bluuebunny/crossref_metadata_2025_split huggingface dataset:
Numerical Study of the Penny Cavity Leakage Effects From Variable Guide Vanes in a High Pressure Compressor: Adjustment of Standard-RANS-CFD-Model to a Hybrid LES Calculation
Authors: Wolf Hannes , Halcoussis Alexander 
Published: November 2019

Abstract
Variable guide vanes are airfoils, normally in the front stages of multistage compressors, that can be restaggered to extend the compressor’s operational range. To allow the variable guide vanes to rotate the design will inevitably include a gap or cavity between the vane’s rotating mounting feature (Penny) and the stationary inner and outer sidewalls. These penny cavities cause additional leakages which impact losses, and airfoil turning, so reducing a compressor’s efficiency and stability. A compressor model which accurately simulates the penny cavity leakage is central to improving the design. This paper presents a study looking into how to accurately include penny cavity leakage effects during the design of multistage compressors.
Multiple blade-row RANS-based flow simulations are the current state-of-the-art standard during the design of multistage compressors. However, it is unlikely that such models have the numerical accuracy to simulate the penny cavity leakage effects in detail: firstly the RANS-turbulence model cannot accurately recreate the turbulent mixing which takes place between the leakage and the main flow, and secondly because a typical multiple blade-row mesh is too coarse to resolve the details of the much smaller penny cavity. To compensate for this, the numerical modelling of penny cavities in the design of a compressor would need to be adjusted. On the other hand, a dedicated hybrid LES-model can more accurately simulate the secondary flows with its significant turbulent mixing, at the cost of computational capacity. In this paper, high resolution hybrid LES-simulations have been used as a benchmark to adjust RANS-calculations typical for the design of a multistage compressor.
The paper presents the following steps:
Using a standard Jet-in-Crossflow test case, a high resolution model was evaluated using both RANS and a hybrid LES model, and compared against measurements. The flow structures were analyzed and compared to measurements of this test case available from literature. These show that the hybrid LES-model performed significantly better than the RANS-model, in being able to predict the jet impact and flow structures.
For a second model consisting of a generic compressor variable vane with penny cavity. RANS and hybrid LES simulations were performed with a highly refined mesh in the region of the penny cavity. The modelling is described in detail and the resulting penny cavity effects compared.
Finally, the vane with standard mesh and penny cavity was run using RANS-turbulence CFD and compared to the above. From this conclusions were drawn on how to transfer experience from the higher-fidelity turbulence model to a more industry-standard RANS model, which could for instance be used during the design phase of a multistage compressor.
A Deep Insight Into the Transonic Flow of an Advanced Centrifugal Compressor Design
Authors: Wittrock D. , Junker M. , Beversdorff M. , Peters A. , Nicke E. 
Published: November 2019

Abstract
In the last decades major improvements in transonic centrifugal compressor design have been achieved. The further exploration of design space is enabled by recent progress in structural mechanics and manufacturing. A challenging task of inducer design especially in terms of transonic inflow conditions is to provide a wide flow range and reduced losses due to a sufficient shock control. The use of so called multidisciplinary design optimization with an extensive amount of free parameters leads finally to complex designs. DLR’s latest Fast Rotating Centrifugal Compressor (SRV5) operates at a design speed of Mu2 = 1.72 and a total pressure ratio of 5.72. This compressor design is characterized by an S-shaped leading edge and free-form blade surfaces. Due to the complex design the key design features are difficult to explore. Therefore, non-intrusive measurements are conducted on the highly loaded SRV5. The Laser-2-Focus (L2F) approach that is used in addition with the Doppler Global Velocimetry (DGV) delivers a three dimensional velocity field. Besides the impeller inflow the ouflow is also part of the experimental and numerical verification of the advanced compressor design. Experimental results are compared with the numerical analysis of the compressor using DLR’s RANS Flow Solver TRACE. The deep insight of the inflow leads to a better understanding of the operating behavior of such impeller designs.
Simple Recuperated s-CO2 Cycle Revisited: Optimization of Operating Parameters for Maximum Cycle Efficiency
Authors: Dutta Anchit , Gupta Adhip , Sathish Sharath , Bandooni Aman , Kumar Pramod 
Published: November 2019

Abstract
The paper presents modeling and Design of Experiments (DOE) analysis for a simple recuperated s-CO2 closed loop Brayton cycle operating at a maximum temperature of 600°C and a compressor inlet temperature of 45°C. The analysis highlights the impact of isentropic efficiencies of the turbine and compressor, decoupled in this case, on other equipment such as recuperator, gas cooler and heater, all of which have a bearing on the overall performance of the s-CO2 Brayton cycle. A MATLAB program coupled with REFPROP is used to perform the thermodynamic analysis of the cycle. A design space exploration with a Design of Experiments (DOE) study is undertaken using I-sight™ (multi-objective optimization software), which is coupled with the MATLAB code. The outcome of the DOE study provides the optimal pressure ratios and high side pressures for maximum cycle efficiency in the design space. By varying pressure ratios along with a floating high side pressure, the analysis reveals that the cycle performance exhibits a peak around a pressure ratio of 2.5, with cycle efficiency being the objective function. A further interesting outcome of the DOE study reveals that the isentropic efficiencies of the compressor and turbine have a strong influence not only on the overall cycle efficiency, but also the optimum pressure ratio as well as the threshold pressures (low as well as high side pressure). An important outcome of this exercise shows that the isentropic efficiency of the turbine has a much greater impact on the overall cycle performance as compared to that of the compressor.
The Effect of Sauter Mean Diameter Fluctuations on the Heat Release Rate in a Lean-Burn Aero-Engine Combustor
Authors: Treleaven Nicholas C. W. , Garmory Andrew , Page Gary J. 
Published: November 2019

Abstract
It has been shown that the fluctuations of pressure caused by a thermoacoustic instability can affect the mass flow rate of air and atomisation of the liquid fuel inside a gas turbine. Tests with premixed flames have confirmed that the fluctuations of the mass flow rate of air can affect the heat release rate through purely aerodynamic phenomenon but little work has been done to test the sensitivity of the heat release rate to changes in the fuel atomisation process. In this study, a lean-burn combustor geometry is supplied with a fuel spray fluctuation of SMD (Sauter mean diameter) of 20% with respect to the mean value and the heat release rate predicted using Large Eddy Simulation (LES) with combustion predicted using a presumed probability density function (PPDF), flamelet generated manifolds (FGM) method. Previous work has shown that at atmospheric conditions the SMD may fluctuate by up to 16% percent and at low frequencies may be reasonably well predicted by using a correlation based on the instantaneous velocity and mass flow rate of air close to the air-blast atomiser. Analysis of the flow fields highlights a complicated spray, flame and wall interaction as being responsible for this observed fluctuation of heat release rate. The heat release rate predicted by the LES shows a 20% fluctuation which implies that even small fluctuations of SMD will significantly contribute to thermoacoustic instabilities.
Heavy Duty Gas Turbine Combustion Dynamics Study Using a Two-Can Combustion System
Authors: Venkatesan Krishna , Cross Arin , Yoon Changjin , Han Fei , Bethke Sven 
Published: November 2019

Abstract
In this study, an experimental facility with two combustion cans was built and successfully replicated the field boundary conditions for heavy duty gas turbine combustors. Each combustor consisted of multiple Dry Low NOx (DLN) fuel nozzles, representative of a real gas turbine combustor headend. The two combustor cans were connected at the combustor exits to simulate the cross-talk area in a can-annular combustor configuration of a gas turbine. Moreover, a choked boundary condition, at the exit section of the cross-talk area, simulated the first-stage nozzle of a turbine. The push-push and push-pull tones were excited by varying the fuel flow splits among the various fuel nozzles in each combustor can.
The thermoacoustic behavior of the two-can combustor was modeled using both a reduced-order network approach and a high-fidelity CFD approach. The modeling was carried out to guide rig design and to predict the frequency and relative amplitudes of the various dynamics modes from the experiments. Various combustion dynamics mitigation strategies were demonstrated via the experiments in reducing both push-pull and push-push dynamics tones. Moreover, stable combustor operation was demonstrated with complete mitigation of all dynamics tones.
Numerical Investigation of Two Phase Flow in a Dual Drive Booster (DDB)
Authors: Prabhakar Arun , Ambrose Stephen , Morvan Herve 
Published: November 2019

Abstract
Recent efforts have been devoted in developing cutting edge methods and technologies to overcome the complications involved in extracting power from the spools in turbofan engines to drive the power systems in aircraft. In a contemporary turbofan engine design, a Dual Drive Booster turbofan (DDBTF) summation gear box is employed to derive power from the low pressure (LP) and high pressure (HP) spools. This paper aims to investigate the scavenging of lubrication oil from the Dual Drive Booster gearbox.
It is essential that that the scavenging of oil from the gearbox is efficient to eradicate risks that may arise when oil resides in the gear box for prolonged durations. Longer residence times of oil in the gearbox can lead to rapid oil degradation. Simulations were conducted on a previously optimized geometry and the work in this paper will focus on investigating the effect of different operating conditions on the scavenging performance of the scavenge chamber. The effect of attitude, altitude and the inlet flow rate of oil have been simulated to understand their influence on the oil flow behavior. Emphasis is given on the predicting potential oil churning, recirculation and pooling behaviors in the scavenge chamber that encloses the gear box.
Numerical Investigations are carried out using ANSYS Fluent. The Volume of Fluid (VOF) multiphase model is employed to model the multiphase flow arising between air and oil in the system and the effects of turbulence are modelled using the standard k-ϵ model. The computational domain is discretized using a polyhedral grid comprising of 4 million cells which was adopted based on grid independency tests that were conducted prior to the main simulations. Validation against published experimental data for similar flow regimes was also carried out. Results indicate that the scavenging performance is not affected significantly under the various operating conditions and scenarios that were investigated. This is because the effects of the windage outweigh the effects caused by the different operating conditions that are imposed to the scavenge chamber. The windage in the system drives the oil efficiently out from the chamber with the aid of the tangential sump (shown in Figure 4). Oil is distributed in an axially central section of the chamber and the total residence mass of oil is compared and under 0.5 kg for all the cases presented in this paper.
Characterisation of SiCf/SiC Specimens Using an In-Situ Tensile Stage Within a Scanning Electron Microscope
Authors: Jordan Steven P. , Bache Martin R. , Newton Christopher D. , Gale Louise 
Published: November 2019

Abstract
The present paper will introduce the use of scanning electron microscope based, in-situ tensile testing as a method of detecting cracking in a SiCf/SiC CMC at room temperature. Small scale tensile specimens were prepared, but still sampling multiple longitudinal and transverse fibre tows. Monotonic loading was applied to initiate cracking, whilst contemporary time lapse imaging and retrospective digital image correlation recorded the development of these cracks at the specimen surface. Examples of strain localization, crack initiation and propagation will be presented for a plain gauge section specimen and single edge notched specimen. The critical combination of SEM imaging together with real time loading, in order to identify microscopic cracking in this CMC system, will be demonstrated.
Impact of a Combustor-Turbine Interface on Turbine Vane Aerodynamics and Film Cooling
Authors: Lerch A. , Bauer R. , Krueckels J. , Henze M. 
Published: November 2019

Abstract
Optimizing the aero-thermal performance of the combustor-turbine interface is an important factor in enhancing the efficiency of heavy-duty gas turbines. Also, it is a key requirement to fulfill the lifetime in this hottest area of the gas turbine. Typically transition pieces of can combustors induce a highly non-uniform swirling flow at the turbine inlet. In order to better understand the impact of the non-uniform combustor flow at the first stage vanes, a combined experimental and numerical study was carried out.
The experimental facility consisted of a high speed linear cascade with four vane passages, including an upstream transition piece, which was representative of a heavy duty gas turbine can combustor-turbine interface geometry. The experiments were conducted at engine representative Mach numbers and film cooling effectiveness measurements were performed at three different blowing ratios.
CFD RANS simulations were undertaken using a commercial flow solver. The numerical model was first validated with the experimental data, using inlet traverse 5-hole probe measurements, pressure taps along the airfoil perimeter and oil flow visualization results.
The investigation shows that the position of the vane relative to the combustor transition piece has a significant impact on the vane aerodynamics and also film cooling behavior. This understanding was key to a robust first vane aerothermal design of the GT36.
Improving Steady CFD to Capture the Effects of Radial Mixing in Axial Compressors
Authors: Cozzi Lorenzo , Rubechini Filippo , Arnone Andrea , Schneider Andrea , Astrua Pio 
Published: November 2019

Abstract
The axial compressors of power-generation gas turbines have a high stage count, blades with low aspect ratios and relatively large clearances in the rear section. These features promote the development of strong secondary flows. An important outcome deriving from the convection of intense secondary flows is the enhanced span-wise transport of fluid properties mainly involving the rear stages, generally referred to as “radial mixing”. An incorrect prediction of this key phenomenon may result in inaccurate performance evaluation and could mislead the designers during the compressor design phase.
As shown in a previous work, in the rear stages of an axial compressor the stream-wise vorticity associated with tip clearance flows is one of the main drivers of the overall span-wise transport phenomenon. Limiting it by circumferentially averaging the flow at row interfaces is the reason why a steady-state analysis strongly under-predicts radial mixing. To properly forecast the span-wise transport within the flow-path, an unsteady analysis should be adopted. However, due to the high blade count, this approach has a computational cost not yet suitable for industrial purposes.
Currently, only the steady-state full-compressor simulation can fit in a lean industrial design chain and any model upgrade improving its radial mixing prediction would be highly beneficial for the daily design practice. To attain some progresses in RANS model, its inherent lack of convection of stream-wise vorticity must be addressed. This can be done by acting on another mixing driver, able to provide the same outcome, that is turbulent diffusion. In particular, by enhancing turbulent viscosity one can promote span-wise diffusion, thus improving the radial mixing prediction of the steady approach.
In this paper, this strategy to update the RANS model and its application in simulations on a compressor of the Ansaldo Energia fleet is presented, together with the model tuning that has been performed using the results of unsteady simulations as the target.
Nonlinear Reduced Dynamic Model of Turbofan Engine for Investigation of Engine Structural Frame Vibrations After Fan Blade Out Event
Authors: Ivanov Ilya , Blinnik Boris , Myasnikov Vladislav 
Published: November 2019

Abstract
This paper proposes an approach to construct a nonlinear dynamic model of a whole turbofan engine using the static condensation technique. Nonlinear dynamic behavior of the engine is described by a matrix differential equation, where the right side of the equation represents unbalance load and contact loads between the blades and casings, low-pressure (LP) shaft and high-pressure shaft. Elements of the matrices are calculated by static condensation of three-dimensional finite element models of rotors, casings, engine mounts, and wing attachment system. On the basis of the proposed approach, a model of the entire engine was constructed. The model considered contact interactions as well as effects associated with both instantaneous application of the unbalance load and the passage of the LP rotor through the critical rotational speed during the deceleration phase. The model has a modular structure that allows for the easy replacement of individual components and analysis of the various engine structural frame options. The results of engine structural frame load calculations after a fan blade-out event and during deceleration of the rotors to windmill mode are presented in this paper. In addition, the influence of the flexibility of fan supports, blade wheel nonlinear radial stiffness, and slowdown rates of rotors on load magnitudes are analyzed.
Foreign Object Impact Damage in Ceramic Matrix Composites: Experiments and Computational Predictions
Authors: Kumar Rajesh S. , Mordasky Matthew M. 
Published: November 2019

Abstract
Foreign object impact of Ceramic Matrix Composite (CMC) materials and components in a gas turbine engine environment could be detrimental to engine performance and hence must be accounted for in the design of such components. This paper is concerned with experiments and computational modeling of foreign object impact phenomenon in Silicon Carbide-based CMC. Controlled impact experiments were conducted on the CMC material using a gas-gun apparatus with spherical hardened steel projectile. The internal damage state within the CMC specimens was assessed using X-ray computed tomography scan technique. The computational modeling involved explicit dynamic finite element simulation of the impact process wherein either delamination mechanism is modeled or both ply damage and delamination mechanisms are modeled in a coupled manner. The delamination mechanism is modeled explicitly using cohesive-zone fracture mechanics approach, whereas, the ply damage mechanisms are modeled implicitly using simplified continuum damage mechanics approach. The simulation results were found to be in reasonable qualitative and quantitative agreement with the experimental results. Furthermore, it is shown that modeling both the ply damage and delamination mechanisms are essential to predict the correct delamination pattern even for intermediate velocity impacts that leads to predominantly delamination damage. The predictive nature of the modeling approach is demonstrated and approaches to enhance the models are also discussed.
Air-Assisted Atomization at Constant Mass and Momentum Flow Rate: Investigation of the Ambient Pressure Influence With the SPH Method
Authors: Chaussonnet G. , Joshi S. , Wachter S. , Koch R. , Jakobs T. , Kolb T. , Bauer H.-J. 
Published: November 2019

Abstract
A twin-fluid atomizer configuration is simulated by means of the 2D weakly-compressible Smooth Particle Hydrodynamics method, and compared to experiments. The Gas-to-Liquid-Ratio, the momentum flux ratio and the velocity ratio are set constant for different ambient pressures, which leads to different gaseous flow sections. The objectives of this study are to (i) investigate the effect of ambient pressure at constant global parameters, and (ii) to verify the capability of 2D SPH to qualitatively predict the proper disintegration mechanism and to recover the correct evolution of the spray characteristics. The setup consists of an axial liquid jet of water fragmented by a co-flowing high-speed air stream (Ug = 80 m/s) in a pressurized atmosphere up to 16 bar. The results are compared to the experiment, and presented in terms of (i) mean velocity profiles, (ii) drop size distributions and (iii) Sauter Mean Diameter of the spray. It is found that there exists an optimal pressure to minimize the mean size of the spray droplets. Finally, two new quantities related to atomization are presented: (i) the breakup activity that quantifies the number of breakup events per time and volume unit and (ii) the fragmentation spectrum of the whole breakup chain, which characterizes the cascade phenomenon in terms of probability. The breakup activity confirms the presence of the optimal pressure and the fragmentation spectrum gives information on the type of breakup, depending on the ambient pressure.
Efficient Smoke Suppressant Reduces the Particulate Matter Emissions of Crude Oil Fired Gas Turbines
Authors: Vierling Matthieu , Moliere Michel , Glaser Paul , Denolle Richard , Nayani Sathya , Amadou Nouri , Dutta Amit , Aboujaib Maher , Westrup Brandon , Sokolov Dmitry , Montagne Pierre 
Published: November 2019

Abstract
Gas turbines are often the master pieces of the utilities that power Oil and Gas (O&G) installations as they most often operate in off-grid mode and must reliably deliver the electric power and the steam streams required by all the Exploration/Production (EP) or refining processes.
In addition to reliability, fuel flexibility is an important score card of gas turbines since they must permanently accommodate the type of fuel which is available on the particular O&G site. For instance, during the operation of an associated gas field, crude oil comes out from the well heads as the gas reserves are declining or depleted. The utility gas turbine must then be capable to successively burn natural gas and crude oil and often to co-fire both fuels.
An important feature of crude oils is that their combustion tends to emit significantly more particulate matter (PM) than do distillate oil and natural gas as they contain some heavier hydrocarbon ends.
Taking account of the fact that some alternative liquid fuels emit more particulates matter (PM) than distillate oils, GE has investigated a class of soot suppressant additives that have been previously tested on light distillate oil (No 2 DO).
As a continuation of this development, these products have been field-tested at an important refining site where several Frame 6B gas turbines have been converted from natural gas to crude oil with some units running in cofiring mode.
This field test showed that proper injections of these fuel additives, at quite moderate concentration levels, enable a substantial abatement of the PM emissions and reduction of flue gas opacity.
This paper outlines the main outcomes of this field campaign and consolidates the overall results obtained with this smoke suppression technology.