Underwater Flow Noise from a Turbulent Boundary Layer over a Wavy Surface

2021 ◽  
pp. 115-127
Author(s):  
Jan Abshagen ◽  
Volkmar Nejedl
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Wavy Surface ◽  
Flow Noise

The effect of large-eddy breakup devices on flow noise

1989 ◽  
Vol 208 ◽  
pp. 193-223 ◽  
Author(s):  
A. P. Dowling
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Scaling Laws ◽  
Plane Surface ◽  
Pressure Fluctuations ◽  
Skin Friction Coefficient ◽  
Dipole Source ◽  
Flow Noise ◽  
Low Mach Number Limit ◽  
Large Eddy

The installation of large-eddy breakup devices (LEBUs) or ‘flow manipulators’ in a turbulent boundary layer over a rigid plane surface is known to lead to reductions in skin-friction coefficient, turbulence intensity and fluctuating Reynolds stress. We investigate the effect of such devices on the surface pressure spectrum and the far-field sound radiation. A model problem, in which a two-dimensional elliptical vortex is convected past a LEBU, is solved analytically in the low-Mach-number limit. The main noise source mechanisms are identified in this idealized problem and we go on to obtain scaling laws for the sound produced by a turbulent boundary-layer flow over a LEBU. The introduction of a LEBU reduces the strength of the Lighthill quadrupole source terms, but it produces an additional dipole source. However, the pressure fluctuations in this dipole field decay rapidly with distance from a LEBU, and we find that an array of LEBU's could have a beneficial effect on the flow noise for radian frequencies which are large in comparison with c/30Δ, where c is the sound speed and Δ denotes the boundary-layer thickness. At lower frequencies the LEBUs are predicted to increase the flow noise.

Oblique shock wave interaction with turbulent boundary layer over a wavy surface

2017 ◽  
Author(s):  
Saeedur Rahman ◽  
Md. Saddam Hossain Joy ◽  
A. B. M. Toufique Hasan ◽  
Y. Mitsutake ◽  
S. Matsuo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Turbulent Boundary Layer ◽  
Wave Interaction ◽  
Oblique Shock ◽  
Wavy Surface ◽  
Oblique Shock Wave ◽  
Shock Wave Interaction

Effects of Surface Waviness on the Interaction of Oblique Shock Wave With Turbulent Boundary Layer

2017 ◽  
Vol 140 (4) ◽  
Author(s):  
Md. Saddam Hossain Joy ◽  
Saeedur Rahman ◽  
A. B. M. Toufique Hasan
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Oblique Shock ◽  
Wavy Surface ◽  
Oblique Shock Wave ◽  
Surface Waviness

Present investigation deals with the interaction of an incident oblique shock wave on a turbulent boundary layer over a wavy surface. The oblique shock wave was generated by an 8 deg wedge in a freestream Mach number of 2.0. Three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) equations with k–ω shear stress transport (SST) turbulence model were used for numerical computation. The computed results are in good agreement with the experimental measurement and direct numerical simulation (DNS) data in case of the interaction of an oblique shock with plain flat plate. To identify the effect of surface waviness on shock wave/turbulent boundary layer interaction (SWBLI), a section of the flat plate was replaced by a wavy surface. Computations have been conducted for different magnitudes of wavy amplitude. Further, the wavelength of the wavy surface has been varied. Results showed that the presence of wavy surface induces supplementary shock and expansion waves in the flow field, which are referred as topographic waves. This supplementary system of waves interacts with the counterpart of intrinsic SWBLI in a complex manner. Flow structure, separation behavior, and aerodynamic characteristics are studied. It is revealed that the amplitude is dominant than the wavelength of waviness in case of SWBLI on a wavy surface.

scholarly journals Numerical Prediction of Wall Pressure Fluctuations in a Turbulent Boundary Layer on a Cylinder in Axial Flow

2019 ◽  
Vol 9 (1S4) ◽  
pp. 625-628
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Fluctuations ◽  
Axial Flow ◽  
Wall Pressure ◽  
Flow Noise ◽  
Eddy Simulation ◽  
Wall Pressure Fluctuations ◽  
Large Eddy ◽  
Long Cylinder

Flow noise originating in the turbulent boundary layer (TBL) often severely limits the performance of towed sonar cylinder and therefore it is necessary to predict this noise for the design of efficient towed cylinder. This paper presents large eddy simulation methodology to establish the TBL properties and wall pressure fluctuations on a 3 m long cylinder with length to diameter ratio of 315 in the operating speed of 11.4 m/s in air. The computed flow induced sound is compared with experimental measurement available in the literature successfully. The effectiveness of scaling the flow noise spectra with diameter and tow speed is discussed and non-dimensional wall pressure spectra presented with respect to non-dimensional frequency. The overall sound pressure levels are also compared with experimental data that show good accuracy achieved by the proposed numerical methodology.

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