Numerical investigation of flow structure and air entrainment of breaking bow wave generated by a rectangular plate

2021 ◽  
Vol 33 (12) ◽  
pp. 122113
Author(s):  
Yiding Hu ◽  
Cheng Liu ◽  
Changhong Hu ◽  
Decheng Wan
Keyword(s):  
Numerical Investigation ◽  
Rectangular Plate ◽  
Flow Structure ◽  
Air Entrainment ◽  
Bow Wave

Numerical Investigation of Passive Flow Control Using Wavy Blades in a Highly-Loaded Compressor Cascade

2018 ◽  
Author(s):  
Bo Wang ◽  
Yanhui Wu ◽  
Kai Liu
Keyword(s):  
Numerical Investigation ◽  
Flow Structure ◽  
Cross Flow ◽  
Leading Edge ◽  
Control Flow ◽  
Streamwise Vortices ◽  
Compressor Cascade ◽  
Control Effect ◽  
Suction Surface ◽  
Highly Loaded

Driven by the need to control flow separations in highly loaded compressors, a numerical investigation is carried out to study the control effect of wavy blades in a linear compressor cascade. Two types of wavy blades are studied with wavy blade-A having a sinusoidal leading edge, while wavy blade-B having pitchwise sinusoidal variation in the stacking line. The influence of wavy blades on the cascade performance is evaluated at incidences from −1° to +9°. For the wavy blade-A with suitable waviness parameters, the cascade diffusion capacity is enhanced accompanied by the loss reduction under high incidence conditions where 2D separation is the dominant flow structure on the suction surface of the unmodified blade. For well-designed wavy blade-B, the improvement of cascade performance is achieved under low incidence conditions where 3D corner separation is the dominant flow structure on the suction surface of the baseline blade. The influence of waviness parameters on the control effect is also discussed by comparing the performance of cascades with different wavy blade configurations. Detailed analysis of the predicted flow field shows that both the wavy blade-A and wavy blade-B have capacity to control flow separation in the cascade but their control mechanism are different. For wavy blade-A, the wavy leading edge results in the formation of counter-rotating streamwise vortices downstream of trough. These streamwise vortices can not only enhance momentum exchange between the outer flow and blade boundary layer, but also act as the suction surface fence to hamper the upwash of low momentum fluid driven by cross flow. For wavy blade-B, the wavy surface on the blade leads to a reduction of the cross flow upwash by influencing the spanwise distribution of the suction surface static pressure and guiding the upwash flow.

scholarly journals Wake behind a three-dimensional dry transom stern. Part 1. Flow structure and large-scale air entrainment

2019 ◽  
Vol 875 ◽  
pp. 854-883 ◽  
Author(s):  
Kelli Hendrickson ◽  
Gabriel D. Weymouth ◽  
Xiangming Yu ◽  
Dick K.-P. Yue
Keyword(s):  
Froude Number ◽  
Flow Structure ◽  
Large Scale ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Breaking Waves ◽  
Variable Density ◽  
Entrainment Rate ◽  
Two Phase ◽  
Density Spectrum

We present high-resolution implicit large eddy simulation (iLES) of the turbulent air-entraining flow in the wake of three-dimensional rectangular dry transom sterns with varying speeds and half-beam-to-draft ratios $B/D$. We employ two-phase (air/water), time-dependent simulations utilizing conservative volume-of-fluid (cVOF) and boundary data immersion (BDIM) methods to obtain the flow structure and large-scale air entrainment in the wake. We confirm that the convergent-corner-wave region that forms immediately aft of the stern wake is ballistic, thus predictable only by the speed and (rectangular) geometry of the ship. We show that the flow structure in the air–water mixed region contains a shear layer with a streamwise jet and secondary vortex structures due to the presence of the quasi-steady, three-dimensional breaking waves. We apply a Lagrangian cavity identification technique to quantify the air entrainment in the wake and show that the strongest entrainment is where wave breaking occurs. We identify an inverse dependence of the maximum average void fraction and total volume entrained with $B/D$. We determine that the average surface entrainment rate initially peaks at a location that scales with draft Froude number and that the normalized average air cavity density spectrum has a consistent value providing there is active air entrainment. A small parametric study of the rectangular geometry and stern speed establishes and confirms the scaling of the interface characteristics with draft Froude number and geometry. In Part 2 (Hendrikson & Yue, J. Fluid Mech., vol. 875, 2019, pp. 884–913) we examine the incompressible highly variable density turbulence characteristics and turbulence closure modelling.

Experimental and Numerical Investigation on Film Cooling Performance and Flow Structure of Film Holes

2019 ◽  
Author(s):  
Nan Cao ◽  
Xue Li ◽  
Ze-yu Wu ◽  
Xiang Luo
Keyword(s):  
Flow Visualization ◽  
Numerical Investigation ◽  
Flow Structure ◽  
Film Cooling ◽  
Cylindrical Hole ◽  
Cooling Effectiveness ◽  
Cooling Performance ◽  
Blowing Ratio ◽  
Visualization Experiment ◽  
Shaped Hole

Abstract Discrete hole film cooling has been commonly used as an effective cooling technique to protect gas turbine blades from hot gas. There have been numerous investigations on the cylindrical hole and shaped hole, but few experimental investigations on the cooling mechanism of the novel film holes with side holes (anti-vortex hole and sister hole) are available. This paper presents an experimental and numerical investigation to study the film cooling performance and flow structure of four kinds of film holes (cylindrical hole, fan-shaped hole, anti-vortex hole and sister hole) on the flat plate. The film holes have the same main hole diameter of 4mm and the same inclination angle of 45°. The adiabatic film cooling effectiveness is obtained by the steady-state Thermochromic Liquid Crystal (TLC). The flow visualization experiment and numerical investigation are performed to investigate the flow structure and counter-rotating vortex pair (CRVP) intensity. The smoke is selected as the tracer particle in the flow visualization experiment. The mainstream Reynolds number is 2900, the blowing ratio ranges from 0.3 to 2.0, and the density ratio of coolant to mainstream is 1.065. Experimental results show that compared with the cylindrical hole, the film cooling performance of the anti-vortex hole and sister hole shows significant improvement at all blowing ratios. The sister hole can achieve the best cooling performance at blowing ratios of 0.3 to 1.5. The fan-shaped hole only performs well at high blowing ratios and it performs best at the blowing ratio of 2.0. Flow visualization experiment and numerical investigation reveal that the anti-vortex hole and sister hole can decrease the CRVP intensity of the main hole and suppress the coolant lift-off because of side holes, which increases the film coverage and cooling effectiveness. For the sister hole, the side holes are parallel to the main hole, but for the anti-vortex hole, there are lateral angles between them. The coolant interaction between the side holes and main hole of the sister hole is stronger than that of the anti-vortex hole. Therefore, the sister hole provides better film cooling performance than the anti-vortex hole.

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