bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation on the Aerodynamic Performance of an Annular Exhaust System for a Small Turboshaft Engine
Authors: de la Calzada Pedro , Parra Jorge , Mínguez Belén 
Published: November 2013

An annular exhaust system design for being used in the bench testing of MTR390-E turboshaft engine has been performed at ITP. The exhaust system is aimed at improving the aerodynamic performance at high power compared with an existing exhaust system used in the previous version of the engine. The exhaust cone emulates to some extend the exhaust system in the helicopter and it is comprised of outer and inner cones supported by three struts.
The CFD commercial code FLUENT is used to investigate the aerodynamic performance of the baseline design and to optimise the inner and outer cone angles in the new design based on 2D axisymmetric models. Representative radial exit turbine conditions and far field conditions are imposed in the model comprising the exhaust cones plus a large external domain. Two outer and inner cone angles and two inner cone lengths are analysed at low and high power conditions. The aerodynamic performance of the exhaust shows high sensitivity to the inlet flow angle which varies up to 30°/40° between the high and low power conditions.
In all the simulated cases a large separation region is generated after the inner cone. Due to the high swirling flow the separation bubble behind the plug growths downstream hence reducing the effective flow exit area compared with the geometry area and reducing the pressure recovery downstream once the flow has been separated from the inner cone. Although all cases show similar qualitative behaviour, the best case based on the computed figures of merit (i.e., lowest total pressure loss) is chosen for the new design.
In order to further optimise the behaviour of the exhaust at high power, in the new design the three struts are aligned with the flow angle at high power conditions (struts were axially oriented in the baseline design) and the resulting geometry is analysed by 3D CFD simulations. As expected, the orientation of the struts has a dramatic impact in the aerodynamic behaviour of the exhaust. The new design shows an improvement of 29% in pressure recovery at high power compared with the baseline configuration, although it shows a degradation of 12% at low power.
Both the baseline and the new exhaust systems are tested with the real engine in the test bench. The general aerodynamic performance of the new design is compared with the CFD simulation. As a consequence of the design change an important modification in the aerodynamic behaviour of the exhaust is obtained impacting the whole engine performance. Therefore a new performance model of the exhaust system is proposed to be implemented in the whole engine performance model in order to accurately simulate the behaviour of the engine coupled with the new exhaust.
Fatigue Crack Growth Analysis on a Rotor Blade Under Forced Response
Authors: Dompierre B. , Wyart E. , Mesbah M. , Thirifay F. 
Published: November 2013

This paper focuses on the fatigue crack growth resulting from an aeroelastic behavior of a fan blade when operating under upstream distortion. The forced response of the first bending mode of the blade due to the inlet distortion is analyzed and the mechanical stability of blades is investigated.
The forced response of one blade is evaluated using an uncoupled approach. In this approach, the forced response is calculated in four steps. First, the modal analysis is obtained using Finite Element (FE) calculations. In the second step, the aerodynamic damping is obtained by performing the CFD (Computational Fluid Dynamics) simulation for a single rotor blade with a prescribed harmonic forced motion. The next step is the estimation of the excitation forces when the unsteadiness of the inlet flow has a frequency close to the eigenfrequency of the blade. In the end, by solving the equations of equilibrium forces of the structure, the forced response is computed.
Afterwards, a fatigue crack growth analysis is performed. The crack is assumed to initiate in the area of the maximum principal stress. The crack is inserted into the FE model using the Extended Finite Element Method (XFEM) [1, 2] which is implemented in an in-house plugin “Morfeo-crack” for Samcef (commercial finite element analysis software package). This method allows for easily inserting a crack while minimizing the difficulties inherent to the mesh adaptation since the crack does not need to be explicitly meshed. The calculations are performed under the Linear Elastic Fracture Mechanics hypothesis. Finally, the crack path as well as the lifespan are estimated.
Interaction of Rim Seal and Main Annulus Flow in a Low-Speed Turbine Rig
Authors: Pueblas Jesus , Corral Roque , Schrewe Sebastian 
Published: November 2013

The influence of the sealing flows on the secondary flows of a low-pressure turbine has been assessed numerically using multi-row steady and unsteady simulations. The experimental data obtained at the Large Scale Turbine Rig (LSTR) at Technische Universität Darmstadt have been used to validate the numerical method and complement the simulations.
Steady and unsteady state solutions and experiments are compared to understand the importance of the unsteadiness in the accuracy of numerical simulations. It is concluded that unsteady rotor/stator simulations enhance the prediction of the stator secondary flows, especially in the tip region.
The effect of the sealing air is analysed, varying the cooling mass flow for two operating conditions. The penetration of the sealing flow in the main stream increases withthe cooling flow, displacing the horseshoe and passage vortices towards the mid-span.
Probabilistic CFD Analysis of High Pressure Turbine Blades Considering Real Geometric Effects
Authors: Scharfenstein Jens , Heinze Kay , Voigt Matthias , Vogeler Konrad , Meyer Marcus 
Published: November 2013

This paper addresses the consideration of variability due to manufacturing and abrasion of high pressure turbine (HPT) blades through probabilistic CFD investigations. Currently, the influences of those effects onto relevant aerodynamic quantities are covered by safety factors and conservative assumptions. The probabilistic investigation on the other hand, based on realistic input parameters, will enable designers to possibly reduce safety factors and provide the foundation for more robust blade designs.
In order to establish a sound statistical database, 500 new and used HPT blades were digitised with an optical 3D scanning system in order to record the outer geometric variability. As described in the work of Heinze et al. [1], the measured point clouds are parameterized using classical profile parameters and a process to rebuild various blade geometries has been developed. In terms of probabilistic investigations, in our case by applying sampling-based methods, a large number of 3D CFD simulations for a 1.5 HPT stage have been conducted using probabilistic blade geometries, followed by a sensitivity analysis and a detailed investigation of the probabilistic system behaviour. For visualization of possible correlations, the technique of Statistics on Passage (SoP) was chosen, as described in [2].
Axial Compressor Aerodynamics Under Sub-Idle Conditions
Authors: Illana Enric , Grech Nicholas , Zachos Pavlos K. , Pachidis Vassilios 
Published: November 2013

With stricter regulations on engine altitude relight capability, the understanding of low-speed axial compressor performance is becoming increasingly important. At such far off-design conditions, compressors behave differently from design point, with large changes in the flow phenomena and reduced reliability on the established empirical equations and assumptions.
This work focuses on the aerodynamics of a locked-rotor axial compressor at high inlet Mach number conditions, using a validated numerical simulation approach. In a locked-rotor compressor there is very little compression of the inflow. The air is forced to accelerate, with the rear stages seeing the highest velocities. Depending on the inlet Mach number, the velocity at the rear stages can be close to sonic, until choking conditions are reached. To predict accurately the zero-speed compressor performance close to the choking point, the corresponding blade aerodynamic coefficients are evaluated as a function of the blade’s physical parameters and the inlet Mach number. In addition, the blockage due to the separated flow as a result of the high negative incidences is investigated as a function of inlet Mach number, incidence, solidity and stagger angle. Models that predict the characteristics and choking mass flow of the compressor, require such data.
This work offers a better insight into the low-speed and locked rotor characteristics of the compressor. The zero-speed line can be calculated through a stage-stacking technique using the aerodynamic coefficients and flow blockage derived from the numerical simulations. Low-speed lines between the zero and idle-speed line can subsequently be created through interpolation. Using this methodology, it is possible to generate a complete sub-idle map for a multi-stage axial compressor, enhancing the predictive capability of whole engine performance solvers.
Development of a Novel Mixing Plane Interface Using a Fully Implicit Averaging for Stage Analysis
Authors: Hanimann Lucian , Mangani Luca , Casartelli Ernesto , Mokulys Thomas , Mauri Sebastiano 
Published: November 2013

This paper describes the development and validation steps of a characteristics-based explicit as well as a novel fully implicit mixing plane implementation for turbomachinery applications. The framework is an unstructured 3D RANS in-house modified solver, based on open-source libraries.
Particular attention was paid to mass-conservation, accurate variables interpolation and algorithm stability in order to improve robustness and convergence. By introducing a specific interface, allowing the use of algebraic multigrid solvers together with multiprocessor computation, a speed up of the numerical solution procedure was achieved. The validation of both mixing plane algorithms is carried out on an industrial radial compressor and a cold air 1.5 stages axial turbine.
Partial Arc Steam Admission Optimization in Order to Reduce Vibration of Steam Turbine With Tilting-Pad Journal Bearings
Authors: Nekrasov Alexander 
Published: November 2013

In the investigated high pressure steam turbine, with increasing steam flow rate the exciting aerodynamic forces rise and cause high, but limited vibration of turbine bearings. The tilting-pad journal bearing load and load angle are changing as the steam flow rate changes in turbine with partial arc admission, and accordingly the dynamic characteristics of bearings change.
The field experiments results at fossil fuel power plant presented. The aim of experiments was the partial arc steam admission optimization to reducing the effect associated with change of bearing load/load angle. At first, conventional (consecutive) order of valve opening was investigated. In this case, the bearing vibrations are rising while steam flow and valve outlet pressure are increasing. At some “critical point” the vibration level rises stepwise. Situation repeats symmetrically during turbine unloading/loading.
In the second part of experiments, the consecutive order of valve opening was changed to “diagonal” one. As a result, the bearing vibration weakly depends on the steam flow rate and its value is significantly lower. Long-term turbine operation shows that “diagonal” steam admission is optimal for this type of turbine.
From the analysis of the forces vectors follows that the “critical point” corresponds to static force, which acts in the direction between neighbor tilting-pads. It is contrary to operation and idle modes where this force is acting on pad. The static steam force is bigger and bearing loading is lower at the “critical point”. Numerical investigation of rotor-bearing threshold stability was performed for different bearing loading conditions with exciting aerodynamic steam forces. Two configurations of bearings were included into the model: LBP and LOP — at the “critical point”. Consecutive and so-called “diagonal” orders of valve opening were modeled. Threshold capacity is higher for the “diagonal” valve opening order.
Experimental Study of 700-mm Fan Model Noise at CIAM Anechoic Chamber
Authors: Khaletskiy Yuri , Mileshin Victor 
Published: November 2013

The results of 700-mm fan model study in terms of acoustic response obtained at the CIAM C-3A test rig anechoic chamber are represented. The fan model is a bypass universal propulsion simulator UPS (bypass ratio 8.5, pressure ratio 1.54, fan tip speed 395 m/s, scaled factor k = 2.7) with one-stage fan and nacelle inside which hush kit may be installed.
At the CIAM test rig C-3A acoustic investigation of the S-2 wide chord fan model was carried out. The results showed that at Runway and Flyover the S-2 fan model noise spectra practically did not differ from the noise spectra of single stage fan models with conventional blades.
At Approach mode the S-2 fan model noise spectra radiated in front hemisphere contains several high level tonal components which could be identified as tonal noise at sum frequencies of rotor interaction with the first booster stage. It should be mentioned, that at Approach mode tonal noise at BPF practically does not exceed the broadband noise.
The UPS noise matrices obtained allowed noise prediction of the hypothetical aircraft equipped with turbofan, the scaled fan model of which was tested.
Investigation of the Effect of Perforated Sheath on Thermal-Flow Characteristics Over a Gas Turbine Reverse-Flow Combustor: Part 2 — Computational Analysis
Authors: Wang Liang , Wang Ting 
Published: November 2013

The objective of Part 2 is to employ a computational scheme to investigate the difference in flow pattern, pressure drop, and heat transfer in a gas turbine’s dump diffuser and over the outer surface of the combustor with and without a sheath. Both experimental and computational studies are performed. In Part 1, the experiments are conducted under low pressure and temperature laboratory conditions to provide a database to validate the computation model, which is then used to simulate the thermal-flow field surrounding the combustor and transition piece under elevated gas turbine operating conditions.
For laboratory conditions, the CFD results show that (a) the predicted local static pressure values are higher than the experimental data but the prediction of the global total pressure losses matches the experimental data very well; (b) the total pressure losses are 1.19% for the no-sheath case and 1.89% for the sheathed case, which are within 3% of the experimental values; and (c) the temperature difference between the sheathed and non-sheathed cases is in the range of 5∼10K or 16%–32% based on the temperature scale between the highest and lowest temperature in the computational domain.
In summary, removing the sheath can harvest a significant pressure recovery of approximately 3% of the total pressure, but it will be subject to a wall temperature increase of about 500K (900°F or a 36% increase) on the outer radial part of the transition piece, where the flow is slow due to diffusion and recirculation in the large dump diffuser cavity near the turbine end. If modern advanced materials or coatings could sustain a wall temperature of about 200K higher than those currently available, the shield could be removed with the condition that a special cooling scheme (such as a water spray system) must be applied locally in this region. Otherwise, removal of the shield is not recommended.
Power Augmentation Approaches for Mechanical Drive Turbines
Authors: Meher-Homji Cyrus B. , Chaker Mustapha A. 
Published: November 2013

Mechanical drive gas turbine can benefit significantly by power augmentation. In the oil and gas, petrochemical and process industries, the reduction in output of mechanical drive gas turbines curtails plant output or throughput. Gas turbines exhibit a drop in power output with an increase in air compressor inlet temperature of the order of 0.7% / °C for heavy duty gas turbines and approximately 1% / °C for aeroderivative turbines. Power augmentation by inlet cooling is an attractive means to minimize production swings. Designing gas turbine driven refrigeration compressors for high ambient temperature swings is also a design challenge due to power limitations at high ambient temperatures and high refrigerant condensing pressures. This paper will address a range of gas turbine inlet cooling techniques, and provide a technical perspective of different inlet cooling approaches.
Technical approaches including inlet evaporative cooling, inlet fogging, wet compression, inlet mechanical and absorption chilling are covered. Other approaches such as water injection are briefly discussed. The judicious selection of the dry bulb temperature and coincident relative humidity for the design and selection of the cooling technology is discussed.
A Study on the Performance of Steam Injection in a Typical Micro Gas Turbine
Authors: De Paepe Ward , Delattin Frank , Bram Svend , Contino Francesco , De Ruyck Jacques 
Published: November 2013

Microturbines are very promising for small-scale Combined Heat and Power (CHP) production. Due to the simultaneous production of heat and power, the Turbec T100 microturbine CHP System has the potential of realizing considerable energy savings, compared to classic separate production. The power production however is strictly bound to the heat production. A reduction in heat demand will mostly lead to a shutdown of the unit, since electric efficiency is too low and not competitive with electricity from the net. The reduced amount of running hours has a severe negative impact on the lifetime profitability of the unit. A solution is proposed by injecting auto-generated steam in the T100 micro Gas Turbine (mGT), in order to increase electric efficiency during periods with low heat demand. By doing so, a forced shut down of the unit can be avoided.
The goal of this study was to investigate and quantify the beneficial effect of steam injection on the performance of a typical recuperated mGT. This paper reports on an extended series of steam injection experiments performed on a Turbec T100 microturbine. Previous experiments revealed the necessity for a more accurate determination of the mass flow rate and more precise compressor characteristics. Therefore the test rig was equipped with an additional oxygen analyzer in the exhaust and a pressure gauge to allow for the accurate determination of the pressure ratio. Experiments with steam injection in the compressor outlet of the T100 were performed to demonstrate and validate the benefits of introducing steam in the cycle and to verify its ability to handle the injected steam. It is expected that the mGT will produce a constant power at reduced shaft speed and increased electric efficiency.
Steam injection experiments validated the increase in electric efficiency during stable operation of the mGT. At nominal 100 kWe power production, the replacement of 3.5% of the air mass flow with steam (adiabatic steam injection limit) resulted in an absolute electric efficiency increase of 1.7%. The experiments successfully demonstrated the potential for steam/water injection in the T100 mGT.
An Improved Catcher Bearing Model and an Explanation of the Forward Whirl/Whip Phenomenon Observed in Active Magnetic Bearing Transient Drop Experiments
Authors: Wilkes Jason , Vannini Giuseppe , Moore Jeff , Ransom David 
Published: November 2013

Though many approaches have been proposed in the literature to model the reaction forces in a catcher bearing (CB), there are still phenomena observed in experimental tests that cannot be explained by existing models. The following paper presents a novel approach to model a CB system. Some of the elements in the model have been previously introduced in the literature; however, there are other elements in the proposed model that are new, providing an explanation for the forward whirling phenomena that has been observed repeatedly in the literature. The proposed CB model is implemented in a finite element rotordynamic package, and nonlinear time-transient simulations are performed to predict published experimental results of a high speed vertical sub-scale compressor; with no other forces present in the model, the agreement between simulations and experimental data is favorable.
The results presented herein show that friction between the journal and axial face of the catcher bearing results in a forward cross-coupled force that pushes the rotor in the direction of rotation. This force is proportional to the coefficient of friction between the axial face of the rotor and catcher bearing and the axial thrust on the rotor. This force results in synchronous whirl when the running speed is below a combined natural frequency of the rotor-stator system, and constant frequency whip when the speed is above a whip frequency.
A Rothalpy Analysis for the Isothermal Boundary Condition at Casing Applied to the Rotor 37 Transonic Axial Flow Compressor
Authors: Bruna Dario , Turner Mark G. 
Published: November 2013

CFD simulations have been set-up with an isothermal boundary condition at the casing for running the NASA Rotor 37 axial compressor. The casing temperature was set to the inlet total temperature. The comparison to data was much improved for the efficiency for the 100% speed line relative to the adiabatic simulations. The efficiency difference between the isothermal and adiabatic solutions is about 1%, with the isothermal calculation matching the low flow test condition. The profiles of total temperature with the isothermal boundary condition matched the data near the casing without any overshoot, typical of most compressor calculations. Also the efficiency profile had a similar improvement in matching the data because of its relationship to temperature.
A similar comparison between isothermal and adiabatic cases has been carried out for the same geometry with double the design clearance. The working range based on the steady CFD calculations is about half that of the design clearance case which is felt to be realistic.
Moreover a detailed analysis based on conservation of Rothalpy has been made and applied to the rotor. Mass averaged Rothalpy is not conserved due to a frictional power term associated with the stationary case as well as heat transfer. The effects of these terms show the extent of the heat transfer is between 10–20% of span away from the casing.
The heat transfer effect calculated with the isothermal boundary condition simulation is thought to be real, and accounting for it matches data better than using an adiabatic assumption. However, the real rig would probably not be isothermal at the casing and may require more complex simulations such as a conjugate heat transfer approach.