bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Jetting Orifice Geometry Parameters and Channel Reynolds Number on Bended Channel Cooling for a Novel Internal Cooling Structure
Authors: He Wei , Deng Qinghua , He Juan , Gao Tieyu , Feng Zhenping
Published: November 2019

A novel internal cooling structure has been raised recently to enhance internal cooling effectiveness and reduce coolant requirement without using film cooling. This study mainly focuses on verifying the actual cooling performance of the structure and investigating the heat transfer mechanism of the leading edge part of the structure, named bended channel cooling. The cooling performances of the first stage of GE-E3 turbine with three different blade leading edge cooling structures (impingement cooling, swirl cooling and bended channel cooling) were simulated using the conjugate heat transfer method. Furthermore, the effects of jetting orifice geometry and channel Reynolds number were studied with simplified models to illustrate the flow and heat transfer characteristics of the bended channel cooling.

The results show that the novel internal cooling structure has obvious advantages on the blade leading edge and suction side under operating condition. The vortex core structure in the bended channel depends on orifice width, but not channel Reynolds number. With the ratio of orifice width to outer wall thickness smaller than a critical value of 0.5, the coolant flows along the external surface of the channel in the pattern of “inner film cooling”, which is pushed by centrifugal force and minimizes the mixing with spent cooling air. Namely, the greatly organized coolant flow generates higher cooling effectiveness and lower coolant demand. Both the Nusselt number on the channel surfaces and total pressure loss increase significantly when the orifice width falls or channel Reynolds increases, but the wall jet impingement distance appears to be less influential.
Transient CFD Co-Simulation of a 3D Compressor Model in its 1D System Environment
Authors: Spille-Kohoff Andreas , Hetze Farai , Du Toit Bennie
Published: November 2019

Rotary compressors such as screw compressors, roots blowers, and turbo compressors are used in industry to compress process gases, or as vacuum or backing pumps to evacuate vessels. Gas is sucked in at low-pressure side, transported and compressed by size-changing chambers (PD machines) or energy transmission from rotor to fluid (turbo machinery), and released at high-pressure side. In expanders or turbines, flow direction is from high to low pressure side to gain energy from pressurized gases. The 3D CFD simulation of such compressors/expanders is complex and time-consuming due to its transient nature and fine meshes to ensure a proper representation of radial and axial gaps in the range of some microns with machine dimensions up to meters. Due to this complexity, 3D CFD simulation should focus on the component, i.e. the compressor, and the attached overall system with vessels, valves, pipes, and consumers should be simulated in a 1D network or system simulation. Due to oscillations in the gas flow and interaction with the connected system a transient coupling is necessary. In this paper we show a 3D CFD simulation of a screw compressor using ANSYS CFX in a co-simulation with the 1D Flownex simulation environment of a network modelling the pressurized gas distribution. Whereas the 3D solver works on meshes with up to several million nodes in parallel on HPC systems, the 1D solver typically works serially on several thousand nodes that discretize the flow direction. The transient coupling is based on the exchange of variables at the boundaries of each simulation for every time step allowing for detailed analysis. The impact of the acoustic propagation of pressure fluctuations and the pulsating fluid flow provided by the compressor on the distribution system, and in return the effects of the system response on the compressor are evaluated. Furthermore transient scenarios such as start-up procedures or component failure will be shown.
Prediction of the Flow Response of a Turbulent Flame to Acoustic Pertubations Based on Mean Flow Resolvent Analysis
Authors: Kaiser Thomas Ludwig , Lesshafft Lutz , Oberleithner Kilian
Published: November 2019

Resolvent analysis is applied to a non-reacting and a reacting swirled jet flow. Time-averaged flows as input for the resolvent analysis and validation for the results of the resolvent analysis are obtained by experiments. We show that in the non-reacting (cold) flow case, the resolvent analysis is capable of predicting the hydrodynamic response to upstream harmonic acoustic forcing if the flow shows low-rank behavior. This is the case for low and moderate acoustic forcing amplitudes. Even for very strong acoustic velocity amplitudes, that are of the same order of magnitude as the flow velocity, the resolvent analysis still provides reasonable results. The method also yields very good results for the reacting flow in terms of velocity fluctuation and heat release response to the acoustic forcing. This confirms the idea that the resolvent method could be applied to estimate the Flame Transfer Function based on the mean flow and flame.
Influence of Lubrication Oil on the Performance of Carbon Fibre Brush Seals for Aero-Engines Bearing Chambers
Authors: Outirba Bilal , Hendrick Patrick
Published: November 2019

Carbon fibre brush seals are an alternative to labyrinth seals in aero-engines lubrication systems due to better sealing ability with low power loss. However, the use of brush seals still raises concerns about coking issues. In addition, the influence of oil on the brush seal behaviour needs to be fully assessed. This paper provides an experimental investigation of the effect of lubrication oil on the performance of carbon fibre brush seals under static and dynamic conditions. Eight brush seal samples of various geometrical designs were submitted to an environment recreating the working conditions of a modern aero-engine bearing chamber in terms of rotational speed, air pressure, and oil type of injection and temperature. The test results indicated that the performance of carbon fibre brush seals was deeply influenced by the presence of oil within fibres. Oil deeply influences leakage performance, depending on geometrical parameters (density, fibre length and interference) and operating conditions (oil temperature, rotational speed). Brush seal fibre pack is mainly prone to hydrodynamic lift and oil soaking, which is defined by the ability of lubrication oil to fill in properly the interstices between fibres. Viscosity and surface tension may be the key properties influencing oil soaking. Seal torque data corroborates the presence of a hydrodynamic lift. In addition, in absence of differential pressure, seal torque decrease with when oil temperature increases indicates the existence of a critical viscosity. Finally, oil lubrication within the bristles allows reduction of the inter-bristle friction, thus limiting hysteresis.
Modelling and Design of LPC Components With Semi-Analytical Models: Part I — Model Formulation and Validation
Authors: di Mare Luca , Carnevale Mauro , Rife Max E. , Kulkarni Davendu , Northall Richard
Published: November 2019

The adoption of very high bypass ratios is an effective strategy to improve the performance of turbofans for civil aviation. Very high-bypass ratio turbofans are characterized by large-diameter fans and large intake diameters, whereas the overall length of the engine and its installation have to be contained to prevent excessive weight growth. As a result, the main components of the low-pressure compression system (LPC) are closer to each other in modern and future engines than they were in less recent designs, if distances are measured in terms of engine diameter. As the axial decay of potential distortions takes place over distances comparable to their tangential wavelength, modern and future engines also display stronger interactions between the intake, the fan, the OGVs and the pylons, causing performance and integrity issues that need to be addressed at the design stage.

The direct computation of whole LPC systems through CFD is expensive on account of the large extent of the domain and the wide range of wavelengths/frequencies that need to be resolved. This makes CFD unsuitable for bypass design. However, as the interaction between intake, fan, OGV and bypass takes place mainly through flow potential over long wavelengths, drastic simplifications can be introduced. Correspondingly, considerable computational savings are possible by resorting to semi-analytical models.

In this Part I of a two-part paper, a model for the intake/fan/OGV bypass interaction problem based on potential flow is presented. The model can describe the potential component of the LPC flow field, as well as vorticity distortions transmitted through the fan and those generated by the fan as a result of the non-uniform work done around the circumference. The method is validated against CFD results on a configuration typical of modern machines for civil aviation service and is demonstrated as a useful preliminary design tool.
Off-Design Performance Evaluation of a LNG Production Plant Coupled With Renewables
Authors: Ancona M. A. , Bianchi M. , Branchini L. , Catena F. , De Pascale A. , Melino F. , Peretto A.
Published: November 2019

In the last years, the increased demand of the energy market has led to the increasing penetration of renewable energies, in order to achieve the primary energy supply. Simultaneously, natural gas is predicted to play a vital and strategic role in the energy market, on account of its lower environmental impact than other fossil fuels, both as gaseous fuel for stationary energy generation and as liquefied fuel. In particular, the Liquefied Natural Gas (LNG) is becoming interesting in transports as an alternative to diesel fuel, allowing a decrease in pollutant emissions and a reduction in fuel’s costs for the users. As a consequence, in this context, the LNG production process can be seen as an electrical storage system by the integration with renewables, becoming an interesting solution to avoid the issues related to intermittency and unpredictability of renewables.

The aim of the paper is the development of a calculation code and the evaluation of the off-design operation of a LNG production plant coupled with wind renewable energy sources. With this purpose, on the basis of mathematical models from literature, a dedicated calculation code has been developed, able to thermodynamically analyze both design and off-design operation of the integrated process. In addition, in this study the proposed model is employed to investigate the correct integration between renewables and LNG generation, in order to define the optimal choice of the wind size for a given LNG production plant. With this purpose, the LNG plant size of a real prototype has been considered and an economic analysis has been carried out, accounting for the revenue of the LNG sale, the costs for NG purchase, for operation and maintenance and for the initial investment costs, but also with the aim to minimize the electricity introduction into the grid, considered in this study as a penalty.
Numerical Simulation of Non-Equilibrium Condensation in Supercritical CO2 Compressors
Authors: Brinckman Kevin W. , Hosangadi Ashvin , Liu Zisen , Weathers Timothy
Published: November 2019

There is increasing interest in supercritical CO2 processes, such as Carbon Capture and Storage, and electric power production, which require compressors to pressurize CO2 above the critical point. For supercritical compressor operation close to the critical point there is a concern that the working fluid could cross into the subcritical regime which could lead to issues with compressor performance if condensation was to occur in regions where the fluid dropped below the saturation point. Presently, the question of whether there is sufficient residence time at subcritical conditions for condensation onset in supercritical CO2 compressors is an unresolved issue. A methodology is presented towards providing a validated simulation capability for predicting condensation in supercritical CO2 compressors. The modeling framework involves the solution of a discrete droplet phase coupled to the continuum gas phase to track droplet nucleation and growth. The model is implemented in the CRUNCH CFD® Computational Fluid Dynamics code that has been extensively validated for simulation at near critical conditions with a real fluid framework for accurate predictions of trans-critical CO2 processes.

Results of predictions using classical nucleation theory to model homogeneous nucleation of condensation sites in supersaturated vapor regions are presented. A non-equilibrium phase-change model is applied to predict condensation on the nuclei which grow in a dispersed-phase droplet framework. Model validation is provided against experimental data for condensation of supercritical CO2 in a De Laval nozzle including the Wilson line location. The model is then applied for prediction of condensation in the compressor of the Sandia test loop at mildly supercritical inlet conditions. The results suggest that there is sufficient residence time at the conditions analyzed to form localized nucleation sites, however, droplets are expected to be short lived as the model predicts they will rapidly vaporize.
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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Capacity Matching of Aeroderivative Gas Generator With Free Power Turbine: Challenges, Uncertainties, and Opportunities
Authors: Thirumurthy Deepak , Casado Coca Jose Carlos , Suraweera Kanishka
Published: November 2019

For gas turbines with free power turbines, the capacity or flow parameter matching is of prime importance. Accurately matched capacity enables the gas turbine to run at its optimum conditions. This ensures maximum component efficiencies, and optimum shaft speeds within mechanical limits.

This paper presents the challenges, uncertainties, and opportunities associated with an accurate matching of a generic two-shaft aeroderivative HP-LP gas generator with the free power turbine. Additionally, generic performance trends, uncertainty quantification, and results from the verification program are also discussed. These results are necessary to ensure that the final free power turbine capacity is within the allowable range and hence the product meets the performance guarantees.

The sensitivity of free power turbine capacity to various design variables such as the vane throat area, vane trailing edge size, and manufacturing tolerance is presented. In addition, issues that may arise due to not meeting the target capacity are also discussed. To conclude, in addition to design, analysis, and statistical studies, a system-of-systems approach is mandatory to meet the allowed variation in the free power turbine capacity and hence the desired gas turbine performance.
X-Ray Phase Contrast Imaging of Liquid Film and Spray Development Inside an Aircraft Engine Swirler
Authors: Sforzo Brandon A. , Kastengren Alan L. , Matusik Katarzyna E. , Gomez del Campo Felipe , Powell Christopher F.
Published: November 2019

Modern aircraft engines combine liquid fuel and air using an intricate flow device with many fuel and air flow passages. To date, the process by which the fuel atomizes within this swirler set has not been examined directly due to optical access limitations. In this work, high-speed x-ray phase-contrast imaging of a liquid spray inside a gas turbine engine swirler geometry is presented. Measurements were carried out at the 7-BM beam-line of the Advanced Photon Source at Argonne National Laboratory using the high-energy broadband x-ray beam. The synchrotron x-ray source provides the necessary photon energy and flux to capture time-resolved fluid phenomena within the confines of the relevant geometry while liquid and air are flowing. Spray nozzle hardware and geometries were provided by the National Jet Fuels Combustion Program, allowing for characterization of the spray using a commercially relevant configuration. Modified swirlers were 3D printed with acrylic to improve imaging access while maintaining influential internal features. Water was used as a surrogate fluid for these studies to demonstrate the visualization capabilities. The experiments were conducted at atmospheric exit pressure conditions with a pressure drop of 6% across the swirler. High-speed imaging of the pilot spray cone revealed sheet breakup several millimeters downstream of the orifice exit, upon interaction with the radial assist air flow. These droplets and ligaments were observed to impinge on the inner filming surface of the swirler and flow toward the exit while developing a tangential flow. Under these conditions, the liquid film grows up to several hundred microns in thickness on the filming surface, and subsequently forms ligaments up to several millimeters in length before breaking up. This work demonstrates the capability of x-ray diagnostics in visualizing liquid flows within solid geometries of technical relevance. Furthermore, the spatial quantification of filming flows and liquid interaction with the swirler air provides validation data for modeling of the multi-phase flows and surface interactions within the swirler.
An Impact Assessment of Erosion of Nozzle Guide Vanes and Rotor Blades on Aerodynamic Performance of a Gas Turbine by CFD
Authors: Yonezawa Koichi , Takayasu Masahiro , Nakai Genki , Sugiyama Kazuyasu , Sugita Katsuhiko , Umezawa Shuichi , Ohmori Shuichi
Published: November 2019

Nozzle guide vanes (NGVs) and rotor blades deteriorate due to erosion, and this may affect the aerodynamic characteristics of gas turbines. According to previous studies, the erosion of first-stage NGVs significantly affected the blade loading of the first-stage rotor. An increase in the tip gap also may significantly affect the gas turbine performance. In the present study, numerical investigations have been carried out using a real eroded nozzle and blade geometries for two purposes. One purpose was to clarify the influences underlying the deterioration of the nozzle and the rotor blade, such as the effects on the erosion of NGVs in the first stage and the effects of the tip gap on the gas turbine performance. The other was to develop a method to estimate the total gas turbine performance using a CFD simulation and a heat balance analysis. The results show that the erosion of NGV leads to an increased flow rate and affects the operating condition of the gas turbine cycle. This, in turn, can decrease the total thermal efficiency. The experimental results suggest that an increase in the tip gap width decreases rotor output almost linearly, and the numerical results showed the same tendency. The influence of the tip gap in the real gas turbine condition was also examined, revealing that an increase in the tip gap leads to an increase in the pressure loss in the nozzle downstream as well as around the rotor blade itself. Consequently, the total power output and the isentropic efficiency of the turbine decreased.
Effect of Rotating Instabilities on Aerodynamic Damping of Axial Flow Fan Blades
Authors: Yang Weichao , Wang Yanrong , Han Le , Zhang Xiaobo , Li Zichao
Published: November 2019

Rotating instabilities (RIs) have been reported in axial flow fans as well as in low-speed and high-speed axial compressors during recent years. They can cause the non-synchronous vibrations (NSV) and generate noise.

In this paper, numerical simulations are performed on an axial flow fan to investigate the influence of RIs on aerodynamic damping of fan blades. The phenomena of RIs in the axial fan were first observed during an experimental test. The spectrum of the pressure signal captured by the case-mounted unsteady pressure transducers near blade tips contains narrow frequency bands below the blade passing frequency, of which the dominant frequency does not equal harmonics of rotor shaft frequency.

The numerical investigation is performed with an unsteady 3D Navier-Stokes method that solves for the entire blade row at near-stall point to confirm the phenomena. Flow separation and blade tip vortex shedding are captured at the tip region of the blades in the simulation. Although the spectrums are different between numerical simulation and experimental results, the simulation predicts a dominant pressure fluctuation frequency of RI that is almost the same as the experimentally measured value, which verified the accuracy of the numerical simulation. Aeroelasticity of the fan blade is investigated by influence coefficient method based eigenvalue method. At near-maximum-efficiency point and near-stall point, aerodynamic modal damping ratios (AMDRs) and distribution of local AMDR of first two modes (first and second flapping mode) are computed respectively. The separation region improves the stability of both modes. However, the vortex shedding area on suction side reduce the AMDRs of 1F mode while the vortex impingement region on pressure side reduces local AMDR for both modes.
On the Interaction of Swirling Flames in a Lean Premixed Combustor
Authors: Ramachandran Gopakumar , Dutta Ankit Kumar , Durairaj Harish , Chaudhuri Swetaprovo
Published: November 2019

Premixed or partially premixed swirling flames are widely used in gas turbine applications because of their compactness, high ignition efficiency, low NOx emissions and flame stability. A typical annular combustor consists of about eighteen to twenty-two swirling flames which interact (directly or indirectly) with their immediate neighbors even during stable operation. These interactions significantly alter the flow and flame topologies thereby bringing in some discrepancies between the single nozzle (SN) and multi nozzle (MN), ignition, emission, pattern factor and Flame Transfer Functions (FTF) characteristics. For example, in MN configurations, application of a model based on SN FTF data could lead to erroneous conclusions. Due to the complexities involved in this problem in terms of size, thermal power, cost, optical accessibility etc., a limited amount of experimental studies has been reported, that too on scaled down models with reduced number of nozzles. Here, we present a detailed experimental study on the behavior of three interacting swirl premixed flames, arranged in-line in an optically accessible hollow cuboid test section, which closely resembles a three-cup sector of an annular gas turbine combustor with very large radius. Multiple configurations with various combinations of swirl levels between the adjacent nozzles and the associated flame and flow topologies have been studied. Spatio-temporal information of the heat release rate obtained from OH* chemiluminescence imaging was used along with the acoustic pressure signatures to compute the Rayleigh index so as to identify the regions within the flame that pumps energy into the self-excited thermoacoustic instability modes. It was found that the structure of the flame-flame interaction regions plays a dominant role in the resulting thermoacoustic instability. To resolve the flow and reactive species field distributions in the interacting flames, two-dimensional, three component Stereoscopic Particle Image Velocimetry (SPIV) and Planar Laser Induced Fluorescence (PLIF) of hydroxyl radical was applied to all the test conditions. Significant differences in the flow structures among the different configurations were observed. Simultaneous OH-PLIF and SPIV techniques were also utilized to track the flame front, from which the curvature and stretch rates were computed. Flame surface density which is defined as the mean surface area of the reaction zone per unit volume is also computed for all the test cases. These measurements and analyses elucidate the structure of the interaction regions, their unique characteristics and possible role in thermoacoustic instability.