Low-Wavenumber Wall Pressure Fluctuations Due to Boundary-Layer Transition PDF Download
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Languages : en
Pages : 0
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Boundary layer transition is an important contributor to sensor flow-induced self noise. The pressure fluctuations caused by this spatially bounded and intermittent, phenomenon encompass a very wide range of spatial wave numbers and temporal frequencies. Here, we analyze the wavevector-frequency spectrum of the wall pressure fluctuations due to subsonic boundary-layer transition as it occurs on a flat plate under zero pressure gradient conditions. Based on previous measurements of the statistic of the boundary-layer intermittence it is found that transition induces higher low-streamwise wave number wall pressure level than does a fully-developed turbulent boundary layer (TBL) that might superficially exist at the same location and at the same Reynolds number. The transition zone spanwise wavenunmber pressure components are virtually unchanged from the TBL ease. The results suggest that transition may be more effective than the TBL in forcing structural excitation at low Mach numbers and it may have a more intense radiated noise contribution on a per unit area basis. This may help explain increases in measured sensor self noise when the sensors are placed near the transition zone.
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Languages : en
Pages : 0
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Book Description
Boundary layer transition is an important contributor to sensor flow-induced self noise. The pressure fluctuations caused by this spatially bounded and intermittent, phenomenon encompass a very wide range of spatial wave numbers and temporal frequencies. Here, we analyze the wavevector-frequency spectrum of the wall pressure fluctuations due to subsonic boundary-layer transition as it occurs on a flat plate under zero pressure gradient conditions. Based on previous measurements of the statistic of the boundary-layer intermittence it is found that transition induces higher low-streamwise wave number wall pressure level than does a fully-developed turbulent boundary layer (TBL) that might superficially exist at the same location and at the same Reynolds number. The transition zone spanwise wavenunmber pressure components are virtually unchanged from the TBL ease. The results suggest that transition may be more effective than the TBL in forcing structural excitation at low Mach numbers and it may have a more intense radiated noise contribution on a per unit area basis. This may help explain increases in measured sensor self noise when the sensors are placed near the transition zone.
Author: Mark Jay Moeller
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ISBN:
Category :
Languages : en
Pages : 85
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Author: Mark Jay Moeller
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Languages : en
Pages : 87
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The low wavenumber components of the turbulent boundary layer wavenumber frequency spectrum of wall pressure fluctuations were measured with two flush-mounted rectangular plates having approximately clamped boundary conditions. The plates were designed to provide low wavenumber measurements at higher frequencies and wavenumbers than previous plate experiments in order to provide data comparable with measurements made by Farabee and Geib (7) with an array of flush-mounted microphones. The low wavenumber measurements were made in the M.I.T. low noise low turbulence subsonic wind tunnel under zero and adverse pressure gradient conditions. When nondimensionalized on outer boundary layer variables the adverse pressure gradient data do not exhibit increased levels from those of the zero pressure gradient data. The zero pressure gradient data are in good agreement with the levels reported by Farabeen and Geib (7) for the same nondimensional frequency and wavenumber range. (Author).
Author: D. R. Blackman
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Category :
Languages : en
Pages :
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Author: M. A. Josserand
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Category :
Languages : en
Pages : 184
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The laminar to turbulent transition zone continues to be of interest from the flow noise point of view. A theoretical model was developed to predict the radiated component (wavenumber less than or equal to the sonic wavenumber) of the pressure fluctuations that occur in this zone. It is also recognized that wavenumbers greater than the sonic wavenumber are also important because pressure fluctuations at these higher wavenumbers may couple with structural vibrations. Keywords: flow noise; turbulence, pressure fluctuations; boundary layer; transition; theoretical; experimental; spectrum.
Author: Eric Manoha
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Category :
Languages : en
Pages :
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Author: W. W. Willmarth, C. E. Wooldridge
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Category :
Languages : en
Pages : 60
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Category :
Languages : en
Pages : 18
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Author: Thomas S. Mautner
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Languages : en
Pages : 9
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Experiments have been conducted to measure the wall pressure fluctuations associated with artificially generated turbulent spots in a laminar boundary layer. The results show that both the rms wall pressure and the wall pressure spectra of turbulent spots are influenced by the local mean flow pressure gradient. The zero and favorable pressure gradient wall pressure data are in agreement with turbulent boundary layer results. However, the current spot data shows that, in the presence of an adverse pressure gradient, the spot's rms wall pressure is approximately 1.5-2.5 times larger than that found for the zero and favorable pressure gradient cases. These results are in general agreement with the adverse pressure gradient data of Huang and Hannan (1975). Additionally, the nearly constant magnitude of the spot's adverse pressure gradient wall pressure spectrum indicates a nearly even distributions of energy with frequency. Keywords: Turbulent boundary layer, Laminar boundary layer, Wall pressure fluctuations.
Author: Charles Joseph Gedney
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Category : Boundary layer noise
Languages : en
Pages : 114
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Detailed measurements of wall pressure fluctuations have been made in the intermittent region of a flat plate boundary layer. Digital sampling and processing were used. The properties of these pressure fluctuations were found to be similar to the previous measurements made in the fully turbulent region. The measurements were repeated with a single two dimensional surface roughness on the plate. The only changes in the results were a decrease in the transition Reynolds number from 2.0 to 1.2 million per foot and an increase in the decay rate of the longitudinal cross-spectral density magnitude by a factor of about 1.5. Emmons' analytical model of the burst rate in the transition region was found to be inaccurate. His model treats the sources of the turbulent spots as independent random events with prescribed probability density functions. Both a delta function and a constant were used as the source density functions and in each case the burst rate was about two times higher than the present measurements. (Author).
