Time-Series Axisymmetric Base-Pressure Measurements with Simultaneous Near-Wake Planar Visualizations

2005 ◽  
Author(s):  
Patricia Cannon ◽  
Gregory Elliott ◽  
J. Craig Dutton
Keyword(s):  
Time Series ◽  
Base Pressure ◽  
Pressure Measurements ◽  
Near Wake

Analysis of the Near Wake of Bluff Bodies in Ground Proximity

2002 ◽  
Author(s):  
Szabolcs R. Balkanyi ◽  
Luis P. Bernal ◽  
Bahram Khalighi
Keyword(s):  
Vector Fields ◽  
Aerodynamic Drag ◽  
Base Pressure ◽  
Wake Flow ◽  
Vehicle Body ◽  
Recirculation Region ◽  
Bluff Bodies ◽  
Pressure Measurements ◽  
Near Wake ◽  
Mean Velocity

The effect of several drag reducing devices on the near wake of a generic ground vehicle body was investigated. Drag and base pressure measurements were conducted to identify the effects of the devices on the base drag. A Particle Image Velocimetry (PIV) study was conducted to determine changes of the near wake flow field. Averages of more than 200 PIV velocity vector fields were used to compute the mean velocity and turbulent stresses at several cross section planes. The results of the drag and base pressure measurements show that significant reductions of the total aerodynamic drag (as high as 48%) can be achieved with relatively simple devices. The results also indicated that models with base cavity have lower drag than their counter parts without it. The base pressure distributions showed a strong effect of the ground, resulting in decrease of pressure towards the lower half of the base. The PIV study showed that the extent of the recirculation region is not strongly affected by the drag reducing devices. The tested devices however, were found to have a strong effect on the underbody flow. A rapid upward deflection of the underbody flow in the near wake was observed. The devices were also found to reduce the turbulent stresses in the near wake. The turbulent stresses were found to decrease in magnitude with increasing drag reduction.

Flow behind castellated blunt-trailing-edge aerofoils at supersonic speeds

1998 ◽  
Vol 375 ◽  
pp. 85-111 ◽  
Author(s):  
E. C. MAGI ◽  
S. L. GAI
Keyword(s):  
Quantitative Data ◽  
Base Pressure ◽  
Qualitative Description ◽  
Wake Flow ◽  
Spanwise Direction ◽  
Pressure Measurements ◽  
Near Wake ◽  
Trailing Edge ◽  
Blunt Trailing Edge ◽  
The Mean

A study of the near-wake flow of castellated blunt-trailing-edge aerofoils at a Mach number of 2 was conducted to understand the nature of the flow and the mechanisms of base pressure recovery. The investigation has shown that strong gradients exist in the spanwise direction and that the formation of the wake recompression shock occurs further away from the wake axis. Also, the wake neck is broader and diffused. Detailed quantitative data involving pressure measurements, schlieren and holographic interferometry, and laser transit velocimetry, are presented. A theoretical model to predict the mean base pressure on a castellated base is also proposed. Comparison with experimental data shows that the model provides a qualitative description of the flow behind a castellated base at supersonic speeds.

The Effect of Oscillatory Boat-Tail Flaps on the Near Wake of a Prototypical Heavy Vehicle

2010 ◽  
Author(s):  
Martin Johansson ◽  
John Sheridan ◽  
Sverker Fredriksson
Keyword(s):  
Drag Coefficient ◽  
Shear Layer ◽  
Fuel Consumption ◽  
Water Channel ◽  
Base Pressure ◽  
Heavy Vehicle ◽  
Reattachment Length ◽  
Near Wake ◽  
Back Plate ◽  
Strongly Connected

Due to the increased interest in the aerodynamics of truck / trailer combinations as a means to reduce their fuel consumption, experiments have been conducted on a model of a trailer to study possible changes in its near wake arising form attached aft-flaps. The model was fitted with vertical flaps on both sides of the back plate, which were set to oscillate at given frequencies and amplitudes. Experiments were carried out using the PIV system in a Water Channel at Monash University. The oscillation of the flaps perturbed the flow in such a way that the shear layer was significantly changed and the roll up of vortices was moved further upstream, causing a rise in the rate of entrainment and a shorter reattachment length. It also had the effect of a reduced wake size and higher velocities within the wake. These are all effects that are consistent with an increase in the base pressure at the back plate of the trailer and therefore also a reduced drag coefficient, since they are strongly connected.

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