A pinboard by Shivaram Arunachalam

PhD Student at École de technologie supérieure studying Carbon Nanotube MEMS. I also love F1!

Pinboard Summary

There is more than meets the eye

What is it? Wikipedia defines Formula One (F1) as the highest class of professional motor racing in the world.

Numbers don't lie Here are some numbers associated with the sport. The budget for a midfield team in 2015 was 130 million pounds. Bigger teams like Mercedes spend close to 500 million pounds. An F1 car can accelerate from 0 to 60 mph and decelerate back to 0 in 3 seconds. Under braking, the driver pulls close to 7g or 7 times the weight of his body.

More than meets the eye To the average viewer, it would seem like cars going round and round in circles but the science and complexity involved in the design of a car is on another level. There is only one objective of an F1 car - to go fast. Strangely, what makes F1 cars quick is air.

To be more precise, aerodynamics or the science of air flow. Modern airliners also are designed on the same principle. Every part of a F1 car is designed to serve a purpose and is designed to optimize air flow around the car. This way, the car is able to "pierce" the air effectively and face less air resistance.

If you follow F1, one word that you will hear constantly is "downforce" - simply put it is the weight of the air that is pressing down on the car. This weight helps the car to take corners at unbelievable speeds. A Formula One car is not as impressive in a straight line as it is through the corners. So, more downforce means a better car. You will be amazed to know that even the brakes are designed to make the car faster (when not braking)! Teams use supercomputers and CFD to run their simulations to study vehicle dynamics and optimize design.

Technology exercise F1 is basically a technological demonstration of the big automobile technologies. These days F1 is focused on using greener and more efficient engine technologies which can be transferred to our normal everyday automobiles in the near future. Today's creature comforts such as ABS, Traction Control and Buttons on the steering wheel are all derived from F1 Tech.

8 items pinned

Variation in Aerodynamic Coefficients with Altitude

Abstract: Precise aerodynamics performance prediction plays key role for a flying vehicle to get its mission completed within desired accuracy. Aerodynamic coefficients for same Mach number can be different at different altitude due to difference in Reynolds number. Prediction of these aerodynamics coefficients can be made through experiments, analytical solution or Computational Fluid Dynamics (CFD). Advancements in computational power have generated the concept of using CFD as a virtual Wind Tunnel (WT), hence aerodynamic performance prediction in present study is based upon CFD (numerical test rig). Simulations at different altitudes for a range of Mach numbers with zero angle of attack are performed to predict axial force coefficient behavior with altitude (Reynolds number). Similar simulations for a fixed Mach number ‘3’ and a range of angle of attacks are also carried out to envisage the variation in normal force and pitching moment coefficients with altitude (Reynolds number). Results clearly depict that the axial force coefficient is a function of altitude (Reynolds number) and increase as altitude increases, especially for subsonic region. Variation in axial force coefficient with altitude (Reynolds number) slightly increases for larger values of angle of attacks. Normal force and pitching moment coefficients do not depend on altitude (Reynolds number) at smaller values of angle of attacks but show slight decrease as altitude increases. Present study suggests that variation of normal force and pitching moment coefficients with altitude can be neglected but the variation of axial force coefficient with altitude should be considered for vehicle fly in dense atmosphere. It is recommended to continue this study to more complex configurations for various Mach numbers with side slip and real gas effects.

Pub.: 22 Mar '17, Pinned: 12 Apr '17

Effect of Static Shape Deformation on Aerodynamics and Aerothermodynamics of Hypersonic Inflatable Aerodynamic Decelerator

Abstract: The inflatable aerodynamic decelerator (IAD), which allows heavier and larger payloads and offers flexibility in landing site selection at higher altitudes, possesses potential superiority in next generation space transport system. However, due to the flexibilities of material and structure assembly, IAD inevitably experiences surface deformation during atmospheric entry, which in turn alters the flowfield around the vehicle and leads to the variations of aerodynamics and aerothermodynamics. In the current study, the effect of the static shape deformation on the hypersonic aerodynamics and aerothermodynamics of a stacked tori Hypersonic Inflatable Aerodynamic Decelerator (HIAD) is demonstrated and analyzed in detail by solving compressible Navier-Stokes equations with Menter's shear stress transport (SST) turbulence model. The deformed shape is obtained by structural modeling in the presence of maximum aerodynamic pressure during entry. The numerical results show that the undulating shape deformation makes significant difference to flow structure. In particular, the more curved outboard forebody surface results in local flow separations and reattachments in valleys, which consequently yields remarkable fluctuations of surface conditions with pressure rising in valleys yet dropping on crests while shear stress and heat flux falling in valleys yet rising on crests. Accordingly, compared with the initial (undeformed) shape, the corresponding differences of surface conditions get more striking outboard, with maximum augmentations of 379 pa, 2224 pa, and 19.0 W/cm2, i.e., 9.8%, 305.9%, and 101.6% for the pressure, shear stress and heat flux respectively. Moreover, it is found that, with the increase of angle of attack, the aerodynamic characters and surface heating vary and the aeroheating disparities are evident between the deformed and initial shape. For the deformable HIAD model investigated in this study, the more intense surface conditions and changed flight aerodynamics are revealed, which is critical for the selection of structure material and design of flight control system.

Pub.: 23 Mar '17, Pinned: 12 Apr '17

Fluctuating wind pressure distribution around full-scale cooling towers

Abstract: At present, external wind pressure description around cooling towers in various loading Codes is based on full-scale measurement data. The data has been collected during 1960s–1990s for hyperbolic cooling towers with heights of about 90 m~120 m, and focus has been usually on the average wind pressure distribution. In fact, modern cooling towers taller than 165 m show sensitivity to wind-induced effects under strong wind excitation. The performance of these flexible structures is closely related to the fluctuating wind action in the atmospheric boundary layer. Modeling of these features is underscored by the difficulty in matching supercritical Reynolds number in boundary layer wind tunnels. Accordingly, it has been difficult to accurately establish a relationship between fluctuating pressures on the surface of a cooling tower to inflow conditions. This has caused a bottleneck for enhancements in the state of wind resistant structural design of larger cooling towers. In view of this difficulty, high Reynolds number flows were simulated in the wind tunnel using scaled model with a combination of surface roughness elements to establish a relationship between the inflow turbulence intensity and pressure fluctuations. This was supplemented by a validation using data from long-term measurements of wind pressure around a 166.68 m cooling tower. Wind tunnel experiments were in a general agreement with full-scale observations which offered a relationship between the fluctuating wind pressure distribution and the incoming turbulence intensity at supercritical Reynolds number conditions (Re≥4×10E7).

Pub.: 06 Mar '17, Pinned: 12 Apr '17