scholarly journals An Experimental Investigation of the Surface Pressure Fluctuations for Round Cylinders

2018 ◽  
Vol 141 (6) ◽  
Author(s):  
R. Maryami ◽  
M. Azarpeyvand ◽  
A. A. Dehghan ◽  
A. Afshari
Keyword(s):  
Experimental Study ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Pressure Fluctuations ◽  
Flow Structures ◽  
Bluff Bodies ◽  
Number Range ◽  
Aerodynamic Loading ◽  
Unsteady Aerodynamic ◽  
Round Cylinder

An experimental study is carried out to investigate the unsteady pressure exerted on the surface of a round cylinder in the subcritical Reynolds number range. Results are presented for the surface pressure fluctuations, spanwise coherence, lateral correlation length, and peripheral coherence. Discussions are provided for the dominance of the first three vortex shedding tones at different regions of the cylinder and the size of the flow structures around the cylinder. The dataset provided have shed new light on the unsteady aerodynamic loading acting on cylinders and provides the impetus for further research on the aerodynamics and aeroacoustics of bluff bodies.

Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder

2011 ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Unsteady Flow ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Mean Flow ◽  
The Mean ◽  
Velocity Spectra

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α = 60° to α = 90°. Multi-point fluctuating surface pressure and hotwire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, span-wise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused and was still present and correlated from front to back, at least for the larger yaw angles investigated. When the cylinder was yawed to α = 60°, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.

Pressure fluctuations on an oscillating trailing edge

1989 ◽  
Vol 203 ◽  
pp. 307-346 ◽  
Author(s):  
Thomas Staubli ◽  
Donald Rockwell
Keyword(s):  
Surface Pressure ◽  
Vortex Shedding ◽  
Pressure Fluctuations ◽  
Resonant Peak ◽  
Trailing Edge ◽  
Vortical Structures ◽  
Instantaneous Pressure ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency ◽  
Edge Displacement

Turbulent boundary layers separating from a blunt trailing edge give rise to organized vortical structures in the downstream wake. The perturbation of this inherent flow-instability at f0 by controlled oscillations of the edge at fe produces corresponding, organized components of unsteady surface pressure along the edge. For edge excitation near the ‘natural’ vortex shedding frequency f0, the phase between the local pressure fluctuations and the edge displacement shows large changes for small changes in excitation frequency. Moreover, in this range of excitation, there is quenching (or attenuation) of the surface pressure component at f0 and resonant peaking of the component at fe. These phenomena are related to the change in sign of the energy transfer between the fluid and the body. Integration of the instantaneous pressure distributions along the surfaces of the edge leads to the instantaneous lift at fe and f0 acting upon the oscillating trailing edge. The location of the lift varies as the cotangent of the dimensionless time during an oscillation cycle. When the edge is excited near, or at, the natural vortex shedding frequency, there is a resonant peak in the amplitude of oscillation of the lift location at fe; that at f0 is invariant. Moreover, the mean location of the lift at fe undergoes abrupt changes in this region of excitation. Flow visualization allows determination of the phasing of the organized vortical structures shed from the trailing edge relative to the edge displacement. Modulation of the flow structure at the frequencies f0 and fe, as well as interaction of small-scale vortices at high excitation frequencies, was observed. These aspects of the near-wake structure are related to the instantaneous pressure field.

scholarly journals Experimental study of the unsteady aerodynamic loading for a tandem cylinder configuration

2019 ◽  
Author(s):  
Reza Maryami ◽  
Syamir Alihan Showkat Ali ◽  
Mahdi Azarpeyvand ◽  
Ali Dehghan ◽  
Abbas Afshari
Keyword(s):  
Experimental Study ◽  
Aerodynamic Loading ◽  
Unsteady Aerodynamic

Unsteady pressure fluctuations measured on a hammerhead space vehicle and comparison with Coe and Nute's 1962 data

2018 ◽  
Vol 17 (1-2) ◽  
pp. 70-87 ◽  
Author(s):  
J Panda ◽  
TJ Garbeff ◽  
NJ Burnside ◽  
JC Ross
Keyword(s):  
Surface Pressure ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Space Vehicle ◽  
Frequency Bandwidth ◽  
Data Set ◽  
Number Range ◽  
Unsteady Pressure ◽  
Present Test ◽  
Payload Fairing

A detailed survey of pressure fluctuations was conducted on a replica of the generic, “hammerhead” shaped space vehicle tested more than half century ago by Coe and Nute (1962). A large number of current and past space vehicles follow this general hammerhead configuration. The present test was conducted in the 11-by-11 ft Transonic Wind Tunnel of NASA Ames Research Center over the critical transonic Mach number range of 0.6 ≤ M ≤ 1.2 where typical vehicles encounter very high levels of surface pressure fluctuations during ascent through the atmosphere. Out of the many different types of instrumentations used for this test, data from the dynamic pressure sensors are presented in this paper. In addition, shadowgraph flow visualizations, and a qualitative measure of turbulent fluctuations, estimated from high-speed photography, are also presented. The data set provided a clear insight into the local high level of fluctuations from the formation of the transonic shocks on the payload fairing and also from the impingement of the separated shear layer on the second stage. Space–time correlation showed interesting physics of upstream propagation of pressure fluctuations on the payload fairing when local shock waves were present. A comparison of the magnitude of pressure fluctuations between the present test and that done earlier by Coe and Nute showed good agreement when the limited frequency bandwidth of equipment used in the latter was accounted for. Similarly, when accounting for the differences in the free-stream dynamic pressure, the spectra of surface pressure fluctuations were in reasonable agreement between the present and Coe–Nute tests. The present test provides a far more complete picture of pressure fluctuations due to the usage of a large number of pressure transducers (216 versus 30), wider frequency bandwidth (50 kHz versus 1 kHz), and unsteady pressure-sensitive paint.

Experimental Investigation of a Tandem Cylinder System With a Yawed Upstream Cylinder

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Stephen J. Wilkins ◽  
Joseph W. Hall
Keyword(s):  
Experimental Investigation ◽  
Flow Field ◽  
Surface Pressure ◽  
Vortex Shedding ◽  
Flow Direction ◽  
Pressure Fluctuations ◽  
Hot Wire ◽  
Mean Flow ◽  
The Mean ◽  
Velocity Spectra

The unsteady flow field produced by a tandem cylinder system with the upstream cylinder yawed to the mean flow direction is investigated for upstream cylinder yaw angles from α=60 deg to α=90 deg. Multipoint fluctuating surface pressure and hot-wire measurements were conducted at various spanwise positions on both the upstream and downstream cylinders. The results indicate that yawing the front cylinder to the mean flow direction causes the pressure and velocity spectra on the upstream and downstream cylinders to become more broadband than for a regular tandem cylinder system, and reduces the magnitude of the peak associated with the vortex-shedding. However, spanwise correlation and coherence measurements indicate that the vortex-shedding is still present and was being obscured by the enhanced three-dimensionality that the upstream yawed cylinder caused. When the cylinder was yawed to α=60 deg, the pressure fluctuations became extremely broadband and exhibited shorter spanwise correlation.

An experimental study of pressure fluctuations on fixed and oscillating square-section cylinders

1982 ◽  
Vol 119 ◽  
pp. 297-321 ◽  
Author(s):  
P. W. Bearman ◽  
E. D. Obasaju
Keyword(s):  
Experimental Study ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Vortex Shedding ◽  
Pressure Fluctuations ◽  
The Body ◽  
Front Face ◽  
Side Face ◽  
Lock In ◽  
Fixed Cylinder

Measurements are presented of the pressure fluctuations acting on a stationary squaresection cylinder, with the front face normal to the flow, and one forced to oscillate, transverse to a flow, at amplitudes up to 25% of the length of a side. The range of reduced velocities investigated, 4–13, includes the vortex lock-in regime. At lock-in the amplification of the coefficient of fluctuating lift is found to be much less than that found for a circular cylinder. The variation of the phase angle, between lift and displacement, is also different from that measured on a circular cylinder, and vortex-induced oscillations are possible only at the high-reduced-velocity end of the lock-in range. At reduced velocities sufficiently far below lock-in the natural vortex-shedding mode is suppressed and vortices are found to form over the side faces at the body frequency. Intermittent reattachment occurs over the side faces and, for an amplitude of oscillation equal to 10% of the length of a side face, the time-mean drag coefficient can be reduced to 60% of its fixed-cylinder value.

The Relationship Between Energy Separation and Base Drag in Turbine Blade Wakes

2013 ◽  
Author(s):  
J. P. Gostelow ◽  
W. E. Carscallen ◽  
M. Kurosaka ◽  
A. Mahallati
Keyword(s):  
Vortex Shedding ◽  
Large Scale ◽  
Base Pressure ◽  
Energy Separation ◽  
Bluff Bodies ◽  
Number Range ◽  
Pressure Losses ◽  
Central Regions ◽  
Total Temperature ◽  
High Base

During annular cascade testing of a highly-loaded turbine stage of aggressive design, the nozzle blading experienced a redistribution of the downstream total temperature field. In this ostensibly adiabatic arrangement, the central regions of the vane wakes exhibited a significant decrease in total temperature and their edges showed an unexpected increase. To resolve these anomalous results and obtain detailed information over the Mach number range, the mid-span section of the nozzle was tested in a large scale transonic planar cascade. At high subsonic speeds, vortex shedding created energy redistribution in the wake. This was measured using an 80 kHz bandwidth temperature probe, making it possible to investigate wake total temperature fluctuations in addition to fluctuations in total pressure, and hence entropy. ‘Hot spots’ of increased total temperature were found to be located at the edge of the wake and ‘cold spots’ of decreased total temperature were located close to the wake center line. The results from the turbine cascade were consistent with the phenomenon of energy separation behind bluff bodies. High base pressure losses were observed and were also related to the vortex shedding. The blade had a thick trailing edge and the high base pressure loss condition coincided with the peak of energy separation in the wake. The analysis indicates that in the subsonic speed range the phenomena of energy separation and of base pressure deficit are inextricably linked to, and are caused by, vortex shedding. A strategy for minimizing the related adverse impacts on performance is outlined.

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