Current Undertray Technology
Aerodynamic improvements in automotive racing have been a vital effect on the performance of the vehicle. Recent developments in Formula SAE (Society of Automotive Engineers) have included in design of aerodynamics devices including inverted wings and undertrays for improvising performance (Tyagi and Madhwesh 2017). Computational Fluid Dynamics simulations have been used for iterating design and identify the impact of downforce developed of several parameters including speed, height and ride. Design of aerodynamic elements of race cars has been complex
This work focuses on a literature of undertray technology has been presented and design of an undertray for Global Formula Racing car. An Undertray Diffuser is just as the front and back wing of race cars. The design of Formula SAE undertray has been developed using CFD and on-track testing for determining actual vehicle perfirmnece on road.
The concept of understray has been developed for close proximity of vehicle on ground and creating a venture effect under the vehicle. Therefore, as like a venture, there will be a nozzle that helps in increasing speed of the vehicle. This nozzle help in increasing velocity of air underneath vehicle and throat where maximum throat is provided by the diffuser (Khokhar and Shirolkar 2015). This condition can be equalize with the Bernouli’s Equation that describes the local velocity increases relative to free stream velocity as local pressure get decreased. Using Bernoulli’s equation in case of steady, incompressible, in viscid flows along a streamline, theoretical pressure drop at the constriction is given by
?1 − ?2 = ? 2 (?2 2 − ?1 2)
where is ρ density of fluid, u1 is the slower fluid velocity where pipe is wider, u2 is faster fluid velocity where pipe is narrower.
Figure 1: Venturi effect Inside a Venturi tube
(Source: Biswal, Prasanth and Naranje 2016)
Downforce can be created by using this low pressure under designed vehicle. The efficiency of an udertray has been proper as the efficiency of the diffusion. The high visibility relative to rest of undertray has been creating some misconception in race car industry for working if diffuser. As argued by Trzesniowski (2017), diffuser helps in creating a downforce of the undertray and it expands air under vehicle causing lowered pressure.
Figure 2: Race cars use inverted airplane wings to produce downforce instead of lift
(Source: Grabis and Agarwal 2017)
However, both this concepts abut diffuser have been driven wrong as the diffuser has been role for slowing down air under vehicle back down for free streaming and reducing drag for increasing the overall efficiency of undertray. The location of entrance o diffuser has been affecting low pressure in the understray of vehicle. The angle of diffuser has been relative to the affect over the ground that has been affecting the magnitude of downforce. It has been highest angle without flow of separation for generating maximum downforce (Bosch 2018). Two-dimensional simulation of diffuser angle has been showing maximum downforce for reaching an angle of 5 degree. As commented by Milan (2018), experiments and 3D simulation has been effective in maintaining these changes in the pressure. A vortex helps in adding a rotational component to the velocity by decreasing the pressure along its length, therefore, vortex flow has been adding their energy in flowing and create delay in separation allowing larger diffuser angles. Vortices has been used in other parts of the undertray (Prasanth et al. 2016). Large vortex generators has been replaced in the entrance of the understray that helps vortices in travelling along the length of the vehicle. However, all of these ideas can be put together for creating an effective undertray for producing a large amount of downforce with survey small for increasing drag.
CFD Simulation of Vehicle Aerodynamics
As commented by Hady (2018), CFD simulation can help in clearing up the interactions of flow around the vehicle. This solution has been used to observe pressure, downforce, velocity and drag by other fluid properties. However, there has been some work done in the 2D simulation of airfoils. As suggested by Mercadal Llobera (2017), fizzing up the CFD model in geometry of Computer Aided Design (CAD) package has been imported for creating the design of vehicle (Hady 2018). The use of the CAD has been beneficial for the designing the outer layer of the race car. The geometry of the design has been properly maintained and balanced in the CAD that might help in generating velocity.
Figure 3: Drag force acting on a moving race car
(Source: Grabis and Agarwal 2018))
The aberrance in the wind tunnel of the race car has been kept long for proper flow of fluid. However, the exit to the wind tunnel has been laced at many car lengths. Therefore, the simulation of the open wheeled car must be with tires rotating on ground for setting a movement on ground. The CFD model have helped in rotating tires that will help in capturing the behavior of flow. The airflow in the race car has been very turbulent, therefore a model needs to be verification of simulation of flow (Soliman, Martins and Schommer 2015). There are four major turbulence models in the automotive industry including k-ε, k-ω, Lattice-Boltzmann and Large Eddy Simulation (LES). Direct Numerical Simulation (DNS) has been applied in automotive industry that requires large mesh numbers for computing power and time for traditional design turn around. Therefore mesh numbers have been widely depending on simulation of computational power. These simulations have been beneficial for designer as there can be visual ads and data of interactions (Bradford, Montomoli and D’Ammaro 2014). Therefore, this simulation has been set up using commercial program Star-CCM+. Imported CAD geometry has been used in all surfaces. A box has been made along geometry for serving as boundary condition for providing extra space 1 car length in front, 3 lengths rear and 1 length to side.
Figure 4: Simulation geometry with labels
(Source: Mathijsen 2017)
Mesh size has been chosen that helps in detailing vehicle as accurately captured for cell count on order of a million. Therefore, a prism layer mesh consisting of live layers have been included near wall effects. The mess has been allowed for growing large sizes away from the vehicle geometry for reducing cell count in detailed solution (Dahlberg 2014).
FSAE Aerodynamic Devices
Figure 5: Prism layer mesh detail
(Source: Unni 2017)
There have been various upgrades in Aerodynamics as FSAE car development has become easy for the industry. The speed of the race cars have been increased with laps of time. The ugradation in the technology in automotive dusty have helped in developing a safer approach towards the development of race cars. The main aim of the companies have been reducing risks of accidents due to high speed of race cars (Kalyan, Rajak and Annamalai 2017). They have focused on developing aerodynamic devices having balanced body and design with high speed. Streamlined updates are one of key regions in a FSAE auto improvement which can undoubtedly have effect in opposition occasions, with coordinate impact on best and cornering speed. Contingent upon required objectives of each group being referred to, they can either diminish drag and increment top speed, increment down power and drag levels for cornering paces, or go for a harmony between two.
Streamlined redesigns come in a wide range of structures and have developed generally from the beginning of FSAE rivalries with a streamline plan in the plain start. This was trying to expand generally top speeds and played a major effect on outline headings. Most regular gadgets and numerous others are utilized to influence FSAE autos to build their streamlined proficiency, this thusly keeps the tires planted on the ground and expand hold (Weingart 2015). There are numerous contrasts between “open wheel” and “shut wheel” streamlined plans and a few parts are not material in two determinations but rather they share shared objective to increment downforce levels with the insignificant measure of drag (Patidar and Bhamidipati 2014). Delivering downforce without formation of drag is incomprehensible and it is dependably an exercise in careful control to achieve the best exchange off and augment streamlined productivity.
The initial segment of a FSAE auto which interacts with air is certainly front wing. This implies it initial segment of auto that associates with air, thusly it has imperative part to decide under-stream course through whatever remains of auto. Front wings are ordinarily mounted near suspension, or even on mounts so as to transmit descending heaps of power as successfully as could be expected under circumstances and make downforce so as to press feels worn out on the front wheels into ground and produce higher hold levels. The front wing creates up 20% – 30% of aggregate downforce on the auto (Volk 2014). The fundamental plan of a FSAE front wing is for most part a multi-component airfoil which is normally firmly coupled airfoils comprising of two or even four components stretched out from two sides of nosecone, with mobile folds fused in outline to alter of approach. The wing’s principle component is generally a symmetric airfoil which is brought up in middle keeping in mind end goal to enable a somewhat better wind current to the underfloor, however it additionally lessens the wings ride stature affectability.
In any case, both this ideas adjoin diffuser have been driven wrong as the diffuser has been part to back off air under vehicle withdraw with the expectation of complimentary spilling and decreasing drag for expanding the general proficiency of undertray (Janson and Piechna 2015). The area of passageway o diffuser has been influencing low weight in the understray of vehicle. The point of the diffuser has been with respect to the effect over the ground that has been influencing the size of downforce. It has been the most elevated point without stream of partition for creating greatest downforce. Two-dimensional recreation of diffuser edge has been demonstrating greatest downforce for achieving an edge of 5 degree. As remarked by Leyva (2014), investigations and 3D reenactment has been successful in keeping up these adjustments in the weight. A vortex helps in adding a rotational segment to the speed by diminishing the weight along its length, hence, the vortex stream has been including their vitality in streaming and make delay in partition permitting bigger diffuser points. Vortices has been utilized in different parts of the undertray (Milan 2018). Huge vortex generators has been supplanted in the passageway of the understray that helps vortices in going along the length of the vehicle. In any case, these thoughts can be assembled for making a viable undertray for delivering a lot of downforce with review little to increase drag.
Conclusion
It can be concluded that the downforce of the racing car have been an important factor in increasing the speed of race car. The abnormality in the breeze passage of the race auto has been kept yearn for appropriate stream of liquid. In any case, the exit to the breeze burrow has been bound at numerous auto lengths. Consequently, the recreation of the open wheeled auto must be with tires pivoting on ground for setting a development on ground. The CFD show have helped in pivoting tires that will help in catching the conduct of the stream. The wind current in the race auto has been extremely fierce, in this manner a model should be confirmation of reenactment of the stream.
References
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