Numerical research on the influence of sail leading edge shapes on the hydrodynamic noise of a submarine

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.

Download Full-text

Analysis of Severe Erosion in Industrial Centrifugal Slurry Pumps

Volume 2, Fora: Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation; Microfluidics; Multiphase Flows: Work in Progress ◽

10.1115/fedsm2013-16435 ◽

2013 ◽

Cited By ~ 1

Author(s):

Jafar Madadnia ◽

Mostafa Amjad ◽

Jeffry Kusnan

Keyword(s):

Leading Edge ◽

Centrifugal Pumps ◽

Wear Model ◽

Experimental Modelling ◽

Flow Acceleration ◽

Field Samples ◽

Severe Erosion ◽

Slurry Flows ◽

In Series ◽

Numerical Research

Centrifugal pumps designed for homogenous slurries experience inefficiency, off-design operations, shorter service-life expectancy, and rapid geometry change due to localized and uneven erosion. Experimental and numerical research to design erosion-free pumps has been inconclusive due to complexity of heterogeneous, multiphase slurry flows and mechanism of the localized material losses. This paper reports on erosion-effects of slurry flows on a number of industrial centrifugal pumps selected from an active copper mine field. The field samples include three metallic pumps operating in a serial-arrangement, and a number of worn pump-components with fully rubber-lined or metallic wetted-surfaces. Physical samples were also collected and photographed under an electronic microscope. The analysis of the photographs shows directional groves, ripples-formations, pitting, cavities, spots, and abrasive-embedding on the pump surfaces. The effected regions included a) hub or tip of the vane leading edge of impellers, b) internal and external surfaces of shroud and downstream of expellers, c) front-liners/throat bush all at the proximity of the inlet throat/tube, and d) Volute surface close to the discharge throat/tube on the spiral tail. Analysis of eroded regions suggests a combination of mechanisms some similar with those found with a sustained flow acceleration and momentum change towards a surface. A wear model is therefore recommended for the severe erosion in pumps which resembles erosion by cavitation. To further understand and verify the finding and to be able to predict and to avoid accelerated-erosion, an experimental modelling and a numerical modelling of slurry flows in two identical-centrifugal-pumps are conducted in series and preliminary results are presented. The project is in progress.

Download Full-text

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

Journal of Marine Science and Engineering ◽

10.3390/jmse7030068 ◽

2019 ◽

Vol 7 (3) ◽

pp. 68 ◽

Cited By ~ 1

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.

Download Full-text

Optimizing Effect of Wavy Leading Edge (WLE) in Rectangular Wing and Taper Wing

Journal of Mechanical Engineering, Science, and Innovation ◽

10.31284/j.jmesi.2021.v1i2.2296 ◽

2021 ◽

Vol 1 (2) ◽

pp. 56-68

Author(s):

Iis Rohmawati ◽

Hiroshi Arai ◽

Hidemi Mutsuda ◽

Takuji Nakashima ◽

Rizal Mahmud

Keyword(s):

Reynolds Number ◽

Aspect Ratio ◽

Lift Coefficient ◽

Leading Edge ◽

Wing Shape ◽

Aspect Ratios ◽

Impressive Result ◽

Rectangular Form ◽

Numerical Research ◽

Wing Aspect Ratio

Experimental and numerical research have been performed to investigate the Wavy Leading Edge (WLE) effect on the rectangular wing. The WLE is inspired by humpback whale flipper morphology which is blunt and rounded in certain form pattern. This flipper shape plays an important role for its behaviour specially capturing their prey. This advantage could be applied to other systems such as fin stabilizers or wind turbines. Steady cases in various aspect ratios were conducted to find out the optimum effect of WLE with baseline NACA 0018 profile at Reynolds number 1.4 x 105. The chord length of the wing (c) was 125 mm. The WLE shape defined as wavelength (W) 8% of c and amplitude (d) is 5% of c. The aspect ratio (AR) variations were 1.6; 3.9; 5.1; 7.9 and 9.6. A simple rectangular form of the wing was selected to analysis the WLE effect on the various ARs. The taper wing shape is applied to find out the WLE effect at the AR 7.9. three types of taper ratio (TR) are 0.1; 0.3 and 0.5. The results show that the WLE on the taper wing has better advantage to control the stall in steady case. Another impressive result was the WLE wing with AR 7.9 and TR 0.3 has the best lift coefficient and pressure distribution.Keywords: stall, wavy leading edge, steady case, rectangle wing, taper wing, aspect ratio.

Download Full-text

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

Applied Sciences ◽

10.3390/app9040737 ◽

2019 ◽

Vol 9 (4) ◽

pp. 737 ◽

Cited By ~ 1

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.

Download Full-text

Numerical Research of Pump-as-Turbine Performance with Synergy Analysis

Processes ◽

10.3390/pr9061031 ◽

2021 ◽

Vol 9 (6) ◽

pp. 1031

Author(s):

Zheng Cao ◽

Jianqiang Deng ◽

Linkun Zhao ◽

Lin Lu

Keyword(s):

Flow Rate ◽

Three Dimensional ◽

Flow Characteristics ◽

Leading Edge ◽

Operating Conditions ◽

Field Analysis ◽

Sensitivity Index ◽

Computational Fluid Dynamics Cfd ◽

Numerical Research ◽

Hydraulic Devices

The wide use of pumps and turbines has significant value in energy conservation and utilization. In this work, a three-dimensional Computational Fluid Dynamics (CFD) model and a one-dimensional theoretical model of a Pump as Turbine (PAT) were established. On this basis, the correlation between pressure and velocity was quantitatively investigated by a proposed sensitivity index (SPV). A synergy field analysis was then applied to evaluate the flow characteristics of a pump and PAT, providing a perspective from the mechanism of the energy transfer enhancement for hydraulic devices. Moreover, the hydraulic and synergy performances of PAT were studied under various operating conditions. The results show that the minimum SPV is obtained in the impeller. With increasing flow rate, the SPV of the PAT generally increases, and the synergy angle of the impeller surface increases as well. A strong disordered synergy field is observed in regions of the blade leading edge, trailing edge, and volute tongue. The variations in efficiency and head with flow rate showed similar trends, respectively, with the synergy angle of the outlet and the mid-plane. This study provides an analytical method for quantitative evaluation of flow synergy characteristics, and it supplies a basis for further design improvement of the pump and PAT.

Download Full-text