Hybrid RANS-LES Modeling of the Aerothermal Field in an Annular Hot Streak Generator for the Study of Combustor–Turbine Interaction

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
A. Andreini ◽  
T. Bacci ◽  
M. Insinna ◽  
L. Mazzei ◽  
S. Salvadori
Keyword(s):  
Navier Stokes ◽  
Test Rig ◽  
Complex Flow ◽  
Lean Burn ◽  
Flow Physics ◽  
Safety Margins ◽  
Viable Approach ◽  
Sas Model ◽  
Aero Engines ◽  
Eu Project

The adoption of lean-burn technology in modern aero-engines influences the already critical aerothermal conditions at turbine entry, where the absence of dilution holes preserves the swirl component generated by burners and prevents any control on pattern factor. The associated uncertainty and lack of confidence entail the application of wide safety margins in turbine cooling design, with a detrimental effect on engine efficiency. Computational fluid dynamics (CFD) can provide a deeper understanding of the physical phenomena involved in combustor–turbine interaction, especially with hybrid Reynolds-averaged Navier–Stokes (RANS) large eddy simulation (LES) models, such as scale adaptive simulation (SAS), which are proving to overcome the well-known limitations of the RANS approach and be a viable approach to capture the complex flow physics. This paper describes the numerical investigation on a test rig representative of a lean-burn, effusion cooled, annular combustor developed in the EU Project Full Aerothermal Combustor-Turbine interactiOns Research (FACTOR) with the aim of studying combustor–turbine interaction. Results obtained with RANS and SAS were critically compared to experimental data and analyzed to better understand the flow physics, as well as to assess the improvements related to the use of hybrid RANS-LES models. Significant discrepancies are highlighted for RANS in predicting the recirculating region, which has slight influence on the velocity field at the combustor outlet, but affects dramatically mixing and the resulting temperature distribution. The accuracy of the results achieved suggests the exploitation of SAS model with a view to the future inclusion of the nozzle guide vanes in the test rig.

Hybrid RANS-LES Modeling of the Aero-Thermal Field in an Annular Hot Streak Generator for the Study of Combustor-Turbine Interaction

2016 ◽  
Author(s):  
A. Andreini ◽  
T. Bacci ◽  
M. Insinna ◽  
L. Mazzei ◽  
S. Salvadori
Keyword(s):  
Navier Stokes ◽  
Test Rig ◽  
Lean Burn ◽  
Turbine Cooling ◽  
Safety Margins ◽  
Viable Approach ◽  
Sas Model ◽  
Aero Engines ◽  
Eu Project ◽  
Nozzle Guide

Turbine entry conditions are characterized by unsteady and strongly non-uniform velocity, temperature and pressure fields. The uncertainty and the lack of confidence associated with these conditions require the application of wide safety margins during the design of the turbine cooling systems, with a detrimental effect on engine efficiency. The adoption of lean-burn technology in modern aero-engines to reduce NOx emissions exacerbates the situation, as the absence of dilution holes keeps the strong swirl component generated by the burners up to the combustor outlet and prevents to control the pattern factor. Complexity and costs associated with the experimental investigation of combustor-turbine interaction, makes Computational Fluid Dynamics (CFD) paramount to understand the physical phenomena involved. Moreover, due to the well-known limitations of the Reynolds-Averaged Navier-Stokes (RANS) approach and the increase in computational resources, hybrid RANS-LES models, such as Scale Adaptive Simulation (SAS), are proving to be a viable approach to capture the main structures of the flow field. This paper reports the main findings of the numerical investigation on a test rig representative of a lean-burn, effusion cooled, annular combustor, developed in the context of the EU Project FACTOR (Full Aerothermal Combustor-Turbine interactiOns Research) with the aim of studying combustor-turbine interaction. Results obtained with RANS and unsteady SAS were critically compared to experimental data and analysed in order to better understand the flow physics within such a device, as well as to assess the improvements related to the use of hybrid models. The main discrepancies between RANS and SAS are highlighted in predicting the recirculating region, which has slight influence on the velocity field at the combustor outlet, but affects dramatically mixing and the resulting temperature distribution. Accuracy of the results achieved suggest a possible exploitation of SAS model with a view to the future inclusion of the nozzle guide vanes within the test rig.

Hybrid RANS-LES Modeling of a Hot Streak Generator Oriented to the Study of Combustor-Turbine Interaction

2015 ◽  
Author(s):  
A. Andreini ◽  
B. Facchini ◽  
M. Insinna ◽  
L. Mazzei ◽  
S. Salvadori
Keyword(s):  
Lean Burn ◽  
Turbine Cooling ◽  
Safety Margins ◽  
Annular Combustor ◽  
Viable Approach ◽  
Compact Design ◽  
Eu Project ◽  
Hot Streak ◽  
Physical Phenomena ◽  
The Impact

Turbine entry conditions are characterized by unsteady and strongly non-uniform velocity and temperature and pressure fields. The uncertainty and the lack of confidence associated to these conditions require the application of wide safety margins during the design of the turbine cooling systems, which are detrimental for the efficiency of the engine. These issues have been further complicated by the adoption of lean-burn technology in modern aeroengines, identified by many manufacturers as the most promising solution for a significant reduction of NOx emission. Such devices are in fact characterized by a very compact design, whereas the strong swirl component generated by the injector is maintained up to the end of the flametube due to the absence of dilution holes, which in conventional combustors provides the required pattern factor. Bearing in mind complexity and costs associated to the experimental investigation of combustor-turbine interaction, CFD has become a key and complementary tool to understand the physical phenomena involved. Due to the well-known limitations of the RANS approach and the increase in computational resources, hybrid RANS-LES models, such as Scale Adaptive Simulation (SAS), are proving to be a viable approach to resolve the main structures of the flow field. This paper reports the main findings of the numerical investigation of a hot streak generator for the study of combustor-turbine interaction. The results were compared to experimental data obtained from a test rig representative of a lean-burn, effusion cooled, annular combustor, developed in the context of the EU project FACTOR. Steady RANS and unsteady SAS runs were carried out in order to assess the improvements related to hybrid models. Additional simulations were performed to investigate the effect of the periodicity assumption and the impact of liner cooling modelling on the exit conditions.

Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak Generation

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Charlie Koupper ◽  
Gianluca Caciolli ◽  
Laurent Gicquel ◽  
Florent Duchaine ◽  
Guillaume Bonneau ◽  
...  
Keyword(s):  
Computational Cost ◽  
Navier Stokes ◽  
Special Focus ◽  
Hot Wire ◽  
Test Rig ◽  
Combustion Chambers ◽  
Lean Burn ◽  
Safety Margins ◽  
University Of Florence ◽  
Hot Streak

Nowadays, the lack of confidence in the prediction of combustor-turbine interactions and more specifically our ability to predict the migration of hot spots through this interface leads to the application of extra safety margins, which are detrimental to an optimized turbine design and efficiency. To understand the physics and flow at this interface, a full 360 deg nonreactive combustor simulator (CS) representative of a recent lean burn chamber together with a 1.5 turbine stage is instrumented at DLR in Gottingen (Germany) within the European project FACTOR. The chamber operates with axial swirlers especially designed to reproduce engine-realistic velocity and temperature distortion profiles, allowing the investigation of the hot streaks transport through the high pressure (HP) stage. First, a true scale three injector annular sector of the CS without turbine is assembled and tested at the University of Florence. To generate the hot steaks, the swirlers are fed by an air flow at 531 K, while the liners are cooled by an effusion system fed with air at ambient temperature. In addition to static pressure taps and thermocouples, the test rig will be equipped with an automatic traverse system which allows detailed measurements at the combustor exit by means of a 5-hole probe, a thermocouple, and hot wire anemometers. This paper presents the design process and instrumentation of the trisector CS, with a special focus on large Eddy simulations (LES) which were widely used to validate the design choices. It was indeed decided to take advantage of the ability and maturity of LES to properly capture turbulence and mixing within combustion chambers, despite an increased computational cost as compared to usual Reynolds averaged Navier Stokes (RANS) approaches. For preliminary design, simulations of a single periodic sector (representative of the DLR full annular rig) are compared to simulations of the trisector test rig, showing no difference on the central swirler predictions, comforting the choice for the trisector. In parallel, to allow hot wire anemometry (HWA) measurements, the selection of an isothermal operating point, representative of the nominal point, is assessed and validated by use of LES.

Experimental and Numerical Investigation on Windage Power Losses in High Speed Gears

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Daniele Massini ◽  
Tommaso Fondelli ◽  
Antonio Andreini ◽  
Bruno Facchini ◽  
Lorenzo Tarchi ◽  
...  
Keyword(s):  
High Speed ◽  
Spur Gear ◽  
Relative Magnitude ◽  
Navier Stokes ◽  
Power Losses ◽  
Test Rig ◽  
Viscosity Models ◽  
Image Velocimetry ◽  
And Performance ◽  
Aero Engines

Enhancing the efficiency of gearing systems is an important topic for the development of future aero-engines with low specific fuel consumption. An evaluation of its structure and performance is mandatory in order to optimize the design as well as maximize its efficiency. Mechanical power losses are usually distinguished into two main categories: load-dependent and load-independent losses. The former are all those associated with the transmission of torque, while the latter are tied to the fluid dynamics of the environment, which surrounds the gears. The relative magnitude of these phenomena is dependent on the operative conditions of the transmission: load-dependent losses are predominant at slow speeds and high torque conditions, load-independent mechanisms become prevailing in high speed applications, like in turbomachinery. A new test rig was designed for investigating windage power losses resulting by a single spur gear rotating in a free oil environment. The test rig allows the gear to rotate at high speed within a box where pressure and temperature conditions can be set and monitored. An electric spindle, which drives the system, is connected to the gear through a high accuracy torque meter, equipped with a speedometer providing the rotating velocity. The test box is fitted with optical accesses in order to perform particle image velocimetry (PIV) measurements for investigating the flow field surrounding the rotating gear. The experiment has been computationally replicated, performing Reynolds-averaged Navier–Stokes (RANS) simulations in the context of conventional eddy viscosity models, achieving good agreement for all of the speed of rotations.

Propulsive jets and their acoustics

2007 ◽  
Vol 365 (1859) ◽  
pp. 2443-2467 ◽  
Author(s):  
Alexander N Secundov ◽  
Stanley F Birch ◽  
Paul G Tucker
Keyword(s):  
Navier Stokes ◽  
Jet Flows ◽  
Complex Flow ◽  
Flow Physics ◽  
Eddy Simulation ◽  
Daunting Task ◽  
Wide Range ◽  
Large Eddy ◽  
Computational Resources ◽  
Hybrid Forms

The complex flow physics challenges and asks questions regarding these challenges a wide range of jet flows found in aerospace engineering. Hence, the daunting task facing Reynolds-averaged Navier–Stokes (RANS) technology, for which the time average of the turbulent flow field is solved, is set out. Despite the clear potential of large eddy simulation (LES)-related methods and hybrid forms involving some RANS modelling, numerous current deficiencies, mostly related to the limitations of computational resources, are identified. It is concluded that currently, these limitations make LES and hybrids most useful for understanding flow physics and refining RANS technology. The use of LES in conjunction with a ray-tracing model to elucidate the physics of acoustic wave transmission in jets and thus improved RANS technology is described. It is argued that, as a stopgap measure, pure RANS simulations can be a valuable part of the design process and can now predict acoustics spectra and directivity diagrams with useful accuracy. Ultimately, hybrid RANS–LES-type methods, and then pure LES, will dominate, but the time-scales for this transition suggests that improvements to RANS technology should not be ignored.

Assessment of Scale Adaptive Simulation Model for Honeywell Combustor

2015 ◽  
Author(s):  
Debabrata Mahapatra ◽  
Jaydeep Basani ◽  
Samir Rida
Keyword(s):  
Computation Time ◽  
Navier Stokes ◽  
Complex Flow ◽  
Turbulent Structures ◽  
Time Step ◽  
Ansys Fluent ◽  
Eddy Simulation ◽  
Adaptive Simulation ◽  
Flow Domain ◽  
Sas Model

The complex flow phenomena inside a gas turbine combustor demands alternative simulation methods to the Reynolds Averaged Navier-Stokes (RANS) model, where a portion of turbulence scales is resolved inside the flow domain. Large Eddy Simulation (LES) is the most-widely acknowledged method for its attractive feature of resolving large turbulent structures down to the grid limit for the entire flow domain. However, for practical industrial problems where the Reynolds number is high and the flow domain is large, the grid resolution for LES becomes excessively high making it computationally very expensive. Scale Adaptive Simulation (SAS), on the other hand, adjusts to the resolved structures in an Unsteady RANS (URANS) simulation resulting in LES-like behavior in unsteady regions of the flow field. At the same time, it provides RANS capabilities in the stable flow regions. It allows a larger time step than LES resulting in the possibility of computation time advantage with LES-like solution fidelity. In the current paper, the SAS model is compared to the LES model for a Honeywell combustor using the commercial CFD code ANSYS FLUENT. Several time-steps are considered for SAS simulations. Results show that SAS is promising in terms of predicting combustor performance parameters like LES, but with a substantially reduced turn-around time.

scholarly journals Development of a robust solver to model the flow inside the engines for high-speed propulsion

2019 ◽  
Vol 304 ◽  
pp. 03013
Author(s):  
Ludovico Nista ◽  
Bayindir H. Saracoglu
Keyword(s):  
High Speed ◽  
Time Discretization ◽  
Propulsion System ◽  
Navier Stokes ◽  
Complex Flow ◽  
Riemann Solvers ◽  
Flow Physics ◽  
Multiple Test ◽  
Stability Robustness ◽  
Volume Method

The demand for discovering new commercial routes as well as the possibility to shortening civilian long-haul flights boosted the interest of civil hypersonic vehicle designs. Among all the multiple projects started by the various nations, the European community funded project STRATOFLY aims at refining the baseline LAPCAT II-MR2.4 design for further improvements. The new aircraft would enable a flight shorter that 3 hours from Brussels to Sydney, carrying 300-passengers above the already crowed atmosphere. The wide Mach range operability, up to Mach 8, demands the use of multiple engines, leading to a highly integrated propulsion system. The current study is focused on the development of new CFD platform to estimate the performance of the combined propulsion system during the supersonic to hypersonic transition. In order to control the complex flow physics, highfidelity CFD simulations remain the fundamental tools for the preliminary investigations. On the current framework, an advanced robust compressible solver has been develop d in order to handle the different flow regimes. The new tool solves Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations by employing cell-centered Finite Volume Method constructed on openFoam toolbox. Two innovative high-order discretization schemes, with different abilities, based on approximated Riemann solvers were developed for capturing the flow physics within high-speed propulsion systems. Advanced time discretization has been taken into account to increase the temporal accuracy. At the end, the whole implementation has been validated in multiple test cases, ranging from incompressible to hypersonic regimes, confirming its excellent stability, robustness and accuracy.

Development of an Engine Representative Combustor Simulator Dedicated to Hot Streak Generation

2014 ◽  
Author(s):  
Charlie Koupper ◽  
Guillaume Bonneau ◽  
Gianluca Caciolli ◽  
Bruno Facchini ◽  
Lorenzo Tarchi ◽  
...  
Keyword(s):  
Computational Cost ◽  
Special Focus ◽  
Hot Wire ◽  
Test Rig ◽  
Combustion Chambers ◽  
Lean Burn ◽  
Safety Margins ◽  
High Pressure Stage ◽  
University Of Florence ◽  
Hot Streak

Nowadays, the lack of confidence in the prediction of combustor-turbine interactions and more specifically our ability to predict the migration of hot spots through this interface leads to the application of extra safety margins, which are detrimental to an optimized turbine design and efficiency. To understand the physics and flow at this interface, a full 360° non-reactive combustor simulator representative of a recent lean burn chamber together with a 1.5 turbine stage is instrumented at DLR in Gottingen (Germany) within the European project FACTOR. The chamber operates with axial swirlers especially designed to reproduce engine-realistic velocity and temperature distortion profiles allowing the investigation of the hot streaks transport through the high pressure stage. First, a true scale three injector annular sector of the combustor simulator without turbine is assembled and tested at the University of Florence. To generate the hot steaks the swirlers are fed by an air flow at 531 K, while the liners are cooled by an effusion system fed with air at ambient temperature. In addition to static pressure taps and thermocouples, the test rig will be equipped with an automatic traverse system which allows detailed measurements at the combustor exit by means of a 5-hole probe, a thermocouple and hot wire anemometers. This paper presents the design process and instrumentation of the trisector combustor simulator, with a special focus on Large Eddy Simulations (LES) which were widely used to validate the design choices. It was indeed decided to take advantage of the ability and maturity of LES to properly capture turbulence and mixing within combustion chambers, despite an increased computational cost as compared to usual RANS approaches. For preliminary design, simulations of a single periodic sector (representative of the DLR full annular rig) are compared to simulations of the trisector test rig, showing no difference on the central swirler predictions, comforting the choice for the trisector. In parallel, to allow hot wire anemometry measurements, the selection of an isothermal operating point, representative of the nominal point, is assessed and validated by use of LES.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

Rotordynamic Coefficients of Labseals for Turbines: Comparing CFD Results With Experimental Data on a Comb-Grooved Labyrinth

2005 ◽  
Author(s):  
Joachim Schettel ◽  
Martin Deckner ◽  
Klaus Kwanka ◽  
Bernd Lu¨neburg ◽  
Rainer Nordmann
Keyword(s):  
Stokes Equations ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Test Rig ◽  
Navier Stokes Equations ◽  
Detailed Model ◽  
Identification Methods ◽  
Rotating Speed ◽  
Flow Models ◽  
Rotordynamic Coefficients

The main goal of this paper is to improve identification methods for rotordynamic coefficients of labseals for turbines. This aim was achieved in joint effort of the Technische Universita¨t Mu¨nchen, working on experimental identification methods for rotordynamic coefficients, the University of Technology, Darmstadt, working on prediction methods, and Siemens AG, realizing the results. The paper focuses on a short comb-grooved labyrinth seal. Short labseals, amongst others the above mentioned comb-grooved labyrinth, were examined. by means of a very accurately measuring test rig. The rotor was brought into statically eccentric positions relative to the stator, in order to measure the circumferential pressure distribution as a function of pressure, rotating speed and entrance swirl. The data collected were used to validate results obtained with a numerical method. The theoretical approach is based on a commercial CFD tool, which solves the Navier Stokes equations using numerical methods. As a result, a detailed model of the flow within the test rig is produced. The efforts of computation here are greater than when compared with the likewise wide-spread Bulk flow models, however improved accuracy and flexibility is expected. As the validation of the model is successful, it could then be used to gain further insight in the flow within the seal, and to understand the results better. This showed that rotordynamic coefficients of labseals gained from different test rigs are not necessarily comparable.

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