bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fast Conjugate Heat Transfer Simulation of Long Transient Flexible Operations Using Adaptive Time Stepping
Authors: Maffulli R. , He L. , Stein P. , Marinescu G. 
Published: August 2018

The emerging renewable energy market calls for more advanced prediction tools for turbine transient operations in fast startup/shutdown cycles. Reliable numerical analysis of such transient cycles is complicated by the disparity in time scales of the thermal responses in fluid and solid domains. Obtaining fully-coupled time-accurate unsteady Conjugate Heat Transfer (CHT) results under these conditions would require to march in both domains using the time step dictated by the fluid domain: typically, several orders of magnitude smaller than the one required by the solid.
This requirement has strong impact on the computational cost of the simulation as well as being potentially detrimental to the accuracy of the solution due to accumulation of round-off errors in the solid. A novel loosely coupled CHT methodology has been recently proposed, and successfully applied to both natural and forced convection cases that removes these requirements through a source-term based modelling approach of the physical time derivative terms in the relevant equations. The method has been shown to be numerically stable for very large time steps with adequate accuracy.
The present effort is aimed at further exploiting the potential of the methodology through a new adaptive time stepping approach. The proposed method allows for automatic time step adjustment based on estimating the magnitude of the truncation error of the time discretization. The developed automatic time stepping strategy is applied to natural convection cases under long (2000 s) transients: relevant to the prediction of turbine thermal loads during fast startups/shutdowns. The results of the method are compared with fully coupled unsteady simulations showing comparable accuracy with a significant reduction of the computational costs.
Demonstration of a Remotely-Controlled Swirl Generator for Simulating Aircraft Inlet Secondary Flows During Turbine Engine Ground Tests
Authors: Beale David 
Published: August 2018

The development of superior combat aircraft demands the complex integration of the airframe, engine, control system, avionics, and on-board weapon systems. The integration of the engine and the inlet is tantamount to prevailing in an engagement due to the thrust required to execute combat maneuvers. For this reason, test and evaluation methods have been developed to help ensure inlet-engine compatibility by design. The most commonly used methodology characterizes inlet distortion in terms of total-pressure descriptors and correlations. The method includes ground tests employing both wind tunnel and engine test facilities, to acquire the information needed to establish inlet-engine compatibility prior to flight test. Advanced aircraft employing evolving technologies never seen in legacy systems have introduced new challenges to the methodology, and to the ground test methods employed by the methodology. One such challenge arises from the significant flow angularity, or swirl, often found in advanced inlet systems. This paper focuses on the simulation of aircraft inlet swirl during direct-connect turbine engine ground tests.
To meet the engine test challenges introduced by advanced aircraft, the Arnold Engineering Development Complex (AEDC) embarked on the development of a swirl generator capable of simulating the different types of swirl expected in future inlet systems over a wide range of swirl angles, and with the ability to remotely set steady-state or transient swirl patterns. The development progressed through a five-step process that culminated in the validation and demonstration of a fully-functional prototype.
This paper focuses on the prototype swirl generator and the progression from the establishment of simulation requirements through the prototype validation. Following summaries of each development step, the results of the validation test are presented. The paper also summarizes a recent application of the prototype which not only demonstrated the device in an engine test, but which provided a data set to support swirl methodology development.
LES Investigation of Boussinesq Constitutive Relation Validity in a Corner Separation Flow
Authors: Monier Jean-François , Poujol Nicolas , Laurent Mathieu , Gao Feng , Boudet Jérôme , Aubert Stéphane , Shao Liang 
Published: August 2018

The present study aims at analysing the Boussinesq constitutive relation validity in a corner separation flow of a compressor cascade. The Boussinesq constitutive relation is commonly used in Reynolds-averaged Navier-Stokes (RANS) simulations for turbomachinery design. It assumes an alignment between the Reynolds stress tensor and the zero-trace mean strain-rate tensor. An indicator that measures the alignment between these tensors is used to test the validity of this assumption in a high fidelity large-eddy simulation. Eddy-viscosities are also computed using the LES database and compared.
A large-eddy simulation (LES) of a LMFA-NACA65 compressor cascade, in which a corner separation is present, is considered as reference. With LES, both the Reynolds stress tensor and the mean strain-rate tensor are known, which allows the construction of the indicator and the eddy-viscosities. Two constitutive relations are evaluated. The first one is the Boussinesq constitutive relation, while the second one is the quadratic constitutive relation (QCR), expected to render more anisotropy, thus to present a better alignment between the tensors.
The Boussinesq constitutive relation is rarely valid, but the QCR tends to improve the alignment. The improvement is mainly present at the inlet, upstream of the corner separation. At the outlet, the correction is milder. The eddy-viscosity built with the LES results are of the same order of magnitude as those built as the ratio of the turbulent kinetic energy k and the turbulence specific dissipation rate ω. They also show that the main impact of the QCR is to rotate the mean strain-rate tensor in order to realign it with the Reynolds stress tensor, without dilating it.
Large Eddy Simulations of a Low-Pressure Turbine: Roughness Modeling and the Effects on Boundary Layer Transition and Losses
Authors: Hammer F. , Sandham Neil D. , Sandberg Richard D. 
Published: August 2018

Large eddy simulations of a linear low-pressure turbine cascade with the T106A profile and different surface roughness patches were carried out. The aim was to investigate the effects on the laminar and turbulent boundary layer on the blade suction surface. Two different approaches were used to represent the roughness patches. Firstly, a forcing model, reducing the computational costs compared to fully resolved roughness surfaces, was incorporated. Secondly, an immersed boundary method representing an as-cast roughness surface was used, for a more detailed analysis of flow mechanisms over roughness.
It was found that the roughness model was able to induce boundary layer transition and alter the turbulent boundary layer, with the results in line with findings in the literature. The instantaneous flow data at different time instants of the as-cast roughness case showed the development of streaks due to distinct roughness peaks, resulting in highly uneven transition positions across the spanwise direction.
Foreign Object Damage Diagnosis of Aero-Engine Compressor Based on Damping Averaging Built-in Matrix Method
Authors: Wu Shuming , Chen Xuefeng , Russhard Pete , Wang Shibin , Zhai Zhi , Zhao Zhibin 
Published: August 2018

Blade Tip Timing (BTT) methods are being implemented that have led to a non-intrusive technique being deployed in certain sectors of Industry. Data sets produced during the development cycle are now providing upfront information that is being used to develop monitoring capability supporting in-service health monitoring. Recent years have witnessed a growing interest in blade health monitoring and its potential to detect the occurrence of both transient and permanent foreign object damage (FOD) and estimate the severity of damage to blades. FOD damage detection is beneficial to both the fan and first stage compressors and the ability to detect it leads to a reduction in the number of inspection that recurrently scheduled.
The expected behaviour under transient FOD condition is a ‘ringing’ signal which is a damped exponential signal. The lack of real FOD data collected requires that a signal is simulated and used to develop and validate detection systems.
Blade tip timing is an effective implementation of non-intrusive technology by circumferentially arranged sensors to obtain the time of arrival (TOA) of blades. However, due to the high degree of undersampling inherent in the data the detection of short-lived events poses a problem.
In this paper the use of a method called ‘Damping Averaging Built-in Matrix’ (DABM), which use the combination of several revolutions data and OPR (once per revolution) data to enhance the sample rate while eliminating the damping effect. After solving the matrix we are able to obtain the frequency and damping of the blade when transient FOD occurs. The FEM (finite element model) of the blade is also built to infer the stress of blade at different levels of FOD. The method is applied to both the simulated data and experimental data to verify its effectiveness. By developing this method further we can provide a capability that could reduce the operation and maintenance cost and increase the security of the engine whilst in operation.
Experimental and Numerical Study on Emission Characteristics of the Double Annular Swirler Under Different Pilot Fuel Ratios
Authors: Zong Chao , Lyu Yaya , Guo Desan , Li Chengqin , Zhu Tong 
Published: August 2018

Micro gas turbine is one of the ideal prime movers for small-distributed energy systems. It can effectively reduce the emission of greenhouse gases and nitrogen oxides. Moreover, the use of micro gas turbines will contribute to burning fossil fuels in a much cleaner way. The staged combustion technology is the favorite way for low pollution combustion chamber such like. Therefore, the influence of the proportion of pilot fuel in the combustion chamber on pollutant emission deserves further study.
The object of this research is the Double annular swirler (Das), which was applied to a 100 kW micro gas turbine combustion chamber. The combustion performance and emission characteristics under different Pilot Fuel Ratios (PFR) were obtained in prototype experimental system.
Under the experimental conditions, Computational fluid dynamics (CFD) method was applied to research the reacting flow field and the formation of NOx in the combustion chamber and then analyze the influences of PFRs on combustion process. Experimental results show that the NOx emission of Das decreased at first and then increased with the augment of PFR. When PFR was near to 11%, the per unit NOx emission concentration reached its minimum. The numerical simulation agreed well with the experimental data. Further analysis of the simulation results indicate that there is a strong correlation between Φlocal and NOx concentration. When it is lower than a certain value, the number of nitrogen oxides will be significantly reduced. The value has a lot to do with the inlet air temperature and the pressure of the combustion chamber under the design condition, and it needs to be confirmed by calculating the adiabatic temperature. Simultaneously, we also find that although the percentage of total air flowing into the combustor remains unchanged, the increase of PFR would reduce the airflow ratio in inner swirler. This implies that for some particular combustion chambers, special attention should be paid to the changes in air allocation caused by PFR.
Influence of Reactor Pressure on the Primary Jet Breakup of High-Viscosity Fuels: Basic Research for Simulation-Assisted Design of Low-Grade Fuel Burner
Authors: Müller Thomas , Kadel Kathrin , Habisreuther Peter , Trimis Dimosthenis , Zarzalis Nikolaos , Sänger Alexander , Jakobs Tobias , Kolb Thomas 
Published: August 2018

Detail investigations on the primary breakup of high-viscosity liquids using external-mixing twin-fluid nozzles at increased system pressure are scarce. Therefore, the research work of the present study is focused on the investigation of pressure influence (1 - 11 bar (abs)) on the primary breakup by numerical simulation based on a previously studied nozzle [Müller et al., ASME Turbo Expo 2016, GT2016-56371]. The pressure influence was investigated for two liquids applying a wide range of viscosities (100 mPa s; 400 mPa s) and two atomizing air velocities (58 m/s; 74 m/s). To describe the disintegration process of the fluids, characteristic features like liquid jet morphology, breakup length and breakup frequency were evaluated.
The primary breakup was investigated using the open source CFD software OpenFOAM. To gather the morphology of the primary breakup and the flow field characteristics compressible large eddy simulations (LES) were performed and the movement of the gas-liquid interface was captured by means of the Volume of Fluid-Method (VOF).
The conducted simulations showed good agreement with experimental results with respect to the characteristic features (e.g. morphology and breakup length) and revealed a decrease of the breakup length with increasing ambient pressure for a constant liquid mass flow and atomizing air velocity. Moreover, those findings will contribute to a better understanding of the physics of the breakup of high-viscosity liquid jets and as well to create an experimentally validated CFD based tool for future burner development and optimization.
Analytical Heat Transfer Correlation for a Multistage Steam Turbine in Warm-Keeping Operation With Air
Authors: Toebben Dennis , Hellmig Adrian , Luczynski Piotr , Wirsum Manfred , Mohr Wolfgang F. D. , Helbig Klaus 
Published: August 2018

Due to the growing share of volatile renewable power generation, conventional power plants with a high flexibility are required. This leads to high thermal stresses inside the heavy components which reduces the lifetime. To improve the ability for fast start-ups, information about the metal temperature inside the rotor and the casing are crucial. Thus, an efficient calculation approach is required which enables the prediction of the temperature distribution in a whole multistage steam turbine. Considerable improvements of the computing power and numerical simulation tools today allow detailed investigations of the heat transfer and the flow phenomena by Conjugate-Heat-Transfer (CHT) simulations. However, these simulations are still restricted to smaller geometries mostly by the number of elements. This leads to coarser numerical meshes for larger geometries and thus, to a reduced accuracy. A highly accurate 3D-CHT simulation of a whole multistage steam turbine can only be conducted with huge computational expense. Therefore, a simplified calculation approach is required. Heat transfer correlations are a commonly used tool for the calculation of the heat exchange between fluid and solid. Heat transfer correlations for steam turbines have been developed in a multitude of investigations. However, these investigations were based on design or to some extent on part-load operations with steam as the working fluid.
The present paper deals with the theoretical investigation of steam turbine warm-keeping operation with hot air. This operation is totally different from the conventional operation conditions, due to the different working fluid with low mass flow rates and a slow rotation. Based on quasi-steady transient multistage CHT simulations, an analytical heat transfer correlation has been developed, since, the commonly known calculation approaches from literature are not suitable for this case. The presented heat transfer correlations describe the convective heat transfer separately at vane and blade as well as the seal surfaces. The correlations are based on a CHT model of three repetitive steam turbine stages. The simulations show a similar behavior of the Nusselt-number in consecutive stages. Hence, the developed area related heat transfer correlations are independent of the position of the stage. Finally, the correlations are implemented into a solid body Finite-Element model and compared to the fluid-dynamic simulations.
Effect of Dimple/Protrusion Depth on Flow Structure and Heat Transfer in a Rotating Channel With Pin Fin
Authors: Du Wei , Luo Lei , Wang Songtao 
Published: August 2018

In this study, numerical simulations are performed to investigate the effect of the dimple/ protrusion depth on the flow structure and heat transfer characteristics in a rotating channel with pin fins. The pin fins are arranged with staggered layout. The longitudinal and transverses pitches of the pin fin are 2.5. The dimples/protrusions are located on the endwall surface between the pin fins. The print diameter of the dimple/protrusion is same as the pin fin. Five different dimple/protrusion depth-to-diameter ratios are investigated, i.e. δ/D = 0, 0.1, 0.2, 0.3, 0.4.
Results of the flow structure, heat transfer on the endwall are included in this study. It is found that the flow structure and heat transfer are sensitive to the rotational Coriolis forces, both on the leading side and trailing side. In the dimpled channel, the area of the low-speed recirculation is increased as the dimple depth increased. The trailing side has higher pressure and TKE compared to the leading side. In addition, the Nu number is high at the trailing side due to the Coriolis forces. In protrusion channel, the pressure is increased at the front of the protrusion as the protrusion depth increases. A counter-rotating vortex is found at the top of the protrusion. The Nusselt number is also higher at the trailing side compared to the leading side.
An Experimental Investigation of Adiabatic Film Cooling Effectiveness and Heat Transfer Coefficient on a Transonic Squealer Tip
Authors: Saul Andrew J. , Ireland Peter T. , Coull John D. , Wong Tsun Holt , Li Haidong , Romero Eduardo 
Published: August 2018

The effect of film cooling on a high pressure turbine blade with an open squealer tip has been examined in a high speed linear cascade. The cascade operates at engine realistic Mach and Reynolds numbers, producing transonic flow conditions over the blade tip. Tests have been performed on two uncooled tip geometries with differing pressure side rim edge radii, and a cooled tip matching one of the uncooled cases.
The pressure sensitive paint technique has been used to measure adiabatic film cooling effectiveness on the blade tip at a range of tip gaps and coolant mass flow rates. Complementary tip heat transfer coefficients (HTC) have been measured using transient infrared thermography, and the effects of the coolant film on the tip heat transfer and engine heat flux examined.
The uncooled data show that the tip heat transfer coefficient distribution is governed by the nature of flow reattachments and impingements. The squealer tip can be broken down into three regions, each exhibiting a distinct response to a change in the tip gap, depending on the local behaviour of the overtip leakage flow. The edge radius of the pressure side rim causes the overtip leakage flow to change dramatically at low clearance. Complementary CFD shows that the addition of casing motion causes no further change on the pressure side rim.
Injected coolant interacts with the overtip leakage flow, which can locally enhance the tip heat transfer coefficient compared to the uncooled tip. The film effectiveness is dependent on both the coolant mass flow rate and tip clearance. At increased coolant mass flow, areas of high film effectiveness on the pressure side rim coincide strongly with a net heat flux reduction and in the subsonic tip region with low heat transfer coefficient.
Towards an Improved Lifing Methodology for Thermocouple Probes Used in Gas Turbines
Authors: Scervini Michele , Rae Catherine , Page Richard , Rudkin Mark , Loveless Daniel , O’Dell Stephen 
Published: August 2018

The reliability of temperature probes in gas turbines is dependent on their capability to withstand the harsh environment they experience when installed in an engine. The severe conditions sensors experience during operation requires the use of appropriate methodologies to assess their life. During the ALPHET project the University of Cambridge and Esterline Advanced Sensors have been working on developing an advanced lifing methodology: in order to predict the life of thermocouple probes used in gas turbines, this combines accelerated laboratory tests based on the salt deposition method, combustor rig tests, metallurgical analysis of probes returned after engine service and information extracted from their associated temperature data acquired during their long term operation in aero gas turbines.
The work included analysis of materials used in current temperature probes and investigation of advanced materials for future thermocouple sensors that will work at temperatures higher than today’s probes.
This paper will summarise the main features of the improved lifing methodology and the challenges associated with the use of complex engineering data obtained from engines.
Numerical Investigation of Non-Isothermal Cavitating Flows on Hydrofoils by Means of an Extended Schnerr-Sauer Model Coupled With a Nucleation Model
Authors: De Giorgi Maria Grazia , Ficarella Antonio , Fontanarosa Donato 
Published: August 2018

The present work aims to investigate cavitating flows of water, liquid hydrogen and nitrogen on hydrofoils numerically, using the open source code OpenFOAM. The Eulerian homogeneous mixture approach has been used, consisting in a mass transfer model which is based on the combination of a two-phase incompressible unsteady solver with a Volume of Fluid (VOF) interface tracking method. Thermal effects have been introduced by means of the activation of energy equation and latent heat source terms plus convective heat source term. The dependency of the saturation conditions to the temperature has been defined using Antoine-like equations. An extended Schnerr-Sauer model based on the Classical Nucleation Theory (CNT) has been implemented for the computation of the interfacial mass transfer rates.
In order to investigate the nucleation effects, an extension of the Classical Nucleation Theory has been considered by coupling the Population Balance Equation/Extended Quadrature-Based Method of Moments (PBE-EQBMM) with the CFD model, which has been defined in combination with a transport equation for the nuclei density. Results showed that nucleation determined a non-uniform field of nuclei density so as to produce a reduction of the temperature drop inside the vapor bubbles, as well as a warmed wake downstream the vapor cavity. Unsteady computations also revealed an influence of the nucleation on the dynamics of the vapor cavity and the bubble detachment.