Intensification of non-uniformity in convergent near-conical hypersonic flow

2021 ◽  
Vol 931 ◽  
Author(s):  
Junze Ji ◽  
Zhufei Li ◽  
Enlai Zhang ◽  
Dongxian Si ◽  
Jiming Yang
Keyword(s):  
Free Stream ◽  
Mach Disk ◽  
Circular Ring ◽  
Windward Side ◽  
Leeward Side ◽  
Strength Increase ◽  
Regular Reflection ◽  
Shock Surface ◽  
Conical Shock ◽  
Free Stream Mach Number

The inevitable formation of a Mach disk at the central axis of a convergent conical shock wave may suffer from fundamental changes when the flow deviates from the axisymmetric condition. In this paper, the behaviours of near-conical shocks, which are generated by a circular ring wedge of $10^{\circ }$ at typical angles of attack (AoAs), are investigated at a free stream Mach number of 6 in a shock tunnel. To reveal the characteristics and mechanism of the flow, numerical analyses are carried out under the same conditions. The results indicate that when the flow deviates from axial symmetry, the circumferential non-uniformity is remarkably intensified as the shock converges downstream. The converging centre shifts against the inclination of the incoming flow and moves to the leeward side. For a sufficiently small AoA, the formation of a Mach disk remains similar to that in the axisymmetric case, although the Mach disk shrinks in size and is slightly flattened. As the circumferential non-uniformity of the shock increases at an AoA of approximately $3^{\circ }$ , a pair of kinks separate the shock surface into two discontinuous segments with the stronger shock segment on the windward side and the weaker shock segment on the leeward side. When the AoA increases further, the shrinkage of the Mach disk continuously occurs, and the Mach disk is eventually replaced by a regular reflection. The discontinuity of a convergent shock with flattening on the separated shock segments and the insufficient strength increase during the subsequent convergence are responsible for the appearance of regular reflection.

Investigation on the drag effect of a rolling element confined in the cavity of a cylindrical roller bearing

2021 ◽  
pp. 135065012110260
Author(s):  
Wenjun Gao ◽  
Shuo Zhang ◽  
Xiaohang Li ◽  
Zhenxia Liu
Keyword(s):  
Open Space ◽  
Roller Bearing ◽  
Flow Characteristics ◽  
Experimental Tests ◽  
Windward Side ◽  
Leeward Side ◽  
Drag Effect ◽  
Rolling Element ◽  
Cylindrical Roller Bearing ◽  
Cylindrical Roller

In cylindrical roller bearings, the drag effect may be induced by the rolling element translating in a fluid environment of the bearing cavity. In this article, the computational fluid dynamics method and experimental tests are employed to analyse its flow characteristics and pressure distribution. The results indicate that the pressure difference between the windward side and the leeward side of the cylinder is raised in view of it blocking the flow field. Four whirl vortexes are formed in four outlets of two wedge-shaped areas between the front part of the cylindrical surface and adjacent walls for the cylinder of L/ D = 1.5 at Re = 4.5 × 103. Vortex shedding is found in the direction of cylinder axis at Re = 4.5 × 104. The relationship between drag coefficient and Reynolds number is illustrated, obviously higher than that of the two-dimensional cylinder in open space.

scholarly journals 2.5D Flexible Wind Sensor Using Differential Plate Capacitors

Sensors ◽  
2021 ◽  
Vol 21 (9) ◽  
pp. 3101
Author(s):  
Yu Wan ◽  
Zhenxiang Yi
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Parallel Plate ◽  
Electrode Array ◽  
Copper Electrode ◽  
Windward Side ◽  
Leeward Side ◽  
Electrode Layer ◽  
Young’S Moduli ◽  
Speed Up

In this paper, a novel 2.5-dimensional (2.5D) flexible wind sensor is proposed based on four differential plate capacitors. This design consists of a windward pillar, two electrode layers, and a support layer, which are all made of polydimethylsiloxane (PDMS) with different Young’s moduli. A 2 mm × 2 mm copper electrode array is located on each electrode layer, forming four parallel plate capacitors as the sensitive elements. The wind in the xy-plane tilts the windward pillar, decreasing two capacitances on the windward side and increasing two capacitances on the leeward side. The wind in the z-axis depresses the windward pillar, resulting in an increase of all four capacitances. Experiments demonstrate that this sensor can measure the wind speed up to 23.9 m/s and the wind direction over the full 360° range of the xy-plane. The sensitivities of wind speed are close to 4 fF·m−1·s and 3 fF·m−1·s in the xy-plane and z-axis, respectively.

Air movement and heat loss from sheep. II. Thermal insulation of fleece in wind

1980 ◽  
Vol 209 (1175) ◽  
pp. 209-217 ◽  
Keyword(s):  
Thermal Diffusivity ◽  
Heat Loss ◽  
Thermal Insulation ◽  
General Relation ◽  
Windward Side ◽  
Leeward Side ◽  
Sensible Heat ◽  
Bulk Resistance ◽  
Air Movement ◽  
Dimensionless Constant

Penetration of an animal’s coat by wind reduces its thermal insulation and increases heat loss to the environment. From studies of the sensible heat loss from a life-sized model sheep covered with fleece, the average fleece resistance r¯ f (s cm -1 ) was related to windspeed u (m s -1 ) by 1/ r¯ f ( u ) = l/ r¯ f (0) + cu , where c is a dimensionless constant. As c is expected to be inversely proportional to coat depth Î , the more general relation k¯ ( u ) = k¯ (0) + c'u was evaluated, where k¯ = Î / r¯ f is the thermal diffusivity (cm 2 s -1 ) of the fleece and c' = cÎ is another constant (cm). The orientation of the model to the wind had little effect on the bulk resistance of the fleece, but the resistance on the windward side was substantially lower than on the leeward side.

Further Developments in the Aerodynamic Analysis of Unsteady Supersonic Cascades—Part 2: Aerodynamic Response Predictions

1977 ◽  
Vol 99 (4) ◽  
pp. 517-525 ◽  
Author(s):  
J. M. Verdon
Keyword(s):  
Free Stream ◽  
Narrow Range ◽  
Axial Flow ◽  
Stable Condition ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Numerical Predictions ◽  
Free Stream Mach Number ◽  
Parameter Values ◽  
Phase Angles

This paper is the second of a two-part report on a theoretical analysis of the aerodynamic response to an oscillating supersonic cascade in subsonic axial flow. Supersonic resonance criteria are discussed and lead to the distinction between subresonant and superresonant cascade motions. Numerical predictions, based on the unsteady solution reported in Part 1, are presented for two typical cascade configurations. These reveal the possibility of both subresonant and superresonant single-degree-of-freedom torsional instabilities. Subresonant instabilities occur over a broad range of frequencies and interblade phase angles, whereas superresonant instabilities occur only over a narrow range of such cascade parameter values. For a given blade motion frequency and free-stream Mach number, it appears that the least stable condition will usually lie in the subresonant region.

Direct numerical simulation of flow past a transversely rotating sphere up to a Reynolds number of 300 in compressible flow

2018 ◽  
Vol 857 ◽  
pp. 878-906 ◽  
Author(s):  
T. Nagata ◽  
T. Nonomura ◽  
S. Takahashi ◽  
Y. Mizuno ◽  
K. Fukuda
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Mach Number ◽  
Direct Numerical Simulation ◽  
Drag Coefficient ◽  
Rotation Rate ◽  
Free Stream ◽  
Rotating Sphere ◽  
Free Stream Mach Number ◽  
Low Reynolds

In this study, direct numerical simulation of the flow around a rotating sphere at high Mach and low Reynolds numbers is conducted to investigate the effects of rotation rate and Mach number upon aerodynamic force coefficients and wake structures. The simulation is carried out by solving the three-dimensional compressible Navier–Stokes equations. A free-stream Reynolds number (based on the free-stream velocity, density and viscosity coefficient and the diameter of the sphere) is set to be between 100 and 300, the free-stream Mach number is set to be between 0.2 and 2.0, and the dimensionless rotation rate defined by the ratio of the free-stream and surface velocities above the equator is set between 0.0 and 1.0. Thus, we have clarified the following points: (1) as free-stream Mach number increased, the increment of the lift coefficient due to rotation was reduced; (2) under subsonic conditions, the drag coefficient increased with increase of the rotation rate, whereas under supersonic conditions, the increment of the drag coefficient was reduced with increasing Mach number; and (3) the mode of the wake structure becomes low-Reynolds-number-like as the Mach number is increased.

scholarly journals Dust-related impacts of mining operations on rangeland vegetation and soil: a case study in Yazd province, Iran

2021 ◽  
Author(s):  
Shahab IbrahimPour ◽  
Alireza KhavaninZadeh ◽  
Ruhollah Taghizadeh mehrjardi ◽  
Hans De Boeck ◽  
Alvina Gul
Keyword(s):  
Seed Germination ◽  
Vegetation Cover ◽  
Microbial Respiration ◽  
Germination Rate ◽  
Windward Side ◽  
Leeward Side ◽  
Mining Operations ◽  
Soil Microbial ◽  
Soil Microbial Respiration ◽  
The Impact

Abstract Destructive mining operations are affecting large areas of natural ecosystems, especially in arid lands. The present study aims at investigating the impact of iron mine exploitation on vegetation and soil in Nodoushan (Yazd province, central Iran). Based on the dominant wind, topography, slope, vegetation and soil of the area, soil and vegetation parameters close to ​the mine were recorded and analyzed according to the distance from the mine. In order to obtain the vegetation cover, a transect and plot on the windward and leeward side of the mine, with 100 m intervals and three replicates at each sampling location was used, yielding 96 soil samples. The amount of dust on the vegetation, the seed weight and seed germination rate of Artemisia sp. as the dominant species within the area, and the soil microbial respiration were measured. The relationship between vegetation cover and distance from the mine was not linear, which was due to an interplay between pollution from the mine and local grazing, while other factors did increase or decrease linearly. The results showed that, as the distance from the mine increased, the weight of 1000 seeds of Artemisia sp. was significantly increased from 271 to 494 mg and seed germination rate and soil microbial respiration were significantly increased from 11.7 to 48.4 % and from 4.5 to 5.9 mg CO2 g− 1 soil day− 1 respectively, while the amount of dust significantly decreased from 43.5 to 6 mg (g plant)−1 between the distance of 100 to 600 m from the mine in the leeward direction. A similar trend was observed in the windward side, though negative effects were lower compared to the same distance along the leeward sample locations. The direct and indirect effects on plant growth and health from mining impacts generally decreased linearly with increasing distance from the mine, up to at least 600 m. Our study serves as a showcase for the potential of bio-indicators as a cost-effective method for assessing impacts of mining activities on the surrounding environment.

scholarly journals Звуковой удар от тонкого тела и локальных областей нагрева сверхзвукового набегающего потока

2021 ◽  
Vol 91 (4) ◽  
pp. 558
Author(s):  
А.В. Потапкин ◽  
Д.Ю. Москвичев
Keyword(s):  
Mach Number ◽  
Supersonic Flow ◽  
Free Stream ◽  
Local Heating ◽  
Air Flow ◽  
Sonic Boom ◽  
Incoming Flow ◽  
Combined Method ◽  
Cold Flow ◽  
Free Stream Mach Number

The problem of a sonic boom generated by a slender body and local regions of supersonic flow heating is solved numerically. The free-stream Mach number of the air flow is 2. The calculations are performed by a combined method of phantom bodies. The results show that local heating of the incoming flow can ensure sonic boom mitigation. The sonic boom level depends on the number of local regions of incoming flow heating. One region of flow heating can reduce the sonic boom by 20% as compared to the sonic boom level in the cold flow. Moreover, consecutive heating of the incoming flow in two regions provides sonic boom reduction by more than 30%.

The Removal of the Boundary Layer of a Supersonic Flow by Means of a Slot

1963 ◽  
Vol 30 (2) ◽  
pp. 275-278
Author(s):  
M. Cloutier
Keyword(s):  
Boundary Layer ◽  
Mass Flow ◽  
Static Pressure ◽  
Free Stream ◽  
Subsequent Development ◽  
Displacement Thickness ◽  
Free Stream Mach Number ◽  
Slot Opening ◽  
Flow Through ◽  
Transverse Slot

The influence of slot opening and of suction pressure upon the mass flow through the slot and the subsequent development of the boundary layer has been studied for the case of a single transverse slot opening into a boundary layer with a displacement thickness of 0.168 in. at a free-stream Mach number of 2.92. The results show that as much as 85 percent of the mass flow in the boundary layer between the wall and the position of the slot lip enters the slot, and that this result is independent of the slot reservoir pressure, providing the latter is less than approximately twice the tunnel static pressure.

scholarly journals Topographical Influence on Precipitation Distribution in Different Ranges of Western Himalayas

1995 ◽  
Vol 26 (4-5) ◽  
pp. 259-284 ◽  
Author(s):  
Pratap Singh ◽  
K. S. Ramasastri ◽  
Naresh Kumar
Keyword(s):  
Precipitation Intensity ◽  
Windward Side ◽  
Leeward Side ◽  
Western Himalayas ◽  
Precipitation Distribution ◽  
Post Monsoon ◽  
Seasonal Characteristics ◽  
Annual Distribution

Seasonal and annual distribution of rainfall and snowfall with elevation has been studied for outer, middle and greater Himalayan ranges of Chenab basin in the western Himalayas. Rainfall and snowfall exhibited different trends with elevation on the windward and leeward slopes of the three ranges of Himalayas. Seasonal characteristics of rainfall have shown a spill over effect on leeward side during winter, pre-monsoon, and post-monsoon seasons in the outer Himalayas. The role of orography in the middle Himalayas was found to be more pronounced for both rainfall and snowfall in comparison to other ranges of Himalayas. Variation of snowfall with elevation was more prominent in comparison to variation of rainfall. In the greater Himalayan range it is found that rainfall descreases exponentially with elevation and snowfall increases linearly. Rainfall becomes negligible at elevations beyond 4,000 m on the windward side of the greater Himalayan range. Efforts have also been made to explain whether variation in precipitation is due to changes in precipitation intensity or number of precipitation days or a combination of both.

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