Abstract: Heavy trucks are aerodynamically inefficient due to their un-streamlined body shapes, leading to more than of 60% engine power being required to overcome the aerodynamics drag at 60 m/hr. There are many aerodynamics drag reduction devices developed and this paper presents a study on a drag reduction device called Cross Vortex Trap Device (CVTD) deployed in the gap between the tractor and the trailer of a simplified tractor-trailer model. Numerical simulations have been carried out at Reynolds number 0.51×106 based on inlet flow velocity and height of the trailer using the Reynolds-Averaged Navier-Stokes (RANS) approach. Three different configurations of CVTD have been studied, ranging from single to three slabs, equally spaced on the front face of the trailer. Flow field around three different configurations of trap device have been analysed and presented. The results show that a maximum of 12.25% drag reduction can be achieved when a triple vortex trap device is used. Detailed flow field analysis along with pressure contours are presented to elucidate the drag reduction mechanisms of CVTD and why the triple vortex trap configuration produces the maximum drag reduction among the three configurations tested.
Abstract: Team pursuit is a relatively new event in international
long track speed skating. For a single speed skater the aerodynamic
drag will account for up to 80% of the braking force, thus reducing
the drag can greatly improve the performance. In a team pursuit the
interactions between athletes in near proximity will also be essential,
but is not well studied. In this study, systematic measurements
of the aerodynamic drag, body posture and relative positioning
of speed skaters have been performed in the low speed wind
tunnel at the Norwegian University of Science and Technology, in
order to investigate the aerodynamic interaction between two speed
skaters. Drag measurements of static speed skaters drafting, leading,
side-by-side, and dynamic drag measurements in a synchronized and
unsynchronized movement at different distances, were performed.
The projected frontal area was measured for all postures and
movements and a blockage correction was performed, as the blockage
ratio ranged from 5-15% in the different setups. The static drag
measurements where performed on two test subjects in two different
postures, a low posture and a high posture, and two different distances
between the test subjects 1.5T and 3T where T being the length of the
torso (T=0.63m). A drag reduction was observed for all distances and
configurations, from 39% to 11.4%, for the drafting test subject. The
drag of the leading test subject was only influenced at -1.5T, with
the biggest drag reduction of 5.6%. An increase in drag was seen
for all side-by-side measurements, the biggest increase was observed
to be 25.7%, at the closest distance between the test subjects, and
the lowest at 2.7% with ∼ 0.7 m between the test subjects. A clear
aerodynamic interaction between the test subjects and their postures
was observed for most measurements during static measurements,
with results corresponding well to recent studies. For the dynamic
measurements, the leading test subject had a drag reduction of 3%
even at -3T. The drafting showed a drag reduction of 15% when being
in a synchronized (sync) motion with the leading test subject at 4.5T.
The maximal drag reduction for both the leading and the drafting
test subject were observed when being as close as possible in sync,
with a drag reduction of 8.5% and 25.7% respectively. This study
emphasize the importance of keeping a synchronized movement by
showing that the maximal gain for the leading and drafting dropped to
3.2% and 3.3% respectively when the skaters are in opposite phase.
Individual differences in technique also appear to influence the drag
of the other test subject.
Abstract: The choice of high-speed, low budget hatchback car with diversified options is increasing for meeting the new generation buyers trend. This paper is aimed to augment the current speed of the hatchback cars through the aerodynamic drag reduction technique. The inverted airfoils are facilitated at the bottom of the car for generating the downward force for negating the lift while increasing the current speed range for achieving a better road performance. The numerical simulations have been carried out using a 2D steady pressure-based k-ɛ realizable model with enhanced wall treatment. In our numerical studies, Reynolds-averaged Navier-Stokes model and its code of solution are used. The code is calibrated and validated using the exact solution of the 2D boundary layer displacement thickness at the Sanal flow choking condition for adiabatic flows. We observed through the parametric analytical studies that the inverted airfoil integrated with the bottom surface at various predesigned locations of Hatchback cars can improve its overall aerodynamic efficiency through drag reduction, which obviously decreases the fuel consumption significantly and ensure an optimum road performance lucratively with maximum permissible speed within the framework of the manufactures constraints.
Abstract: This paper presents the results of a Finite Element
based vibration analysis of a solar powered Unmanned Aerial
Vehicle (UAV). The purpose of this paper was to quantify the free
vibration, forced vibration response due to differing point inputs in
order to predict the relative response magnitudes and frequencies at
various wing locations of vibration induced power generators
(magnet in coil) excited by gust and/or control surface pulse-decays
used to help power the flight of the electric UAV. A Fluid Structure
Interaction (FSI) study was performed in order to ascertain pertinent
design stresses and deflections as well as aerodynamic parameters of
the UAV airfoil. The 10 ft span airfoil is modeled using Mylar as the
primary material. Results show that the free mode in bending is 4.8
Hz while the first forced bending mode is on range of 16.2 to 16.7 Hz
depending on the location of excitation. The free torsional bending
mode is 28.3 Hz, and the first forced torsional mode is range of 26.4
to 27.8 Hz, depending on the location of excitation. The FSI results
predict the coefficients of aerodynamic drag and lift of 0.0052 and
0.077, respectively, which matches hand-calculations used to validate
the Finite Element based results. FSI based maximum von Mises
stresses and deflections were found to be 0.282 MPa and 3.4 mm,
respectively. Dynamic pressures on the airfoil range from 1.04 to
1.23 kPa corresponding to velocity magnitudes in range of 22 to 66
m/s.
Abstract: The paper presents a one-dimensional transient
mathematical model of thermal oil-water two-phase emulsion flows
in pipes. The set of the mass, momentum and enthalpy conservation
equations for the continuous fluid and droplet phases are solved. Two
friction correlations for the continuous fluid phase to wall friction are
accounted for in the model and tested. The aerodynamic drag force
between the continuous fluid phase and droplets is modeled, too. The
density and viscosity of both phases are assumed to be constant due
to adiabatic experimental conditions. The proposed mathematical
model is validated on the experimental measurements of oil-water
emulsion flows in horizontal pipe [1,2]. Numerical analysis on
single- and two-phase oil-water flows in a pipe is presented in the
paper. The continuous oil flow having water droplets is simulated.
Predictions, which are performed by using the presented model, show
excellent agreement with the experimental data if the water fraction is
equal or less than 10%. Disagreement between simulations and
measurements is increased if the water fraction is larger than 10%.