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| 2. |
- Knutsson, Magnus, et al.
(författare)
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A study on acoustical time-domain two-ports based on digital filters with application to automotive air intake systems
- 2011
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Ingår i: SAE technical paper series. - : SAE International. - 0148-7191. ; 4:2, s. 970-982
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of pressure pulsations in ducts is an active research field within the automotive industry. The fluid dynamics and the wave-transmission properties of internal combustion (IC) engine intake and exhaust systems contribute to the energy efficiency of the engines and are hence important for the final amount of CO2 that is emitted from the vehicles. Sound waves, originating from the pressure pulses caused by the in- and outflow at the engine valves, are transmitted through the intake and exhaust system and are an important cause of noise pollution from road traffic at low speeds. Reliable prediction methods are of major importance to enable effective optimization of gas exchange systems. The use of nonlinear one-dimensional (1D) gas dynamics simulation software packages is widespread within the automotive industry. These time-domain codes are mainly used to predict engine performance parameters such as output torque and power but can also give estimates of radiated orifice noise. However, components with large cross-dimensions, fluid-structural interaction, frequency-dependent damping and boundary conditions are difficult to describe analytically in 1D in the time domain. Since a frequency-domain description in the form of a two-port is normally straightforward to obtain analytically, numerically or experimentally it is of interest to introduce these in time-domain calculations as black box models. This paper suggests the use of Finite Impulse Response (FIR) filters as a method to achieve this improvement. An initial study is presented where tabulated frequency-domain two-port data representing an air cleaner unit on the impedance form is inversely transformed to the time domain and used as FIR filters in nonlinear time-domain 1D calculations with good accuracy. Favourable attenuation, achieved from the filter paper itself, is demonstrated experimentally as well as by the calculations.
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| 3. |
- Meng, Yang, et al.
(författare)
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Semi-empirical impedance model of perforated plate under grazing flow
- 2019
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Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : American Institute of Aeronautics and Astronautics Inc, AIAA.
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Konferensbidrag (refereegranskat)abstract
- A semi-empirical impedance formula of a circular orifice under grazing flow is derived, based on a linearized potential flow model. The effect of boundary layer is considered by introducing the convection speed of vorticity which is assumed to be a function of the dimensionless boundary layer thickness. Asymptotic expression of the impedance at low Strouhal number is acquired by the method of perturbation, while the impedance at large Strouhal number can be well approximated by that without grazing flow. The model predictions achieve reasonable agreement with the data available in a previous experimental investigation.
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| 4. |
- Netto Spillere, Andre Mateus, et al.
(författare)
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Optimum Impedance in the Presence of an Inviscid Sheared Flow
- 2019
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Ingår i: AIAA Journal. - : AMER INST AERONAUTICS ASTRONAUTICS. - 0001-1452 .- 1533-385X. ; 57:3, s. 1044-1054
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, much effort has been devoted to find the "optimum impedance" (i.e., the impedance that results in the maximum modal decay rate in flow duct acoustics for a given frequency, Mach number, and azimuthal mode order). Although such analysis can be carried out by means of numerical simulations, analytical expressions can also be derived to predict the optimum impedance. Previous works have been concerned with the optimum impedance of higher-order modes in rectangular ducts with uniform flow. In this work, the analysis is expanded to circular ducts for both uniform and sheared inviscid flows. Focus is given to typical operating conditions found in turbofan engine intakes and vehicle exhaust systems. It is shown that, in certain conditions, the optimum impedance is affected even by the presence of a small boundary-layer thickness. It is also noted that, for low Helmholtz numbers, the optimum impedance may have a negative resistance.
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| 5. |
- Qiu, X., et al.
(författare)
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Mode merging design method for non-locally reacting liner with porous bulk materials
- 2019
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Ingår i: 25th AIAA/CEAS Aeroacoustics Conference, 2019. - Reston, Virginia : [publishername] American Institute of Aeronautics and Astronautics Inc, AIAA. - 9781624105883
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Konferensbidrag (refereegranskat)abstract
- The Mode Merging Design Method (MMDM), a theoretical design method further developed based on the Cremer concept, for non-locally reacting liners with porous materials is first proposed and established. The acoustic properties of such non-locally reacting liners are determined by the combined action of porous materials in the chamber and perforated plate adjacent to porous backing and grazing flow, which are described by the Delany & Bazley (DB)-like models and the combined Guess & Kirby-Cummings (Guess-KC) impedance model in this study, respectively. According to the structure characteristics of bulk liner, the porous chamber depth Lc and flow resistivity σ, are selected to be optimized to maximize the sound attenuation at a target frequency when a single circumferential mode is incident. In the spirit of the mode merging theory, the eigen equation and the branch point equation for this physical problem are derived, from which the merging double eigenvalue/mode can be solved, in turn, the optimum chamber depth Lc and flow resistivity σ can be simultaneously determined, which can produce theoretically maximum sound attenuation. Then, a Finite Element (FE) sound propagation model is established to validate the liner design of theoretical optimization by MMDM. The accuracies of the eigen-analysis method, the DB model, the Guess-KC model and the FE model are validated through several benchmark cases. Further, the MMDM is applied in four design cases of bulk liners with finite length, and the results indicate that the MMDM can accurately aim at a given condition of grazing flow Ma, circumferential mode order m and target frequency f to effectively optimize the structural parameters for actual bulk liners. Finally, an optimality analysis performed through two concrete cases demonstrates that the MMDM can avoid locally optimal solution and successfully find optimal structures for an infinite non-locally reacting liner, thus producing the maximum sound attenuation at target frequency.
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| 6. |
- Qiu, Xianghai, et al.
(författare)
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Mode-Merging Design Method for Nonlocally Reacting Liners with Porous Materials
- 2020
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Ingår i: AIAA Journal. - : AMER INST AERONAUTICS ASTRONAUTICS. - 0001-1452 .- 1533-385X. ; 58:6, s. 2533-2545
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Tidskriftsartikel (refereegranskat)abstract
- A mode-merging design method (MMDM) for bulk liners with porous materials is proposed to maximize transmission losses in flow ducts. The eigenequation and its partial derivative equation governing the coupled acoustic fields in the duct and backchamber are derived, from which the merging double eigenvalue is obtained at a target frequency for a single incident circumferential mode. The crucial liner parameters (namely. the chamber depth and the flow resistivity of the porous material) can be optimized simultaneously. A finite element propagation model is employed to evaluate the MMDM-based design for a finite-length liner, demonstrating the effectiveness of the method for selected typical design cases. It is found that mode merging can be realized for a nonlocally reacting liner, with or without a perforated plate, mainly for protecting the porous material inside its chamber. The MMDM, under the assumption of an infinite-length liner, can give an almost globally optimal design for a finite-length liner when the length exceeds five times the duct diameter. It is expected that the proposed MMDM can be useful in the preliminary designs for actual bulk liners due to its rapidness and accuracy.
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| 7. |
- Qiu, Xianghai, et al.
(författare)
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Optimality analysis of bulk-reacting liners based on mode-merging design method
- 2020
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Ingår i: Journal of Sound and Vibration. - : Academic Press. - 0022-460X .- 1095-8568. ; 485
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Tidskriftsartikel (refereegranskat)abstract
- The demand for noise control within ducts advances the development of the liner design. Recently, the mode merging thought, originating from the Cremer concept for the optimal impedance of locally reacting liners, was extended to the bulk liner design by the authors and thus the Mode-merging Design Method (MMDM) was proposed. The current research is a continuation of the previous work to systematically investigate the acoustic optimality of bulk liners with porous material protected by a large-porosity faceplate based on the MMDM. The optimal transmission loss (TL) is focused on, along with the optimal chamber depth and flow resistivity of the porous material, in the parameter spaces spanning the Helmholtz number, the circumferential mode order and the Mach number. Besides, the effect of different faceplates on the optimality is investigated briefly. Some interesting conclusions are drawn and expected to be beneficial to the bulk liner design.
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| 8. |
- Spillere, A. M. N., et al.
(författare)
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Optimum impedance in the presence of an inviscid sheared flow
- 2018
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Ingår i: 2018 AIAA/CEAS Aeroacoustics Conference. - Reston, Virginia : American Institute of Aeronautics and Astronautics. - 9781624105609
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Konferensbidrag (refereegranskat)abstract
- In recent years, much effort has been devoted to find the “optimum impedance” i.e. the impedance that results in the maximum modal decay rate in flow duct acoustics. Although such analysis can be carried out by means of numerical simulations, analytical expressions can also be derived in order to predict the optimum impedance. Previous works have been concerned over the optimum impedance of higher order modes in rectangular ducts with uniform flow. In this work, the analysis is expanded to circular and rectangular ducts for both uniform and sheared inviscid flows. Focus is given on a typical aero-engine intake and flight conditions. It is shown that, in certain conditions, the optimum impedance is affected even by the presence of a small boundary layer thickness. It is also noted that for low Helmholtz numbers the optimum impedance may have a negative resistance.
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| 9. |
- Tiikoja, H., et al.
(författare)
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Investigations of automotive turbocharger acoustics
- 2011
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Ingår i: SAE technical paper series. - : SAE International. - 0148-7191. ; 4:2, s. 2531-2542
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Tidskriftsartikel (refereegranskat)abstract
- In this paper an overview of recent experimental studies performed at KTH on the sound transmission and sound generation in turbochargers is presented. The compressor and turbine of the turbochargers are treated as acoustic active 2-ports and characterized using the unique experimental test facility established at KTH. The 2-port model is limited to the plane wave range so for higher frequencies the propagating acoustic power is estimated using an average based on pressure cross-spectra. A number of automotive turbochargers have been studied for a variety of operating conditions systematically selected from the compressor and turbine charts. The paper discusses the experimental procedures including special techniques implemented to improve the quality of the data. Results from a number of experiments on various modern automotive turbochargers including a unit with variable turbine geometry (VTG) are presented. Copyright
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| 10. |
- 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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