Influence of base cavity on base pressure at subsonic and supersonic Mach numbers

2019 ◽  
Author(s):  
J. N. Murugan ◽  
Kiran Chutkey ◽  
S. B. Verma
Keyword(s):  
Base Pressure ◽  
Base Cavity ◽  
Mach Numbers

Mitigation of Antisymmetric Mode and Drag with Base Cavities

2021 ◽  
Author(s):  
Viji M ◽  
Srinivas Nistala Vikramaditya
Keyword(s):  
Cavity Length ◽  
Pressure Fluctuations ◽  
Substantial Reduction ◽  
Base Pressure ◽  
Antisymmetric Mode ◽  
Azimuthal Mode ◽  
Total Drag ◽  
Base Cavity ◽  
Mach Numbers ◽  
The Impact

Abstract Experiments were carried out to examine the impact of base cavities on the base pressure fluctuations and total drag of a cylindrical afterbody for freestream Mach numbers 0.6-1.5. Significant improvement in the base pressure and a substantial reduction in the afterbody drag was noticed in the presence of a base cavity at subsonic Mach numbers. However, on increasing the cavity length beyond a certain value its performance deteriorates. At supersonic Mach numbers their effectiveness drops drastically. Tones in the spectra can be classified into two types depending on the dominant azimuthal mode which is either 0 or 1 and are referred to as symmetric and an antisymmetric mode, respectively. Spectra at subsonic Mach numbers exhibit tones which are related either to mode 0 or 1. However, at supersonic Mach numbers only tones related to mode 0 exist. The base cavity either, effectively suppress the antisymmetric mode or modify it into a symmetric mode resulting in mitigation of the tones related to antisymmetric mode.

Blockage Corrections for Blunt-Based Bodies of Revolution

1968 ◽  
Vol 72 (696) ◽  
pp. 1058 ◽  
Author(s):  
W. A. Mair
Keyword(s):  
Correction Factor ◽  
Experimental Results ◽  
Base Pressure ◽  
Alternative Methods ◽  
Wind Tunnels ◽  
Maximum Diameter ◽  
Bodies Of Revolution ◽  
Blockage Correction ◽  
Mach Numbers ◽  
Experimental Values

Calvert has considered alternative methods of estimating the blockage corrections for blunt-based bodies of revolution in closed wind tunnels at low Mach numbers. His models were all of maximum diameter 152 mm, with an ellipsoidal nose section 203 mm long followed by a cylindrical afterbody. The ratio of overall length L to maximum diameter d varied from about 1.5 to 5.5. For each model the base pressure was measured in wind tunnels of two different sizes, so that the blockage correction factor e for the smaller tunnel could be derived for each model from the experimental results. These experimental values of e were compared with alternative theoretical estimates, using the methods given by Evans, Maskell and Pank-hurst and Holder.

Mach Number Effect on Symmetric and Antisymmetric Modes of Base Pressure Fluctuations

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
N. S. Vikramaditya ◽  
M. Viji
Keyword(s):  
Mach Number ◽  
Vortex Shedding ◽  
Pressure Fluctuations ◽  
Base Pressure ◽  
Antisymmetric Mode ◽  
Recirculation Bubble ◽  
Pressure Drops ◽  
Wide Range ◽  
Convective Motions ◽  
Mach Numbers

An experimental study aimed at evaluating the influence of Mach number on the base pressure fluctuations of a cylindrical afterbody was performed over a wide range of Mach numbers from subsonic to supersonic speeds. Time-averaged results indicate that the coefficient of base pressure drops with the increase in the freestream Mach number at subsonic speeds and increases at supersonic Mach numbers. The coefficient of root-mean-square of the pressure fluctuations follows a decreasing trend with the increase in the Mach number. Examination of the spectra reveals different mechanisms dominate the pressure fluctuations from the center to the periphery of the base as well as with the change in the Mach number. Analysis of the azimuthal coherence indicates that all the dominant tones in the spectra can be classified either into a symmetric or an antisymmetric mode at subsonic Mach numbers. However, at supersonic Mach numbers, all the dominant tones in the spectra are symmetric in nature. The results from the cross-correlation suggest that two possible mechanisms of recirculation bubble pulsing and convective motions/vortex shedding are driving the dynamics on the base at subsonic Mach numbers. However, at supersonic Mach numbers, only single mechanism of the recirculation bubble pulsing dominates. Moreover, it indicates that the symmetric mode is associated with the dynamics of the recirculation bubble and the antisymmetric mode is related to the convective motions/vortex shedding.

scholarly journals Investigation and back-propagation modeling of base pressure at sonic and supersonic Mach numbers

2020 ◽  
Vol 32 (9) ◽  
pp. 096109
Author(s):  
Asif Afzal ◽  
Sher Afghan Khan ◽  
Md. Tariqul Islam ◽  
R. D. Jilte ◽  
Ambareen Khan ◽  
...  
Keyword(s):  
Back Propagation ◽  
Base Pressure ◽  
Propagation Modeling ◽  
Mach Numbers

Aerodynamic Performance of a Transonic Turbine Cascade at Off-Design Conditions

2000 ◽  
Vol 123 (3) ◽  
pp. 510-518 ◽  
Author(s):  
D. B. M. Jouini ◽  
S. A. Sjolander ◽  
S. H. Moustapha
Keyword(s):  
Axial Velocity ◽  
Density Ratio ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Base Pressure ◽  
Turbine Cascade ◽  
Blade Loading ◽  
Profile Losses ◽  
Transonic Turbine ◽  
Mach Numbers

The paper presents detailed measurements of the midspan aerodynamic performance of a transonic turbine cascade at off-design conditions. The measurements were conducted for exit Mach numbers ranging from 0.5 to 1.2, and for Reynolds numbers from 4×105 to 106. The profile losses were measured for incidence values of +14.5 deg, +10 deg, +4.5 deg, 0 deg, and −10 deg relative to design. To aid in understanding the loss behavior and to provide other insights into the flow physics, measurements of blade loading, exit flow angles, trailing-edge base pressures, and the axial velocity density ratio (AVDR) were also made. It was found that the profile losses at transonic Mach numbers can be closely related to the base pressure behavior. The losses were also affected by the AVDR.

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