bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generalization of Machine-Learned Turbulent Heat Flux Models Applied to Film Cooling Flows
Authors: M. Milani Pedro , Ling Julia , Eaton John K. 
Published: November 2019

Abstract
The design of film cooling systems relies heavily on Reynolds-Averaged Navier-Stokes (RANS) simulations, which solve for mean quantities and model all turbulent scales. Most turbulent heat flux models, which are based on isotropic diffusion with a fixed turbulent Prandtl number (Prt), fail to accurately predict heat transfer in film cooling flows. In the present work, machine learning models are trained to predict a non-uniform Prt field, using various datasets as training sets. The ability of these models to generalize beyond the flows on which they were trained is explored. Furthermore, visualization techniques are employed to compare distinct datasets and to help explain the cross-validation results.
Accelerated Multi-Fidelity Emulator Modeling for Probabilistic Rotor Response Study
Authors: Bae Harok , Boyd Ian M. , Carper Emily , Brown Jeff 
Published: November 2019

Abstract
This paper presents an efficient methodology to build a modal solution emulator for the probabilistic study of geometrically mistuned bladed rotors by using the newly developed localized-Galerkin multi-fidelity modeling and eigensolution reanalysis with the symmetric successive matrix inversion methods. The key idea of the mistuned blade emulator is to establish a reduced functional relationship between the stochastic geometric variations and the disturbed modal responses. The prediction accuracy of an emulator depends on how many training samples of modal solutions are available and how well the potential modal switching due to stochastic mistuning is captured. To reduce the computational costs of generating training samples without sacrificing accuracy, this paper introduces the collaborative framework of the new approaches of multi-fidelity modeling and eigensolution reanalysis. The proposed framework is demonstrated for its computational benefits with several numerical examples including the point-cloud scanned mistuned blade problem.
Numerical and Experimental Study of Ice Accretion Process and Ice Protection on Turbo-Fan Engine Splitter
Authors: Zheng Yutao , Zhang Fukun , Wang Daijun , Li Si 
Published: November 2019

Abstract
The splitter, a steady component in the downstream of fan blades in the turbo-fan engine, will be exposed to an icing environment when the engine is working in icing conditions. An anti-icing system should be used on the splitter in order to make the engine work well and not be affected by icing. In this study, both of experiments and CFD simulations were applied to acquire icing characteristics and the electronic anti-icing system’ energy requirement for this component. Factors of icing conditions varied from attacking angle, ambient temperature and pressure, air velocity and droplet factors. Experiments were performed in the AVIC Aerodynamics Research Institute Icing Wind Tunnel (FL-61). The test component was a combination of an arc segment of splitter and seven pieces of inlet guide vanes, covered by electrical heating film. The experiment was carried out under different icing conditions in the icing wind tunnel. Ice profiles, the results of icing experiment, were collected by 3D scanner. Anti-icing surface temperature profiles were collected by thermocouples. The CFD results of icing process were compared with the experimental data for validation, and showed that the droplet collection of on the lower surface of splitter was significant. The CFD simulation was established on the two-phase flow analysis conducted by ANSYS-CFX and Fensap-ice for the prediction on ice accretion, and a coupled simulation method was introduced to replace the conjugate simulation method for thermal analysis with a higher working efficiency in engineering design. Through the icing simulation, an estimated external boundary condition was applied on the thermal model of the test piece and the temperature field on the test piece was calculated.
Testing Propeller Tip Modifications to Reduce Acoustic Noise Generation on a Quadcopter Propeller
Authors: Van Treuren Kenneth , Wisniewski Charles 
Published: November 2019

Abstract
Electric propulsion is gaining popularity with over 100 electrically propelled aircraft in development worldwide. There is a growing interest in vertical lift vehicles either for package delivery or for urban air taxis. If these vehicles are to operate near population centers, they must be both quiet and efficient. The goal of this research is to develop a propeller that is more efficient and generates less noise than a stock DJI Phantom 2 quadcopter propeller. Since a large contribution of near field noise generation for a propeller comes from the tip vortex, reducing or minimizing this generated tip vortex was the main objective. After studying the literature on aircraft wing tip vortices and techniques proposed to minimize the wing tip vortex, seven promising tip treatments were selected and applied to a stock DJI Phantom 2 propeller in an attempt to reduce the tip vortex, and, thus, the generated noise. These tip treatments were: 1. Leading Edge Notch, 2. Trailing Edge Notch, 3. Hole, 4. Vortex Generators, 5. Tip Thread, 6. Trailing Edge Sawtooth, and 7. Reverse Half-Delta.
An optimum design would be one that reduces near field noise while at the same time minimizes any additional required power. Several different configurations were tested for each tip treatment to determine the RPM and required power to hold 0.7 lbf thrust, which simulated a static hover condition. For each test, a radial traverse one inch behind the propeller permitted the measurement of the Sound Pressure Level (SPL) to find the maximum SPL and its radial location. Several configurations tested resulted in 8–10 dBA reductions in SPL when compared to the stock propeller, however, these configurations also resulted in an unacceptable increase in the power required to achieve the desired thrust. Thus, in these cases a decrease in SPL comes at the expense of power, a tradeoff that must be considered for any propeller modification.
The most promising tip treatment tested was the Trailing Edge Notch at a radial location of 0.95 r/R with a Double Slot width and a Double Depth (DSDD). The DSDD configuration as tested reduced the SPL 7.2 dBA with an increase in power required of only 3.96% over the stock propeller. This tradeoff, while not the largest reduction in noise generation measured, seems to be an acceptable power increase for the decrease in SPL achieved. Smoke visualization confirms that the tip vortex is minimized for this configuration.
Numerical Investigation on the Effect of Bleed Port With Self-Recirculating Casing Treatment on the Stability of a 1.5-Stage Transonic Compressor
Authors: Zhong Yiming , Chu WuLi , Zhang HaoGuang 
Published: November 2019

Abstract
Compared to the traditional casing treatment, the self-recirculating casing treatment (SCT) can improve or not decrease the compressor efficiency while achieving the stall margin improvement. For the bleed port, the main design indicator is to reduce the flow loss caused by suction, while providing sufficient jet flow and jet pressure to the injector. In order to gain a better study of the bleed port stabilization mechanisms, the bleed configuration was parameterized with the bleed port inlet width and the bleed port axial position. Five kinds of recirculating casing treatments were applied to a 1.5-stage transonic axial compressor with the method of three-dimensional unsteady numerical simulation. Fifteen identical self-recirculating devices are uniformly mounted around the annulus. The numerical results show that the SCT can improve compressor total pressure ratio and stability, shift the stall margin towards lower mass flows. Furthermore, it has no impact on compressor efficiency. The optimal case presents that stability margin is improved by 6.7% employing 3.1% of the annulus mass flow. Expanding bleed port inlet width to an intermediate level can further enhance compressor stability, but excessive bleed port inlet width will reduce the stabilization effect. The optimal bleed port position is located in the blocked area of the low energy group at the top of the rotor.
In the case of solid casing, stall inception was the tip blockage, which was mainly triggered by the interaction of the tip leakage vortex and passage shock. From radial distribution, the casing treatment predominantly affects the above 70% span. The reduction of tip reflux region by suction effect is the main reason for the extension of stable operation range. The SCT also has an obvious stability improvement in tip blockage stall, while delaying the occurrence of compressor stall.
Effect of Noise and Nonlinearities on Thermoacoustics of Can-Annular Combustors
Authors: Ghirardo G. , Moeck J. P. , Bothien M. R. 
Published: November 2019

Abstract
Can-annular combustors consist of N distinct cans set up symmetrically around the axis of the gas turbine rotor. Each can is connected to the turbine inlet by means of a transition duct. At the turbine inlet a small gap between the neighbouring transition ducts allows acoustic communication between the individual cans. Thermoacoustic pulsations in the cans are driven by the respective flames, but also the communication between neighbouring cans through the gap plays a significant role. In this study we focus in particular on the effect of the background noise intensity and of the nonlinear flame saturation. We predict how usually clusters of thermoacoustic modes are unstable in the linear regime and compete with each other in the nonlinear regime, with each cluster consisting of axial, azimuthal and push-pull modes. Since linear theory cannot predict the nonlinear solution, stochastic simulations are run to study the non-linear solution in a probabilistic sense. One outcome of these simulations are the various pulsation patterns, which are in principle different from one can to the next. This is done for several configurations, with a focus on the effect of a loss of rotational symmetry of the system. We recover how a stronger flame response in one can give rise to the phenomenon of mode localization, but also how the nonlinearity of the flame saturation and the competition between modes have an effect on the nonlinear average mode shape. We finally predict the coherence and phase pattern between cans on the linearized system subject to stochastic noise, and compare the predictions with direct engine measurements, both in terms of spectra of pulsation amplitude in each can and coherence and phase between different cans, observing a good match.
A No-Calibration Approach to Modelling Compressor Blade Rows With Body Forces Employing Artificial Neural Networks
Authors: Pazireh S. , Defoe J. J. 
Published: November 2019

Abstract
Body force modelling in numerical simulations of axial compressors and fans has been used extensively in the literature to assess aerodynamic performance in uniform and non-uniform flow at relatively low computational cost. Existing approaches require calibration or, in the case of purely analytical models, are unable to accurately predict losses. It can also be challenging to capture the chordwise loading distribution with existing analytical models. This paper introduces a new body force modelling approach in which blade loading is computed using an isolated-airfoil, analytical model supplemented by a trained artificial-neural-network-based correction factor for finite pitch effects. The loading model is derived from potential flow theory and accounts for both camber and thickness effects; it captures both the overall and local loading. The approach is currently implemented for low-Mach number (incompressible) flows. The body forces causing flow turning derive directly from the corrected loading model. Forces arising from viscous losses are modeled by solving the integral boundary layer equations along streamlines within blade rows based on the fictitious edge velocities computed by the loading model. The viscous loss force is a function of the local dissipation coefficients. The approach is implemented within a traditional finite-volume computational fluid dynamics solver. In this paper, the application is limited to 2D cascades. To assess the approach, results from the body force model are compared to blade-to-blade solutions from MISES. The key findings are (1) that a relatively modest set of training data for the neural network produces a robust finite pitch correction, and (2) that the modelling approach is able to successfully capture the flow turning and losses associated with a variety of low-speed compressor cascades without any calibration specific to the blade row(s) being modeled.
Thermo-Structural Analysis of Steam Turbine in Pre-Warming Operation With Hot Air
Authors: Łuczyński Piotr , Toebben Dennis , Pehle Lukas , Wirsum Manfred , Mohr Wolfgang F. D. , Helbig Klaus 
Published: November 2019

Abstract
In pursuit of flexibility improvements and extension of lifetime, a concept to pre-warm steam turbines using hot air was developed. In order to further optimize the pre-warming operation, an extensive numerical investigation is conducted to determine the time-dependent temperature and stress fields.
In this work, the transient thermal and structural analyses of an IP 19-stage steam turbine in pre-warming operation with hot air are presented. Based on the previous investigations, a hybrid (HFEM - numerical FEM and analytical) approach especially developed for this purpose is applied to efficiently calculate the solid body temperatures of a steam turbine in pre-defined pre-warming scenarios. The HFEM model utilizes the Nusselt number correlations to describe the heat transfer between the hot air and the turbine components in the flow channel. These correlations were developed based on unsteady CHT-simulations of multistage turbine models. In addition, most of the thermal energy in turbine pre-warming operation is transferred through vanes and blades. Therefore, the HFEM approach considers the thermal contact resistance (TCR) on the surfaces between vanes/casing and blades/rotor. After the calibration of the HFEM model with experimental data based on measurements of the natural cooling curve, the pre-warming processes for different pre-warming scenarios are simulated. Subsequently, the obtained temperature fields are imported to an FEM model in order to conduct a structural analysis, which, among other variables, includes the values and locations of highest stresses and displacements.
A New Physics Based Unsteady Transition Model Using the Universal Intermittency Function
Authors: Nikparto Ali , Schobeiri Meinhard T. 
Published: November 2019

Abstract
The flow inside a gas turbine engine has unique complexities. One of the important characteristics of such flow field is the existence of periodic unsteady wakes, originating from stator–rotor interaction. The unsteady wakes, with their highly vortical core, impinge on the downstream blade surfaces and cause an intermittent transition of the boundary layer from laminar to turbulent. The relative intermittency value corresponding to the wake vortical core and the calm region outside the wake, irrespective of freestream turbulence intensity and wake frequency, exhibits a universal behavior which is best described by the universal intermittency function of Chakka and Schobeiri [1, 2]. This study aims at introducing a new physics-based universal intermittency function that in conjunction with the current turbulence models accurately predicts the unsteady behavior of an intermittent flow. For that reason, a transport equation for turbulence intermittency was proposed based on this function and was integrated into a RANS based solver with k-ω turbulence model. The model was tested for reliability. Experimental aerodynamics and heat transfer measurements conducted at Turbomachinery Performance and Flow research Lab (TPFL) at Texas A&M University, were used as benchmark tests. For experimental measurements, an unsteady linear cascade facility in TPFL was used to produce the periodic unsteady flow condition. Moving wakes, originating from upstream blades, were simulated in this facility by rods attached to two parallel timing belts in front of the turbine blades. Heat transfer measurements along the suction surface were conducted utilizing a specially manufactured blade with an internal heater core, instrumented with liquid crystal. All Measurements and calculations were conducted at Reynolds number of 264,000. The computational results, obtained from implementing the new enhanced intermittency transport equation into the solver, are compared with (a) experimental measurements and (b) with the computational results from RANS that incorporates Langtry-Menter [3, 4] method.
Robust Optimization of Flexible Rotor Systems With Uncertain Parameters via Interval Analysis Method
Authors: Hong Jie , Yang ZheFu , Ni YaoYu , Ma YanHong 
Published: November 2019

Abstract
Uncertainties in the input parameters are inevitable in any design process. Along with the demands for higher rotational speed and higher efficiency of rotating machinery, parameter uncertainties (e.g. support stiffness, the effective bending stiffness of connecting structures) resulted from the increasing load on rotor systems lead to significant scatter of its dynamic performance. These parameters are “uncertain but bounded” which means the distributions are unknown, but the intervals are always got easier. This paper presents a method to robustly optimize the dynamic performance of flexible rotor systems taking into account parameter uncertainties via interval analysis method.
Interval analysis methods for modal properties and dynamic response behavior of rotor systems are developed with the interval variables introduced into the equation of motion. The aim of the robust design method is to optimize the critical speed margins and dynamic load on bearings, in the meanwhile, minimizing the variability of the objective items by the means of reducing their sensitivity to parameter uncertainties. A numerical example is presented, results show that, for the high-speed flexible rotor systems, the optimal choices of design variables could reduce of sensitivity to rotor parameter uncertainties, thus optimizing the variability of dynamic performance, which has important practical significance in engineering.
Generation and Migration of Hot Streaks Within an LPP Combustor
Authors: Tao Wenjie , Wang Jing , Mao Ronghai , Wang Xinyao , Zhang Chi , Lin Yuzhen 
Published: November 2019

Abstract
The exit temperature profile of an LPP combustor has been studied experimentally and numerically in this paper. The combustor has been designed to incorporate three sectors within which the flow, spray and exit temperature characteristics have been investigated by PIV, PLIF and thermocouple measurements. The numerical simulation has been performed by the RANS method. Turbulences have been modeled by the realizable k-ϵ method and the combustion chemistry described by the FGM model. Liquid droplets have been tracked in the Lagrangian framework. The discrete effusing cooling flows on the flame tube have been modeled by source term method. Compared to the experimental results, the proposed CFD method predicted well the flow structure, spray distribution as well as the exit temperature of the tri-sector combustor and it has been employed to study the effect of main swirler designs on the exit temperature. Four main swirlers with different swirl numbers and axial velocities have been calculated and results have shown that the associated structure of the central recirculation zone had dominant impact on the exit temperature pattern. It has been finally proposed that designing the main swirler to generate a wide yet short recirculation zone could improve both the pattern and profile factor for the given LPP combustor.
Experimental Investigation on the Plasma Flow Control of Axial Compressor Rotating Stall
Authors: Zhang Haideng , Wu Yun , Yu Xianjun , Li Yinghong , Liu Baojie 
Published: November 2019

Abstract
Experimental investigation on the plasma flow control of axial compressor rotating stall is implemented in this paper. The control effects of axial plasma actuation (inducing body force of compressor axial direction) with three different locations as well as stagger angle plasma actuation (inducing body force perpendicular to the compressor rotor tip chordwise direction) at different rotation speeds are studied. An unsteady plasma actuation is designed to influence the unsteady rotor tip flow at near stall point, and is found to be the most powerful in improving the compressor stall margin. Both the compressor rotation speed and the plasma actuation voltage are found to be very influential on the control effects of the plasma actuation. The abilities of the plasma actuation in suppressing the compressor rotating stall and influencing the compressor static pressure rise coefficient are not directly related. All the plasma actuations studied can improve the compressor stall margin, but the compressor static pressure rise coefficient can be decreased or increased with different plasma actuation layouts.
Design of Cryogenic Centrifugal Compressor Stages With Heat Transfer Considerations
Authors: Xiong Jin , Zhang Yingkun , Guo Penghua , Li Jingyin 
Published: November 2019

Abstract
The large superconducting magnet are widely used and play an important role in nuclear fusion device, high-energy accelerator, space target infrared and other forefront fields. In this paper, we design several cryogenic centrifugal compressor stages for helium refrigerator with 3.3K∼11K inlet temperature, used in exhausting the low-pressure and low-temperature saturated helium steam, further producing superfluid helium and cooling the large superconducting magnet.
Due to the cryogenic compressor running environment and the internal structure, about 30W heat leakage from impeller hubs and the end of shafts into the flow passages are unavoidable, and it is necessary to consider this heat leakage in the centrifugal compressor impeller design. Firstly, adding the heat leakage into thermodynamic process and centrifugal compressor effective formula, then adjusting the inlet and outlet design parameters according to the heat transfer rate and make the preliminarily designs of each stage of the compressor. Four different methods for varying p design condition parameters are compared by CFD simulation. The 3-D impellers are designed by the Streamline Curvature Method, and the vaneless diffusers and volutes are designed by the inlet and outlet section aerodynamic parameters. When the best design method is determined, the blade profiles are further adjusted in order to improve the stage performance. Finally, the characteristic curves under variable working conditions and the generalized stage performance curves of each stage are calculated. In this paper, we delve into a high efficiency centrifugal compressor stage design method with the consideration of heat transfer effect. In the next step, more running data will be obtained after the further experiments and the long-term operation.