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Vehicle Aerodynamics | Reducing Drag On A Car

What makes vehicle aerodynamics makes safer and more efficient?

Vehicle Aerodynamics is a potential area to minimize fuel consumption. Because the air drag acting on the vehicle is directly proportional to the square of the vehicle speed. So by thoroughly studying and by providing necessary modification the drag force is reduced and there by the following advantages can be achieved.

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Automobile Aerodynamics resistance or drag

Drag is the most significant force in aerodynamics because it affects practically everything that moves in the air. When an airplane moves through the air, it encounters drag as the force opposing it. To generate drag, a solid object must be encountered by air traveling in the same direction as the object. Because it necessitates more effort to overcome, drag is generally considered a bad thing in vehicles and airplanes. In other circumstances, such as when parachutes are used, drag can actually be an advantage.

Objects are weighed and their drag coefficient (Cd) is calculated using this number. Other than the object’s shape, this number is affected by a variety of other variables, including its speed, surface roughness, air density, and whether the flow is laminar or turbulent. The air pressure against the object’s face, the friction along the object’s sides, and the relatively negative pressure, or suction, on the object’s back all contribute to drag.

A flat plate traveling face-on through the air has a Cd of roughly 1.3, which is nearly the same as the Cd of a face-on cube moving face-on through the air. It is 0.01 to 0.03 for aircraft and 0.25 to 0.35 for modern automobiles. Comprehending Cd can be a challenge. Therefore, computer simulations or wind tunnel tests are commonly used to determine it.

What is Aerodynamics?

As the name suggests, “Aerodynamics” refers to the movement of air. In other words, aerodynamics is the study of how wind affects a moving object. the two factors influence the airflow as the vehicle moves.

1. The rate at which the vehicle is moving.

2. The amount of wind in the region.

The vehicle’s body design, including its size and shape, must have acceptable aerodynamic properties.

This field studies how air moves around and through automobiles. Because air is such a thin fluid, it’s better referred to as “Fluid Dynamics” instead. The acceleration, top speed, fuel efficiency, and handling of a car are all affected by the airflow around and through the vehicle once it leaves the slow speeds.

Improving airflow past moving vehicles by modifying the flow characteristics

1. Fuel usage is reduced

2. Better quality of comfort for the occupants

3. Enhancement of vehicle performance and handling (stability, handling, traffic safety)

Fluid dynamics is the study of moving liquids, and aerodynamics is a major component. However, the primary purpose of the subject is to minimize aerodynamic drag. Airflow is the result of aerodynamics.

  • Resistance to Airflow or aerodynamic drag
  • The Wind noises
  • Amount of Noise
  • Preventing lifts that aren’t needed
  • Boost the stability at high speeds.
  • Efficiency.

Without going into the nitty-gritty, the car’s aerodynamic drag is directly proportional to its speed squared. Because of this, a cube of the velocity is required to overcome the drag.

Speed and fuel consumption are strongly linked in terms of the amount of drag a vehicle has to overcome, in other words.

Advantages of Vehicle Aerodynamics

  • Minimum speed and acceleration for the same power output
  • Fuel consumption is reduced, about 35 % of the fuel cost can be reduced by proper streamlining
  • Good appearance
  • By reducing the various forces and moments, good stability and safety can be achieved
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Study of Vehicle Aerodynamics

The study of aerodynamics is carried out in two stages as follows:

  • Making a solid model of the car to a suitable scale for wind tunnel testing for body exterior optimization
  • By conducting a road test to check the drag co-efficient
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Aerodynamic Forces and moments

The aerodynamic forces and moment characteristics should be incorporated into the design of the body. A vehicle is subjected to three forces.

1. Air drag force in the direction of vehicle motion (wind acting along the longitudinal axis), Px.

2. vertically upward-acting aerodynamic lift, Pz

3. Crosswind force in the lateral directions on the side of the car, Py.

Rather than the center of gravity, all these forces exert their influence on the center of pressure. Moments are the result of these forces. The vehicle body is subjected to the combined effects of these forces and moments. The effects of acceleration and deceleration on a moving object Factors affecting the automobile,

  • Force Py on the x-axis generates Mx – the rolling moment induced by this force.
  • Pitching moment,  My, is created by the y-axis force Px (or) P.
  • Force  Py about the z-axis causes a yawing moment, Mz.
Longitudinal (X-axis)DragRolling moment (due to side force)
Lateral (Y-axis)Side forcePitching moment (due to lift force)
Vertical (Z-axis)LiftYawing moment (due to side force)

It’s the ground plan at the mid-wheelbase and mid-brake position that the force measurement originates, not the vehicle’s center of gravity (which may or may not be known during a wind tunnel test).

Reynolds Model Law to calculate car aerodynamics simulation

Here the model is made according to the calculation done by the Reynolds model law:

If viscous forces alone are predominant, a model may be taken to be dynamically similar to the prototype if the ratio of the inertial to the viscous forces is the same in the model and the prototype.

Re = ρVL/μ

The law in which models are based on Reynold’s Number is called as Reynold’s Model Law.

(Re)prototype  =  (Re)mode
ρp Vp LP / μp  =  ρm Vm Lm / μm
ρp Vp LP / ρm Vm Lm  . 1/ μp / μm = 1
ρr Vr Lr / μr = 1

Where scale ratios are:

ρr = ρp / ρ’  Vr  =  Vp / Vm
Lr =  Lp / Lm,  μr = μp / μm

Now, Time scale ratio Tr = Lr / Vr

Velocity scale ratio Vr  =  Vr / Lr

Acceleration scale ratio ar  =  V

Force scale ratio:

Fr  =  mr ar =  (ρr ArLr) ar
Fr =  (ρr L3r)ar

Discharge scale ratio:

Qr =  ρr Ar Vr
Qr =  ρr Lr2 Vr

Road Vehicle Aerodynamics

The road test is carried out by Coast down method, where the vehicle speed is raised to a predetermined value, and the time elapsed for every 10 kph deceleration is noted. Here the vehicle is driven on the narrow road without any disturbances such as braking, turning, gradient, obstacles, etc. Now the recorded values are substituted in the formulae and the drag co-efficient value is calculated. The test is conducted on the vehicle in two conditions.

  • Windows are kept opened
  • Windows are kept closed

In flow visualization the air blower is used to study the flow pattern around the model is photographed and the results were discussed. Finally, suggestions are given for lowering the air drag.

01-Variation of drag with vehicle speed - characteristics curve of aerodynamics drag

Car Aerodynamics and The Car’s Fuel Economy.

A car’s design is a monumental undertaking in and of itself. Every component of a vehicle’s design must be taken into account, but this is especially true for race cars. Nonetheless, since we’re not discussing a race car, let’s concentrate on-road vehicles for now. As a result, ‘aerodynamics,’ in addition to appearance, has a significant impact on fuel economy and driving dynamics.

Road vehicles may be argued to not need to be aerodynamic because they travel at modest speeds. To be clear, aerodynamic drag is a vehicle resistance that must be overcome starting at speeds as low as 80 kph (Even less, but the effect is not that prominent). Here’s a brief definition of aerodynamics in a car to clear things up for you.

01-resistance drag force vs vehicle speed - variation of drag force with vehicle speed

The trade-off between fuel economy and aerodynamic drag

Real-world considerations show that aerodynamic drag accounts for a significant portion of the energy loss in automobiles.

It is the highway where the car experiences the maximum amount of drag, and in the city, the effect is marginal.

In other terms, when the aerodynamic drag is reduced by 10 percent the fuel economy experiences a 5 percent increase out on the highway. But in the city, the gain is about 2 percent.

Real-Life Vehicle Aerodynamics Case Study

Since highway speed limits are rising, aerodynamics is playing an increasingly important part in determining how much fuel a car uses. Is it still unclear to you?

Let’s take a look at this from the perspective of the future. The 2020 Hyundai Verna and 2020 Hyundai Creta both use the same engine, whether it’s a normally aspirated petrol or a diesel-powered model.

In comparison to Verna, Creta has a bigger surface area that is in direct touch with the air.

To accommodate its front part, Creta will need to expend more air. As a result, in order for the vehicle to reach or maintain high speeds, additional gasoline will be required.

In contrast, the lower and more aerodynamic surface area of the Hyundai Verna, a sedan, significantly reduces the vehicle’s aerodynamic drag.

Since the Hyundai Verna is more fuel-efficient than the Hyundai Creta, it will be better for the environment.

10 Race Car Aerodynamics Features and car aerodynamics parts

1. Splitter

On the front of an automobile, the vehicle’s leading edge is designed to block high-pressure air from flowing underneath it. As a result, the splitter generates more downforce.

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2. Dive planes

Usually found on the right and left sides of the front bumper, these attachments are curved to deflect airflow forward, so providing downforce at the front of the vehicle. For this purpose, they can also be employed in an effort to reduce the quantity of high-pressure air that penetrates the vehicle’s underside (which would cause lift and reduce downforce).

3. Vents on the hood

As the air passes through the radiator, it needs a clear path out of the engine compartment to keep the temperature of the engine down.

4. NACA Ducts

These air scoops are designed to have a minimum impact on airflow while still providing an inlet for airflow. Air intakes, radiators, and even cooling for the driver can all benefit from the employment of these devices. NACA ducts were extensively utilized in the Ferrari F40.

5. Vents on the Side

It is possible to see side vents behind the front (or back) wheels of the vehicle. These vents allow airflow to depart the wheel wells, which normally remain turbulent due to the movement of the wheels. Hot air from the engine compartment can be expelled using these.

6. The Side Skirts

Splitters and side skirts share many similarities. To keep the vehicle from being buffeted by high-pressure air, they are positioned as low as feasible.

7. The bowels

To reduce drag and turbulence beneath the vehicle, these are usually smooth and flat when used in motorsports competitions. As a result of a diffuser and low-pressure air under the vehicle, downforce can be generated significantly.

8. Diffuser

Cars with diffusers have a section of the lower body shaped to create an area with increasing air volume below the rear of the vehicle. In this way, the low-pressure air beneath the vehicle can slow down and expand at the rear of it. The diffuser aids in reducing downforce by accelerating the air beneath the vehicle, thus reducing its pressure. Downforce can also be improved by directing airflow upward.

9. Spoiler.

Race car spoilers are not to be confused with a rear wing. They are used to prevent lift by obstructing the path of lift-creating airflow. As a result, airflow from the vehicle’s tailpipe exits in a horizontal or upward direction, resulting in a lack of lift. When a passenger plane is about to land, you can see something similar. Lift is reduced and drag is created when the wing (spoilers) flaps are raised. This helps slow the plane down.

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10. Tailfeather or Rear wing

Wings are airfoils in planes, but in cars, they are used to push the vehicle down by deflecting airflow directly upward. When the wing is interacting with airflow, the vehicle is lowered. In exchange for the reduced drag that downforce provides, however, there is a price to pay:

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