bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Rotor-Speed-Ratio and Crosswind Inlet Distortion on Off-Design Performance of Contra-Rotating Propelling Unit
Authors: Vouros Stavros V. , Chasoglou Alexandros C. , Efstathiadis Theofilos G. , Kalfas Anestis I. 
Published: September 2016

This paper presents an investigation of the effects of rotor-speed-ratio (RSR) and inlet crosswind distortion on the off-design performance of a contra-rotating propelling unit. A dedicated wind tunnel has been built in order to study the off-design performance in distorted and undistorted conditions. A miniature 8-hole pressure rake has been calibrated to measure the total and static pressure field across the blade span, upstream and downstream of the propellers. A data analysis algorithm has been developed for the rapid exportation of desensitized and reliable mass-averaged characteristics, while wall blockage effects are accounted for incorporating a correction factor. Investigation of rotor-speed-ratio effects at undistorted inlet conditions show that, efficiency is the highest when the front rotor operates at rotational speed equal to 90% of the aft rotor’s speed.
For the optimum RSR, the effects of crosswind inlet distortion are investigated. Crosswind mass-flow is generated by a 16-fan array, accommodated in a secondary square wind-tunnel, with its center axis perpendicular to propeller main flow direction. In order to achieve realistic crosswind flow characteristics, the pressure side of the secondary wind tunnel is being used, after proper flow conditioning. Total and static pressure distribution highlights the location of a primary and a secondary stall cell, both upstream and downstream of the propellers. The results indicate a spanwise shift of the inlet pressure profile towards the direction of crosswind. A rotation of the wake is also observed due to propellers’ remaining swirl. Finally, the effect of distortion on the overall performance is being investigated, by the exportation of averaged total pressure rise for the various examined inlet distortion cases. Mass-flow is slightly increased; however, total pressure rise is dramatically reduced due to crosswind flow effects. Especially for the case of landing under extremely strong crosswind, the ratio between total pressure rise and inlet dynamic head is 4.2 times lower, compared to undistorted inlet operating conditions.
Turbines and Structures for Ultra-High Pressure Ratio Aero-Engines
Authors: Lundbladh Anders , von der Bank Ralf , Avellán Richard , Forsman Stefan , Donnerhack Stefan , Sturm Wolfgang , Versluis Joris , Rae Anthony , Stokes Mark , Caballero Oscar , Soldevilla Natalia , Ornat Artur , Mrugala Tomasz , Kraj Lucjan , Bourgois Sebastien 
Published: September 2016

This paper describes the research carried out in the European Commission co-funded project LEMCOTEC (Low Emission Core Engine Technology) on aerodynamics for turbines and structures for compressors, combustors and turbines. The aim is to significantly contribute to the reduction of the environmental footprint of aviation with regard to emissions from aero engines.
The LEMCOTEC turbine and structure technologies are directed primarily to act as enablers for higher thermal efficiency arising from increased overall pressure ratio. Thus the work is supporting increased operating temperatures, reduced core deformation, reduced cooling flows and increased performance to weight ratio, in addition to direct reduction of flow losses and associated component efficiency increases.
The article details the targets for performance improvements, the validation of the technologies and how they, together with LEMCOTEC’s improved technologies on compressors and combustors, relate to the goal of building ultra-high pressure ratio engines.
GT13E2 Low Part Load Operation: Extended Flexibility Down to 30% Load
Authors: Magni Fulvio , Grimm Frank , Sorato Sebastiano , Micheli Marco 
Published: September 2016

This paper describes the development work of the Low Part Load upgrade package for the GT13E2 gas turbine fleet and the related test results of the engine validation phase.
The GT13E2 gas turbine was originally designed for operation at high combined cycle efficiency and low emissions in the range from about 60% to 100% load. The upgrade package improves the minimum environmental load of the GT13E2 making it possible to operate the GT with full flexibility down to 30% relative load. In fact, in today’s energy market operational flexibility is one of the key requirements for our customers. The extended low part load capability will allow the customers to operate the power plant in combined cycle mode with high efficiency and to rapidly change the load as soon as the grid demands. The upgrade package can be retrofitted to the installed service fleet with AEV burner technology.
The main challenge at low part load operation is to keep the NOx and especially the CO emissions under control. Increased emissions at lower loads were acceptable since it was not intended to operate for long periods of time at these loads. The low part load upgrade improves combustion of the gas turbine by keeping the flame temperature at higher levels. The key to success for improved combustion behavior at part load is mainly the reduction of the burner air mass flow and the redistribution of the corresponding fuel mass flow. The main measures used for the low part load concept are a further closing of the inlet guide vanes and a redistribution of the fuel gas to fewer burners. Additional measures for further reduction of the burner air mass flow at part load were also evaluated and tested. Only a combination of several measures really improves the minimum environmental load of the gas turbine and of the combined cycle efficiency, compared to the original operation concept.
During the development of the low part load project each single measure was extensively validated on GT13E2 engines independently. The combination of the different measures was finally validated on a customer engine and the projected emission targets down to 30% load were successfully confirmed.
Validation and Assessment of the Continuous Random Walk Model for Particle Deposition in Gas Turbine Engines
Authors: Forsyth Peter , Gillespie David R. H. , McGilvray Matthew , Galoul Vincent 
Published: September 2016

Threats to engine integrity and life from deposition of environmental particulates that can reach the turbine cooling systems (i.e. <10 micron) have become increasing important within the aero-engine industry, with an increase of flight paths crossing sandy, tropical storm-infested, or polluted airspaces. This has led to studies in the turbomachinery community investigating environmental particulate deposition, largely applying the Discrete Random Walk (DRW) model in CFD simulations of air paths. However, this model was conceived to model droplet dispersion in bulk flow regimes, and therefore has fundamental limitations for deposition studies. One significant limitation is an insensitivity to particle size in the turbulent deposition size regime, where deposition is strongly linked to particle size. This is highlighted within this study through comparisons to published experimental data.
Progress made within the wider particulate deposition community has recently led to the development and application of the Continuous Random Walk (CRW) model. This new model provides significantly improved predictions of particle deposition seen experimentally in comparison to the DRW for low temperature pipe flow experiments. However, the CRW model is not without its difficulties. This paper highlights the sensitivities within the CRW model and actions taken to alleviate them where possible. For validation of the model at gas turbine conditions, it should be assessed at engine-representative conditions. These include high-temperature and swirling flows, with thermophoretic and wall-roughness effects. Thermophoresis is a particle force experienced in the negative direction of the temperature gradient, and can strongly effect deposition efficiency from certain flows. Previous validation of the model has centred on low temperatures and pipe flow conditions. Presented here is the validation process which is currently being undertaken to assess the model at gas turbine-relevant conditions. Discussion centres on the underlying principles of the model, how to apply this model appropriately to gas turbine flows and initial assessment for flows seen in secondary air systems. Verification of model assumptions is undertaken, including demonstrating that the effect of boundary layer modelling of anisotropic turbulence is shown to be Reynolds-independent. The integration time step for numerical solution of the non-dimensional Langevin equation is redefined, showing improvement against existing definitions for the available low temperature pipe flow data. The grid dependence of particle deposition in numerical simulations is presented and shown to be more significant for particle conditions in the diffusional deposition regime. Finally, the model is applied to an engine-representative geometry to demonstrate the improvement in sensitivity to particle size that the CRW offers over the DRW for wall-bounded flows.
Analysis of the Sources and the Modal Content of the Acoustic Field in a Radial Compressor Outflow
Authors: Banica Marius C. , Limacher Peter , Feld Heinz-Jürgen 
Published: September 2016

In large modern turbochargers, compressors often constitute the main source of noise, with a frequency spectrum typically dominated by tonal noise at the blade passing frequency (BPF) and its harmonics. In transonic operation, inflow BPF noise is mainly generated by rotor locked shock fronts. These and the resulting acoustic fields can be predicted numerically with reasonable accuracy. Outflow noise, while also dominated by BPF tones, is linked to more complex source mechanisms. Its modal structure and the relationships between sources and modal sound pressure levels (SPL) are less well understood. Perhaps this is linked to the intrinsically non-axisymmetric geometries, which results in the need for full stage simulations if high accuracy is of paramount importance.
In order to shed some light on outflow noise generation, a transient simulation of a 360° model of a radial compressor stage, including a vaned diffuser and a volute, was carried out using state-of-the-art CFD. Additionally, experimental data was gathered at a multitude of data points downstream of the volute exit for post processing and modal analysis. The sources and the propagation were calculated directly. Optimized values for tempo-spatial acoustic wave resolution and buffer layer design were chosen, based on extensive studies on simplified models. Two grid refinement levels were used to check grid convergence and time step size independence of the results was ensured.
Numerical and experimental data match within 1% for total pressure ratio, volume flow and exit total temperature for the studied operating point. Both show the same modal content at the 1st BPF and indicate the presence of the same single dominating mode. The numerical results underpredict overall sound power levels (PWL) at the 1st BPF by 6.6dB. This difference is expected to decrease with further grid refinement and improved accounting for numerical damping. At the 2nd BPF, the experimental data show a significant broadening of the modal content with homogeneous modal PWL distributions. The multitude of modes leads to the generation of complex interference patterns, which shows that single-point acoustic measurements are often inadequate for component noise qualification and should be substituted by modal techniques. The dominating dipole sound sources are found in narrow areas around the vane leading edges and the rotor blade trailing edges. Because of the non-axisymmetric geometry, vane dipole source strengths become a function of circumferential position. The unsteady shedding of vortices from the vane suction surfaces is identified as a further possible source mechanism. However, the contributions of structural vibrations and mode scattering due to small manufacturing imperfections remain unclear.
CFD Analysis of a SGT-800 Burner in a Combustion Rig
Authors: Abou-Taouk Abdallah , Andersson Niklas , Eriksson Lars-Erik , Lörstad Daniel 
Published: September 2016

This work focuses on 3D turbulent reacting flow modeling of a SGT-800 3rd generation dry low emission (DLE) burner at both atmospheric and engine-like conditions. At atmospheric pressure the burner is fitted in a test rig with high pre-heating of the incoming air. To reduce the computational cost, the M4 mechanism previously developed by Abou-Taouk et al. (2013) is used for operating pressure of 1 bar. A new novel optimized 4-step reaction mechanism for methane-air mixture is developed in the present work at an operating pressure of 20 bar. The mechanism is based on a large sample of detailed chemistry solutions that are processed by an iterative optimization procedure. This leads to a reduced 4-step mechanism, reproducing the targeted detailed chemistry solutions in terms of laminar flame speeds, species profiles and temperatures.
The CFD simulations are performed using the combined eddy dissipation model / finite rate chemistry (EDM/FRC) turbulence chemistry interaction model. The turbulence is modeled using both the k-ω SST and the scale adaptive simulation (SAS) turbulence models. A comprehensive testing and measurement campaign carried out at atmospheric pressure for this burner was previously performed in a combustion test rig. The CFD results are compared to measurement data which includes for example flame position and pressure drop.
Experimental Investigation on Impingement Array Cooling Systems Through IR Thermography
Authors: Cocchi L. , Facchini B. , Giuntini S. , Winchler L. , Tarchi L. , Innocenti L. , Andrei L. , Bonini A. 
Published: September 2016

This paper reports the results of an experimental campaign involving heat transfer measurements on the target surface of an impingement jet array. Test were performed with the help of an open loop wind tunnel test rig, housing a model of the cooling system. The model general layout consists of an impingement channel, designed as a straight duct with rectangular section. A side of the channel is a steel impingement plate, while the opposite side acts as the impingement target surface and is composed of an electrically heated Inconel sheet supported by a thin steel plate. The coolant flow is provided by a plenum located upstream the impingement plate. The combined use of an inverter controlled electric fan and four rotary vanes vacuum pumps allows air circulation inside the model.
Convective heat transfer coefficient on the impingement target surface is evaluated through a steady-state technique. The temperature of the target surface is measured through IR thermography: the outer side of the target surface is painted with a high-emissivity black coating and is observed by an IR camera; the inner temperature is then obtained through a simple finite difference model of the target plate.
In the present work, different impingement layouts were tested (3 ≤ Sx/d ≤ 10, 3 ≤ Sy/d ≤ 20, 2.5 ≤ H/d ≤ 3.33) for different values of jet Reynolds number (2000 ≤ Rej ≤ 19000).
Heat transfer results show a good agreement with the existing correlations, thus providing a validation for the adopted measurement technique, and extend the investigation to holes pitch values outside from correlations.
Body Force Modeling of the Aerodynamics of the Fan of a Turbofan at Windmill
Authors: Dufour Guillaume , Thollet William 
Published: September 2016

The windmilling regime of a turbofan corresponds to a freewheeling mode of the fan rotor, driven by the ram pressure at the inlet. Early in the design process, determination of the windmilling rotational speed of the fan can be critical in the design of the supporting structure of the engine. Therefore, prediction of key parameters in windmilling is an important part of engine design. In particular, given the very high bypass ratio obtained at windmill (typically around 50), the flow in the fan stage and bypass duct is of prime interest, as it drives the establishment of the rotational speed of the low pressure spool and the overall drag. Classical CFD simulations have been shown to provide an adequate representation of the flow, but extensive parametric studies can be needed, which underlines the need for reduced-cost modeling of the flow in the engine. In this context, a body force modeling (BFM) approach to windmilling simulations is examined in the present contribution. The main objective is to assess the capability of the BFM approach to reproduce the aerodynamics of the flow in the fan rotor of a turbofan at windmill, and to propose a method to predict the rotational speed of the fan. The test case considered is a high-bypass ratio geared turbofan (the DGEN 380), which has been tested in an experimental facility designed to reproduce ground level windmilling conditions. The available global and local experimental data are used to validate the model. Furthermore, classical RANS simulations are also provided as reference simulations to assess the accuracy of the BFM results.
It is found that the overall performance of the fan is well predicted by the BFM simulations, in particular at the low rotational regime associated to windmilling. In terms of local validation, radial profiles are also found to be in good agreement, except close to the shroud. Analysis of the CFD results shows this can be traced back to massive flow separation in the rotor tip area. In terms of cost, a BFM simulation is about 80 times faster than the baseline CFD computation, making this approach very efficient in term of accuracy-to-cost ratio. Finally, assuming zero-work exchange across the rotor, a transient equation for the rotational speed is derived and included in the time-marching process to the steady state. As a result, the rotational speed of the fan becomes an output of the simulations. The rotational speed predicted by the present model shows good agreement with engine experimental data. However, as only the rotor is modeled, the internal losses are not fully accounted for, and the massflow has to be specified from the experimental data. Further improvement of the approach will consist in modeling the stator and the complete secondary duct so that the loss, and therefore the massflow, can be predicted.
Efficient Modeling Strategy of an Axial Compressor Fan-Stage Under Inlet Distortion
Authors: Lobo Bryan , Zori Laith , Galpin Paul , Holmes William 
Published: September 2016

The front fan of a turbofan aircraft engine often operates under distorted inlet flow conditions. This distortion is caused by either flight operating conditions, such as a crosswind or boundary layer ingestion, or due to its nacelle installation. These flow conditions negatively impact the aerodynamic performance of the compression system. Moreover, the asymmetry of the flow causes non-uniform circumferential pressure distortions which can trigger a strong aeromechanical response in the fan blades.
Numerical simulation can contribute to the design process if it can accurately predict the aerodynamic performance penalties and the loads experienced by the fan blades, thereby identifying potential problems early in the design phase. This requires accurate accounting of the pressure loads on the fan from the upstream inlet distortion and the potential effect of the downstream stator row. The loads are inherently transient in nature, requiring solutions on the full wheel geometry. However, full wheel modeling is expensive and not practical early in the design cycle. In this work, an efficient modeling strategy is proposed for an axial compressor fan with a downstream stator row (NASA Stage 67, rotor/stator) undergoing inlet distortion.
A multi-frequency frozen gust analysis using the Fourier-Transformation (FT) pitch-change method is utilized to solve this flow problem on a reduced geometry (two rotor-passages only). A once-per-revolution inlet distortion modeled as a cosine variation in total pressure is imposed upstream of the rotor. The influence of the stator row on the fan is accounted for within a transient simulation by imposing a 360 degree profile at the exit of the rotor. The profile from the stator row is obtained previously from a steady-state simulation using a multiple mixing-plane approach. In this approach the stator potential flow and the pressure variation in the stator row due to inflow distortion are accounted for.
The paper compares the reduced geometry model with full wheel transient predictions, thereby demonstrating the efficiency of the proposed method both in terms of accuracy and solution speedup. Important aerodynamic performance parameters as well as flow field solution monitors are compared to assess the viability of this modeling strategy.
Experimental Investigation on Double Anti-Stall Ring Effects on Reversible Ventilation Fan Performance
Authors: Corsini Alessandro , Delibra Giovanni , Sheard Anthony G. , Volponi David 
Published: September 2016

Stall margin improvement is a crucial issue during fan design, selection and installation. In fact, several industrial fans are operated in extreme applications and requested to be highly flexible in order to be able to withstand abrupt changes in operating conditions. This is the case of fans operated under distorted inlet conditions or interacting with other fans or used for reversible operations in tunnel and metro applications.
This paper reports on a systematic experimental study on the effects of the use of casing treatments on the performance of a single stage, reversible, axial fan. Tests focused on the performance of up-stream single treatment and up- and downstream double treatment, respectively designed to prevent the fan to run into stall in forward-only operations and forward- and reverse- operations. The study reports on the assessment of the change in performance, in normal and stalled operations, with an emphasis on the relative axial position between casing treatments and the impeller blades. The analysis demonstrates the achievement of significant improvements in performance in the unstable region for all the tested configurations with marginal losses in the stable counter-part.