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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 03 Nov 2024 23:34:41 GMT2024-11-03T23:34:41ZModeling aeroacoustic excitations by subsonic wave packets in the Kirchhoff formalism
http://hdl.handle.net/10985/7454
Modeling aeroacoustic excitations by subsonic wave packets in the Kirchhoff formalism
SERRE, Romain; MARGNAT, Florent
The present work aims at linking the shape of a wave packet to its acoustic e ciency through numerical integration of the homogeneous Helmholtz equation in the Kirchho formalism. We shall consider the case of a bidimensional, rectangular domain where one side is a ected by a spatially evolving wave packet as a boundary condition with subsonic convection velocity. In the rst place, the numerical tool is validated by comparison with analytical developments available in literature. Then, an extension to more advanced forms of wave packet is approached. The appearance of a criterion for acoustic e ciency is discussed, as well as the need for a proper de nition regarding the acoustic energy of a wave packet and its radiated energy output.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/74542013-01-01T00:00:00ZSERRE, RomainMARGNAT, FlorentThe present work aims at linking the shape of a wave packet to its acoustic e ciency through numerical integration of the homogeneous Helmholtz equation in the Kirchho formalism. We shall consider the case of a bidimensional, rectangular domain where one side is a ected by a spatially evolving wave packet as a boundary condition with subsonic convection velocity. In the rst place, the numerical tool is validated by comparison with analytical developments available in literature. Then, an extension to more advanced forms of wave packet is approached. The appearance of a criterion for acoustic e ciency is discussed, as well as the need for a proper de nition regarding the acoustic energy of a wave packet and its radiated energy output.On compressibility assumptions in aeroacoustic integrals: a numerical study with subsonic mixing layers
http://hdl.handle.net/10985/8641
On compressibility assumptions in aeroacoustic integrals: a numerical study with subsonic mixing layers
MARGNAT, Florent; GLOERFELT, Xavier
Two assumptions commonly made in predictions based on Lighthillâ€™s formalism are investigated: a constant density in the quadrupole expression, and the evaluation of the source quantity from incompressible simulations. Numerical predictions of the acoustic field are conducted in the case of a subsonic spatially evolving two-dimensional mixing layer at Re = 400. Published results of the direct noise computation (DNC) of the flow are use as reference and input for hybrid approaches before the assumptions on density are progressively introduced. Divergence free velocity fields are obtained from an incompressible simulation of the same flow case, exhibiting the same hydrodynamic field as the DNC. Fair comparisons of the hybrid predictions with the reference acoustic field valid both assumptions in the source region for the tested values of the Mach number. However, in the observer region, the inclusion of flow effects in the Lighthill source term is not preserved, which is illustrated through a comparison with the Kirchhoff wave-extrapolation formalism, and with the use of a convected Green function in the integration process.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/10985/86412014-01-01T00:00:00ZMARGNAT, FlorentGLOERFELT, XavierTwo assumptions commonly made in predictions based on Lighthillâ€™s formalism are investigated: a constant density in the quadrupole expression, and the evaluation of the source quantity from incompressible simulations. Numerical predictions of the acoustic field are conducted in the case of a subsonic spatially evolving two-dimensional mixing layer at Re = 400. Published results of the direct noise computation (DNC) of the flow are use as reference and input for hybrid approaches before the assumptions on density are progressively introduced. Divergence free velocity fields are obtained from an incompressible simulation of the same flow case, exhibiting the same hydrodynamic field as the DNC. Fair comparisons of the hybrid predictions with the reference acoustic field valid both assumptions in the source region for the tested values of the Mach number. However, in the observer region, the inclusion of flow effects in the Lighthill source term is not preserved, which is illustrated through a comparison with the Kirchhoff wave-extrapolation formalism, and with the use of a convected Green function in the integration process.High Accuracy Volume Flow Rate Measurement Using Vortex Counting
http://hdl.handle.net/10985/8577
High Accuracy Volume Flow Rate Measurement Using Vortex Counting
ZAARAOUI, Abdelkader; MARGNAT, Florent; RAVELET, Florent; KHELLADI, Sofiane
A prototype device for measuring the volumetric flow-rate by counting vortices has been designed and realized. It consists of a square-section pipe in which are placed a two-dimensional bluff body and a strain gauge force sensor. These two elements are separated from each other, unlike the majority of vortex apparatus currently available. The principle is based on the generation of a separated wake behind the bluff body. The volumetric flow-rate measurement is done by counting vortices using a flat plate placed in the wake and attached to the beam sensor. By optimizing the geometrical arrangement, the search for a significant signal has shown that it was possible to get a quasi-periodic signal, within a good range of flow rates so that its performances are well deduced. The repeatability of the value of the volume of fluid passed for every vortex shed is tested for a given flow and then the accuracy of the measuring device is determined. This quantity is the constant of the device and is called the digital volume (V_p). It has the dimension of a volume and varies with the confinement of the flow and with the Reynolds number. Therefore, a dimensionless quantity is introduced, the reduced digital volume (V_r) that takes into account the average speed in the contracted section downstream of the bluff body. The reduced digital volume is found to be independent of the confinement in a significant range of Reynolds numbers, which gives the device a good accuracy.
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/85772013-01-01T00:00:00ZZAARAOUI, AbdelkaderMARGNAT, FlorentRAVELET, FlorentKHELLADI, SofianeA prototype device for measuring the volumetric flow-rate by counting vortices has been designed and realized. It consists of a square-section pipe in which are placed a two-dimensional bluff body and a strain gauge force sensor. These two elements are separated from each other, unlike the majority of vortex apparatus currently available. The principle is based on the generation of a separated wake behind the bluff body. The volumetric flow-rate measurement is done by counting vortices using a flat plate placed in the wake and attached to the beam sensor. By optimizing the geometrical arrangement, the search for a significant signal has shown that it was possible to get a quasi-periodic signal, within a good range of flow rates so that its performances are well deduced. The repeatability of the value of the volume of fluid passed for every vortex shed is tested for a given flow and then the accuracy of the measuring device is determined. This quantity is the constant of the device and is called the digital volume (V_p). It has the dimension of a volume and varies with the confinement of the flow and with the Reynolds number. Therefore, a dimensionless quantity is introduced, the reduced digital volume (V_r) that takes into account the average speed in the contracted section downstream of the bluff body. The reduced digital volume is found to be independent of the confinement in a significant range of Reynolds numbers, which gives the device a good accuracy.