Aerodynamics of Cyclist Posture, Bicycle and Helmet Characteristics in Time Trial Stage

2012 ◽  
Vol 28 (3) ◽  
pp. 317-323 ◽  
Author(s):  
Vincent Chabroux ◽  
Caroline Barelle ◽  
Daniel Favier
Keyword(s):  
Statistical Analysis ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Drag Force ◽  
Time Trial ◽  
Frontal Area ◽  
Significant Gain ◽  
Upper Limbs ◽  
Force Coefficient ◽  
Coefficient Reduction

The present work is focused on the aerodynamic study of different parameters, including both the posture of a cyclist’s upper limbs and the saddle position, in time trial (TT) stages. The aerodynamic influence of a TT helmet large visor is also quantified as a function of the helmet inclination. Experiments conducted in a wind tunnel on nine professional cyclists provided drag force and frontal area measurements to determine the drag force coefficient. Data statistical analysis clearly shows that the hands positioning on shifters and the elbows joined together are significantly reducing the cyclist drag force. Concerning the saddle position, the drag force is shown to be significantly increased (about 3%) when the saddle is raised. The usual helmet inclination appears to be the inclination value minimizing the drag force. Moreover, the addition of a large visor on the helmet is shown to provide a drag coefficient reduction as a function of the helmet inclination. Present results indicate that variations in the TT cyclist posture, the saddle position and the helmet visor can produce a significant gain in time (up to 2.2%) during stages.

scholarly journals A wind-tunnel case study: Increasing road cycling velocity by adopting an aerodynamically improved sprint position

2019 ◽  
pp. 175433711986696
Author(s):  
Timothy Crouch ◽  
Paolo Menaspà ◽  
Nathan Barry ◽  
Nicholas Brown ◽  
Mark C Thompson ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Time Trial ◽  
Force Measurements ◽  
Sampling Errors ◽  
Repeated Testing ◽  
Road Cycling ◽  
Wind Tunnel Study

The main aim of this study was to evaluate the potential to reduce the aerodynamic drag by studying road sprint cyclists’ positions. A male and a female professional road cyclist participated in this wind-tunnel study. Aerodynamic drag measurements are presented for a total of five out-of-seat sprinting positions for each of the athletes under representative competition conditions. The largest reduction in aerodynamic drag measured for each athlete relative to their standard sprinting positions varied between 17% and 27%. The majority of this reduction in aerodynamic drag could be accounted for by changes in the athlete’s projected frontal area. The largest variation in repeat drag coefficient area measurements of out-of-seat sprint positions was 5%, significantly higher than the typical <0.5% observed for repeated testing of time-trial cycling positions. The majority of variation in repeated drag coefficient area measurements was attributed to reproducibility of position and sampling errors associated with time-averaged force measurements of large fluctuating forces.

scholarly journals Modelling of Drag Force Reduction for a Waterjet Propulsion System

2021 ◽  
Vol 58 (5) ◽  
pp. 3-14
Author(s):  
M. Cerpinska ◽  
M. Irbe ◽  
A. Pupurs ◽  
K. Burbeckis
Keyword(s):  
Drag Coefficient ◽  
Drag Force ◽  
Velocity Ratio ◽  
The Body ◽  
Inlet Velocity ◽  
Minimum Drag ◽  
Simulation Results ◽  
Force Reduction ◽  
Design Options ◽  
Coefficient Reduction

Abstract The paper provides simulation results for SUP (Stand Up Paddle) board appendage resistance. Additional propulsion is added to the SUP board. It is equipped with a waterjet. The waterjet is attached to the board rudder. This increases the drag coefficient for rudder five times. To reduce the drag variable, design options for the waterjet duct were proposed. The simulation tests were performed using SolidWorks Flow software using two types of simulations, namely, the pressure on the body and the flow around the body. The objective was to streamline the bluff duct of the waterjet and thus to create the appendage design with minimum drag force from fluid flow and possibly greater Inlet Velocity Ratio. Calculations showed that rounding-off the edges of waterjet duct resulted in 35 % of drag coefficient reduction, while further streamlining reduced it by additional 10 %.

Test Research on Aerodynamic Interference Effect on Aerostatic Coefficients of Main Beam in Parallel Bridge

2012 ◽  
Vol 178-181 ◽  
pp. 2131-2134
Author(s):  
Jie Wang ◽  
Jian Xin Liu
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Wind Tunnel Test ◽  
Lateral Force ◽  
Main Beam ◽  
Interference Effects ◽  
Force Coefficient ◽  
Long Span ◽  
Rigid Frame ◽  
Aerodynamic Interference

Against the problem of the aerodynamic interference effects on aerostatic coefficients between parallel continuous rigid frame bridges with high-pier and long-span, the aerodynamic interference effects on aerostatic coefficients of main beam in the parallel long-span continuous rigid frame bridges were investigated in details by means of wind tunnel test. The space between the two main beams and wind attack angles were changed during the wind tunnel test to study the effects on aerodynamic interferences of aerostatic coefficients of main beam. The test got aerostatic coefficients of 10 conditions. The research results have shown that the aerodynamic interference effects on aerostatic coefficients of main beam in parallel bridges can not be ignored. The aerodynamic interference effects on parallel bridge main beam is shown mainly as follows: The drag coefficient of main beam downstream dropped and the drag coefficient of main beam upstream changed but not change significantly. There are also the aerodynamic interference effects of lateral force coefficient and torque coefficient between the main beams upstream and downstream. The effects upstream are smaller and the effects downstream are larger.

Design for Wind Tunnel Testing of Scaled Model by CFD Method

2013 ◽  
Vol 275-277 ◽  
pp. 567-571
Author(s):  
Zhu Hui ◽  
Zhi Gang Yang
Keyword(s):  
Wind Tunnel ◽  
Drag Force ◽  
Wind Tunnel Testing ◽  
Force Coefficient ◽  
Scaled Model ◽  
Supporting System ◽  
Scheme Design ◽  
Testing Scheme ◽  
Cfd Method ◽  
Tunnel Testing

The numerical investigations presented in this paper deal with wind tunnel testing scheme design for 1/4 scaled MIRA model including supporting system. Based on the structure of aerodynamic and aero-acoustic full scale wind tunnel, using computational fluid dynamics (CFD), focus on MIRA model and supporting system, the drag force of scaled models and supporting system were calculated. By comparing with the wind tunnel testing results and drag force coefficient of reference, it is certain that the wind tunnel testing scheme is available and effective and that the value calculated by CFD is in good agreement with experiments.

Numerical Evaluation of AASHTO Drag Force Coefficients of Water Flow Around Bridge Piers

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Amin Almasri ◽  
Shadi Moqbel
Keyword(s):  
Drag Coefficient ◽  
Drag Force ◽  
Bridge Piers ◽  
Design Codes ◽  
Force Coefficient ◽  
Drag Coefficients ◽  
Design Specifications ◽  
A Value ◽  
Similar Range ◽  
Aashto Lrfd

Drag force is usually exerted on bridge piers due to running river water. This force is calculated empirically based on drag coefficients stated in design codes and specifications. Different values of drag coefficients have been reported in literature. For example, AASHTO LRFD Bridge Design Specifications uses a drag coefficient of 1.4 and 0.7 for square-ended and semicircular-nosed pier, respectively, while Coastal Construction Manual (FEMA P-55) recommends a value of two and 1.2 for square and round piles, respectively. In addition, many researchers have obtained other different values of drag coefficient under similar conditions (i.e., similar range of Reynolds number) reaching to 2.6 for square object. The present study investigates the drag coefficient of flow around square, semicircular-nosed, and 90 deg wedged-nosed and circular piers numerically using finite element method. Results showed that AASHTO values for drag force coefficient varied between very conservative to be under-reckoning. The study recommends that AASHTO drag coefficient values should be revised for different circumstances and under more severe conditions.

Experimental Study of Aerodynamic Interference Effects on Double Thin-Walled Hollow Pier in Tandem Arrangement

2011 ◽  
Vol 368-373 ◽  
pp. 1517-1520 ◽  
Author(s):  
Jie Wang ◽  
Jin Yun Zhao ◽  
Jian Xin Liu
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Wind Direction ◽  
Wind Tunnel Test ◽  
Interference Effects ◽  
Force Coefficient ◽  
Long Span ◽  
Rigid Frame ◽  
Aerodynamic Interference ◽  
Thin Walled

Against the problem of the aerodynamic interference effects on aerostatic coefficients between parallel continuous rigid frame bridges with high-pier and long-span, the aerodynamic interference effects on aerostatic coefficients of double thin-walled hollow pier in the parallel long-span continuous rigid frame bridges were investigated in details by means of wind tunnel test．The space between the two piers and wind direction angles were changed during the wind tunnel test to study the effects on aerodynamic interferences of aerostatic coefficients of twin piers. The test got aerostatic coefficients of 8 conditions. The research results have shown that the aerodynamic interference effects on aerostatic coefficients of double thin-walled hollow pier in parallel bridges can not be ignored. The aerodynamic interference effects on parallel bridge pier is shown mainly as follows: The tandem interval and wind direction angles are important factors affecting interference effects. The drag coefficient of pier downstream dropped and the drag coefficient of pier upstream changed but Not change significantly. There are also the aerodynamic interference effects of lateral force coefficient and torque coefficient between the piers upstream and downstream. The effects upstream are smaller and the effects downstream are larger.

A Wind-Tunnel Study of the Effect of Gap Flow and Gap Seals on the Aerodynamic Drag of Tractor-Trailer Trucks

1978 ◽  
Vol 100 (4) ◽  
pp. 434-438 ◽  
Author(s):  
F. T. Buckley ◽  
C. H. Marks
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Aerodynamic Drag ◽  
Motor Fuel ◽  
Center Line ◽  
Gap Flow ◽  
Yaw Angle ◽  
Wind Tunnel Study ◽  
Gap Width ◽  
Coefficient Reduction

The effect of gap width on the aerodynamic drag of a cab-over-engine tractor-trailer combination has been investigated for full-scale gap widths ranging from 0.61 m (24 in) to 1.83 m (72 in.) over a yaw angle range of 0 to 20 deg. The average drag on the vehicle was found to increase by 16 percent as the gap width increased from 0.61 m to 1.83 m. Drag reductions were found when a vertical seal was placed along the vehicle center line between the tractor and the trailer. Generally, the drag reduction increased as the percentage of gap width that was sealed increased, and as the yaw angle increased. The average drag coefficient reduction provided by a full gap seal increased from 0.02 to 0.05 as the gap width increased from 0.61 m to 1.4 m and then decreased slightly for gap widths up to 1.83 m. The effect of vehicle configuration on gap seal effectiveness was evaluated for a gap width of 1.3 m (51 in.) using models of six different tractors and two different trailers. The average drag coefficient reductions that were found ranged from 0.04 to 0.08 with 83 percent of the data being either 0.04 or 0.05. It is shown that the use of gap seals on the nearly half-million vehicles which comprise the nation’s long-haul trucking fleet can result in the conservation of about 1.4 × 109 liters (0.37 × 109 gal) of motor fuel each year.

Experimental investigations of flow over NACA airfoils 0021 and 4412 of wind turbine blades with and without Tubercles

2021 ◽  
pp. 0309524X2110071
Author(s):  
Usman Butt ◽  
Shafqat Hussain ◽  
Stephan Schacht ◽  
Uwe Ritschel
Keyword(s):  
Wind Tunnel ◽  
Drag Coefficient ◽  
Wind Turbine ◽  
Critical Region ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Experimental Investigations ◽  
Wind Turbine Blades

Experimental investigations of wind turbine blades having NACA airfoils 0021 and 4412 with and without tubercles on the leading edge have been performed in a wind tunnel. It was found that the lift coefficient of the airfoil 0021 with tubercles was higher at Re = 1.2×105 and 1.69×105 in post critical region (at higher angle of attach) than airfoils without tubercles but this difference relatively diminished at higher Reynolds numbers and beyond indicating that there is no effect on the lift coefficients of airfoils with tubercles at higher Reynolds numbers whereas drag coefficient remains unchanged. It is noted that at Re = 1.69×105, the lift coefficient of airfoil without tubercles drops from 0.96 to 0.42 as the angle of attack increases from 15° to 20° which is about 56% and the corresponding values of lift coefficient for airfoil with tubercles are 0.86 and 0.7 at respective angles with18% drop.

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