| 1. |
- Rämmal, Hans, et al.
(författare)
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Experimental facility for the complete determination of sound transmission in turbochargers
- 2010
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Ingår i: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. ; , s. SAE Technical Paper 2010-01-1424-
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Konferensbidrag (refereegranskat)abstract
- In this paper a unique experimental facility designed for a complete determination of the sound transmission in turbochargers is introduced. The facility can be used to characterize the passive acoustic effect for turbocharger compressors and turbines working in realistic operating conditions by extracting the acoustic two-port data. The acoustic pressure transmission loss results for a passenger car turbocharger compressor and turbine measured in up- and downstream directions regarding the mean flow are presented. The data are obtained for various operating points of the turbocharger and the influence of operating conditions on the sound transmission is discussed.
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| 2. |
- Rämmal, Hans, 1976-
(författare)
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Methods for Modelling and Characterization of In-Duct Sources
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Methods to characterize acoustic sources in flow ducts have been investigated. In the first part of this thesis a measurement procedure to characterize an air terminal device using an acoustic one-port source model based on the two microphone technique has been tested and validated. In order to provide a prediction of flow noise generation at different operating points for the device a scaling law was derived. Successful validation experiments were performed. In the second part a new method based on the multi-load technique was developed and used to characterise the source data of various piston-engines with non-linear behaviour. The source characterisation results were compared to results obtained using the well-known linear two-load technique. It was shown that the new non-linear multi-load technique gave improved results when the source was slightly non-linear. In the third part an improved method to characterize noise sources in high temperature flowducts has been suggested. As a test environment for the standard two microphone technique a helium-air mixture has been used to simulate acoustical conditions similar to hot exhaust gas systems. In order to test the method the passive acoustic properties of automotive diesel engine and an unflanged flow duct termination have been experimentally determined. The experimental results for duct termination have been compared to theoretical predictions. Keywords: Acoustic source, one–port, source model, duct termination, source impedance, reflection coefficient, source strength, IC-engine, flow duct, multi-load method, non-linear
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| 3. |
- Rämmal, Hans, et al.
(författare)
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Modified multi-load method for non-linear source characterization
- 2004
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Ingår i: ICSV11-St Petersburg.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Linear frequency domain prediction codes are used for calculation of low frequency sound transmission in and sound radiation from IC-engine exhaust systems. To calculate insertion loss of mufflers or the level of radiated sound information about the engine as an acoustic source is needed. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. The exhaust pulsations of an IC-engine are of high level, which means that the engine is not a perfectly linear and time invariant source. It is therefore of interest to develop source models and experimental techniques that try to take this non-linearity into account. In this paper a modified version of the two-load method to improve the characterization of the non-linear acoustic 1-port sources has been developed and tested. Simulation results from various source configurations of a simplified IC-engine model were used to validate the method. The influence of parameters controlling the linearity of the system was investigated. The time-variance of the source model was varied and the source characterization quality using the two-load method and the modified two-load method was evaluated.
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| 4. |
- Rämmal, Hans, et al.
(författare)
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Modified multi-load method for nonlinear source characterisation
- 2007
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 299:4-5, s. 1094-1113
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Tidskriftsartikel (refereegranskat)abstract
- Linear frequency domain prediction codes are useful for calculation of low-frequency sound transmission in duct and pipe systems. To calculate insertion loss of mufflers or the level of radiated sound information about the acoustic source is needed. The source model used in the low-frequency plane wave range is the linear time invariant one-port model. The acoustic source data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. The exhaust pulsations of for example an IC-engine are of high level, and the engine is not a perfectly linear and time invariant source. It is therefore of interest to develop source models and experimental techniques that try to take this nonlinearity into account. In this paper a modified version of the two-load method to improve the characterisation of nonlinear acoustic one-port sources has been developed and tested. Simulation results as well as experimental data from various source configurations for a modified compressor and experimental data from 6-cylinder turbocharged truck diesel engine were used to validate the method. The influence of parameters controlling the linearity of the system was investigated. The time-variance of the source model was varied and the accuracy of source characterisation results using the two-load method and the modified two-load method was evaluated.
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| 5. |
- Rämmal, Hans, 1976-
(författare)
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Studies of flow duct acoustics with applications to turbocharged engines
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A number of experimental and theoretical studies, performed in the field of technical flow duct acoustics are presented in this thesis. The acoustical methods treated are implemented on turbocharged IC-engines and engine gas exchange system components. A new method based on the well-known two-load technique has been developed. The method was applied to characterise the source data of various piston-engines with non-linear behaviour including a 6 cylinder turbo-charged truck diesel engine. The source characterisation results were compared to the results obtained using the linear two-load technique. It was demonstrated that the new non-linear multi-load technique gives improved results when the source is slightly non-linear. The use of active one-port models has been tested to characterize an air terminal device (ATD) as a source of flow generated noise. In order to predict the noise generation at different operating points of the device a scaling law was derived and verified. In the experimentally derived scaling law a flow speed dependence of 3 was found for the narrow band spectra, corresponding to a dipole-like behavior of the source in the plane wave range. The proposed technique was validated successfully and the results indicated a good prediction of in-duct sound generation by the air terminal device. Sound reflection from hot flow duct openings has been investigated experimentally. The reflection coefficient was measured for flow temperatures up to 500 ºC and jet velocities up to 108m/s. The results have been compared with famous Munt’s theory. It was concluded that at low Mach number and Helmholz number cases the results agree well with the Munt’s model. This was the first experimental validation of the theory for hot flow conditions. Experimental procedures to determine the sound transmission through automotive turbo-charger compressors were developed and described in detail. An overview of a unique turbocharger testing facility established at KTH CICERO in Stockholm is given. The facility can be used to measure acoustic two-port data for turbo-compressors. Results from measurements on a passenger car turbo-compressor are presented and the influence of operating conditions on the sound transmission is discussed. Current wave action models developed in CMT for computation of the gas exchange processes in I.C. engines have been implemented to determine the acoustic wave transmission through the turbo- compressor. The models are validated with the experimental data and the results are presented for different operating conditions of a Volvo passenger car turbo-compressor.
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| 6. |
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| 7. |
- Tiikoja, Heiki, et al.
(författare)
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Sound transmission in automotive turbochargers
- 2011
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Ingår i: SAE technical paper series. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191.
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Tidskriftsartikel (refereegranskat)abstract
- Turbochargers are common parts of a modern automotive engine. This paper presents an overview of the recent studies performed in the competence center for gas exchange studies at KTH on the sound transmission in turbochargers. The compressor and turbine of the turbochargers are treated as acoustic 2-ports and the scattering matrix for these devices are determined. A unique experimental facility established in the competence center for gas exchange research at KTH has been utilized to study the turbochargers at a variety of operating conditions systematically selected from compressor and turbine charts. A description of the experimental procedures to determine the acoustic 2-port data including techniques implemented to improve the quality of the results is presented. Results from a number of experiments on various modern automotive turbochargers including a unit with variable turbine geometry (VTG) are included. By plotting the up- and downstream transmission loss data against a dimensionless (He-number) frequency scale general characteristics for the sound transmission of turbochargers is found.
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| 8. |
- Tiikoja, Heiki, et al.
(författare)
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Test-rig for complete acoustic characterization of turbochargers
- 2010
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Ingår i: 16th AIAA/CEAS Aeroacoustics Conference (31st AIAA Aeroacoustics Conference). - 9781600867446
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Konferensbidrag (refereegranskat)abstract
- The aim of this paper is to present description of a novel experimental facility designed and set up in KTH Cicero Centre for complete acoustic characterization of turbochargers. The facility is created to determine both the passive (scattering) and active (source) acoustic properties of automotive turbochargers. In this paper the currently most accurate experimental technique to determine the passive acoustic effect of the turbocharger is described. A detailed overview of the test-rig is given together with the mathematical procedures followed to obtain the acoustic 2-port data for turbochargers. The results, including transmission loss and scattering matrix elements, are presented for the compressor and turbine side of a typical automotive turbocharger working in a number of different operating conditions. The influence of the operating conditions on the passive acoustic effect of the device is studied and summarized.
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| 9. |
- Wallin, Hans Petter, et al.
(författare)
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Sound and vibration
- 2010. - 2., rev. uppl.
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Bok (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Albertson, F., et al.
(författare)
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Comparison of different methods to couple nonlinear source descriptions in the time domain to linear system descriptions in the frequency domain - Application to a simple valveless one-cylinder cold engine
- 2006
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Ingår i: Journal of Sound and Vibration. - : Elsevier BV. - 0022-460X .- 1095-8568. ; 291:05-mar, s. 963-985
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Tidskriftsartikel (refereegranskat)abstract
- In duct acoustics the fundamental sound generating mechanisms must often be described by nonlinear time domain models. A linear frequency domain model is in many cases sufficient for describing the sound propagation in the connected duct system. This applies both for fluid machines such as IC-engines and compressors and for musical wind instruments. Methods for coupling a nonlinear source description to a linear system description have been proposed by several authors. In this paper some of those methods are compared concerning accuracy, calculation time and the possibility to perform parametric studies. The model problem used is a simple piston-restriction system connected to a linear system with varying complexity. The piston and restriction are considered as the source part and are modelled nonlinearly.
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