scholarly journals Numerical Investigation on Cavitation Suppression of Microchannel over a NACA0012 Hydrofoil

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhouhao Shi ◽  
Zhanshan Xie ◽  
Weidong Shi ◽  
Qinghong Zhang ◽  
Lingwei Tan
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Numerical Investigation ◽  
Turbulent Kinetic Energy ◽  
Working Conditions ◽  
Low Pressure ◽  
Fluid Machinery ◽  
Pressure Area ◽  
First Time ◽  
Microchannel Design

To find a better method to suppress cavitation, a microchannel design connecting the internal low-pressure area with the outside is proposed for the first time in this paper; the method was adopted to replenish fluid in the interior of the low-pressure area to inhibit cavitation. Through numerical simulation, it is found that the size and position of microchannel have a certain influence on the cavitation inhibition. The results show that the generation and development of cavitation, under the same working conditions, can be effectively restrained by adopting appropriate microchannel (x = 0.05 c, d = 6 cm). Compared with the original hydrofoil, the scale of cavitation is reduced by nearly 50%, and its turbulent kinetic energy remains unchanged. Therefore, it is considered that microchannel technology, as a new means of cavitation suppression, is of great significance to other types of fluid machinery.

Uncertainty analysis of CFD and performance prediction for an pumpjet propulsor

2020 ◽  
pp. 2150083
Author(s):  
Chao Liu ◽  
Hongxun Chen ◽  
Zhengchuan Zhang ◽  
Zheng Ma
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Uncertainty Analysis ◽  
Turbulent Kinetic Energy ◽  
Guide Vane ◽  
Outer Region ◽  
Turbulence Models ◽  
Operating Conditions ◽  
Operating Characteristics ◽  
Standard Formula

In order to reveal the operating characteristics of the pumpjet propulsor, standard [Formula: see text]–[Formula: see text], standard [Formula: see text]–[Formula: see text], RNG [Formula: see text]–[Formula: see text] and SST [Formula: see text]–[Formula: see text] turbulence models were used to conduct steady calculation for the whole flow channels. By comparing the calculation results with experimental data, it was found that the calculation errors were very large in some operating conditions. Therefore, the uncertainty analysis was carried out at all operating conditions of the pumpjet propulsor and the error source was finally determined that it is mainly derived from the model error. Then, the applicability of different turbulence models was analyzed to numerical simulation for the pumpjet propulsor by comparing the internal and external characteristics. It can be seen that the strong turbulent kinetic energy in the guide vane will inevitably cause energy loss, but not necessarily in the impeller. In this area, the increase of turbulent kinetic energy will enhance the mixing and transport of fluids, and the impeller makes the fluids get more energy. In addition, a modified hybrid Reynolds Average Numerical Simulation/Large Eddy Simulation (RANS/LES) model was proposed for unsteady calculation, and the performances, internal flow states and the interaction between the pump and the outer region were further revealed under various conditions of the pumpjet propulsor, which provides some references for predicting accurately and selecting conditions optimally in the future.

The Unsteady Development of a Turbulent Wake Through a Downstream Low-Pressure Turbine Blade Passage

2005 ◽  
Vol 127 (2) ◽  
pp. 388-394 ◽  
Author(s):  
R. D. Stieger ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Production Mechanism ◽  
Blade Passage ◽  
Low Pressure Turbine ◽  
Blade Row ◽  
Turbulence Production

This paper presents two-dimensional LDA measurements of the convection of a wake through a low-pressure turbine cascade. Previous studies have shown the wake convection to be kinematic, but have not provided details of the turbulent field. The spatial resolution of these measurements has facilitated the calculation of the production of turbulent kinetic energy, and this has revealed a mechanism for turbulence production as the wake convects through the blade row. The measured ensemble-averaged velocity field confirmed the previously reported kinematics of wake convection while the measurements of the turbulence quantities showed the wake fluid to be characterized by elevated levels of turbulent kinetic energy (TKE) and to have an anisotropic structure. Based on the measured mean and turbulence quantities, the production of turbulent kinetic energy was calculated. This highlighted a TKE production mechanism that resulted in increased levels of turbulence over the rear suction surface where boundary-layer transition occurs. The turbulence production mechanism within the blade row was also observed to produce more anisotropic turbulence. Production occurs when the principal stresses within the wake are aligned with the mean strains. This coincides with the maximum distortion of the wake within the blade passage and provides a mechanism for the production of turbulence outside of the boundary layer.

Effects of surface roughness on self-excited cavitating water jet intensity in the organ-pipe nozzle: Numerical simulations and experimental results

2019 ◽  
Vol 33 (27) ◽  
pp. 1950324
Author(s):  
Xiangdong Han ◽  
Yong Kang ◽  
Deng Li ◽  
Weiguo Zhao
Keyword(s):  
Numerical Simulation ◽  
Surface Roughness ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Energy Intensity ◽  
Volume Fraction ◽  
Water Jet ◽  
The Self ◽  
Simulation Results ◽  
Organ Pipe

This study was conducted to investigate effects of surface roughness on self-excited cavitating water jet intensity in an organ-pipe nozzle. Roughness average (Ra) values are 0.8, 1.6, 3.2, 6.3, 12.5, and 25 [Formula: see text]m, respectively. Numerical simulation results indicate that at inlet pressure of 10 MPa, the maximum, minimum, and real-time pressures in the self-excited oscillation chamber reach their respective peak values. The turbulent kinetic energy intensity in the external flow region is also most intense at this point, the vapor volume fraction in orifice is the highest, the vortex distribution scope in the orifice is the largest under [Formula: see text], and the self-excited cavitating water jet intensity is the strongest. The opposite variations emerge at [Formula: see text] compared to those of [Formula: see text], where the intensity is weakest. Pressure varies only slightly as Ra varies from 0.8 [Formula: see text]m to 6.3 [Formula: see text]m. Turbulent kinetic energy intensity behaves similarly as Ra increases from 0.8 [Formula: see text]m to 3.2 [Formula: see text]m. At [Formula: see text], it was weaker than at Ra = 0.8–3.2 [Formula: see text]m. Similarly, there are only slight differences in vapor volume fraction and vortex distribution scope with Ra from 0.8 [Formula: see text]m to 6.3 [Formula: see text]m. The intensities at Ra = 0.8–3.2 [Formula: see text]m are similar, and weaker at Ra = 6.3 [Formula: see text]m. Pressure values are maximal at inlet pressure of 20 MPa, turbulent kinetic energy intensity is most intense, vapor volume fraction is highest, vortex distribution scope is largest under [Formula: see text] [Formula: see text]m, and intensity is strongest. Distinctions among pressure, turbulent kinetic energy intensity, vapor volume fraction, and vortex distribution scope values with Ra from 0.8 [Formula: see text]m to 3.2 [Formula: see text]m are slight. Differences in the corresponding intensities are also slight; all decrease with Ra from 12.5 [Formula: see text]m to 25 [Formula: see text]m as the intensity gradually weakens. Numerical simulation results were validated by comparison against corresponding experimental phenomena.

scholarly journals Turbulent Kinetic Energy Production in the Vane of a Low-Pressure Linear Turbine Cascade with Incoming Wakes

2015 ◽  
Vol 2015 ◽  
pp. 1-15 ◽  
Author(s):  
V. Michelassi ◽  
J. G. Wissink
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Turbulent Kinetic Energy ◽  
Suction Side ◽  
Low Pressure ◽  
Eddy Simulation ◽  
Transition Mechanism ◽  
Principal Axes ◽  
Large Eddy

Incompressible large eddy simulation and direct numerical simulation of a low-pressure turbine atRe=5.18×104and1.48×105with discrete incoming wakes are analyzed to identify the turbulent kinetic energy generation mechanism outside of the blade boundary layer. The results highlight the growth of turbulent kinetic energy at the bow apex of the wake and correlate it to the stress-strain tensors relative orientation. The production rate is analytically split according to the principal axes, and then terms are computed by using the simulation results. The analysis of the turbulent kinetic energy is followed both along the discrete incoming wakes and in the stationary frame of reference. Both direct numerical and large eddy simulation concur in identifying the same production mechanism that is driven by both a growth of strain rate in the wake, first, followed by the growth of turbulent shear stress after. The peak of turbulent kinetic energy diffuses and can eventually reach the suction side boundary layer for the largest Reynolds number investigated here with higher incidence angle. As a consequence, the local turbulence intensity outside the boundary layer can grow significantly above the free-stream level with a potential impact on the suction side boundary layer transition mechanism.

The Unsteady Development of a Turbulent Wake Through a Downstream Low-Pressure Turbine Blade Passage

2004 ◽  
Author(s):  
R. D. Stieger ◽  
H. P. Hodson
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Isotropic Turbulence ◽  
Low Pressure ◽  
Boundary Layer Transition ◽  
Production Mechanism ◽  
Principal Stresses ◽  
Blade Passage ◽  
Turbulence Production

This paper presents two-dimensional LDA measurements of the convection of a wake through a low-pressure (LP) turbine cascade. Previous studies have shown the wake convection to be kinematic but have not provided details of the turbulent field. The spatial resolution of these measurements has facilitated the calculation of the production of turbulent kinetic energy and this has revealed a mechanism for turbulence production as the wake convects through the bladerow. The measured ensemble-averaged velocity field confirmed the previously reported kinematics of wake convection while the measurements of the turbulence quantities showed the wake fluid to be characterised by elevated levels of turbulent kinetic energy (TKE) and to have an anisotropic structure. Based on the measured mean and turbulence quantities, the production of turbulent kinetic energy was calculated. This highlighted a TKE production mechanism that resulted in increased levels of turbulence over the rear suction surface where boundary layer transition occurs. The turbulence production mechanism within the bladerow was also observed to produce more nearly isotropic turbulence. Production occurs when the principal stresses within the wake are aligned with the mean strains. This coincides with the maximum distortion of the wake within the blade passage and provides a mechanism for the production of turbulence outside of the boundary layer.

scholarly journals Direct Numerical Simulation and Visualization of Biswirling Jets

2014 ◽  
Vol 6 ◽  
pp. 193731 ◽  
Author(s):  
Jie Yan ◽  
Nan Gui ◽  
Gongnan Xie ◽  
Jinsen Gao
Keyword(s):  
Numerical Simulation ◽  
Kinetic Energy ◽  
Direct Numerical Simulation ◽  
Turbulent Kinetic Energy ◽  
Vortex Structures ◽  
Small Scale ◽  
Convergence Region ◽  
Swirling Jets ◽  
Vortex Interactions ◽  
Close Distance

Two parallel swirling/rotating jets with a distance between them are termed biswirling jets here, which have important and complicated vortex structures different from the single swirling jet due to the negligible vortex-vortex interactions. The visualization of vortex-vortex interaction between the biswirling jets is accomplished by using direct numerical simulation. The evolution of vortex structures of the biswirling jets is found rather complicated. The turbulent kinetic energy and turbulence dissipation in the central convergence region are augmented locally and rather strongly. The modulation of turbulent kinetic energy by jet-jet interaction upon different scales of vortices is dominated by the swirling levels and the distance between the jets. The turbulent kinetic energy upon intermediate and small scale vortices in bijets with not very high swirling level and at a very close distance is smaller than that in single swirling jets, whereas the opposite is true under a far distance, and so forth.

scholarly journals Observations of turbulent kinetic energy dissipation at the Labrador Sea surface layer

2017 ◽  
Vol 8 (3) ◽  
pp. 161-172
Author(s):  
Silvia Gremes-Cordero
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Phytoplankton Bloom ◽  
Global Climate ◽  
Energy Dissipation Rate ◽  
Labrador Sea ◽  
Wave Phase ◽  
Dissipation Rates ◽  
First Time

We present an analysis of turbulent kinetic energy dissipation rates in the upper ocean using in situ measurements collected by a coherent Doppler sonar in the Labrador Sea during summer 2004. The sonar recorded horizontal velocity fluctuations of the upper 2 m with an uncommonly small spatial resolution of 0.8 cm, allowing direct calculations of wavenumber spectra and the application of Kolmogorov theory to obtain turbulent kinetic energy dissipation rates for the first time in this area. The project presented a unique opportunity for the study of air–sea exchange during a phytoplankton bloom, being the first time a specialized air–sea interaction spar buoy was deployed during such particular event. An additional uniqueness of this experiment resulted from being the first turbulent kinetic energy dissipation rate observations obtained at higher latitudes, coincidentally in a well-known region of dense water formation, with a fundamental role in both global circulation and forecasting studies of global climate change. Focusing on the relationship between turbulent kinetic energy dissipation rates and wave phase in the upper 2 m, we estimated O[Formula: see text] turbulent kinetic energy dissipation rates, consistent with previous estimates obtained through similar devices and methods. A T-test between dissipation rates calculated at the crest and at the trough of waves showed no dependency of turbulent kinetic energy dissipation rates on the wave phase at 2 m depth, coinciding with many of the earlier findings available. a comparison with previous research showing conflicting results with our values is also discussed here linking them to the relative roles of experimental design variations, diverse dynamical frames, and particular environmental conditions.

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