scholarly journals Numerical Simulation of Pressure Fluctuation Near an Expansion Corner in a Supersonic Flow of M = 3.01

Fluids ◽  
2021 ◽  
Vol 6 (8) ◽  
pp. 268
Author(s):  
Lei Zhang ◽  
Zi-Niu Wu
Keyword(s):  
Boundary Layer ◽  
Supersonic Flow ◽  
Frequency Band ◽  
Pressure Fluctuation ◽  
High Speed ◽  
Pressure Coefficient ◽  
Feedback Mechanism ◽  
Characteristic Line ◽  
Detached Eddy Simulation ◽  
The Difference

The influence of the expansion corner on pressure fluctuation is an important subject in supersonic flow around high-speed vehicles. Past studies have clarified how the expansion corner alters the root-mean-square of the fluctuating pressure coefficient (Cprms) and the power spectral density (PSD) without considering how these fluctuating properties are related to compressible waves. In this paper, we use characteristics to determine the direction of wave propagation and identified three zones—U-zone, M-zone and D-zone—within which both Cprms and PSD are likely to display different behaviors across the boundary layer. The U-zone is upstream of the characteristic line of the second family and passing through the corner. The D-zone is downstream of the characteristic line of the first family and passing through the corner. The middle zone lies between the U-zone and D-zone. The results of Cprms and PSD at different layers within the boundary layer are obtained using numerical computation through a Detached Eddy Simulation (DES). It is found that in the U-zone and D-zone, both Cprms and PSD are the same in different layers within the boundary layer. In the M-zone, however, both Cprms and PSD may vary in different layers and this variation occurs in the high-frequency band upstream of the corner and mid-frequency band downstream of the corner. A feedback mechanism is tentatively used to explain the difference of spatial distribution of fluctuation properties inside the M-zone.

Experimental and Numerical Investigation on Pressure Fluctuation of the Impeller in an Axial Flow Pump

2019 ◽  
Author(s):  
Xi Shen ◽  
Desheng Zhang ◽  
Bin Xu ◽  
Yongxin Jin ◽  
Xiongfa Gao
Keyword(s):  
Pressure Fluctuation ◽  
High Speed ◽  
Axial Flow ◽  
Suction Side ◽  
High Speed Photography ◽  
Detached Eddy Simulation ◽  
Transient Pressure ◽  
Unstable Flow ◽  
Axial Flow Pump ◽  
Flow Pump

Abstract The Detached Eddy Simulation (DES) has been used to simulate the pressure fluctuation of the impeller in an axial flow pump. The results were combined with experiments including high-speed photography and transient pressure measurements to investigate the unstable flow induced by tip leakage vortex (TLV). Numerical results show that maximum predictive error values of head is 2.9%, compared with experimental results. The pressure fluctuation at different monitoring points present a certain regularity, with 3 peaks and 3 troughs in a period, corresponding to the number of blades. The amplitude of pressure fluctuation at P1 (impeller inlet) is the highest among those monitoring points, where the amplitude decreases with the flow rates. The dominant frequency of pressure fluctuation at impeller under cavitation condition is the blade passing frequency (BPF). Besides, there are also N* = 6, 9, 12 and other more harmonic frequencies. The cavitation flow was analyzed with the pressure fluctuation of the blade tip. For the existence of the pressure difference between pressure side and suction side, the pressure at monitoring points change alternately. The amplitude of the fluctuation near tip is affected seriously by the cavitation bubbles, as the cavitation could is a low pressure region with unstable fluctuation.

scholarly journals A method of skin frictional resistant reduction by creating small bubbles at bottom of ships

2013 ◽  
Vol 35 (4) ◽  
pp. 325-333
Author(s):  
Phan Anh Tuan ◽  
Pham Thi Thanh Huong ◽  
Vu Duy Quang
Keyword(s):  
Boundary Layer ◽  
Energy Consumption ◽  
Turbulent Boundary Layer ◽  
High Speed ◽  
Regular Wave ◽  
Propulsive Force ◽  
Calm Water ◽  
The Difference ◽  
Small Bubbles ◽  
Direction Opposite

Most of ship energy consumption spends for its propulsive device to create a propulsive force that helps the ship to win its resistant force to move forward or backward.The ship resistant is including skin frictional resistant force, wave-making resistant force and wind resistant force. This paper mentions to a method of skin frictional resistant reduction by creating small bubbles at bottom of ships. When a ship moves on/underwater surface, for skin resistant force to be generated, the ship must be in contact with the water. Skin frictional resistant force is generated by the difference in velocity between the ship and the water. Frictional resistant force will act in the direction opposite to the direction of motion of the ship. The method of skin frictional resistant reduction is injecting air flows to creating small bubbles into the turbulent boundary layer developing on the ship skin. Research found that this method may reduce ship energy consumption.This method could be applied to large ships with not high speed movement. A model ship that is scaled 1/33 of a 20000 ton cargo ship had been created for carrying out experiments in calm water and in regular wave conditions. Authors found that the highest effect from creating small bubble method on reduction ship energy consumption in calm water is 15.3% and in regular wave is 10.3%.

Interference effects of three consecutive wall-mounted cubes placed in deep turbulent boundary layer

2014 ◽  
Vol 756 ◽  
pp. 165-190
Author(s):  
Hee Chang Lim ◽  
Masaaki Ohba
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Coefficient ◽  
Azimuth Angle ◽  
Pressure Variation ◽  
Interference Effects ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Mean Pressure ◽  
The Mean

AbstractIn this study we undertook various calculations of the turbulent flow around a building in close proximity to neighbouring obstacles, with the aim of gaining an understanding of the velocity and the surface-pressure variations with respect to the azimuth angle of wind direction and the gap distance between the obstacles. This paper presents the effects of flow interference among consecutive cubes for azimuth angles of $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\theta = 0$, 15, 30, and $45^{\circ }$ and gap distances of $G = 0.5{h}, 1.0{h}, 1.5{h}$, and $\infty $ (i.e. a single cube), where $h$ is the cube height, placed in a turbulent boundary layer. A transient detached eddy simulation (DES) was carried out to calculate the highly complicated flow domain around the three wall-mounted cubes to observe the fluctuating pressure, which substantially contributes to the suction pressure when there is separation and reattachment around the leading and trailing edges of the cubes. In addition, the results indicate that an increasing azimuth angle increases the pressure variation on the centre cube of the three parallel-aligned cubes. The mean pressure variation can even change from negative to positive on the side face. Owing to interference effects, the mean pressure coefficient of the centre cube of the three parallel-aligned cubes was generally lower than the coefficient of the single cube and tended to increase depending on the gap distance. Furthermore, when the three consecutive cubes are in a tandem arrangement, the gap distance has little influence on the first cube but results in significant interference effects on the second and third cubes.

scholarly journals Impact of Different Nose Lengths on Flow-Field Structure around a High-Speed Train

2019 ◽  
Vol 9 (21) ◽  
pp. 4573 ◽  
Author(s):  
Xianli Li ◽  
Guang Chen ◽  
Dan Zhou ◽  
Zhengwei Chen
Keyword(s):  
Numerical Simulation ◽  
High Speed ◽  
Aerodynamic Force ◽  
Pressure Coefficient ◽  
Wake Flow ◽  
Maximum Pressure ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Rapid Reduction ◽  
Comparison Results

In this study, the time-averaged and instantaneous slipstream velocity, time-averaged pressure, wake flows, and aerodynamic force of a high-speed train (HST) with different nose lengths are compared and analyzed using an improved delayed detached-eddy simulation (IDDES) method. Four train models were selected, with nose lengths of 4, 7, 9, and 12 m. To verify the accuracy of the numerical simulation results, they were compared with wind tunnel test results. The comparison results show that the selection of the numerical simulation method is reasonable. The research results show that with increasing nose length, the peak values of the time-averaged slipstream velocity of the trackside position (3 m from the center of track and 0.2 m from the top of rail) and the platform position (3 m from the center of track and 0.2 m from the top of rail) decrease continuously, and show a trend of rapid reduction at first, and then a slow decrease. As the nose length increased from 4 to 12 m, the time-averaged slipstream velocity at the trackside position and platform position are decreased by 57% and 19.5%, respectively. At a height of 1.6 m from the top of the rail, ΔCP max (maximum pressure coefficient), |ΔCP min| (the absolute value of minimum pressure coefficient), and ΔCP (pressure change coefficient) decrease with increasing nose length, which is similar to the peak value of time-averaged slipstream velocity, decreasing rapidly at first and then slowly. As the nose length increased from 4 to 12 m, decreases of ΔCP max, |ΔCP min|, and ΔCP by 26.5%, 58.5%, and 44.8% were shown, respectively. Different nose lengths also have a significant impact on wake flow.

The Effect of Sting Supports on the Base Pressure of a Blunt-Based Body in a Supersonic Stream

1955 ◽  
Vol 6 (3) ◽  
pp. 221-229 ◽  
Author(s):  
I. S. Donaldson
Keyword(s):  
Boundary Layer ◽  
Pressure Coefficient ◽  
Diameter Ratio ◽  
Base Pressure ◽  
Supersonic Stream ◽  
Axially Symmetric ◽  
Nozzle Throat ◽  
Base Diameter ◽  
The Difference ◽  
Made In

SummaryExperiments have been made to find the effect of the ratio of sting to base diameter on the base pressure of an axially symmetric body at zero incidence in a supersonic stream. The Mach number of the flow was 1·994 and the model boundary layer was turbulent. The model used was a one inch diameter circular cylinder without boat-tailing. It passed through and was supported upstream of the nozzle throat. This method of support allowed measurements to be made in the important (and hitherto unexplored) case of zero sting diameter.As the sting to base diameter ratio was increased from 0 to 0·85, the base pressure decreased. The minimum value reached was approximately 0·8 of the value it would have at the base of a two-dimensional body with a similar ratio of boundary layer thickness to base height. The base pressure coefficient rose rapidly to zero as the ratio was further increased to unity.Under the conditions of the experiments, with a sting to base diameter ratio of 0·4 the base pressure coefficient differed from that without a sting by approximately ten per cent. With the more modest ratio of 0·2, the difference was approximately three per cent.

On boundary layers and upstream influence. I. A comparison between subsonic and supersonic flows

1953 ◽  
Vol 217 (1130) ◽  
pp. 344-357 ◽  
Keyword(s):  
Boundary Layer ◽  
Supersonic Flow ◽  
Subsonic Flow ◽  
Pressure Coefficient ◽  
Pressure Rise ◽  
Supersonic Flows ◽  
Turbulent Layer ◽  
Quantitative Theory ◽  
The Dead ◽  
Qualitative Discussion

It is pointed out that there are two separate mechanisms for upstream influence through the boundary layer in supersonic flow, and that one of these (that involving separation) operates also in subsonic flow. A quantitative theory of subsonic flow up a step is given to illustrate this. The main differences between the subsonic and supersonic flows are as follows: (i) The boundaries of dead-air regions are nearly straight in supersonic flow but are usually highly curved in subsonic flow. (ii) Separation (whether of the laminar or turbulent layer) occurs at a much lower pressure coefficient in supersonic flow; this is only slightly due to the fact that the fluid nearest the wall is then lighter and so more easily brought to rest; it is due much more to the relative suddenness of the pressure rise ahead of the dead-air region. (iii) However, for a given pressure coefficient in the dead-air region, the distance of upstream influence is somewhat greater in the subsonic flow, except at the highest pressures. A qualitative discussion of the second mechanism of upstream influence, in supersonic flow, is given; for a quantitative theory of this see part II (Lighthill 1953).

Relations between shear flow and vortices in the near wake of a high speed train

2021 ◽  
pp. 095440972110317
Author(s):  
Yong-chen Pan ◽  
Jian-wei Yao ◽  
Rui Xu ◽  
Tao Liu ◽  
Jun Zheng ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Shear Flow ◽  
High Speed ◽  
Boundary Layer Separation ◽  
High Speed Train ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Dominant Component ◽  
Delayed Detached Eddy Simulation ◽  
Omega Method

Two flow cases for high speed train models with different lengths have been numerically computed by performing the improved delayed detached-eddy simulation. Based on the Omega method and turbulence production (TP) distribution, the relations between the shear flow and vortices in the near turbulent wake of a high speed train have been comparatively analyzed. First, in the wake region immediately close to the tail, the boundary layer separation plays significant roles. And the mechanism makes shear deformation prominent in the region with the formed vortices. Moreover, the shear layers are pertinent to the boundary-layer thicknesses and help to the TP distribution. However, the shear-dominated region is very limited due to high dissipation. One the other hand, a vast majority of the vortices captured with the parameter Omega increasing in the downstream region away from the tail. And the TP distributions are stable at different streamwise positions, though obviously decreased. They are greatly attributed to the mean strain rate in the horizontal plane. Meanwhile, the vortical vorticity is thought to be the dominant component inside the vortex cores, although the shear becomes weaker. And thus the turbulence itself can be spatially sustained due to the relatively stable vortex structure. Moreover, the weak shear is believed to depend upon the interaction between the vortices and the ground.

A Statistical Study of Process Variables to Optimize a High Speed Curtain Coater: Part I

TAPPI Journal ◽  
2009 ◽  
Vol 8 (1) ◽  
pp. 20-26 ◽  
Author(s):  
PEEYUSH TRIPATHI ◽  
MARGARET JOYCE ◽  
PAUL D. FLEMING ◽  
MASAHIRO SUGIHARA
Keyword(s):  
Boundary Layer ◽  
Experimental Design ◽  
High Speed ◽  
Statistical Study ◽  
Process Variables ◽  
High Speeds ◽  
The Stability ◽  
Air Removal ◽  
Removal System

Using an experimental design approach, researchers altered process parameters and material prop-erties to stabilize the curtain of a pilot curtain coater at high speeds. Part I of this paper identifies the four significant variables that influence curtain stability. The boundary layer air removal system was critical to the stability of the curtain and base sheet roughness was found to be very important. A shear thinning coating rheology and higher curtain heights improved the curtain stability at high speeds. The sizing of the base sheet affected coverage and cur-tain stability because of its effect on base sheet wettability. The role of surfactant was inconclusive. Part II of this paper will report on further optimization of curtain stability with these four variables using a D-optimal partial-facto-rial design.

Numerical Studies on Behavior of Lorentz-Force-Applied Boundary Layer in Supersonic Flow

2009 ◽  
Vol 129 (6) ◽  
pp. 831-839
Author(s):  
Keisuke Udagawa ◽  
Sadatake Tomioka ◽  
Hiroyuki Yamasaki
Keyword(s):  
Boundary Layer ◽  
Supersonic Flow ◽  
Lorentz Force ◽  
Numerical Studies
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