental method called constant dissipation rate algorithm (CDRA) for calculating polytropic changes of state for real gases corresponding to the classic definition has been shown. In the first paper different polytropic change of state calculations have been compared with the temperature based CDRA for air gases and in the second paper the applicability of the enthalpy based CDRA for steam both in the vapor and in the wetness range (in equilibrium) has been demonstrated.

The validation of the calculation was first made by comparing with the previously published cycle data. This confirms the applicability of the ideal gas approximations for the data range up to a pressure level of 60 bars reasonably. Then versions with supercharging pressure ratio of up to 30 with a pressure level of up to 289bar were explored using the new temperature based CDRA method. It shows an impressive potential for high power density and low power turndown capability with no loss of efficiency and maintaining low emissions.
Experiences From Changing the Study Platform of Turbomachinery Course From Blended Education to Problem Based Learning
Authors: Grönman Aki , Backman Jari , Jaatinen-Värri Ahti , Grönman Kaisa
Published: September 2016

Improving the quality and productivity of academic teaching is a continuous challenge. To respond to it, the study platform of a graduate level course on design of turbomachinery was changed from blended education to problem based learning (PBL). The main idea behind PBL is to let the students define the solved problem themselves and study what they need to know before the problem can be solved. The learning is connected to a real-life problem-solving environment which reflects real working situations as much as possible. This study presents the results from the first four years of utilizing PBL as a study platform of a graduate level turbomachinery course. The new design and implementation is presented first and is compared with the original one. The performed analysis indicated good student feedback and learning results overall, but also highlighted the importance of teachers’ competence to utilize PBL. In conclusion, the use of PBL is recommended for turbomachinery courses if the challenges in explaining the principles of PBL and tutoring the students are taken into account while organizing the course.
High Temperature Storage for CSP Hybrid Gas Turbine: Test Rig Dynamic Analysis and Experimental Validation
Authors: Barberis Stefano , Traverso Alberto Nicola , Traverso Alberto , Massardo Aristide F.
Published: September 2016

It has long been recognized that the possibility for the integration of Thermal Energy Storage (TES) is one of the key advantages of CSP over other forms of renewable energy technology.

In this work, a high temperature ceramic storage test rig for gas turbine energy systems was presented with its innovative layout, which avoids the use of hot valves. Such experimental plant storage, developed by the University of Genoa, Italy, can be run with compressed air and it is ready for connection with the modified microturbine Turbec T100 onsite. The test rig represents a scaled-down version of a larger system designed for a hybridized solar gas turbine, where the solar input is emulated by an electrical heater.

Hybridized solar gas turbine cycles are attractive because of their high efficiency, potentially equal to combined cycle efficiency, and dispatchable power capability. The layout proposed here does not involve any hot air valve and does include a ceramic thermal storage. The plant dynamic model was developed using the original TRANSEO simulation tool.

This paper presents the test rig experimental results and validation of dynamic model: eventually, design recommendations are drawn to improve the flexibility and the time response of such kind of CSP plants.
Numerical Simulation of Twin Spool Axial Flow Turbines of a Small Gas Turbine Engine
Authors: Rajeevalochanam Prathapanayaka , Seepana Venkata Ramana Murthy , Sunkara S. N. Agnimitra , Mayandi Balamurugan , Kapil Sharad , Kumaran Senthil
Published: September 2016

Reynolds Averaged Navier-Stokes CFD analysis is carried out for a twin spool turbine of a typical small gas turbine engine, using commercial CFD solvers by employing SST turbulence model to understand the 3D flow field. In this work, detailed performance characterization at design and off-design speeds of both the high pressure (HP) and the low pressure (LP) stages is carried out using two approaches. In the First approach, individual HP and LP turbine stages are analyzed separately (case 1) with well-defined inlet and outlet boundary conditions and, in the second approach HP and LP turbine stages are analyzed together (case 2). NUMECA-AutoGrid is used to generate a good quality mesh with y+ around one. RANS CFD simulations are carried out for design speed, using both ANSYS-CFX and NUMECA“s FINE/Turbo solver and compared for conformity of the CFD analysis results. Further ANSYS-CFX is used for the detailed flow simulations for design and off-design speeds. The turbine parameters such as mass flow function, specific work function and total-to-total adiabatic efficiency of the HP and LP turbines are compared for case 1 and case 2. From case 1 & case 2 analysis, it is observed that, LP turbine stage is capable of allowing higher mass flow than required, but HP turbine stage limits the mass flow. Cascade testing of HP turbine mean section profiles has been carried out and compared with CFD analysis results.
Flow Loss Mechanism and Modeling in a Centrifugal Compressor Casing
Authors: Qi Mingxu , Hu Leon , Sun Harold , Wooldridge Margaret
Published: September 2016

The current work presents a simplified flow loss model of centrifugal compressor casing flow. The model can be used to estimate the flow losses and air flow rate through the casing under arbitrary casing geometry definitions. Numerical simulations of a turbocharger centrifugal compressor are presented and experimentally validated, with excellent agreement between the model and experimental data. The numerical results were used to investigate the different casing flow loss mechanisms, and the major sources of flow loss in the casing were identified. The simulations indicate the casing flow losses are due to a combination of dividing flow loss, expansion flow loss and friction loss. The dividing flow loss, caused by a portion of the main flow entering the casing slot, is the major source of flow loss, while the expansion flow loss, caused by the expansion flow returning from the slot to the casing cavity, is the second most important source of flow loss. By simplifying the casing into a 2-D configuration, the flow loss coefficient k in the dividing flow and expansion flow is simplified as a function of the casing geometric parameters and dividing flow loss and expansion flow loss models are developed and numerically validated. The results of this work are a valuable new tool to rapidly evaluate casing designs with low computational costs.
Periodicity and Stability in Transverse Motion of a Nonlinear Rotor-Bearing System Using Generalized Harmonic Balance Method
Authors: Liu Zhiwei , Wang Yuefang
Published: September 2016

Many rotor assemblies of industrial turbo-machines are supported by oil-lubricated bearings. It is well known that the operation safety of these machines is highly dependent on rotors whose stability is closely related to the whirling motion of lubricant oil. In this paper, the problem of transverse motion of rotor systems considering bearing nonlinearity is revisited. A symmetric, rigid Jeffcott rotor is modeled considering unbalanced mass and short bearing forces. A semi-analytical, semi-numerical approach is presented based on the Generalized Harmonic Balance method and the Newton-Raphson iteration scheme. The external load of the system is decomposed into a Fourier series with multiple harmonic loads. The amplitude and phase with respect to each harmonic load are solved iteratively. The stability of the motion response is analyzed through identification of eigenvalues at the fixed point mapped from the linearized system using harmonic amplitudes. The solutions of the present approach are compared to the ones from time-domain numerical integrations using the Runge-Kutta method and they are found in good agreement for stable periodic motions. It is revealed through bifurcation analysis that evolution of the motion in the nonlinear rotor-bearing system is complicated. The Hopf bifurcation of synchronous vibration represents the start of the oil whirl. The phenomenon of oil whip is identified when the saddle-node bifurcation of sub-synchronous vibration takes place.
Numerical Investigation on Flow and Heat Transfer in Matrix Cooling Channels for Turbine Blades
Authors: Luan Yigang , Bu Shi , Sun Haiou , Sun Tao
Published: September 2016

Matrix cooling is one kind of internal cooling structures applied to protect turbine blades. This paper investigated the flow field and heat transfer performance in matrix cooling channels experimentally and numerically. A testing section (rib angle of 45-deg, rib thickness of 30mm, rib height of 30mm and sub-channel width of 30mm) made of Plexiglas was build and connected to a wind tunnel sysytem. And Transient Liquid Crystal (TLC) technique was applied to obtain the detailed heat transfer distribution on the primary surface inside the matrix cooling channel. The experiment was performed under different Reynolds numbers varying from 18428 to 28327, based on the channel inlet hydraulic diameter; also the overall pressure drop across the channel was measured. Experimental results were used to calibrate the numerical solution obtained by computational fluid dynamics (CFD) method. During the numerical simulation process, structured grids and k-w turbulence model was employed. And a good agreement is obtained between experimental and CFD results for both pressure drop and heat transfer performance. Channels of various structural parameters (rib angle, rib thickness and sub-channel width) were then studied by numerical simulation, three rib angles (30-deg, 45-deg and 60-deg), three rib thicknesses (1.8mm, 3mm and 5mm) and three sub-channel widths (3mm, 5mm and 9mm) were considered, with the rib height 3mm for all the cases. Numerical results showed that the sidewall turnings made the greatest contribution to heat transfer enhancement but caused very large pressure drop meanwhile. The overall heat transfer and pressure drop increase with rib angle and rib width but decrease with sub-channel width. The thermal performance factor decreases with rib angle and rib width, while it showed a non-monotonic dependency on sub-channel width. Among the three structural parameters, rib angle has the most significant effect on the performance of matrix cooling channel.
Investigation of a Diffuser-Volute Combination With Variable Cross-Sectional Area for Centrifugal Fans
Authors: Fischer Tore , Rudersdorf Manuel , Burgmann Sebastian , kleine Sextro Thorsten , Seume Joerg R.
Published: September 2016

The present paper focuses on the potential efficiency improvements and the stable operating range of a centrifugal fan for fuel cell applications. Improvements will be achieved by variability of the cross-sectional area of diffuser and volute by use of a moving backplate.

The investigation consists of three parts: The first part describes the design and the performance prediction of a diffuser-volute combination with a variable cross-sectional area, based on empirical correlations and low-resolution CFD (Computational Fluid Dynamics) simulations. For the second part, high-resolution 360 degree CFD simulations are used to gain deeper insight into the flow mechanisms and their influence on fan performance. The last part presents the experimental investigations carried out to validate the numerical models. For this purpose, a demonstrator of the fan including a diffuser-volute combination with variable cross-sectional area is manufactured and investigated using optical PIV (Particle Image Velocimetry) measurements.
Model-Based Fault Diagnosis for Performance Degradations of Turbofan Gas Path via Optimal Robust Residuals
Authors: Yang Chao , Kong Xiangxing , Wang Xi
Published: September 2016

Observers are usually used in model-based FDI system for aero engines, especially for control system sensors. However, when a bank of traditional observers is used to detect gas path faults, it seems difficult to locate or isolate them, which is not a problem for sensor FDI. As a solution, a modified design method for a kind of robust observer called UIO (Unknown Input Observer) is proposed in this paper. An augmented linear model of a big turbofan is built at first. The degradations of compressor and HP turbine efficiencies are integrated as model inputs. Then some functions reflecting the FDI performance of UIO for these degradations can be obtained. DE (Differential Evolution) algorithm is introduced to solve these equations, whose best solution means the residual of observer is only sensitive for the specified gas path fault and not effected by other faults and unknown inputs. Some simulation results for UIOs designed by modified method are given to verify their FDI performance for compressor and HP turbine efficiencies.
A Finite Element Study of the Effect of Crystal Orientation and Misalignment on the Crack Driving Force in a Single-Crystal Superalloy
Authors: Busse Christian , Loureiro Homs Jordi , Gustafsson David , Palmert Frans , Sjödin Björn , Moverare Johan J. , Simonsson Kjell , Leidermark Daniel
Published: September 2016

The elastic and plastic anisotropy of the single-crystalmaterials bring many difficulties in terms of modeling, evaluation and prediction of fatigue crack growth. In this paper a single-crystal material model has been adopted to a finite element-environment, which is paired with a crack growth tool. All simulations are performed in a three-dimensional context. This methodology makes it possible to analyze complex finite element-models, which are more application-near than traditional two-dimensional models. The influence of the crystal orientation, as well as the influence of misalignments of the crystal orientation due to the casting process are investigated. It is shown that both the crystal orientation and the misalignment from the ideal crystal orientation are important for the crack driving force. The realistic maximum limit of 10° misalignment is considered. It can be seen that crack growth behavior is highly influenced by the misalignment. This knowledge is of great interest for the industry in order to evaluate the crack growth in single-crystal components more accurately.
Comparison of Single and Double Lip Rim Seal Geometry
Authors: Savov Svilen S. , Atkins Nicholas R. , Uchida Sumiu
Published: September 2016

The effect of purge flow, engine-like blade pressure field and mainstream flow coefficient are studied experimentally for a single and double lip rim seal. Compared to the single lip, the double lip seal requires less purge flow for similar levels of cavity seal effectiveness. The double lip seal has both a weaker vane pressure field in the rim seal cavity and a smaller difference in seal effectiveness across the lower lip. The smaller gradient across the lower lip of the double lip seal suggests that it is less sensitive to mainstream-cavity interactions across all length scales. Unlike the double lip seal, the single lip seal is sensitive to overall Reynolds number, the addition of a simulated blade pressure field and large-scale non-uniform ingestion.

In both seals, the addition of blades is seen to suppress unsteady activity attributed to shear between the rim seal and mainstream flows. The data suggests that in the case of the single lip seal, the blade pressure field has a more dominant effect in promoting ingress than the unsteadiness it suppresses at an engine-matched flow coefficient. At higher flow coefficients, increased shear between the rim seal cavity flow and the mainstream drives more mixing, reducing the seal effectiveness for both configurations.
Turbine Blade Platform Film Cooling With Simulated Swirl Purge Flow and Slashface Leakage Conditions
Authors: Chen Andrew F. , Shiau Chao-Cheng , Han Je-Chin
Published: September 2016

The combined effects of inlet purge flow and the slashface leakage flow on the film cooling effectiveness of a turbine blade platform were studied using the pressure sensitive paint (PSP) technique. Detailed film cooling effectiveness distributions on the endwall were obtained and analyzed. The inlet purge flow was generated by a row of equally-spaced cylindrical injection holes inside a single-tooth generic stator-rotor seal. In addition to the traditional 90 degree (radial outward) injection for the inlet purge flow, injection at a 45 degree angle was adopted to create a circumferential/azimuthal velocity component toward the suction side of the blades, which created a swirl ratio (SR) of 0.6. Discrete cylindrical film cooling holes were arranged to achieve an improved coverage on the endwall. Backward injection was attempted by placing backward injection holes near the pressure side leading edge portion. Slashface leakage flow was simulated by equally-spaced cylindrical injection holes inside a slot. Experiments were done in a five-blade linear cascade with an average turbulence intensity of 10.5%. The inlet and exit Mach numbers were 0.26 and 0.43, respectively. The inlet and exit mainstream Reynolds numbers based on the axial chord length of the blade were 475,000 and 720,000, respectively. The coolant-to-mainstream mass flow ratios (MFR) were varied from 0.5%, 0.75%, to 1% for the inlet purge flow. For the endwall film cooling holes and slashface leakage flow, blowing ratios (M) of 0.5, 1.0, and 1.5 were examined. Coolant-to-mainstream density ratios (DR) that range from 1.0 (close to low temperature experiments) to 1.5 (intermediate DR) and 2.0 (close to engine conditions) were also examined. The results provide the gas turbine engine designers a better insight into improved film cooling hole configurations as well as various parametric effects on endwall film cooling when the inlet (swirl) purge flow and slashface leakage flow were incorporated.
Unsteady Flow Physics and Performance Prediction of a 1-1/2 Stage Unshrouded High Work Turbine Using the Lattice Boltzmann Approach
Authors: Gonzalez-Martino Ignacio , Gautier Sébastien
Published: September 2016

A comparison between experimental measurements and simulations of a 1-1/2 stage unshrouded high work turbine are presented. The experimental investigations were conducted by the Turbomachinery Laboratory of ETH Zurich. The data was obtained from steady and unsteady probe measurements that were performed in four axial planes between stator and rotor rows.

Simulations have be performed using the commercial CFD solver PowerFLOW based on the Lattice Boltzmann (LB) method to compute unsteady flow fields. The turbulent flow fluctuations are resolved up to a certain scale using a so-called Very Large Eddy Simulation (VLES) approach. One crucial aspect of the present study is the use a new non-isothermal version of the LB model that allows extending the Mach number range of the standard PowerFLOW scheme up to about 0.9. These unsteady simulations have been used to better understand the different flow structures observed in the experiments, and in particular the mechanisms of tip leakage across the blades of the unshrouded turbine rotor.

In the present work, the complete 1-1/2 stage turbine with time-accurate moving rotor geometry has been simulated using the LB solver. This means that no blade reduction technique or almost-periodic flow hypothesis have been used in the simulation. The geometry was modified in order to close the rotor tip gap and do not consider its effects. A thorough comparison of these two simulations with the experimental data has been conducted and presented in the paper: averaged quantities along the turbine stage such as pressure drop, the degree of reaction, the loading coefficient, and the flow coefficient; averaged midspan inlet and exit angles for each turbine blade rows; and flow distribution at four axial planes between the rotor and stator rows. Moreover, a deep analysis of the unsteady flows in the blade channel has been performed in order to better understand the flow features observed in the experimental measurements. Finally, it has been be possible to analyze the interaction modes between turbine rows thanks to the simulation of the full 360° geometry and its time-accurate approach.
Investigation on Jet Breakup of High-Viscous Fuels for Entrained Flow Gasification
Authors: Müller Thomas , Habisreuther Peter , Zarzalis Nikolaos , Sänger Alexander , Jakobs Tobias , Kolb Thomas
Published: September 2016

The present study focuses on the atomization behaviour of liquids in external mixing twin fluid nozzles and investigates a wide range of viscosities as well as different nozzle geometries at a gas to liquid ratio (GLR) typically used in entrained flow gasification.

In a first stage experiments were performed using water and water-glycerol-mixtures as Newtonian model fuels with liquid viscosity up to 400 mPa s. Jet breakup was investigated qualitatively using a high speed camera as well as using a PIV and LDA-System for detailed quantitative investigation of the flow field. Two different primary instabilities flapping and pulsating mode were detected which are dependent on operating conditions of the nozzle (e.g. GLR) and rheological properties of the liquid phase (e.g. liquid viscosity) as well as nozzle geometry. For better interpretation of the phenomena occurring during jet breakup a frequency-analysis of the primary instabilities was performed using the pictures of the high speed camera.

In addition, compressible large eddy simulations (LES) were preformed to describe the experimental observations and to capture the morphology of the primary breakup as well as the important flow field characteristics. The numerical simulations were conducted by means of the open source CFD software OpenFOAM. A Volume of Fluid (VOF) approach was used to track the unsteady evolution and breakup of the liquid jet. Comparison of experimental and numerical results shows a good agreement concerning breakup frequency, velocity fields and morphology. The breakup frequency varied in a range of 430 to 757 Hz depending on operating condition and nozzle geometry.

Based on these results a more detailed understanding of the physics leading to liquid jet breakup and finally atomization process will be available.
LES Validation for a Rotating Cylindrical Cavity With Radial Inflow
Authors: Onori Michel , Amirante Dario , Hills Nicholas J. , Chew John W.
Published: September 2016

This paper describes Large-Eddy Simulations (LES) of the flow in a rotating cavity with narrow inter-disc spacing and a radial inflow introduced from the shroud.

Simulations have been conducted using a compressible, unstructured, finite-volume solver, and testing different subgrid scale models. These include the standard Smagorinsky model with Van Driest damping function near the wall, the WALE model and the implicit LES procedure. Reynolds averaged Navier-Stokes (RANS) results, based on the Spalart-Allmaras and SST k-ω models, are also presented. LES solutions reveal a turbulent source region, a laminar oscillating core with almost zero axial and radial velocity and turbulent Ekman type boundary layers along the discs.

Validations are carried out against the experimental data available from the study of Firouzian et al. [1]. It is shown that the tangential velocity and the pressure drop across the cavity are very well predicted by both RANS and LES, although significant differences are observed in the velocity profiles within the boundary layers.
Experimental and Numerical Investigations of Effusion Cooling for High Pressure Turbine Components: Part 1 — Experimental Study With PSP
Authors: Wang Guanghua , Ledezma Gustavo , DeLancey James , Wang Anquan
Published: September 2016

Gas turbines overall efficiency enhancement requires further increasing of the firing temperature and decreasing of cooling flow usage. Multi-Hole (or effusion, full coverage) film cooling is widely used for hot gas path components cooling in modern gas turbines.

The present study focused on the adiabatic film effectiveness measurement of a round multi-hole flat plate coupon. The measurements were conducted in a subsonic open loop wind tunnel with a generic setup to cover different running conditions. The test conditions were characterized by a constant main flow Mach number of 0.1 with constant gas temperature. Adiabatic film effectiveness was measured by Pressure Sensitive Paint (PSP) through mass transfer analogy. CO2 was used as the coolant to reach the density ratio of 1.5. Rig CFD simulation was conducted to evaluate impact of inlet boundary layer on testing.

Experimental data covers blowing ratios (BR) at 0.4, 0.6, 0.8, 1.0 and 2.0. Both 2D maps and lateral average profiles clearly indicated that film effectiveness increases with increasing BR for BR<0.8 and decreases with increasing BR for BR>0.8. This observation agreed with coolant jet behavior of single film row, i.e. attached, detached then reattached, and fully detached. PSP data quality was then discussed in detail for validating Large Eddy Simulation in Part 2.
Experimental Study on the Use of Synthetic Jet Actuators for Lift Control
Authors: Torres Ricardo B. , Jacobs Gustaaf B. , Cave Michael J.
Published: September 2016

An experimental study on the use of synthetic jet actuators for lift control on a generic compressor airfoil is conducted. A wind tunnel model of a NACA 65(2)-415 airfoil, representative of the cross section of an Inlet Guide Vane (IGV) in an industrial gas compressor, is 3D-printed. Nine synthetic jet actuators are integrated within a planar wing section with their slots covering 61% of pressure side of the airfoil span, located 13% chord upstream of the trailing edge. The Helmholtz frequency of the slot is matched closely with the piezoelectric element material frequency. The slot is designed so that the bi-morph actuation creates a jet normal to the airfoil surface. By redirecting or vectoring the shear layer at the trailing edge, the synthetic jet actuator increases lift and decreases drag on the airfoil without a mechanical device or flap. Tests are performed at multiple Reynolds number ranging from Re=150,000 to Re=450,000. The increased lift of the integrated synthetic jet actuator is dependent on the Reynolds number and free stream velocity, the actuation frequency, and angle of attack. For actuation at 1450 Hz the synthetic jet actuator increases lift up to 7%. The synthetic jet increases L/D up to 15%. Velocity contours obtained through PIV show that the synthetic jet turns the trailing edge shear layer similar to a Gurney flap.
Subsonic Flow Over Open Cavities: Part 2 — Passive Control Methods
Authors: Shao Weidong , Li Jun
Published: September 2016

A global description of the intrinsic instabilities of shear layer for further understanding of the aeroacoustical oscillation of subsonic flow over open cavities has been given in the companion paper. The needs to suppress dynamic pressure loads in open cavities play an important role in many aeronautical applications. Large eddy simulation (LES) of passive control methods including recessed leading edge step and sloping trailing edge wall arrangements is performed. The unsteady flow characteristics and aeroacoustical oscillation mechanism of baseline cavity are given in advance. Effects of both passive control methods on resonant frequency and sound pressure levels are demonstrated and analyzed. Recessed leading edge step tends to decrease the resonant Strouhal numbers and the maximal reduction of overall sound pressure levels (OASPL) reaches 8.5dB. Sloping trailing edge wall reduces OASPL by shifting down the impinging location on cavity back wall. The optimal reduction of OASPL arrives at 11dB when the angle of inclination is maximal. The drag induced by cavity flows is found to be highly correlated with dynamic loads on cavity walls.
Experimental Investigation of Aspiration in a Multi-Stage High-Speed Axial-Compressor
Authors: Siemann Jan , Krenz Ingolf , Seume Joerg R.
Published: September 2016

Reducing the fuel consumption is a main objective in the development of modern aircraft engines. Focusing on aircraft for mid-range flight distances, a significant potential to increase the engines overall efficiency at off-design conditions exists in reducing secondary flow losses of the compressor. For this purpose, Active Flow Control (AFC) by aspiration or injection of fluid at near wall regions is a promising approach.

To experimentally investigate the aerodynamic benefits of AFC by aspiration, a 4½-stage high-speed axial-compressor at the Leibniz Universitaet Hannover was equipped with one AFC stator row. The numerical design of the AFC-stator showed significant hub corner separations in the first and second stator for the reference configuration at the 80% part-load speed-line near stall. Through the application of aspiration at the first stator, the numerical simulations predict the complete suppression of the corner separation not only in the first, but also in the second stator. This leads to a relative increase in overall isentropic efficiency of 1.47% and in overall total pressure ratio of 4.16% compared to the reference configuration.

To put aspiration into practice, the high-speed axial-compressor was then equipped with a secondary air system and the AFC stator row in the first stage. All experiments with AFC were performed for a relative aspiration mass flow of less than 0.5% of the main flow. Besides the part-load speed-lines of 55% and 80%, the flow field downstream of each blade row was measured at the AFC design point. Experimental results are in good agreement with the numerical predictions. The use of AFC leads to an increase in operating range at the 55% part-load speed-line of at least 19%, whereas at the 80% part-load speed-line no extension of operating range occurs.

Both speed-lines, however, do show a gain in total pressure ratio and isentropic efficiency for the AFC configuration compared to the reference configuration. Compared to the AFC design point, the isentropic efficiency ηis rises by 1.45%, whereas the total pressure ratio Πtot increases by 1.47%. The analysis of local flow field data shows that the hub corner separation in the first stator is reduced by aspiration, whereas in the second stator the hub corner separation slightly increases. The application of AFC in the first stage further changes the stage loading in all downstream stages. While the first and third stage become unloaded by application of AFC, the loading in terms of the De-Haller number increases in the second and especially in the fourth stage. Furthermore, in the reference as well as in the AFC configuration, the fourth stator performs significantly better than predicted by numerical results.
Impact of Quarter Wave Tube Arrangement on Damping of Azimuthal Modes
Authors: Zahn Max , Schulze Moritz , Hirsch Christoph , Sattelmayer Thomas
Published: September 2016

The impact of quarter wave tube (QWT) arrangements in terms of axial location, circumferential distribution and number of cavities on damping of azimuthal modes is investigated both experimentally and numerically in an atmospheric annular test rig under isothermal conditions. Well-established measurement techniques are applied to characterize the damping potential for azimuthal modes of different quarter wave tube (QWT) arrangements. For additional insight into the considered configurations eigenfrequency studies are conducted using linearized Euler equations (LEE). Measured boundary conditions are used for inlet and outlet. The reflection coefficient of a single quarter wave tube (QWT) is measured on an impedance rig using longitudinal wave excitation. It is shown that this reflection coefficient can be used for the eigenfrequency analysis of the annular rig in which the QWT is mounted in radial direction.

The effects of different quarter wave tube configurations on the spatial mode shape of the first azimuthal mode and the corresponding change in modal dynamics are analyzed. This provides guidance for the circumferential and axial arrangement of damping devices to most effectively attenuate an annular acoustic system. It is illustrated that the complete acoustic system including the resonators has to be considered to properly dimension the acoustic characteristics of a damping device.
Experimental Study on the Turbomachinery Trailing Edge Noise Reduction
Authors: Tong Fan , Qiao Wei-Yang , Ji Liang , Xu Kun-Bo , Wang Xun-Nian
Published: September 2016

This paper is a continuation of a series of study on the mechanism of the broadband noise reduction for turbomachinery blade using trailing edge serrations. The noise reduction potential of turbine blade with trailing edge serrations is experimentally assessed as well as the various parameters on the noise reduction effect. Special focus is put on whether the trailing edge serrations affect turbine cascade tailing edge noise in the same way as they do on the isolated airfoil. Five different trailing edge serrations were designed for a turbine linear cascade to investigate the effects of serration geometry parameter on the noise reduction. A linear microphone array was used to quantify the difference of sound source levels of turbine cascade with and without trailing edge modifications. The experiment was carried out at various velocities and the Reynolds number (based on cascade inlet velocity and chord) ranges from 1.3×105 to 3.3×105. The experiment results show that trailing edge serrations can reduce turbine trailing edge noise in a wide frequency range that we are interested (from 1600Hz to 10000Hz) and a maximum noise reduction of about 5dB is obtained in the mid frequency range (2000Hz to 4000Hz). The results show that the serration length has an important effect on the noise reduction effect and the longer serration in the experiment lead to more noise reduction. However, serration wavelength has only a little effect on the noise reduction although the wider trailing edge serrations tested in the experiment can achieve slightly more noise reduction. This is quite different from that for airfoils. At all the velocities tested, the cascade trailing edge noise is effectively reduced and the maximum noise reduction occurs at St=2fh/U≈1.
Powerful Interpolation Method Demonstrated on Experimental Data From Fast Response Pressure Transducers in a Turbofan Engine
Authors: Kern Felix , Bindl Stefan , Stößel Marcel , Aberle Svenja , Niehuis Reinhard
Published: September 2016

Interpolation is a common procedure in scientific practice. In many cases, linear interpolation is tacitly applied in order to present measurements or numerical results. The application of sophisticated interpolation methods is rather rare, even though they can help to extract more information from a measurement, especially if the resolution is relatively low. This paper presents an interpolation method and a validation procedure, which is demonstrated on experimental data from a low pressure compressor of a twin spool turbofan engine.

As a research test vehicle the Larzac 04 turbofan engine is used, which is equipped with extensive instrumentation and control systems. This publication focuses on the high speed pressure transducers mounted directly above the tip of the first LPC rotor blades. Besides the installation of those sensors in a jet engine, the processing, the storage, and the analysis of the data is challenging, as the sampling rate is extraordinary high (1 MHz). Those sampling rates result in a high circumferential resolution (1 MHz ≙ 2.69 samples per mm at 90% rel. spool speed) compared to the relatively low geometrical resolution of the nine axial sensors (0.23 samples per mm). Therefore, sophisticated interpolation methods are applied on the data points in axial direction, aiming to get the best possible result from the acquired data. A major part of this paper is the discussion and validation of several different interpolation methods. Especially with the Akima sub-spline interpolation, very promising results were obtained.

Finally, some of the results from the fast response pressure transducers are presented. The casing wall pressure distribution and some flow phenomena at the design operating point are compared to the corresponding near stall conditions.