scholarly journals The Hydrodynamic Noise Suppression of a Scaled Submarine Model by Leading-Edge Serrations

2019 ◽  
Vol 7 (3) ◽  
pp. 68 ◽  
Author(s):  
Yongwei Liu ◽  
Yalin Li ◽  
Dejiang Shang
Keyword(s):  
Noise Reduction ◽  
Experimental Test ◽  
Noise Suppression ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Horseshoe Vortex ◽  
Underwater Vehicles ◽  
Counter Rotation ◽  
Hydrodynamic Noise ◽  
High Reynolds

High hydrodynamic noise is a threat to the survival of underwater vehicles. We investigated a noise suppression mechanism by putting leading-edge serrations on the sail hull of a scaled SUBOFF model, through numerical calculation and an experimental test. We found that the cone shape of leading-edge serrations can decrease the intensity of the adverse pressure gradient and produce counter-rotation vortices, which destroy the formation of the horseshoe vortex and delay the tail vortex. To achieve the optimum hydrodynamic noise reduction, we summarized the parameters of leading-edge serrations. Then, two steel models were built, according to the simulation. We measured the hydrodynamic noise based on the reverberation method in a gravity water tunnel. The numerically calculated results were validated by the experimental test. The results show that leading-edge serrations with amplitudes of 0.025c and wavelengths of 0.05h can obtain hydrodynamic noise reduction of at least 6 dB, from 10 Hz to 2 kHz, where c is the chord length and h is the height of the sail hull. The results in our study suggest a new way to design underwater vehicles with low hydrodynamic noise at a high Reynolds number.

scholarly journals Suppression of the Hydrodynamic Noise Induced by the Horseshoe Vortex through Mechanical Vortex Generators

2019 ◽  
Vol 9 (4) ◽  
pp. 737 ◽  
Author(s):  
Yongwei Liu ◽  
Hongxu Jiang ◽  
Yalin Li ◽  
Dejiang Shang
Keyword(s):  
Noise Reduction ◽  
Noise Suppression ◽  
Flow Direction ◽  
Low Frequency ◽  
Sound Field ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Vortex Generators ◽  
Counter Rotation ◽  
Hydrodynamic Noise

The hydrodynamic noise from the horseshoe vortex can greatly destroy the acoustic stealth of underwater vehicles at low frequency. We investigated the flow-induced noise suppression mechanism by mechanical vortex generators (VGs) on a SUBOFF model. Based on the numerical simulation, we calculated the flow field and the sound field of the three shapes of mechanical VGs: triangular, semi-circular, and trapezoidal. The triangular VGs with an angle of 30° to the flow direction achieved a better noise reduction. The optimum noise suppression is 8.93 dB, when the distance from the triangular VGs to the sail hull’s leading edge is 0.1c, where c is the chord length. The noise reduction mechanism is such that the mechanical VGs can destroy the formation of the horseshoe vortex at the origin and produce counter-rotation vortices to weaken its intensity. We created two steel models according to the simulation, and the experimental measurement was carried out in a gravity water tunnel. The measured results showed that the formation of the horseshoe vortex could be effectively inhibited by the triangular VGs. The results in our study can provide a new method for hydrodynamic noise suppression by flow control.

Aeroacoustic Characteristics of Cavity and Effect Study of Mesh on Noise Suppression

2013 ◽  
Vol 421 ◽  
pp. 104-109
Author(s):  
Jing Sun ◽  
Guang Jun Yang ◽  
Jian Jun Liu
Keyword(s):  
Noise Reduction ◽  
Noise Suppression ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Cavity Flow ◽  
Noise Spectrum ◽  
Effect Study ◽  
Suppression Effect ◽  
Reduction Effect ◽  
Suppression Effects

To explore the noise suppression effect of mesh on cavity, the wind tunnel experiment is carried out based on the analysis of clean cavity flow characteristics. The meshes are arranged both in the cavity and at the leading edge of the cavity. Through the analysis of pressure distribution on the cavity bottom and the noise spectrum monitored at front and rear walls respectively, noise suppression effects of mesh programs relative to the clean cavity and changes in the flow field are studied, the results show that the mesh inside the cavity has a better noise reduction effect. The work in this paper provides an effective way for cavity noise reduction.

scholarly journals The suppression of hydrodynamic noise from underwater sonar domes by flow control

2019 ◽  
Vol 283 ◽  
pp. 08008
Author(s):  
Jie Pei ◽  
Chen Niu ◽  
Junchao Qu ◽  
Yongwei Liu ◽  
Dejiang Shang
Keyword(s):  
Boundary Layer ◽  
Leading Edge ◽  
Underwater Vehicles ◽  
Noise Sources ◽  
Outer Flow ◽  
Cavitation Phenomenon ◽  
Flow Fluctuation ◽  
Hydrodynamic Noise ◽  
High Level ◽  
Transition Areas

Hydrodynamic noise is one of the three major noise sources of underwater vehicles. The sonar dome is a device placed in front of the ship and the submarine to absorb the flow fluctuation and to reduce the hydrodynamic noise, so that the sonar inside the dome is not affected by the external fluid. However, with the increase of the velocity of ships and submarines, cavitation can usually form in the bulge of the sonar domes, which will bring high level of noise to the sonar. The internal self-noise of the sonar dome mainly comes from two areas: the leading-edge stagnation point and the transition zone of boundary layer. In the paper, we designed the leading-edge serrations and dimples in the leading-edge and transition areas of the sonar dome respectively to reduce the movement resistance and prevent the separation of the boundary layer. The research on leading-edge serrations and dimple technology is carried out by using theoretical analysis, numerical calculations. The results show that the leading-edge serrations and dimples can add energy from the outer flow into the boundary layer; the cavitation phenomenon can be delayed. The hydrodynamic noise has been suppressed by about 20dB.

Skin Friction Measurements of Transition in High Reynolds Number, Adverse Pressure Gradient Flow

2018 ◽  
Author(s):  
Brian M. Holley ◽  
Larry W. Hardin ◽  
Gregory Tillman ◽  
Ray-Sing Lin ◽  
Jongwook Joo
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Skin Friction ◽  
High Reynolds Number ◽  
Gradient Flow ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Data Set ◽  
High Reynolds

A combined experimental and analytical modeling effort has been carried out to measure the skin friction response of the boundary layer in high Reynolds number adverse pressure gradient flow. The experiment was conducted in the United Technologies Research Center (UTRC) Acoustic Research Tunnel, an ultra-low freestream turbulence facility capable of laminar boundary layer research. Boundary layer computational fluid dynamics and stability modeling were used to provide pre-test predictions, as well as to aid in interpretation of measured results. Measurements were carried out at chord Reynolds numbers 2–3 × 106, with the model set at multiple incidence angles to establish a range of relevant leading edge pressure gradients. The combination of pressure gradient and flight Reynolds number testing on a thin airfoil has produced a unique data set relevant to propulsion system turbomachinery.

Skin Friction Measurements of Transition in High Reynolds Number, Adverse Pressure Gradient Flow

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Brian M. Holley ◽  
Larry W. Hardin ◽  
Gregory Tillman ◽  
Ray-Sing Lin ◽  
Jongwook Joo
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Skin Friction ◽  
High Reynolds Number ◽  
Gradient Flow ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Data Set ◽  
High Reynolds

Abstract A combined experimental and analytical modeling effort has been carried out to measure the skin friction response of the boundary layer in high Reynolds number adverse pressure gradient flow. The experiment was conducted in the United Technologies Research Center (UTRC) Acoustic Research Tunnel, an ultra-low freestream turbulence facility capable of laminar boundary layer research. Boundary layer computational fluid dynamics and stability modeling were used to provide pre-test predictions, as well as to aid in interpretation of measured results. Measurements were carried out at chord Reynolds numbers 2–3 × 106, with the model set at multiple incidence angles to establish a range of relevant leading edge pressure gradients. The combination of pressure gradient and flight Reynolds number testing on a thin airfoil has produced a unique data set relevant to propulsion system turbomachinery.

scholarly journals Analysis of the unstable Tollmien–Schlichting mode on bodies with a rounded leading edge using the parabolized stability equation

2009 ◽  
Vol 623 ◽  
pp. 167-185
Author(s):  
M. R. TURNER ◽  
P. W. HAMMERTON
Keyword(s):  
Asymptotic Theory ◽  
Free Stream ◽  
Leading Edge ◽  
Adverse Pressure Gradient ◽  
Reynolds Numbers ◽  
Neutral Stability ◽  
S Wave ◽  
Stability Equation ◽  
Stability Point ◽  
Tollmien Schlichting

The interaction between free-stream disturbances and the boundary layer on a body with a rounded leading edge is considered in this paper. A method which incorporates calculations using the parabolized stability equation in the Orr–Sommerfeld region, along with an upstream boundary condition derived from asymptotic theory in the vicinity of the leading edge, is generalized to bodies with an inviscid slip velocity which tends to a constant far downstream. We present results for the position of the lower branch neutral stability point and the magnitude of the unstable Tollmien–Schlichting (T-S) mode at this point for both a parabolic body and the Rankine body. For the Rankine body, which has an adverse pressure gradient along its surface far from the nose, we find a double maximum in the T-S wave amplitude for sufficiently large Reynolds numbers.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Spanwise varying porosity for the enhancement of leading-edge noise reduction

2021 ◽  
Author(s):  
Lorna J. Ayton ◽  
Orestis Karapiperis ◽  
Manuj Awasthi ◽  
Danielle Moreau ◽  
Con J. Doolan
Keyword(s):  
Noise Reduction ◽  
Leading Edge

A Study on the Fan Tone Noise Reduction with Wavy Leading Edge OGV

2021 ◽  
Author(s):  
Hang Tong ◽  
Kangshen Xiang ◽  
Liangji Zhang ◽  
Lin Li ◽  
Weijie Chen ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Leading Edge

A Topological Study of the Genesis of a Horseshoe Vortex in the Symmetry Plane Due to an Adverse Pressure Gradient

2001 ◽  
Author(s):  
Martijn A. van den Berg ◽  
Michael M. J. Proot ◽  
Peter G. Bakker
Keyword(s):  
Pressure Gradient ◽  
Bifurcation Theory ◽  
Nonlinear Differential Equations ◽  
Nonlinear Dynamical System ◽  
Symmetry Plane ◽  
Adverse Pressure Gradient ◽  
Horseshoe Vortex ◽  
Nonlinear Dynamical ◽  
Separating Flow ◽  
Flow Through

Abstract The present paper describes the genesis of a horseshoe vortex in the symmetry plane in front of a juncture. In contrast to a previous topological investigation, the presence of the obstacle is no longer physically modelled. Instead, the pressure gradient, induced by the obstacle, has been used to represent its influence. Consequently, the results of this investigation can be applied to any symmetrical flow above a flat plate. The genesis of the vortical structure is analysed by using the theory of nonlinear differential equations and the bifurcation theory. In particular, the genesis of a horseshoe vortex can be described by the unfolding of the degenerate singularity resulting from a Jordan Normal Form with three vanishing eigenvalues and one linear term which is related to the adverse pressure gradient. The examination of this nonlinear dynamical system reveals that a horseshoe vortex emanates from a non-separating flow through two subsequent saddle-node bifurcations in different directions and the transition of a node into a focus located in the flow field.

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