Experimental and Numerical Calculation of Turbulent Timescales at the Exit of an Engine Representative Combustor Simulator

2015 ◽  
Author(s):  
Charlie Koupper ◽  
Tommaso Bacci ◽  
Bruno Facchini ◽  
Alessio Picchi ◽  
Lorenzo Tarchi ◽  
...  
Keyword(s):  
High Pressure ◽  
Experimental Investigations ◽  
Time Signal ◽  
Small Scale ◽  
Lean Burn ◽  
Integral Scale ◽  
Eddy Simulation ◽  
High Reynolds ◽  
University Of Florence ◽  
Hot Streak

To deepen the knowledge of the interaction between modern lean burn combustors and high pressure turbines, a non-reactive real scale annular trisector Combustor Simulator (CS) has been assembled at University of Florence, with the goal of investigating and characterizing the combustor aerothermal field as well as the hot streak transport towards the high pressure vanes. To generate hot streaks and simulate lean burn combustor behaviors, the rig is equipped with axial swirlers fed by a main air flow stream that is heated up to 531 K, while liners with effusion cooling holes are fed by air at ambient temperature. Detailed experimental investigations are then performed with the aim of characterizing the turbulence quantities at the exit of the combustion module, and specifically evaluating an integral scale of turbulence. To do so, an automatic traverse system is mounted at the exit of the CS and equipped to perform Hot Wire Anemometry (HWA) measurements. In this paper, two-point correlations are computed from the time signal of the axial velocity giving access to an evaluation of the turbulence timescales at each measurement point. For assessment of the advanced numerical method that is Large Eddy Simulation (LES), the same methodology is applied to a LES prediction of the CS. Although comparisons seem relevant and easily accessible, both approaches and contexts have fundamental differences: mostly in terms of duration of the signals acquired experimentally and numerically but also with potentially different acquisition frequencies. In the exercise that aims at comparing high-order statistics and diagnostics, the specificity of comparing experimental and numerical results is comprehensively discussed. Attention is given to the importance of the acquisition frequency, intrinsic bias of having a short duration signal and influence of the investigating windows. For an adequate evaluation of the turbulent time scales, it is found that comparing experiments and numerics for high Reynolds number flows inferring small-scale phenomena requires to obey a set of rules, otherwise important errors can be made. If adequately processed, LES and HWA are found to agree well indicating the potential of LES for such problems.

Experimental and Numerical Calculation of Turbulent Timescales at the Exit of an Engine Representative Combustor Simulator

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Charlie Koupper ◽  
Laurent Gicquel ◽  
Florent Duchaine ◽  
Tommaso Bacci ◽  
Bruno Facchini ◽  
...  
Keyword(s):  
Experimental Investigations ◽  
Time Signal ◽  
Small Scale ◽  
Lean Burn ◽  
Integral Scale ◽  
Eddy Simulation ◽  
High Reynolds ◽  
University Of Florence ◽  
Hot Streak ◽  
High Order Statistics

To deepen the knowledge of the interaction between modern lean burn combustors and high pressure (HP) turbines, a nonreactive real scale annular trisector combustor simulator (CS) has been assembled at University of Florence (UNIFI), with the goal of investigating and characterizing the combustor aerothermal field as well as the hot streak transport toward the HP vanes. To generate hot streaks and simulate lean burn combustor behaviors, the rig is equipped with axial swirlers fed by a main air flow stream that is heated up to 531 K, while liners with effusion cooling holes are fed by air at ambient temperature. Detailed experimental investigations are then performed with the aim of characterizing the turbulence quantities at the exit of the combustion module, and specifically evaluating an integral scale of turbulence. To do so, an automatic traverse system is mounted at the exit of the CS and equipped to perform hot wire anemometry (HWA) measurements. In this paper, two-point correlations are computed from the time signal of the axial velocity giving access to an evaluation of the turbulence timescales at each measurement point. For assessment of the advanced numerical method that is large Eddy simulation (LES), the same methodology is applied to a LES prediction of the CS. Although comparisons seem relevant and easily accessible, both approaches and contexts have fundamental differences: mostly in terms of duration of the signals acquired experimentally and numerically but also with potentially different acquisition frequencies. In the exercise that aims at comparing high-order statistics and diagnostics, the specificity of comparing experimental and numerical results is comprehensively discussed. Attention is given to the importance of the acquisition frequency, intrinsic bias of having a short duration signal and influence of the investigating windows. For an adequate evaluation of the turbulent time scales, it is found that comparing experiments and numerics for high Reynolds number flows inferring small-scale phenomena requires to obey a set of rules, otherwise important errors can be made. If adequately processed, LES and HWA are found to agree well indicating the potential of LES for such problems.

Flow Field and Hot Streak Migration Through a High Pressure Cooled Vanes With Representative Lean Burn Combustor Outflow

2018 ◽  
Vol 141 (4) ◽  
Author(s):  
Tommaso Bacci ◽  
Tommaso Lenzi ◽  
Alessio Picchi ◽  
Lorenzo Mazzei ◽  
Bruno Facchini
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Flow Field ◽  
Fuel Injection ◽  
Leading Edge ◽  
Flame Stabilization ◽  
Lean Burn ◽  
Aero Engine ◽  
University Of Florence ◽  
Hot Streak

Modern lean burn aero-engine combustors make use of relevant swirl degrees for flame stabilization. Moreover, important temperature distortions are generated, in tangential and radial directions, due to discrete fuel injection and liner cooling flows respectively. At the same time, more efficient devices are employed for liner cooling and a less intense mixing with the mainstream occurs. As a result, aggressive swirl fields, high turbulence intensities, and strong hot streaks are achieved at the turbine inlet. In order to understand combustor-turbine flow field interactions, it is mandatory to collect reliable experimental data at representative flow conditions. While the separated effects of temperature, swirl, and turbulence on the first turbine stage have been widely investigated, reduced experimental data is available when it comes to consider all these factors together.In this perspective, an annular three-sector combustor simulator with fully cooled high pressure vanes has been designed and installed at the THT Lab of University of Florence. The test rig is equipped with three axial swirlers, effusion cooled liners, and six film cooled high pressure vanes passages, for a vortex-to-vane count ratio of 1:2. The relative clocking position between swirlers and vanes has been chosen in order to have the leading edge of the central NGV aligned with the central swirler. In order to generate representative conditions, a heated mainstream passes though the axial swirlers of the combustor simulator, while the effusion cooled liners are fed by air at ambient temperature. The resulting flow field exiting from the combustor simulator and approaching the cooled vane can be considered representative of a modern Lean Burn aero engine combustor with swirl angles above ±50 deg, turbulence intensities up to about 28% and maximum-to-minimum temperature ratio of about 1.25. With the final aim of investigating the hot streaks evolution through the cooled high pressure vane, the mean aerothermal field (temperature, pressure, and velocity fields) has been evaluated by means of a five-hole probe equipped with a thermocouple and traversed upstream and downstream of the NGV cascade.

Flow Field and Hot Streak Migration Through High Pressure Cooled Vanes With Representative Lean Burn Combustor Outflow

2018 ◽  
Author(s):  
T. Bacci ◽  
T. Lenzi ◽  
A. Picchi ◽  
L. Mazzei ◽  
B. Facchini
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Flow Field ◽  
Fuel Injection ◽  
Leading Edge ◽  
Flame Stabilization ◽  
Lean Burn ◽  
Aero Engine ◽  
University Of Florence ◽  
Hot Streak

Modern lean burn aero-engine combustors make use of relevant swirl degrees for flame stabilization. Moreover important temperature distortions are generated, in tangential and radial directions, due to discrete fuel injection and liner cooling flows respectively. At the same time, more efficient devices are employed for liner cooling and a less intense mixing with the mainstream occurs. As a result, aggressive swirl fields, high turbulence intensities and strong hot streaks are achieved at the turbine inlet. In order to understand combustor-turbine flow field interactions, it is mandatory to collect reliable experimental data at representative flow conditions. While the separated effects of temperature, swirl and turbulence on the first turbine stage have been widely investigated, reduced experimental data is available when it comes to consider all these factors together. In this perspective, an annular three-sector combustor simulator with fully cooled high pressure vanes has been designed and installed at the THT Lab of University of Florence. The test rig is equipped with three axial swirlers, effusion cooled liners and six film cooled high pressure vanes passages, for a vortex-to-vane count ratio of 1:2. The relative clocking position between swirlers and vanes has been chosen in order to have the leading edge of the central NGV aligned with the central swirler. In order to generate representative conditions, a heated mainstream passes though the axial swirlers of the combustor simulator, while the effusion cooled liners are fed by air at ambient temperature. The resulting flow field exiting from the combustor simulator and approaching the cooled vane can be considered representative of a modern Lean Burn aero engine combustor with swirl angles above ±50°, turbulence intensities up to about 28% and maximum-to-minimum temperature ratio of about 1.25. With the final aim of investigating the hot streaks evolution through the cooled high pressure vane, the mean aerothermal field (temperature, pressure and velocity fields) has been evaluated by means of a five hole probe equipped with a thermocouple and traversed upstream and downstream of the NGV cascade.

Assessment of RANS Against LES for the Aero-Thermal Behavior of High Pressure Turbine Stages Under Realistic Inlet Conditions

2016 ◽  
Author(s):  
Stefano Vagnoli ◽  
Tom Verstraete ◽  
Charlie Koupper ◽  
Guillaume Bonneau
Keyword(s):  
High Pressure ◽  
Thermal Behavior ◽  
Turbulence Modeling ◽  
Engine Performance ◽  
High Pressure Turbine ◽  
Lean Burn ◽  
Field Development ◽  
Safety Margins ◽  
Inlet Conditions ◽  
Hot Streak

Modern Lean Burn combustors generate a complex field at the High Pressure turbine (HPT) inlet, characterized by non-uniform velocity and temperature distributions, together with very high turbulence levels (up to 25%). For these extreme conditions, classical numerical methods employed for the HPT design, such as Reynolds Averaged Navier Stokes (RANS) simulation, suffer from a lack of validation. This leads to a reduced confidence in predicting the combustor-turbine interactions, which requires to use extra safety margins, to the detriment of the overall engine performance. Within the European FACTOR project, a 360° non reactive combustor simulator and a 1.5 HPT stage are designed to get more insight into the mutual interaction of these two components. A first experimental and numerical campaign has demonstrated the potential of Large Eddy Simulations (LES) to accurately reproduce the turbulent flow field development at the combustor outlet. The aim of the present paper is to exploit the accuracy of LES to validate less time-consuming RANS models in predicting the hot streak migration in the turbine stage. In this sense, LES results are used as a reference to discriminate the different RANS simulations in terms of turbulence modeling and aerothermal predictions. The current investigations clearly indicate that turbulence and hot streak diffusion within the HPT are strongly linked. In this sense, the choice of the RANS turbulence model and the inlet turbulent conditions plays a major role in modeling the thermal behavior for the stator and rotor blades.

Large Eddy Simulation of Combustor and Complete Single-Stage High-Pressure Turbine of the FACTOR Test Rig

2019 ◽  
Author(s):  
Martin Thomas ◽  
Jerome Dombard ◽  
Florent Duchaine ◽  
Laurent Gicquel ◽  
Charlie Koupper
Keyword(s):  
High Pressure ◽  
Large Eddy Simulation ◽  
Combustion Chamber ◽  
Measurement Data ◽  
Single Stage ◽  
High Pressure Turbine ◽  
Lean Burn ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Compact Design

Abstract Development goals for next generation aircraft engines are mainly determined by the need to reduce fuel consumption and environmental impact. To reduce NOx emissions lean combustion technologies will be applied in future development projects. The more compact design and the absence of dilution holes in this type of engines shortens residence times in the combustion chamber and reduces mixing which results in higher levels of swirl, turbulence and temperature distortions at the exit of the combustion chamber. For these engines interactions between components are more important, so that the traditional engine design approach of component-wise optimization will have to be adapted. To study new lean burn architectures the European FACTOR project investigates the transport of hot streaks produced by a non-reactive combustor simulator through a single stage high-pressure turbine. In this work high-fidelity Large Eddy Simulation (LES) of combustor and complete high-pressure turbine are discussed and validated against experimental data. Measurement data is available on P40 (exit of the combustion chamber), P41 (exit of the stator) and P42 (exit of the rotor) and generally shows a good agreement to LES data.

Rotor Blade Heat Transfer of High Pressure Turbine Stage Under Inlet Hot-Streak and Swirl

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
A. Rahim ◽  
L. He
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Load ◽  
Design Space Exploration ◽  
Role Reversal ◽  
Dominant Factor ◽  
Inlet Temperature ◽  
Turbine Stage ◽  
Lean Burn ◽  
Hot Streak

A key consideration in high pressure (HP) turbine designs is the heat load experienced by rotor blades. Impact of turbine inlet nonuniformity of combined temperature and velocity traverses, typical for a lean-burn combustor exit, has rarely been studied. For general turbine aerothermal designs, it is also of interest to understand how the behavior of lean-burn combustor traverses (with both hot-streak and swirl) might contrast with those for a rich-burn combustor (largely hot-streak only). In the present work, a computational study has been carried out on the aerothermal performance of a HP turbine stage under nonuniform temperature and velocity inlet profiles. The analyses are primarily conducted for two combined hot-streak and swirl inlets, with opposite swirl directions. In addition, comparisons are made against a hot-streak only case and a uniform inlet. The effects of three nozzle guide vane (NGV) shape configurations are investigated: straight, compound lean (CL) and reverse CL (RCL). The present results reveal a qualitative change in the roles played by heat transfer coefficient (HTC) and fluid driving (“adiabatic wall”) temperature, Taw. It has been shown that the blade heat load for a uniform inlet is dominated by HTC, whilst a hot-streak only case is largely influenced by Taw. However, in contrast to the hot-streak only case, a combined hot-streak and swirl case shows a role reversal with the HTC being a dominant factor. Additionally, it is seen that the swirling flow redistributes radially the hot fluid within the NGV passage considerably, leading to a much ‘flatter’ rotor inlet temperature profile compared to its hot-streak only counterpart. Furthermore, the rotor heat transfer characteristics for the combined traverses are shown to be strongly dependent on the NGV shaping and the inlet swirl direction, indicating a potential for further design space exploration. The present findings underline the need to clearly define relevant combustor exit temperature and velocity profiles when designing and optimizing NGVs for HP turbine aerothermal performance.

scholarly journals Numerical Investigation of Injection, Mixing and Combustion in Rocket Engines Under High-Pressure Conditions

2020 ◽  
pp. 209-221
Author(s):  
Christoph Traxinger ◽  
Julian Zips ◽  
Christian Stemmer ◽  
Michael Pfitzner
Keyword(s):  
High Pressure ◽  
Large Eddy Simulations ◽  
Experimental Investigations ◽  
High Fidelity ◽  
Rocket Engines ◽  
Eddy Simulation ◽  
Liquid Rocket Engines ◽  
Large Eddy ◽  
Numerical Tools ◽  
Liquid Rocket

Abstract The design and development of future rocket engines severely relies on accurate, efficient and robust numerical tools. Large-Eddy Simulation in combination with high-fidelity thermodynamics and combustion models is a promising candidate for the accurate prediction of the flow field and the investigation and understanding of the on-going processes during mixing and combustion. In the present work, a numerical framework is presented capable of predicting real-gas behavior and nonadiabatic combustion under conditions typically encountered in liquid rocket engines. Results of Large-Eddy Simulations are compared to experimental investigations. Overall, a good agreement is found making the introduced numerical tool suitable for the high-fidelity investigation of high-pressure mixing and combustion.

scholarly journals Stochastic Wake Modeling Based on POD Analysis

2016 ◽  
Author(s):  
David Bastine ◽  
Lukas Vollmer ◽  
Matthias Wächter ◽  
Joachim Peinke
Keyword(s):  
Wind Turbine ◽  
Added Value ◽  
Experimental Investigations ◽  
Small Scale ◽  
Eddy Simulation ◽  
Show Evidence ◽  
Aeroelastic Simulations ◽  
Pod Analysis ◽  
Weighting Coefficients ◽  
Les Model

Abstract. In this work, large eddy simulation data is analyzed to investigate a new stochastic modeling approach for the wake of a wind turbine. The data is generated by the LES model PALM combined with an actuator disk with rotation representing the turbine. After applying a proper orthogonal decomposition (POD), three different stochastic models for the weighting coefficients of the POD modes are deduced resulting in three wake models. Their performance is investigated mainly on the basis of aeroelastic simulations of a wind turbine in the wake. Three different load cases and their statistic characteristics are compared for the original LES, truncated PODs and the stochastic wake models including different numbers of POD modes. It is shown that approximately six POD modes are enough to capture the load dynamics on large temporal scales. Modeling the weighting coefficients as independent stochastic processes leads to similar load characteristics as in the case of the truncated POD. To complete this simplified wake description, we show evidence that the small-scale dynamics can be grasped by adding to our model a homogeneous turbulent field. In this way, we present a procedure how to derive stochastic wake models from costly CFD calculations or elaborated experimental investigations. These numerically efficient models provide the added value of possible long-term studies. Depending on the aspects of interest, different minimalized models may be obtained.

Analysis of Radial Migration of Hot-Streak in Swirling Flow Through High-Pressure Turbine Stage

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
B. Khanal ◽  
L. He ◽  
J. Northall ◽  
P. Adami
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Swirling Flow ◽  
Guide Vane ◽  
Lean Burn ◽  
Considerable Impact ◽  
Computational Fluid Dynamics Cfd ◽  
Nozzle Guide ◽  
Hot Streak ◽  
Computational Analyses

The high pressure (HP) turbine is subject to inlet flow nonuniformities resulting from the combustor. A lean-burn combustor tends to combine temperature variations with strong swirl and, although considerable research efforts have been made to study the effects of a circumferential temperature nonuniformity (hot-streak), there is relatively little known about the interaction between the two. This paper presents a numerical investigation of the transonic test HP stage MT1 behavior under the combined influence of the swirl and hot-streak. The in house Rolls-Royce HYDRA numerical computational fluid dynamics (CFD) suite is used for all the simulations of the present study. Baseline configurations with either hot-streak or swirl at the stage inlet are analyzed to assess the methodology and to identify reference performance parameters through comparisons with the experimental data. Extensive computational analyses are then carried out for the cases with hot-streak and swirl combined, including both the effects of the combustor-nozzle guide vane (NGV) clocking and the direction of the swirl. The present results for the combined hot-streak and swirl cases reveal distinctive radial migrations of hot fluid in the NGV and rotor passages with considerable impact on the aerothermal performance. It is illustrated that the blade heat transfer characteristics and their dependence on the clocking position can be strongly affected by the swirl direction. A further computational examination is carried out on the validity of a superposition of the influences of swirl and hot-streak. It shows that the blade heat transfer in a combined swirl and hot-streak case cannot be predicted by the superposition of each in isolation.

Flowfield and Temperature Profiles Measurements on a Combustor Simulator Dedicated to Hot Streaks Generation

2015 ◽  
Author(s):  
Tommaso Bacci ◽  
Gianluca Caciolli ◽  
Bruno Facchini ◽  
Lorenzo Tarchi ◽  
Charlie Koupper ◽  
...  
Keyword(s):  
High Pressure ◽  
Flow Field ◽  
Measurement Techniques ◽  
Symmetry Plane ◽  
Operating Conditions ◽  
Pressure Probe ◽  
Lean Burn ◽  
Experimental Database ◽  
Set Up ◽  
University Of Florence

In order to deepen the knowledge of the interaction between modern lean burn combustors and high pressure turbines, a real scale annular three sector combustor simulator has been assembled at University of Florence, with the goal of investigating and characterizing the generated aerothermal field and the hot streaks transport between combustor exit and the high pressure vanes location. To generate hot streaks and simulate lean burn combustors behavior, the rig is equipped with axial swirlers, fed by main air flow that is heated up to 531 K, and liners with effusion cooling holes that are fed by air at ambient temperature. The three sector configuration is used to reproduce the periodicity on the central sector and to allow to perform measurements inside the chamber, through the lateral walls. Ducts of different length have been mounted on the swirlers, preserving the hot mainflow from the interaction with coolant. Such configurations, together with the one without ducts, have been tested, using different measurement techniques, in order to highlight the differences in the resulting flow fields. First of all, isothermal PIV measurements have been performed on the combustion chamber symmetry plane, to highlight the mixing phenomena between the mainflow and cooling flows. Then a detailed investigation of the mean aerothermal field at combustor exit has been carried out, for nominal operating conditions, by means of a five hole pressure probe provided with a thermocouple, installed on an automatic traverse system. With the aim of analyzing the hot streaks transport and the flow field modification towards the vanes location, such measurements have been performed on two different planes: one located in correspondence of the combustor exit and the further one placed downstream, in the virtual location of the vanes leading edges. Therefore, an experimental database, describing the evolution of the flow field in a combustor simulator with typical traits of modern lean burn chambers, for different injector geometries, has been set up.

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