bluuebunny/crossref_metadata_2025_split huggingface dataset:
An Optimized Correlation for Turbulent Flame Speed for C1-C3 Fuels at Engines-Relevant Conditions
Authors: Burke Eoin M. , Yousefian Sajjad , Güthe Felix , Monaghan Rory F. D. 
Published: January 2021

Abstract
The aim of this work is to examine the state-of-the-art turbulent flame speed (ST) correlations and optimize their adjustable parameters to best match a wide range experimental turbulent premixed combustion results. Four correlations based on previous works by Zimont, Kobayashi, Ronney and Muppala have been selected for the present study. Using a Matlab-based Nelder-Mead simplex direct search method, each correlation’s adjustable parameters are optimized such that their mean absolute percentage error (MAPE) is minimized. In addition to the literature correlations, a new empirical correlation is developed using the same search method to define constants and powers in the expression. Two sets of optimized parameters are proposed to account for atmospheric and elevated (0.2–3.0 MPa) pressure flames. Each correlation is tested further, examining their ability to match ST trends for varying equivalence ratio (φ) and turbulent velocity ratio (u′/SL). It was found that a minimum of two correlations and two sets of adjustable parameters are required to accurately account for the entire range of data, thus showing that there is currently no turbulent flame speed correlation that is applicable across all engine-relevant conditions.
Boundary Conditions for Compressor Cascade Ice Crystal Icing Testing
Authors: Nagorski Matthias , Koch Christian , Staudacher Stephan 
Published: January 2021

Abstract
At the Altitude Test Facility (ATF) of the University of Stuttgart a linear compressor cascade test rig serves the investigation of ice crystal icing (ICI) under engine realistic conditions. A numerical model of the first stage of NASA Stage 67 is validated with experimental data taken from literature and used to investigate the respective ice crystal icing conditions for prospective cascade experiments. Eleven operating points simulating climb conditions with constant non-dimensional power setting through ascending parcels of moist air are selected for analysis. Only the melting-dominated regime is considered. The 3D flow field is obtained using a RANS approach in combination with a Spalart-Allmaras one-equation turbulence model. The droplet and ice crystal trajectories are calculated based on an Eulerian framework. The computation of the surface energy balance is adapted from the Messinger model taking into account unsteady phenomena. Four of eleven selected operating points indicate the onset of substantial ice accretion. A static wet bulb temperature of freezing constitutes in general the lower icing limit for rig experiments. The upper icing limit depends on the ice water content impinging and sticking to the target surface.
A Numerical Study on the Effect of Inter-Stage Water Injection in an Opposed-Setting-Two-Stage Centrifugal Compressor
Authors: Ni Ming , Geng Shaojuan , Wei Zuojun , Gan Xiaohua 
Published: January 2021

Abstract
Inter-stage water injection is currently a common method to reduce the compression work. In this paper, we evaluate the effect of this approach on an opposed-setting-two-stage centrifugal compressor which is designed for a small gas turbine numerically. The Eulerian-Lagrangian method is adopted to calculate the continuous flow field and discrete particle terms with the k-ε turbulence model. 6 water injection conditions are conducted to compare with the dry air condition. The performance curve shift to the right-up side, i.e. higher total pressure ratio, higher efficiency and larger choking mass flow. However, the larger the performance improvement gained by inter-stage injection, the worse the stability will be. Under the micro injection ratio (about 0.1%), the stall margin of the compressor is improved. Additionally, with a proper injection parameter, the loading in the diffuser can be reduced and promise a wider stall margin. Nevertheless, there still exists droplets at the outlet of the high-pressure diffuser because of the insufficient time for evaporation.
Acoustic Energy Balance During the Onset, Growth and Saturation of Thermoacoustic Instabilities
Authors: Gaudron R. , Yang D. , Morgans A. S. 
Published: January 2021

Abstract
Thermoacoustic instabilities can occur in a wide range of combustors and are prejudicial since they can lead to increased mechanical fatigue or even catastrophic failure. A well-established formalism to predict the onset, growth and saturation of such instabilities is based on acoustic network models. This approach has been successfully employed to predict the frequency and amplitude of limit cycle oscillations in a variety of combustors. However, it does not provide any physical insight in terms of the acoustic energy balance of the system. On the other hand, Rayleigh’s criterion may be used to quantify the losses, sources and transfers of acoustic energy within and at the boundaries of a combustor. However, this approach is cumbersome for most applications because it requires computing volume and surface integrals and averaging over an oscillation cycle. In this work, a new methodology for studying the acoustic energy balance of a combustor during the onset, growth and saturation of thermoacoustic instabilities is proposed. The two cornerstones of this new framework are the acoustic absorption coefficient Δ and the cycle-to-cycle acoustic energy ratio λ, both of which do not require computing integrals. Used along with a suitable acoustic network model, where the flame frequency response is described using the weakly nonlinear Flame Describing Function (FDF) formalism, these two dimensionless numbers are shown to characterize: 1) the variation of acoustic energy stored within the combustor between two consecutive cycles, 2) the acoustic energy transfers occurring at the combustor’s boundaries and 3) the sources and sinks of acoustic energy located within the combustor. The acoustic energy balance of the well-documented Palies burner is then analyzed during the onset, growth and saturation of thermoacoustic instabilities using this new methodology. It is demonstrated that this new approach allows a deeper understanding of the physical mechanisms at play. For instance, it is possible to determine when the flame acts as an acoustic energy source or sink, where acoustic damping is generated, and if acoustic energy is transmitted through the boundaries of the burner.
Investigation of Similarity Criteria for an Internally-Cooled Turbine Vane Based on Artificial Neural Networks: Part II — Experimental Validation
Authors: Zhao Weicheng , Wei Jingying , Chi Zhongran , Zang Shusheng 
Published: January 2021

Abstract
In the second part of this two-part paper, several CHT (Conjugate Heat Transfer) CFD (Computational Fluid Dynamics) simulations were conducted at low temperature and pressure conditions which a 100KW or a 400KW blower can provided, in order to investigate the reason caused the modeling deviation when the matched-Biot number criterion is used for modeling. The CFD method used in this paper is the same as the Part I. Afterwards, several experiments were carried out at a mainstream condition which the 100 KW blower can provide to validate whether the deviations predicted by CFD would appear at that target modeling conditions. The mainstream inlet temperature and pressure are 307 K and 113 kPa, respectively. The model used in this paper is the Mark II turbine as well.
The CFD and experiment results show that the main source of the modeling deviation comes from the suction side, the minimum deviation for the four modeling tests has over 0.05 (minimum wall temperature deviation has over 0.75 K). Apart from that, the reason leading to the suction side deviation is the variation of temperature boundary layer, which is caused by the unmatched aerodynamic parameters (such as mainstream Mach number and Reynolds number).
Finding the Best Architecture of an Artificial Neural Network to Model Prefilming Airblast Atomization: Not So Deep Learning
Authors: Chaussonnet G. , Gepperth S. , Holz S. , Koch R. , Bauer H.-J. 
Published: January 2021

Abstract
A fully connected Artificial Neural Network (ANN) is used to predict the spray characteristics of prefilming airblast atomization. The model is trained from the planar prefilmer experiment from the PhD thesis of Gepperth [Experimentelle Untersuchung des Primärzerfalls an generischen luftgestützten Zerstäubern unter Hochdruckbedingungen, Vol. 75. Logos Verlag Berlin GmbH], in which shadowgraphy images of the liquid breakup at the atomizing edge capture the characteristics of the primary droplets and the ligaments. The quantities extracted from the images are the Sauter Mean Diameter, the mean droplet axial velocity, the mean ligament length and the mean ligament deformation velocity. These are the prescribed output of the ANN model. In total, the training database contains 322 different operating points at which different prefilmers, liquid types, ambient pressures, film loadings and gas velocities were investigated. Two types of model input quantities are investigated. First, nine dimensional parameters related to the geometry, the operating conditions and the properties of the liquid are used as inputs for the model. Second, nine non-dimensional groups commonly used for liquid atomization are derived from the first set of inputs. These two types of inputs are compared. The architecture providing the best fitting is determined after testing over 10000 randomly drawn ANN architectures, with up to 10 layers and up to 128 neurons per layer. The striking results is that for both types of model, the best architectures consist of a shallow net with the hidden layers in the form of a diabolo: three layers with a large number of neurons (≥ 64) in the first and the last layer, and very few neurons (≈12) in middle layer. This shape recalls the shape of an autoencoder, where the middle layer would be the feature space of reduced dimensionality. The trend highlighted by our results, to have a limited number of layers, is in contrast with recent observations in Deep Learning applied to computer vision and speech recognition. It was found that the model with dimensional input quantities always shows a lower test and validation errors than the one with non-dimensional input quantities. The best architectures for both types of inputs (dimensional and non-dimensional input) were tested versus the experiments. Both provide comparable accuracy, which is better than typical correlations of SMD and droplet velocity. As the models takes more input parameters into account compared to the correlations, they can predict the experimental data more accurately. Finally the extrapolation capability of the models was assessed by a training them on a confined domain of parameters and testing them outside this domain. It was found that the models can extrapolate at larger gas velocity. With a larger ambient pressure or a lower trailing edge thickness, the accuracy decreases drastically.
The Flow Field Characteristic Correlated With Heat Transfer Performance in a Wide Channel With Staggered Circular Pin Fins
Authors: Duan Jingtian , Zhang Ke , Xu Jin , Lei Jiang , Wu Junmei 
Published: January 2021

Abstract
The velocity field in a wide rectangular channel (AR = 4) with staggered circular pin fin array was measured using Particle Image Velocimetry (PIV). The cylinder pin fin has a diameter of 8 mm and height to diameter ratio (H/D) of 3. The streamwise pitch (X/D) and spanwise pitch (S/D) of pin fins are 4.5 and 2 respectively. The experiment was conducted at two Reynolds number, 10000 and 20000, based on the hydraulic diameter and bulk velocity of the channel. The mean velocity, first-order statistics of velocity fluctuation and turbulent kinetic energy components in the measured plane are given. Results show, the distribution of the cross-stream velocity fluctuation (Vrms), other than second-order statistics, has a similar pattern as that of the local Nusselt number on the end wall between pin fin rows while the flow is in developing. The Nusselt number was achieved through temperature measurement using thermochromic liquid crystal in the same geometry setup. Therefore, compared to second-order statistics, the cross-stream velocity fluctuation might be a simple but crucial flow quantity for heat transfer enhancement using pin fins in the developing region. The shedding of large vortices from circular pin fins is believed to be the primary flow structure inducing the cross-stream velocity fluctuation. Study on pin fins with various geometries is required before further conclusion drawn.
On High-Resolution Pressure Amplitude and Phase Measurements Comparing Fast-Response Pressure Transducers and Unsteady Pressure-Sensitive Paint
Authors: Bitter Martin , Stotz Stephan , Niehuis Reinhard 
Published: January 2021

Abstract
This paper presents the simultaneous application of fast-response pressure transducers and unsteady pressure-sensitive paint (unsteady PSP) for the precise determination of pressure amplitudes and phases up to 3,000 Hz. These experiments have been carried out on a low-pressure turbine blade cascade under engine-relevant conditions (Re, Ma, Tu) in the High-Speed Cascade Wind Tunnel. Periodic blade/vane interactions were simulated at the inlet to the cascade using a wake generator operating at a constant perturbation frequency of 500 Hz. The main goal of this paper is the detailed comparison of amplitude and phase distributions between both flow sensing techniques at least up to the second harmonic of the wake generator’s fundamental perturbation frequency (i.e. 1,000 Hz). Therefore, a careful assessment of the key drivers for relative deviations between measurement results as well as a detailed discussion of the data processing is presented for both measurement techniques. This discussion outlines the mandatory steps which were essential to achieve the quality as presented down to pressure amplitudes of several pascal even under challenging experimental conditions. Apart from the remarkable consistency of the results, this paper reveals the potential of (unsteady) PSP as a future key flow sensing technique in turbomachinery research, especially for cascade testing. The results demonstrate that PSP was able to successfully sense pressure dynamics with very low fluctuation amplitudes down to 8 Pa.
Measurement and Analysis of Buoyancy-Induced Heat Transfer in Aero-Engine Compressor Rotors
Authors: Jackson Richard W. , Luberti Dario , Tang Hui , Pountney Oliver J. , Scobie James A. , Sangan Carl M. , Owen J. Michael , Lock Gary D. 
Published: January 2021

Abstract
The flow inside cavities between co-rotating compressor discs of aero-engines is driven by buoyancy, with Grashof numbers exceeding 1013. This phenomenon creates a conjugate problem: the Nusselt numbers depend on the radial temperature distribution of the discs, and the disc temperatures depend on the Nusselt numbers. Furthermore, Coriolis forces in the rotating fluid generate cyclonic and anti-cyclonic circulations inside the cavity. Such flows are three-dimensional, unsteady and unstable, and it is a challenge to compute and measure the heat transfer from the discs to the axial throughflow in the compressor. In this paper, Nusselt numbers are experimentally determined from measurements of steady-state temperatures on the surfaces of both discs in a rotating cavity of the Bath Compressor-Cavity Rig. The data are collected over a range of engine-representative parameters and are the first results from a new experimental facility specifically designed to investigate buoyancy-induced flow. The radial distributions of disc temperature were collected under carefully-controlled thermal boundary conditions appropriate for analysis using a Bayesian model combined with the equations for a circular fin. The Owen-Tang buoyancy model has been used to compare predicted radial distributions of disc temperatures and Nusselt numbers with some of the experimentally determined values, taking account of radiation between the interior surfaces of the cavity.
The experiments show that the average Nusselt numbers on the disc increase as the buoyancy forces increase. At high rotational speeds the temperature rise in the core, created by compressibility effects in the air, attenuates the heat transfer and there is a critical rotational Reynolds number for which the Nusselt number is a maximum. In the cavity, there is an inner region dominated by forced convection and an outer region dominated by buoyancy-induced flow. The inner region is a mixing region, in which entrained cold throughflow encounters hot flow from the Ekman layers on the discs. Consequently, the Nusselt numbers on the downstream disc in the inner region tend to be higher than those on the upstream disc.
A Robust Model Reference Adaptive Control Framework for Integrated Flight Propulsion System
Authors: Wang Haonan , Wang Xi 
Published: January 2021

Abstract
In this paper, a robust model reference adaptive control framework for the integrated flight propulsion system has been proposed. It could serve as a general controller structure for the integrated flight propulsion system. The linear state feedback controller using LQR method is firstly designed under deterministic uncertainty-free conditions, serving as the reference model. Robust adaptive controller is thereafter introduced to make the system state trajectories converge to the reference model under parametric uncertainties. It is worth noting that, such an arrangement makes the whole control framework easy to be implemented as a modification to existing well designed linear controllers. Besides, high order complexities of the system can be resolved by decomposing it using singular perturbation method based on time scale. A formal stability proof will be provided.
The whole control framework has been implemented on a trim point of an F-16 model. Only actuator anomalies have been concerned as uncertainties to verify the effectiveness of the control framework. However, this structure can be easily extended to accommodate other parametric uncertainties. The simulation results of the controller implemented on the nonlinear system near an equilibrium point will be provided. Superior performance regarding stability and robustness can be observed from the simulation results with robust adaptive augmentation controller used.
Experimental Investigation of a Radial Wave Engine Utilizing a Rotary Valved Pressure Gain Combustor
Authors: Akbari Pejman , Brady Grant M. , Sell Brian C. , Polanka Marc D. 
Published: January 2021

Abstract
In this paper a deflagrative pressure gain combustor employing rotary valves is introduced that can reduce combustor length by allowing the combustion process to take place in the radial direction rather than in the axial direction with sufficient resident time. The engine is described in some detail with respect to geometry, components, and potential benefits. A demonstrator rig was designed, built, and tested for concept verification. A series of initial tests sweeping equivalence ratio from 0.4 to 0.8 using ethylene as fuel and mass flows from 75 g/s to 150 g/s is presented. The turbine rotor was driven to above 200 RPM with just four of the combustor passages operating. The initial results indicate the feasibility of the rotary valve radial engine concept and identified key challenges associated with the concept. Further studies are needed address existing challenges and to promote the engine development.
Comparison of Viscoplastic Modeling of an Equiaxed and Directionally Solidified Ni-Base Superalloy
Authors: O’Nora Nathan , Torkaman Alex , Gordon Ali P. 
Published: January 2021

Abstract
Engine components are subjected to both high temperatures and cyclic loads resulting in fatigue and creep effects. Directionally-solidified (DS) Ni-base superalloys were developed in order to produce favorable creep properties in the primary stress axis of turbine blades by casting the grains longer along this axis. Doing so causes the material to exhibit anisotropic behavior, which allows for improved fatigue and creep strength but also adds complexity to modeling the material. To predict the life of components accurately, it is necessary to use a high-fidelity constitutive model to relate the loading and the deformation of the material. The dual-phase microstructure of these DS superalloys evolves with time, rendering the yield surface of the material a challenge to track. Furthermore, components made from these materials are subjected to complex loading conditions, often seeing cycling temperature in addition to loads, known as thermomechanical fatigue (TMF), and cyclic loads with dwells, known as creep-fatigue (CF). Viscoplasticity models are able to capture the complex behaviors of these materials under complex loading conditions, including the hysteresis effects, rate-dependence, and stress relaxation, etc., making them attractive models to use with critically heated and loaded parts. These models, originally designed for equiaxed materials, have been adapted for use with anisotropic materials, such as DS superalloys. An isothermal anisotropic viscoplasticity model and parameter identification framework has been calibrated within a dedicated parameter identification framework. Principally, the constitutive model is based on the Chaboche viscoplasticity model featuring Armstrong-Frederick kinematic hardening. The performance of a preliminary model is presented for both an equiaxed (i.e., conventionally cast, CC) and DS materials within the same strength class, though more data is needed for validation. With regard to the stress relation associated with creep-fatigue, a fitting-technique for the static recovery model that has shown promise in isotropic materials is expanded to capture the behavior of the DS alloy. Previously developed methods for finding kinematic hardening constants for isotropic material based on Ramberg-Osgood constants at various orientations are expanded to an anisotropic case. These techniques allow for the capturing of more complex loading conditions with a limited number of tests, allowing for cost savings when developing the constitutive model. The model is implemented with three non-linear kinematic hardening terms with static recovery, allowing for the capture of rate and hold time effects, and non-linear isotropic hardening, allowing for the capture of cyclic hardening. The ability to capture the low cycle fatigue (LCF) behavior of both the equiaxed and DS alloys are examined through comparisons with test data.
A Model of Inlet Circumferential Fluctuation in Compressor Cascades
Authors: Yue Zixuan , Li Zefeng , Jin Donghai , Gui Xingmin 
Published: January 2021

Abstract
Through-flow methods are widely used in turbomachinery design and performance prediction due to its fast calculation. In the past, circumferentially-averaging through-flow methods tended to ignore circumferential fluctuation source term (CFST) in the governing equations, leading to an inaccurate result when blades showed a strong three-dimensional feature. To solve this problem, CFST needs to be properly modeled. In this paper, three-dimensional numerical simulation is conducted to find the area where CFST dominates. The influence of inlet Mach number, incidence, camber angles and sweep angle on the CFST in this area is analyzed. A model for CFST is constructed. Three-dimensional verification of this model suggests that within the common scope of use of aerospace compressor designing, this model shows a good accuracy.