Microscale pressure fluctuations near waves being generated by the wind

1972 ◽  
Vol 54 (3) ◽  
pp. 427-448 ◽  
Author(s):  
J. A. Elliott
Keyword(s):  
Static Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Phase Speed ◽  
Sea Waves ◽  
Mean Wind Speed ◽  
The Mean ◽  
Active Wave ◽  
The Waves ◽  
Active Generation

Measurements of static pressure and wave height are used to describe the waveinduced pressure field above generating sea waves. A large hump in the pressure spectra is observed at the wave frequencies. The amplitude of this hump increases and the rate of its vertical decay decreases as the mean wind speed increases. The phase difference between the pressure and the waves during active generation is about 135°, pressure lagging the waves, and does not change vertically for measurements at heights greater than the wave crests. In the present data, active wave generation appears to occur only when the wind at a height of 5 metres is greater than or about equal to twice the phase speed of the waves.

Vertical Profiles of the Wave-Induced Airflow above Ocean Surface Waves

2018 ◽  
Vol 48 (12) ◽  
pp. 2901-2922 ◽  
Author(s):  
Laurent Grare ◽  
Luc Lenain ◽  
W. Kendall Melville
Keyword(s):  
Southern California ◽  
Phase Speed ◽  
Critical Layer ◽  
Wave Age ◽  
Ocean Surface Waves ◽  
Sonic Anemometers ◽  
Mean Wind Speed ◽  
The Mean ◽  
Wave Induced ◽  
The Waves

AbstractAn analysis of coherent measurements of winds and waves from data collected during the ONR Southern California 2013 (SoCal2013) program from R/P FLIP off the coast of Southern California in November 2013 is presented. An array of ultrasonic anemometers mounted on a telescopic mast was deployed to resolve the vertical profile of the modulation of the marine atmospheric boundary layer by the waves. Spectral analysis of the data provides the wave-induced components of the wind velocity for various wind-wave conditions. Results show that the wave-induced fluctuations depend both on the spectral wave age and the normalized height , where c is the linear phase speed of the waves with wavenumber k and is the mean wind speed measured at the height z. The dependence on the spectral wave age expresses the sensitivity of the wave-induced airflow to the critical layer where . Across the critical layer, there is a significant change of both the amplitude and phase of the wave-induced fluctuations. Below the critical layer, the phase remains constant while the amplitude decays exponentially depending on the normalized height. Accounting for this double dependency, the nondimensionalization of the amplitude of the wave-induced fluctuations by the surface orbital velocity collapses all the data measured by the array of sonic anemometers, where a is the amplitude of the waves.

Wave-Coherent Airflow and Critical Layers over Ocean Waves

2013 ◽  
Vol 43 (10) ◽  
pp. 2156-2172 ◽  
Author(s):  
Laurent Grare ◽  
Luc Lenain ◽  
W. Kendall Melville
Keyword(s):  
Momentum Flux ◽  
Wave Spectrum ◽  
Phase Speed ◽  
Ocean Waves ◽  
Naval Research ◽  
Critical Height ◽  
Office Of Naval Research ◽  
Mean Wind Speed ◽  
Wave Induced ◽  
The Waves

Abstract An analysis of coherent measurements of winds and waves from data collected during the Office of Naval Research (ONR) High-Resolution air–sea interaction (HiRes) program, from the Floating Instrument Platform (R/P FLIP), off the coast of northern California in June 2010 is presented. A suite of wind and wave measuring systems was deployed to resolve the modulation of the marine atmospheric boundary layer by waves. Spectral analysis of the data provided the wave-induced components of the wind velocity for various wind–wave conditions. The power spectral density, the amplitude, and the phase (relative to the waves) of these wave-induced components are computed and bin averaged over spectral wave age c/U(z) or c/u*, where c is the linear phase speed of the waves, U(z) is the mean wind speed measured at the height z of the anemometer, and u* is the friction velocity in the air. Results are qualitatively consistent with the critical layer theory of Miles. Across the critical height zc, defined such that U(zc) = c, the wave-induced vertical and horizontal velocities change significantly in both amplitude and phase. The measured wave-induced momentum flux shows that, for growing waves, less than 10% of the momentum flux at z ≈ 10 m is supported by waves longer than approximately 15 m. For older sea states, these waves are able to generate upward wave-induced momentum flux opposed to the overall downward momentum flux. The measured amplitude of this upward wave-induced momentum flux was up to 20% of the value of the total wind stress when Cp/u* > 60, where Cp is the phase speed at the peak of the wave spectrum.

On the decrease of velocity with depth in an irrotational water wave

1953 ◽  
Vol 49 (3) ◽  
pp. 552-560 ◽  
Author(s):  
M. S. Longuet-Higgins
Keyword(s):  
Periodic Motion ◽  
Water Wave ◽  
Pressure Fluctuations ◽  
Periodic Wave ◽  
Finite Amplitude ◽  
Transport Velocity ◽  
Mean Pressure ◽  
Mass Transport Velocity ◽  
The Mean ◽  
The Waves

ABSTRACTThe following theorems are proved for irrotational surface waves of finite amplitude in a uniform, incompressible fluid:(a) In any space-periodic motion (progressive or otherwise) in uniform depth, the mean square of the velocity is a decreasing function of the mean depth z below the surface. Hence the fluctuations in the mean pressure increase with z.(b) In any space-periodic motion in infinite depth, the particle motion tends to zero exponentially as z tends to infinity. The pressure fluctuations at great depths are therefore simultaneous, but they do not in general tend to zero.(c) In a progressive periodic wave in uniform depth the mass-transport velocity is a decreasing function of the mean depth of a particle below the free surface, and the tangent to the velocity profile is vertical at the bottom. This result conflicts with observations in wave tanks, and shows that the waves cannot be wholly irrotational.(d) Analogous results are proved for the solitary wave.

Wind action on water standing in a laboratory channel

1966 ◽  
Vol 26 (4) ◽  
pp. 651-687 ◽  
Author(s):  
G. M. Hidy ◽  
E. J. Plate
Keyword(s):  
Water Surface ◽  
Wind Waves ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Wavy Surface ◽  
Recent Theory ◽  
Waves And Currents ◽  
Mean Wind Speed ◽  
Equilibrium Range ◽  
The Waves

The development of waves and currents resulting from the action of a steady wind on initially standing water has been investigated in a wind–water tunnel. The mean air flow near the water surface, the properties of wind waves, and the drift currents were measured as they evolved with increasing fetch, depth and mean wind speed. The results suggest how the stress on the water surface changes with an increasingly wavy surface, and, from a different viewpoint, how the drift current and the waves develop in relation to the friction velocity of the air. The amplitude spectra calculated for the wavy surface reflected certain features characteristic of an equilibrium configuration, especially in the higher frequencies. The observed equilibrium range in the high frequencies of the spectra fits the f−5 rule satisfactorily up to frequencies f of about 15 c/s. The wave spectra also revealed how the waves grow in the channel, both with time at a fixed point, and with distance from the leading edge of the water. These results are discussed in the light of recent theories for wave generation resulting from the action of pressure fluctuations in the air, and from shearing flow instabilities near the wavy surface. The experimental observations agree reasonably well with the predictions of the recent theory proposed by Miles, using growth rates calculated for the mechanism suggesting energy transfer to the water through the viscous layer in the air near the water surface.

Experimental Investigation of Flow Induced Rotor Oscillations in a Centrifugal Sewage Water Pump

Volume 3 ◽  
2004 ◽  
Author(s):  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen ◽  
Oliver Schneider
Keyword(s):  
Experimental Investigation ◽  
Static Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Sewage Water ◽  
Water Pump ◽  
Flow Rates ◽  
Pump Rotor ◽  
Pump Shaft ◽  
Impeller Geometry

Most of the pumps for sewage transport have a special impeller geometry in order to avoid operational disturbances by clogging. The almost exclusively used single stage machines particularly are equipped with single-blade impellers. With this impeller geometry a strongly uneven pressure field along the perimeter of the pump casing can be expected. The resulting periodically unsteady flow forces affect the impeller and produce strong radial deflections of the pump shaft. In this contribution the experimental investigation of the dynamic behavior of the pump rotor as a consequence of the transient hydrodynamic forces is described. To verify the calculated rotor oscillations measurements were performed at several rotating speeds and at different volume flow rates. The pump which before has been investigated numerical was equipped with several sensors. The deflections of the pump rotor were measured with two proximity sensors. The measurement of the vibration accelerations at the pump casing showed the effects of the transient hydrodynamic stimulation forces. Measurements of the static pressure in the casing allowed a correlation between the rotor oscillations and the pressure fluctuations produced by the single-blade impeller.

scholarly journals Comparative Analysis of Surface Pressure Fluctuations of High-Speed Train Running in Open-Field and Tunnel Using LES and Wavenumber-Frequency Analysis

2021 ◽  
Vol 11 (24) ◽  
pp. 11702
Author(s):  
Songjune Lee ◽  
Cheolung Cheong ◽  
Byunghee Kim ◽  
Jaehwan Kim
Keyword(s):  
Open Field ◽  
Surface Pressure ◽  
High Speed ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
External Flow ◽  
High Speed Train ◽  
Wall Panel ◽  
Mean Flow ◽  
The Mean

The interior noise of a high-speed train due to the external flow disturbance is more than ever a major problem for product developers to consider during a design state. Since the external surface pressure field induces wall panel vibration of a high-speed train, which in turn generates the interior sound, the first step for low interior noise design is to characterize the surface pressure fluctuations due to external disturbance. In this study, the external flow field of a high-speed train cruising at a speed of 300 km/h in open-field and tunnel are numerically investigated using high-resolution compressible LES (large eddy simulation) techniques, with a focus on characterizing fluctuating surface pressure field according to surrounding conditions of the cruising train, i.e., open-field and tunnel. First, compressible LES schemes with high-resolution grids were employed to accurately predict the exterior flow and acoustic fields around a high-speed train simultaneously. Then, the predicted fluctuating pressure field on the wall panel surface of a train was decomposed into incompressible and compressible ones using the wavenumber-frequency transform, given that the incompressible pressure wave induced by the turbulent eddies within the boundary layer is transported approximately at the mean flow and the compressible pressure wave propagated at the vector sum of the sound speed and the mean flow velocity. Lastly, the power levels due to each pressure field were computed and compared between open-field and tunnel. It was found that there is no significant difference in the power levels of incompressible surface pressure fluctuations between the two cases. However, the decomposed compressible one in the tunnel case is higher by about 2~10 dB than in the open-field case. This result reveals that the increased interior sound of the high-speed train running in a tunnel is due to the compressible surface pressure field.

Effect of Clocking on the Second Stator Pressure Field of a One and a Half Stage Transonic Turbine

2004 ◽  
Author(s):  
J. Gadea ◽  
R. De´nos ◽  
G. Paniagua ◽  
N. Billiard ◽  
C. H. Sieverding
Keyword(s):  
Pressure Distribution ◽  
Static Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Fast Response ◽  
Time Resolved ◽  
Pressure Transducers ◽  
Static Pressure Distribution ◽  
Transonic Turbine

This paper focuses on the experimental investigation of the time-averaged and time-resolved pressure field of a second stator tested in a one and a half stage high-pressure transonic turbine. The effect of clocking and its influence on the aerodynamic and mechanical behaviour are investigated. The test program includes four different clocking positions, i.e. relative pitch-wise positions between the first and the second stator. Pneumatic probes located upstream and downstream of the second stator provide the time-averaged component of the pressure field. For the second stator airfoil, both time-averaged and time-resolved surface static pressure fields are measured at 15, 50 and 85% span with fast response pressure transducers. Regarding the time-averaged results, the effect of clocking is mostly observed in the leading edge region of the second stator, the largest effects being observed at 15% span. The surface static pressure distribution is changed locally, which is likely to affect the overall performance of the airfoil. The phase-locked averaging technique allows to process the time-resolved component of the data. The pressure fluctuations are attributed to the passage of pressure gradients linked to the traversing of the upstream rotor. The pattern of these fluctuations changes noticeably as a function of clocking. Finally, the time-resolved pressure distribution is integrated along the second stator surface to determine the unsteady forces applied on the vane. The magnitude of the unsteady force is very dependent on the clocking position.

Measurement of Flow Induced Rotor Oscillations in a Single-Blade Centrifugal Pump

2004 ◽  
Author(s):  
Friedrich-Karl Benra ◽  
Hans Josef Dohmen ◽  
Oliver Schneider
Keyword(s):  
Static Pressure ◽  
Pressure Field ◽  
Pressure Fluctuations ◽  
Sewage Water ◽  
Volume Flow ◽  
Flow Rates ◽  
Pump Rotor ◽  
Simultaneous Measurements ◽  
Pump Shaft ◽  
Impeller Geometry

The composition of sewage water with partially large portions of fibers and solids requires a special impeller geometry, in order to avoid operational disturbances of the pump by clogging. Therefore the almost exclusively used single stage machines particularly are equipped with single-blade impellers. The rotation of the impeller in the pump casing produces a strongly uneven pressure field along the perimeter of the casing. The resulting periodically unsteady flow forces affect the impeller and produce radial deflections of the pump shaft which can be recognized as vibrations at the bearing blocks or at the pump casing [1]. In this contribution the experimental investigation of the dynamic behavior of a pump rotor under the influence of the flow forces is described. To verify calculated results performed earlier a lot of measurements have been carried out at several speeds of rotation and at different volume flow rates. The pump which before was investigated numerical had been equipped with several sensors. The deflections of the pump rotor were measured with two proximity sensors and compared to the computed amounts. Measurements of the static pressure in the casing gave the connection between the rotor oscillations and the pressure fluctuations produced by the single-blade impeller. The simultaneous measurements of the vibration velocities and accelerations at the pump casing showed the effects of the transient hydrodynamic stimulation forces.

On internal gravity waves in an accelerating shear flow

1978 ◽  
Vol 88 (4) ◽  
pp. 623-639 ◽  
Author(s):  
S. A. Thorpe
Keyword(s):  
Gravity Waves ◽  
Phase Distribution ◽  
Phase Speed ◽  
Internal Gravity Waves ◽  
Initial Energy ◽  
Constant Density ◽  
Mean Flow ◽  
Mean Velocity ◽  
The Mean ◽  
The Waves

The investigation of the effects which a changing mean flow has on a uniform train of internal gravity waves (Thorpe 1978a) is continued by considering waves in a uniformly accelerating stratified plane Couette flow with constant density gradient. Experiments reveal a change in the mode structure and phase distribution of the waves, and their eventual breaking near the boundary where the mean flow is greatest, the phase speed of the waves being positive. A linear numerical model is devised which accurately describes the waves up to the onset of their breaking, and this is used to investigate their energetics. The working of the Reynolds stress against the mean velocity gradient results in a very rapid transfer of energy from the waves to the mean flow, so that by the time breaking occurs only a small fraction of their initial energy remains for possible transfer into potential energy of the fluid.The consequences have important applications in oceanography and meteorology, to flow stability and flow generation, and explain some earlier laboratory observations.

The refraction of sea waves in shallow water

1956 ◽  
Vol 1 (2) ◽  
pp. 163-176 ◽  
Author(s):  
M. S. Longuet-Higgins
Keyword(s):  
Shallow Water ◽  
Wave Length ◽  
Sea Waves ◽  
Numerical Examples ◽  
The Mean ◽  
Change In Mean ◽  
The Waves

This paper considers the changes that occur in the character of short-crested sea waves when they are refracted by a shallowing depth of water. Besides a change in mean wave-length and direction there is also a change (usually an increase) in the mean length of the crests. If the waves approach obliquely they become skew, that is, the crests become staggered one behind another.When a short-crested sea is superposed on a long-creasted swell, refraction tends to amplify the longer waves more than the shorter ones. This also produces an increase in the mean length of the crests.Numerical examples are given.

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