Final Report Summary - HOSTEL (Integration of a HOt STrEam Liner into the Turbine Exit Casing (TEC))
Executive Summary:
The objective of this project was to define and tune a hybrid acoustic liner to the Blade Passing Frequencies (BPF) of the SAGE4 Geared Turbofan (GTF) Demonstrator low pressure turbine (LPT). In this specific application, the liner has to be integrated into the TEC structure. As the main purpose of the demonstrator test is the verification of the liner’s integration aspects and the demonstration of structural integrity under realistic engine conditions, the acoustic design of the liner panels did not have to be fully optimized. However, the acoustic performance of the selected design has been demonstrated and validated by simulations and sample testing in a relevant aerodynamic and acoustic environment.
Project Context and Objectives:
The hybrid liner concept consists of a perforate plate in combination with a metallic foam brazed to a classical honeycomb sandwich structure. The metallic foam layer can be compressed to a pre-determined degree for tuning the acoustic impedance of the liner to achieve the desired attenuation.
The project was initiated with wp1 and wp2, where the management of the project is described in wp1. The conceptual design for defining the acoustic properties of the proposed liner was described and carried out in wp2. As well, the liner samples and final hardware will be designed within this wp.
In wp3 and wp4, verification of the acoustic characteristics, manufacturing of test and demonstrator hardware as well as tests for structural integrity of the liner will be carried out. Regarding material selection for the liner, suitable alloys based on Nickel are chosen for a typical temperature of around 700 ºC. These include Inconel 625 or similar, which is used for the solid and perforated sheets as well as the honeycomb core. Various foam configurations and alloys may be used but the preferred metallic foam is Nickel based. The simulation technique used was a frequency-domain, linearized formulation of the Navier-Stokes equations (LNSE), which has been developed at KTH and successfully been applied to duct aero-acoustic validation cases of orifice plates and area expansions with excellent results. The methodology has proven to be extremely time efficient, and capable of accurately simulating acoustic propagation in ducts with flows and fine geometrical details with significant influence of acoustic boundary layers, which is the case with liners.
Project Results:
In the methodology, a mean flow field is first calculated with a steady state Reynold Averaged Navier-Stokes (RANS) solver. The mean flow is then used as input to the frequency domain LNSE where acoustic and vortical perturbations are calculated around the mean flow. Assuming that the liner is locally reacting, that is that a smaller segment of only one or a few liner cells is enough to be modeled, the geometry of the perforates and the associated acoustic boundary layers will be possible to resolve with the LNSE technique.
For the testing the impedance eduction technique used was a Convected Helmholtz equation mode matching method. Both upstream and downstream acoustic excitation has been used in the present study which makes it possible to discuss the effect on the measured liner impedance of this factor. As pointed out by Renou and Auregan the result can become different depending on the acoustic excitation which was attributed to a failure of the Ingard-Myers28 boundary condition which is applied together with plug flow conditions.
In order to investigate if the effect of high temperatures on the liner impedance data can be predicted and scaled using a change in media properties: density, viscosity and speed of sound, comparisons have been made using models from the literature.
The effect on the result of test rig geometry has been discussed and it was found that there is a good agreement between the results of the impedance tube tests and the grazing flow configuration test rig results for no flow room temperature conditions.
In order to investigate if the effect of high temperatures on the liner impedance data can be predicted and scaled using a change in media properties: density, viscosity and speed of sound, comparisons have been made of the effect of varying the temperature on the educed impedance. Comparisons have also been made using models from the literatue29,30. It seems that the effect of high temperature can be fairly well predicted and that the main difficulty is to accurately determine the effect of mean flow. A reasonable agreement has been obtained between one of the models from the literature30 and the effect of flow Mach number on the resistance.
The nonlinear effect of high excitation levels was not studied in any detail. A few tests were made with variation in excitation level and they showed that nonlinear effects could be seen when the level of excitation was higher than approximately 130 dB. The test equipment did not include any control mechanism to keep the excitation level constant for different frequencies. This meant that the level could vary significantly for different frequencies during a test on a specific liner configuration. It is recommended that this should be improved in future studies.
Potential Impact:
By its very nature this project will have a significant environmental impact. Introducing acoustic liners in the TEC structure will contribute to the long-term objective of reducing aircraft noise. It may also have a significant strategic impact in reinforcing the competitiveness of European engine manufacturers and equipment suppliers.
The hybrid liner may create new business opportunities for Creo Dynamics AB, the liner manufacturer and possibly also for the engine manufacturer. Possible exploitation of project results includes commercialization of the acoustic liner concept. This may include licensing of the technology and/or starting manufacture of the acoustic liner,
Furthermore exploitation has included publishing results in scientific journals and at conferences.
Urban Emborg
Creo Dynamics AB
Westmansgatan 37 A
582 16 Linkoping
Sweden
Phone: +46 722 220557
urban.emborg@creodynamics.com
The objective of this project was to define and tune a hybrid acoustic liner to the Blade Passing Frequencies (BPF) of the SAGE4 Geared Turbofan (GTF) Demonstrator low pressure turbine (LPT). In this specific application, the liner has to be integrated into the TEC structure. As the main purpose of the demonstrator test is the verification of the liner’s integration aspects and the demonstration of structural integrity under realistic engine conditions, the acoustic design of the liner panels did not have to be fully optimized. However, the acoustic performance of the selected design has been demonstrated and validated by simulations and sample testing in a relevant aerodynamic and acoustic environment.
Project Context and Objectives:
The hybrid liner concept consists of a perforate plate in combination with a metallic foam brazed to a classical honeycomb sandwich structure. The metallic foam layer can be compressed to a pre-determined degree for tuning the acoustic impedance of the liner to achieve the desired attenuation.
The project was initiated with wp1 and wp2, where the management of the project is described in wp1. The conceptual design for defining the acoustic properties of the proposed liner was described and carried out in wp2. As well, the liner samples and final hardware will be designed within this wp.
In wp3 and wp4, verification of the acoustic characteristics, manufacturing of test and demonstrator hardware as well as tests for structural integrity of the liner will be carried out. Regarding material selection for the liner, suitable alloys based on Nickel are chosen for a typical temperature of around 700 ºC. These include Inconel 625 or similar, which is used for the solid and perforated sheets as well as the honeycomb core. Various foam configurations and alloys may be used but the preferred metallic foam is Nickel based. The simulation technique used was a frequency-domain, linearized formulation of the Navier-Stokes equations (LNSE), which has been developed at KTH and successfully been applied to duct aero-acoustic validation cases of orifice plates and area expansions with excellent results. The methodology has proven to be extremely time efficient, and capable of accurately simulating acoustic propagation in ducts with flows and fine geometrical details with significant influence of acoustic boundary layers, which is the case with liners.
Project Results:
In the methodology, a mean flow field is first calculated with a steady state Reynold Averaged Navier-Stokes (RANS) solver. The mean flow is then used as input to the frequency domain LNSE where acoustic and vortical perturbations are calculated around the mean flow. Assuming that the liner is locally reacting, that is that a smaller segment of only one or a few liner cells is enough to be modeled, the geometry of the perforates and the associated acoustic boundary layers will be possible to resolve with the LNSE technique.
For the testing the impedance eduction technique used was a Convected Helmholtz equation mode matching method. Both upstream and downstream acoustic excitation has been used in the present study which makes it possible to discuss the effect on the measured liner impedance of this factor. As pointed out by Renou and Auregan the result can become different depending on the acoustic excitation which was attributed to a failure of the Ingard-Myers28 boundary condition which is applied together with plug flow conditions.
In order to investigate if the effect of high temperatures on the liner impedance data can be predicted and scaled using a change in media properties: density, viscosity and speed of sound, comparisons have been made using models from the literature.
The effect on the result of test rig geometry has been discussed and it was found that there is a good agreement between the results of the impedance tube tests and the grazing flow configuration test rig results for no flow room temperature conditions.
In order to investigate if the effect of high temperatures on the liner impedance data can be predicted and scaled using a change in media properties: density, viscosity and speed of sound, comparisons have been made of the effect of varying the temperature on the educed impedance. Comparisons have also been made using models from the literatue29,30. It seems that the effect of high temperature can be fairly well predicted and that the main difficulty is to accurately determine the effect of mean flow. A reasonable agreement has been obtained between one of the models from the literature30 and the effect of flow Mach number on the resistance.
The nonlinear effect of high excitation levels was not studied in any detail. A few tests were made with variation in excitation level and they showed that nonlinear effects could be seen when the level of excitation was higher than approximately 130 dB. The test equipment did not include any control mechanism to keep the excitation level constant for different frequencies. This meant that the level could vary significantly for different frequencies during a test on a specific liner configuration. It is recommended that this should be improved in future studies.
Potential Impact:
By its very nature this project will have a significant environmental impact. Introducing acoustic liners in the TEC structure will contribute to the long-term objective of reducing aircraft noise. It may also have a significant strategic impact in reinforcing the competitiveness of European engine manufacturers and equipment suppliers.
The hybrid liner may create new business opportunities for Creo Dynamics AB, the liner manufacturer and possibly also for the engine manufacturer. Possible exploitation of project results includes commercialization of the acoustic liner concept. This may include licensing of the technology and/or starting manufacture of the acoustic liner,
Furthermore exploitation has included publishing results in scientific journals and at conferences.
Urban Emborg
Creo Dynamics AB
Westmansgatan 37 A
582 16 Linkoping
Sweden
Phone: +46 722 220557
urban.emborg@creodynamics.com