bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gradient-Based Adjoint and Design of Experiment CFD Methodologies to Improve the Manufacturability of High Pressure Turbine Blades
Authors: Zamboni Giulio , Banks Gabriel , Bather Simon 
Published: September 2016

The tolerance of a turbine blade aerofoil is determined by the requirements to achieve an aerodynamic performance in operation. In fact, the manufacturing tolerance applied to the profile is driven by the effects of geometrical non-conformances on the efficiency and flow capacity of the aerofoil. However, this tolerance also has an impact on the ease with which the aerofoil can be manufactured, with tighter tolerance leading to lower manufacturing conformity.
This paper details the application of an adjoint RANS solver and the according series of Design of Experiments (DoE) CFD calculations for a high pressure turbine blade to the above problem. There are two aims of this work; the first is to show that simpler linear CFD perturbation can be used to evaluate the effect of the geometric non-conformance. The second is to validate the spatial geometric correlation factor of the control points used in the manufacturing process on the performance evaluation with DoE techniques. This also verified the applicability of the adjoint CFD techniques; in fact the adjoint CFD calculation is an order of magnitude less computationally expensive than a large series of DoE RANS CFD calculations.
The results confirm that the peak suction area is the most critical control region for the effect on the efficiency and flow capacity. Moreover, the CFD investigations show that a significant level of correlation exists between the influence factors at different control points. This suggests that not only the amount of geometric deviation but also the stream surface variation of profile tolerance significantly influence the final aerodynamic performance. The results from this calculation allow the creation of a 3D sensitivity map which will be used during the manufacturing of the aerofoil to optimise the control of the spatial distribution of the geometric non-conformance and to directly assess the expected performance effect during the manufacturing quality inspection.
The methodology detailed in this paper shows how the CFD adjoint methods could be used for improved manufacturability of turbine blades ensuring that the critical characteristic features are controlled on the surface, relaxing the profile tolerance on those surface areas where the impact on the aerodynamic performance is predicted to be lower.
Detecting Transition in Flat Plate Flow With Laser Interferometric Vibrometry (LIV)
Authors: Bader Pascal , Sanz Wolfgang , Peterleithner Johannes , Woisetschläger Jakob , Heitmeir Franz , Meile Walter , Brenn Günter 
Published: September 2016

Flow in turbomachines is generally highly turbulent. The boundary layers, however, often exhibit laminar-to-turbulent transition. Relaminarization from turbulent to laminar flow may also occur. The state of the boundary layer is important since it strongly influences transport processes like skin friction and heat transfer.
It is therefore vitally important for the designer to understand the process of laminar-to-turbulent transition and to determine the position of transition onset and the length of the transitional region. In order to better understand transition and relaminarization it is helpful to study simplified test cases first. Therefore, in this paper the flow along a flat plate is experimentally studied to investigate laminar-to-turbulent transition.
Measurements were performed for the different free-stream velocities of 5 m/s and 10 m/s. Several measurement techniques were used in order to reliably detect the transitional zone: the Preston tube, hot wire anemometry, thermography and Laser Interferometric Vibrometry (LIV). The first two measurement techniques are extensively in use at the institute ITTM and by other research groups. They are therefore used as a reference for validating the LIV measurement results.
An advantage of the LIV technique is that it does not need any seeding of the fluid and that it is non-intrusive. Therefore this measurement technique does not influence the flow, and it can be used in narrow flow passages since there is no blockage, in contrast to probe-based measurement techniques.
Further to the measurements, computational simulations were performed with the Fluent® and CFX® codes from ANSYS®, as well as with the in-house code Linars. The Menter SST k-ω turbulence model with the γ-ReΘ transition model was used in order to test its capability to predict the laminar-to-turbulent transition.
The Investigations of the Balance Hole Area and Radial Seal Clearance’s Influences on Turbine Efficiency in the Wheel Chamber
Authors: Deng Guoliang , Sun Qi , Wang Shan , Tian Chaoyang , Wu Qi , Zhang Xiaodan , Du Xiaoqin 
Published: September 2016

First of all, this paper presents the overall efficiency correlation to the balance hole diameter of the 3-stages air turbine test results. All 3 wheels have the same balance hole geometry, with total 5 holes in the wheel, and the variation of diameter is 0 mm, 16 mm, 25 mm, 30 mm, 40 mm, 50 mm, and 60 mm, respectively. The test results show that the lowest efficiency condition is the one without balance hole, and increases with the hole diameter until 25–30 mm, but decreases after it. Then, a single stage CFD model, including the first stage stator, moving blade, stator hub leakage, and wheel chamber, is built to simulate the stage efficiency trend under steady flow condition. The relative efficiency correlation of the simplified single stage CFD model matches very well with the test results. The CFD results show that, the maximum efficiency happens when there is minor gas suction from the main gas path, about 0.1%–0.2% compared with the main mass flow, but when the gas suction is above 0.2% of the main mass flow, the efficiency decreases, as less flow is passing through the moving blade to convert energy.
Finally, the radial seal clearance’s influences in the wheel chamber between the diaphragm and the wheel is checked by CFD using the same geometry pattern. Five different radial seal clearances model, including 0 mm (ideal condition), 0.6 mm, 1.2 mm, 1.8 mm and 6 mm (without radial seal) are built, under two different balance hole diameter (14 mm and 25 mm), and three different hub seal clearances (0 mm, 0.6 mm and 1.2 mm) conditions. The CFD results show that the throttling effect is very small when the radial clearance is above or equal to 0.6 mm, with almost constant efficiency variation with the clearance up to 6 mm, under specified stator hub clearance and balance hole diameter. Very small deficiency (0.2%) is detected under small balance hole diameter (14 mm) and large stator hub clearance (1.2 mm) condition, as the hub leakage mass flow is much beyond the balance hole flow capability.
Experimental Study of the Interaction of Water Sprays With Swirling Premixed Natural Gas Flames
Authors: Lellek Stephan , Barfuß Christoph , Sattelmayer Thomas 
Published: September 2016

Water injection is often used to control NOx emissions or to increase power output from non-premixed combustion of gaseous and liquid fuels. Since the emission level in premixed natural gas combustion is significantly lower than for non-premixed combustion, water injection for emission reduction is usually not an issue. However, the increasing share of fluctuating power output from renewables motivates research activities on the improvement of the operational flexibility of combined cycle power plants. One aspect in that context is power augmentation by injection of liquid water in premixed combustors without drawbacks regarding emissions and flame stability. For research purposes, water injection technology has therefore recently been transferred to premixed combustors burning natural gas. In order to investigate the influence of water injection on premixed combustion of natural gas, an atmospheric single burner test rig has been set up at Lehrstuhl für Thermodynamik, TU München. The test rig is equipped with a highly flexible water injection system to study the influence of water atomization behavior on flame shape, position and stabilization. Presented investigations are conducted at gas turbine like preheating temperatures (673K) and flame temperatures (1800–1950K) to ensure high technical relevance. In this paper, the interaction between water injection, atomization and macroscopic flame behavior is outlined. Favorable and non-favorable operating conditions of the water injection system are presented in order to clarify the influence of water atomization and vaporization on flame stability and the emission behavior of the test rig. Water spray quality is assessed externally with a Malvern laser diffraction spectrometer whereas spray distribution in the test rig is determined by means of Mie scattering images at reacting conditions. The flame shape is analyzed using time-averaged OH* chemiluminescence images while the efficiency of water injection at various operating points is evaluated using global emission concentration measurements. Finally, the important influence of the water injection system design on the combustor performance will be shown using combined Mie scattering and OH* chemiluminescence images.
At constant adiabatic flame temperatures, a stable flame could be established for water-to-fuel ratios of up to 2.25. While only minor changes could be detected for the heat release distribution in the combustion chamber, the water distribution changes significantly while increasing the amount of water. Finaly, changes in NOx emission concentrations can directly be related to water droplet sizes and the global water distribution in the combustion chamber.
Robust Optimization of the HPT Blade Cooling and Aerodynamic Efficiency
Authors: Vinogradov Kirill A. , Kretinin Gennady V. , Otryahina Kseniya V. , Didenko Roman A. , Karelin Dmitry V. , Shmotin Yury N. 
Published: September 2016

Constant rise of hot gas temperature is crucial for the creation of modern gas-turbines engines requiring considerable improvement of cooling configurations. A high pressure turbine blade is one of the most crucial and loaded details in gas-turbine engines. A HPT blade is affected by different operational deviations: stochastic fluctuations of inlet parameters and difference in operational parameters for manufactured engines. Combination of these factors makes the task of uncertainty quantification and robust optimization of the HPT blade relevant in modern science.
The authors make an attempt to implement robust optimization to the HPT blade of the gas-turbine engine. The two most important areas of the cooling blade (the leading edge (LE) and the blade tip) were taken into account. The operational and the aleatoric uncertainties were analyzed. These uncertainties represent the fluctuations in the operational parameters and the random-unknown conditions such as the boundary values and or geometrical variations.
Industrial HPT blade with a serpentary cooling system and film cooling at the LE was considered. Results of many engine tests were applied to construct probability density function distributions for operational uncertainties. More than 100 real gas-turbines were examined. The following operational uncertainties were reviewed: inlet hot gas pressure and temperature together with cooling air pressure. The tip gap was used as geometrical variation. Conjugate Heat Transfer computations were carried out for the temperature distribution obtained.
Geometrical variations of the LE film cooling rows and the tip gap are variables in the robust optimization process. The authors developed a special technology for full parameterization of the LE film-cooling rows only by two parameters.
A surrogate model technique (the response surface and the Monte-Carlo method) was applied for the uncertainty quantification and the robust optimization processes. The IOSO technology was employed as one of the robust optimization tools. This technology is also based on the widespread application of the response surface technique.
Robust optimal solution (the Pareto set) between cooling effectiveness of the leading edge and the blade tip and aerodynamic efficiency was obtained as the result. At chosen point from the Pareto set (angle point) we calculated necessary levels of robust criteria characterized LE and blade tip cooling effectiveness and kinetic energy losses.
Origins and Structure of Rotating Instability: Part 1 — Experimental and Numerical Observations in a Subsonic Axial Compressor Rotor
Authors: Wu Yanhui , Chen Zhiyang , An Guangyao , Liu Jun , Yang Guowei 
Published: September 2016

Rotating instability (RI) is an obvious unsteady flow phenomenon occurring in the tip region of compressors, which is potentially linked to tip clearance flow noise, blade vibration and rotating stall/surge. The existing investigations for RI indicate the origins of RI are closely related to unsteady flow behaviors in given blade passages in the rotating reference frame, which depend on the design specifics of axial machines. However, no efforts are made to set up a quantitative link between the time scale of unsteady behavior in a given passage and the characteristic parameters of RI, let alone to define the fluid dynamic processes/events which are causally linked with the RI inception. This is the motivation for the current investigations.
In Part I, the experimental and numerical investigations are carried out to investigate tip flow unsteadiness in a subsonic axial compressor rotor. The measurement results show RI appears at operating points near the stability limit of the test rotor. It becomes more pronounced with mass flow rate decreased. The corresponding computational experiments show that flow unsteadiness in given passages also appears close to the stability limit with its initial origination confined to the tip region. The appearance of tip flow unsteadiness is accompanied by a phase lag pattern in different passages across the circumference similar to the detection of stall flutter. The well-developed Fourier-decomposed method is thus used to evaluate the mode characteristics of circumferential traveling waves. It turns out the circumferential traveling wave rotating against the rotor rotation direction with the mode order of 4 is prominent in the flow field with its frequency in the absolute frame equivalent to the mean frequency value of RI detected in measurements. The further analyses of the simulated flow fields indicate that tip flow unsteadiness in a given passage attributes to the periodic oscillation of “secondary clearance flow”, which induces a blockage tranfer across the passage. The mode order and propagation speed of RI depend on the blockage transfer induced by the periodic oscillation of “secondary clearance flow” between two neighbouring passages along the whole circumference. The investigation results presented in the paper implies that one of early ideas to interpret the origin of RI might be altered to such an extent that it contains any unsteady behavior associated with tip leakage flow, rather than limited to “periodical oscillation of tip leakage vortex”.
A Database of Optimal Airfoils for Axial Compressor Throughflow Design
Authors: Schnoes Markus , Nicke Eberhard 
Published: September 2016

This text describes methods to organize a large set of optimized airfoils in a relational database and its application in throughflow design. Optimized airfoils are structured in five dimensions: inlet Mach number, blade stagger angle, pitch-chord ratio, maximum thickness-chord ratio and a parameter for aerodynamic loading. In this space, a high number of airfoil geometries is generated by means of numerical optimization. Each airfoil geometry is tailored to its specific requirements and optimized for a wide working range as well as low losses. During the optimization of each airfoil, performance in design and off-design conditions is evaluated with the blade-to-blade flow solver MISES. Together with airfoil geometry, the database stores automatically calibrated correlations which describe cascade performance in throughflow calculation.
Based on these methods, two subsonic stages of a 4.5-stage transonic research compressor are redesigned. Performance of baseline and updated geometries is evaluated with 3D CFD.
The overall approach offers accurate throughflow design incorporating optimized airfoil shapes and a fast transition from throughflow to 3D CFD design.
Blade Incipient Crack Determination for Centrifugal Compressor Based on Pressure Pulsation Signal Feature Extraction
Authors: Li Hongkun , He Changbo , Jiang Daren , Wang Xuejun 
Published: September 2016

Centrifugal compressor is a piece of key equipment for factories. Among the components of a centrifugal compressor, impeller is a pivotal part as it is used to transform kinetic energy to pressure energy. The blades are exposed to centrifugal forces, gas pressure, and the friction force which usually lead to cracks.
Therefore, early crack feature extraction and pattern recognition are important to prevent it from failure. Although time series analysis for monitored signals can be used on feature extraction, it is not enough. So the incipient weak feature extraction method should be investigated. In this research, pressure pulsation sensors arranged close to crack area are used to monitor the blade crack signal and extract the feature information. As the different kinds of interference of flow, the pressure pulsation signals for a centrifugal compressor are full of nonlinear characteristics. Therefore, how to obtain the weak information from monitored signals effectively should be investigated. A method on blade crack classification is present by continuous wavelet transform (CWT) and envelope spectrum in this research. Simulation signal analysis and experimental investigation on blade crack classification are carried out to verify the effectiveness of this method. The results show that it is an effective tool for blade incipient crack classification for a centrifugal compressor.
Steady State Performance Simulation of Natural Gas Pipeline Driven by Compressor Stations
Authors: Suleiman S. M. , Li Y. G. 
Published: September 2016

Natural gas pipeline plays an important role in transporting natural gas over a long distance. Its performance and operating behavior are affected by many factors, such as ambient conditions, natural gas flow rate, operation and control of compressor pumping stations, etc. Better understanding of the performance and behavior of an integrated pipeline-compressor system used for gas transmission will be beneficial to both design and operation of natural gas pipelines.
This paper introduces a novel steady-state thermodynamic performance simulation approach for natural gas pipelines based on fundamental thermodynamics with the inclusion of the coupling between a pipeline and compressor pumping stations. A pipeline resistance model, a compressor performance model characterized by an empirical compressor map and a pipeline control schedule for the operation of an integrated pipeline-compressor system are included in the simulation approach. The novel approach presented in this paper allows the analysis of the thermodynamic coupling between compressors and pipes and the off-design performance analysis of the integrated pipeline-compressor system.
The introduced simulation approach has been applied to the performance simulation of a typical model pipeline driven by multiple centrifugal compressor pumping stations. It is assumed in the pipeline control schedule that the total pressure at the inlet of compressor stations is kept constant when pipeline operating condition changes. Such pipeline operating conditions include varying ambient temperature and varying natural gas volumetric flow rate. The performance behavior of the pipeline corresponding to the change of operating conditions has been successfully simulated. The introduced pipeline performance simulation approach is generic and can be applied to different pipeline-compressor systems.
Influence of Unsteady Wakes on the Secondary Flows in the Linear T106 Turbine Cascade
Authors: Kirik Ilker , Niehuis Reinhard 
Published: September 2016

The present work extends previous investigations on the secondary flows around a steady and unsteady base flow to detailed time-averaged and time-resolved flow field measurements up- and downstream of the cascade.
As a representative of modern low pressure turbine rotors of moderate aerodynamic loading, the LPT cascade T106 with parallel sidewalls was chosen for these investigations. Previous investigations have shown that the intensity of secondary flows in the endwall region within a first test set-up was fairly low due to the thin endwall boundary layer at the inlet of the cascade which impeded to study the influence of periodically incoming wakes on the temporal development of the secondary flow field. For that reason a new test-up was built providing a thicker inlet boundary. Measurements have been performed in the High-Speed Cascade Wind Tunnel of the University of the Federal Armed Forces Munich under realistic Mach and Reynolds numbers. In order to simulate real turbomachinery situtations, a wake generator is installed generating temporally representative wakes in the inlet plane of the cascade by a moving bar system.
The inlet conditions were determined using a hot wire and a Pitot probe. Detailed measurements of the three-dimensional flow field were carried out downstream of the cascade with a triple hot wire probe, a conventional five hole pressure probe, and a dynamic pressure probe equipped with a single Kulite sensor. All measurements were performed with and without moving bars. Based on previous investigations, a pitch of the moving bars of 40 mm and a circumferential speed of 20 m/s was chosen as the configuration with the highest influence on the secondary flow field.
It is shown that the intended increase of the inlet boundary layer was achieved by putting plates on top of each other in the inlet plane endwalls. This leads to more pronounced secondary flow parameters in the spanwise distribution of the pitchwise averaged secondary flow angle (Δβ2,sec) and the secondary losses (ζ2,sec).