INVESTIGATION ON AEROACOUSTIC CHARACTERISTICS IN CAVITY FLOW

2010 ◽  
Vol 24 (13) ◽  
pp. 1417-1420
Author(s):  
JIFEI WU ◽  
ZHAOLIN FAN ◽  
YANG TAO
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Static Pressure ◽  
Cavity Length ◽  
Dynamic Pressure ◽  
Cavity Flow ◽  
Pressure Waves ◽  
Acoustic Characteristics ◽  
Acoustic Environment ◽  
Depth Ratio

An experiment was conducted in a high speed wind tunnel to study the effects of dynamic pressure waves in a cavity from subsonic speeds to supersonic speeds. The effects on dynamic pressure of various parameters such as the Mach number, cavity length to depth ratio and the number of generic store were demonstrated. Detailed static-pressure and fluctuating pressure were measured on the cavity floor to determine the variation of the steady and unsteady pressures. Results show that cavity flow aero-acoustic characteristics are closely related to the Mach number and the cavity length to depth ratio. It is also found that installing store/stores in cavity can effectively improve the aero-acoustic environment in the cavity.

scholarly journals Bubbly shock propagation as a mechanism for sheet-to-cloud transition of partial cavities

2016 ◽  
Vol 802 ◽  
pp. 37-78 ◽  
Author(s):  
Harish Ganesh ◽  
Simo A. Mäkiharju ◽  
Steven L. Ceccio
Keyword(s):  
Mach Number ◽  
Void Fraction ◽  
High Speed ◽  
Large Scale ◽  
Dynamic Pressure ◽  
Cavity Flow ◽  
Laboratory Frame ◽  
Shock Propagation ◽  
Time Resolved ◽  
Cloud Cavitation

Partial cavitation in the separated region forming from the apex of a wedge is examined to reveal the flow mechanism responsible for the transition from stable sheet cavity to periodically shedding cloud cavitation. High-speed visualization and time-resolved X-ray densitometry measurements are used to examine the cavity dynamics, including the time-resolved void-fraction fields within the cavity. The experimentally observed time-averaged void-fraction profiles are compared to an analytical model employing free-streamline theory. From the instantaneous void-fraction flow fields, two distinct shedding mechanisms are identified. The classically described re-entrant flow in the cavity closure is confirmed as a mechanism for vapour entrainment and detachment that leads to intermittent shedding of smaller-scale cavities. But, with a sufficient reduction in cavitation number, large-scale periodic cloud shedding is associated with the formation and propagation of a bubbly shock within the high void-fraction bubbly mixture in the separated cavity flow. When the shock front impinges on flow at the wedge apex, a large cloud is pinched off. For periodic shedding, the speed of the front in the laboratory frame is of the order of half the free-stream speed. The features of the observed condensation shocks are related to the average and dynamic pressure and void fraction using classical one-dimensional jump conditions. The sound speed of the bubbly mixture is estimated to determine the Mach number of the cavity flow. The transition from intermittent to transitional to strongly periodic shedding occurs when the average Mach number of the cavity flow exceeds that required for the generation of strong shocks.

ANALYSIS OF THE EFFECTS OF MASS-INJECTION AT THE LEADING EDGE ON CAVITY FLOW CHARACTERISTICS

2009 ◽  
Vol 23 (03) ◽  
pp. 413-416 ◽  
Author(s):  
JI FEI WU ◽  
ZHAO LIN FAN ◽  
XIN FU LUO
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Flow Characteristics ◽  
Leading Edge ◽  
Cavity Flow ◽  
Fluctuating Pressure ◽  
Pressure Distributions ◽  
Mass Injection ◽  
Varying Mass ◽  
Hole Number

An experimental investigation was conducted in a high speed wind tunnel to explore the effects of mass-injection on cavity flow characteristics. Detailed static-pressure and fluctuating pressure measurements were obtained at the cavity floor to enable the effects of the mass-injection at the leading edge to be determined. Results indicate that varying mass-injection hole number and the flux rate of mass-injection has no significant effect on cavity flow characteristics. However, mass-injection can reduce the cavity static pressure gradient when the cavity flow type is transitional-cavity flow. The study also indicates that Mach number can influence the effect of mass-injection on cavity fluctuating pressure distributions, and at supersonic speeds, mass-injection can suppress the cavity tones effectively.

Research on Superfine Wood Powder Disintegrator with Multi-Granularity Used in Power Generation

2009 ◽  
Vol 419-420 ◽  
pp. 505-508 ◽  
Author(s):  
Lan Yu Yang ◽  
Yan Ma
Keyword(s):  
Power Generation ◽  
High Speed ◽  
Static Pressure ◽  
Dynamic Pressure ◽  
Low Noise ◽  
Raw Material ◽  
High Speed Rotation ◽  
Speed Rotation ◽  
High Dynamic ◽  
Main Spindle

Both dynamic cutters installed on the shaft and fixed cutters installed on the shell has realized to form the high-pressured superimposition produced the high dynamic pressure and the static pressure due to the Reynolds effect during process of high-speed rotation, which forms high pressure required by super velocity centrifugal grinding, and raw material of the sawdust or fibrous fragments can be stricken and cut into the wood powders which are in line with granularity of requirement for power generation through treble percussion effect including percussion between the particles and the dynamic and fixed cutters, percussion between particles and particles, and percussion between the particles and the shell. Simultaneously, the disintegrator has realized integration between the main motor and the main spindle, which has many characteristics such as contact construction, low noise and slight vibration. This machine is possible to realize 3 kind of granularity that could be selected.

Magnetosheath high speed jets observed simultaneously by Cluster and MMS

2020 ◽  
Author(s):  
C.-Philippe Escoubet ◽  
Keyword(s):  
Solar Wind ◽  
Mach Number ◽  
High Speed ◽  
Smooth Surface ◽  
Dynamic Pressure ◽  
Dust Cloud ◽  
Bow Shock ◽  
Solar Wind Dynamic Pressure ◽  
Typical Size ◽  
Dust Clouds

<p>The supersonic solar wind is decelerated and thermalized when it encounters the Earth's magnetosphere and cross the bow shock. Sometimes, however, due to discontinuities in the solar wind, bow shock ripples or ionised dust clouds carried by the solar wind, high speed jets (HSJs) are observed in the magnetosheath. These HSJs have typically a Vx component larger than 200 km s-1 and their dynamic pressure can be a few times the solar wind dynamic pressure. They are typically observed downstream from the quasi-parallel bow shock and have a typical size around one Earth radius (RE) in XGSE. We use a conjunction of Cluster and MMS, crossing simultaneously the magnetopause, to study the characteristics of these HSJs and their impact on the magnetopause. Over one hour-fifteen minutes interval in the magnetosheath, Cluster observed 21 HSJs. During the same period, MMS observed 12 HSJs and entered the magnetosphere several times. A jet was observed simultaneously by both MMS and Cluster and it is very likely that they were two distinct HSJs. This shows that HSJs are not localised into small regions but could span a region larger than 10 RE, especially when the quasi-parallel shock is covering the entire dayside magnetosphere under radial IMF. During this period, two and six magnetopause crossings were observed respectively on Cluster and MMS with a significant angle between the observation and the expected normal deduced from models. The angles observed range between from 11° up to 114°. One inbound magnetopause crossing observed by Cluster (magnetopause moving out at 142 km s-1) was observed simultaneous to an outbound magnetopause crossing observed by MMS (magnetopause moving in at -83 km s-1), showing that the magnetopause can have multiple local indentation places, most likely independent from each other. Under the continuous impacts of HSJs, the magnetopause is deformed significantly and can even move in opposite directions at different places. It can therefore not be considered as a smooth surface anymore but more as surface full of local indents. Four dust impacts were observed on MMS, although not at the time when HSJs are observed, showing that dust clouds would have been present during the observations. No dust cloud in the form of Interplanetary Field Enhancements was however observed in the solar wind which may exclude large clouds of dust as a cause of HSJs. Radial IMF and Alfvén Mach number above 10 would fulfill the criteria for the creation of bow shock ripples and the subsequent crossing of HSJs in the magnetosheath.</p>

Comparison of Various Methods for Determining Flight Speed at Great Altitudes

1944 ◽  
Vol 48 (397) ◽  
pp. 12-23
Author(s):  
R. Schmidt
Keyword(s):  
Mach Number ◽  
Indirect Method ◽  
Static Pressure ◽  
Dynamic Pressure ◽  
Accurate Method ◽  
Temperature Variations ◽  
Mean Values ◽  
High Speeds ◽  
The Mean ◽  
Static Head

The speed of flight of an aircraft at high altitudes is still usually determined by the indirect method of measuring the dynamic pressure in flight. The acknowledged defects of this method—the effect of interference by near parts of the aircraft on the static pressure at the tapping point, the necessity of calibration of the pressure readings by tedious quadrilateral flights over measured ground distances or a suspended static head, the indeterminate effect of the Mach number at high speeds, inaccuracy of the ‘air temperature measurements owing to stagnation of the flow at the instrument, errors of the elastic pressure capsule owing to hysteresis and temperature variations, and the inaccuracy of the mean values obtained by averaging the measured dynamic pressures—have all contributed to raise a demand for a simpler and more accurate method of airspeed measurement.

Experimental Study on Flow-Induced Disk Flutter Dynamics by Measuring the Pressure Between Disks

2006 ◽  
Vol 129 (3) ◽  
pp. 368-375 ◽  
Author(s):  
Shigenori Takada ◽  
Norio Tagawa ◽  
Atsunobu Mori ◽  
Yoshiaki Mizoh ◽  
Masaru Nakakita
Keyword(s):  
Pressure Fluctuation ◽  
High Speed ◽  
Static Pressure ◽  
Dynamic Pressure ◽  
Hard Disk Drives ◽  
Laser Doppler Vibrometer ◽  
Disk Drives ◽  
Flow Induced Vibrations ◽  
The Mean ◽  
Disk Flutter

It is important to clarify the characteristics of flow-induced vibrations in hard disk drives in order to achieve an ultrahigh magnetic recording density. In particular, it is necessary to reduce the flow-induced disk vibrations referred to as disk flutter. This paper describes the correlation between the disk vibration amplitude and the pressure fluctuation between a pair of high-speed corotating disks. It also reveals the effects of the arm thickness and arm shape on the disk vibrations and the static pressure between the disks. The disk vibrations were measured using a laser Doppler vibrometer (LDV). The static pressure downstream of the arm between a pair of narrow disks was measured by a method in which a side-hole needle was used as a measurement probe. In addition, the direction of air flow along the trailing edge of the arm was measured using a hot-wire anemometer. The experimental results revealed that the arm inserted between the disks suppresses the disk vibrations. However, the shape and thickness of the arm did not quantitatively affect the disk vibrations. The root-mean-square (RMS) static pressure fluctuation downstream of the arm decreased remarkably, whereas the mean static pressure increased when the arm was inserted between the disks. Furthermore, the circumferential variations in both the RMS and mean static pressures reduced when the arm was inserted. Therefore, it is suggested that the disk vibrations are excited by an increase in the static pressure fluctuation, mean dynamic pressure, and circumferential variation in the static pressure between the disks. Consequently, the disk vibrations can be suppressed by inserting the arm or a spoiler.

Review of Research on Hydrostatic Bearings

2020 ◽  
Vol 13 ◽  
Author(s):  
Xiaodong Yu ◽  
Yu Wang ◽  
Junfeng Wang ◽  
Wenkai Zhou ◽  
Hongwei Bi ◽  
...  
Keyword(s):  
High Speed ◽  
Static Pressure ◽  
Development Trend ◽  
Cnc Machining ◽  
Pressure Effects ◽  
Cnc Machine Tools ◽  
Future Research ◽  
Theoretical Formula ◽  
Hydrostatic Bearing ◽  
Hydrostatic Bearings

Background: Hydrostatic bearings have the advantages of strong bearing capacity, good stability, small friction coefficient and long life. The performance of liquid hydrostatic bearings directly affect the accuracy and efficiency of CNC machining equipment. The performance is conducive to the development of CNC machine tools towards high speed and heavy load, so it is necessary to sort out and summarize the existing research results. Objective: This study summarizes the current development status of hydrostatic bearings and explains the development trend of hydrostatic bearings. Methods: According to the recently published journal articles and patents, the recent experimental research on hydrostatic thrust bearings is summarized. This paper summarizes many factors that affect the performance of hydrostatic bearings, and discusses the causes of various factors on hydrostatic bearings. Finally, future research on hydrostatic bearings is presented. Results: The study discusses experimental methods, simulation processes, and experimental results. Conclusion: This study can produce dynamic and static pressure effects by changing the structure of the oil cavity of the hydrostatic bearing. This effect can make up for the static pressure loss. By improving the theoretical formula and mathematical model and proposing a new simulation method, the accuracy of the hydrostatic bearing simulation is satisfied; the future development trend of the hydrostatic bearing is proposed.

scholarly journals Aerodynamic Losses in Turbines with and without Film Cooling, as Influenced by Mainstream Turbulence, Surface Roughness, Airfoil Shape, and Mach Number

2012 ◽  
Vol 2012 ◽  
pp. 1-28 ◽  
Author(s):  
Phil Ligrani
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Film Cooling ◽  
Total Pressure ◽  
High Speed ◽  
Density Ratio ◽  
Aerodynamic Loss ◽  
Pressure Losses ◽  
Loss Coefficients ◽  
Exit Mach Number

The influences of a variety of different physical phenomena are described as they affect the aerodynamic performance of turbine airfoils in compressible, high-speed flows with either subsonic or transonic Mach number distributions. The presented experimental and numerically predicted results are from a series of investigations which have taken place over the past 32 years. Considered are (i) symmetric airfoils with no film cooling, (ii) symmetric airfoils with film cooling, (iii) cambered vanes with no film cooling, and (iv) cambered vanes with film cooling. When no film cooling is employed on the symmetric airfoils and cambered vanes, experimentally measured and numerically predicted variations of freestream turbulence intensity, surface roughness, exit Mach number, and airfoil camber are considered as they influence local and integrated total pressure losses, deficits of local kinetic energy, Mach number deficits, area-averaged loss coefficients, mass-averaged total pressure loss coefficients, omega loss coefficients, second law loss parameters, and distributions of integrated aerodynamic loss. Similar quantities are measured, and similar parameters are considered when film-cooling is employed on airfoil suction surfaces, along with film cooling density ratio, blowing ratio, Mach number ratio, hole orientation, hole shape, and number of rows of holes.

Auto and Cross Correlation Measurements in a Turbine Cascade Using a Digital Correlator

1982 ◽  
Author(s):  
P. J. Bryanston-Cross ◽  
J. J. Camus
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Cross Correlation ◽  
Turbine Blades ◽  
Image Plane ◽  
Strongly Correlated ◽  
Trailing Edge ◽  
Number Range ◽  
Cross Correlations ◽  
Digital Correlator

A simple technique has been developed which samples the dynamic image plane information of a schlieren system using a digital correlator. Measurements have been made in the passages and in the wakes of transonic turbine blades in a linear cascade. The wind tunnel runs continuously and has independently variable Reynolds and Mach number. As expected, strongly correlated vortices were found in the wake and trailing edge region at 50 KHz. Although these are strongly coherent we show that there is only limited cross-correlation from wake to wake over a Mach no. range M = 0.5 to 1.25 and variation of Reynolds number from 3 × 105 to 106. The trailing edge fluctuation cross correlations were extended both upstream and downstream and preliminary measurements indicate that this technique can be used to obtain information on wake velocity. The vortex frequency has also been measured over the same Mach number range for two different cascades. The results have been compared with high speed schlieren photographs.

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