INTRODUCTION
Aerodynamic drag manifests as a counteracting force against the relative movement of an object in relation to the encompassing fluid. It can also be interpreted as resistance arising between two disparate fluids or between a fluid and a solid interface. This frictional resistance diminishes the fuel efficiency of vehicles, as elucidated by Ageev and Pavlenko (2016). In contemporary times, fuel efficiency is a paramount consideration for engineers striving to uphold the sustainability of motor vehicles, often prompting modifications in their structural frameworks.
This report will delve into several methodologies aimed at diminishing aerodynamic drag across various vehicle types. The principal objective of this examination is to quantify the energy loss induced by drag and to scrutinize a range of strategies designed to analyze the energy required to counteract aerodynamic drag. Furthermore, the mechanisms for calculating fuel consumption attributable to drag will be discussed in detail. Some assumptions are required to contextualize the analysis, and these will also be addressed within the scope of the report, offering accounting assignment help for those delving into the technicalities.
MAIN BODY
Aerodynamic Drag is a mechanical force on the object that resist the motion through the fluid called drag and if fluid is gas like air called aerodynamic and if fluid is water it is hydrodynamic. Which are induced interaction between solid and fluid like gas and liquid. Drag is generate through the difference of velocity, if the velocity of the solid and fluid are different drag is occurs (Aschwanden and Gopalswamy, 2019). Drag is act in the direction of opposite of object motion. Drag aerodynamic is one type of force so it is a vector quantity so that having both magnitude and direction. The aero dynamic drag force depend upon the various factor like density of the fluid (Air / liquid, cross section area which are direction of the motion, velocity, and aero dynamic coefficient.
Drag reduction using rear screen : In this method certain installation like the plate (Rear screen) is placed at back of the vehicle. By this rear screen air separation is create at the end wall of the vehicle. By this rear screen the vortex is generate between the rear screen and end wall of the vehicle. The generation n of vortex reduce the air separation (Merkes, Menaspà and Abbiss, 2019). By this method the drag aerodynamic is reduced and if increase the distance between rear screen and rear wall of the vehicle we got a better result.
Drag reduction using rear fairing : Rear fairing is addition extended structure at air separation area in vehicle. The extended structure make perfect no air separation. The full size of rear fairing reduce drag aerodynamic 26%,half size reduce approx 22% and quarter length reduce approx 16% drag aerodynamic.
Using of vortex generator : Mostly the drag generate through the air separation formed at the rear end so the vortex generator array and rear spoiler placed on the trunk (boot) side of the vehicle. The counter rotating of vortex generator reduce the drag. By the vortex generator approx 23% reduce drag and also it saving 11.5% fuel reduction.
Use of bumped shaped vortex generator : the bump shaped vortex generator having a rear slope 25 to 30 degree but the perfectly formed vortex at 27 degree. The 20 to 25 mm height of bumped shaped generator effectively reduce the drag (Shim, Lee and Kim, 2017). By the effective size of bumped generator reduced the drag coefficient to 0.003.
Use of delta-wing shaped vortex generator : The delta wing shaped vortex generator are placed at 15 degree angle at the centre of the vehicle. The effective height of delta wing shaped vortex generator 15 mm, 20 mm and 25 mm. By this effective height the reduction of drag coefficient is 0.006. The main reason of effective result is low frontal projection area.
The drag also depend upon the shape of the object so the drag coefficient depend upon the shape of the body. Various methods that can be used to evaluate the energy loss due to aerodynamic drag. The most of drag that is faced by a moving vehicle or object is due to the pressure difference (SkrucAny, SArkAn and GnAp, 2016). The drag is a resistive force that works in the opposite to the direction of vehicle. These force force reduces the speed of the vehicle and reduce its fuel efficiency. This condition can be explained with a equation that includes various forces that are felt by the vehicle in the movement with an constant speed.
D = CD* S * (1/2)pU2
D = Drag
CD = Drag Coefficient (dependent on the shape of the vehicle)
S = Cross Sectional Area of Vehicle
pU2 = Dynamic Pressure
These are some factors and variables are considered in the report that can help to evaluate the Drag force faced by the vehicle during the movement.
Power = D * U * RR * U AuxP
Fuel Consumption = FC = (bsfc) * Power
The relationship Between the change in drag force and changes in consumption of fuel can be represented as -
ΔFC / FC = ΔP / P= Æž * {(ΔCD / CD) + (ΔS / S) + (3ΔU / U)}
Æž is considered as property of th driving cycle. The value of for a car or a truck at highway speed is 0.5 to 0.7.
(ΔCD / CD) is known as the change in the shape of the vehicle in order to make proper improvement in the aerodynamics of vehicles.
(ΔS / S) is known as the changes that is made in the cross section area of vehicle that is considered for the evaluation.
(3ΔU / U) is considered as the change that is made in the speed of the vehicle.
The energy lost due to resistance can be considered as one factor that can affect fuel efficiency of the vehicle (Szmuk, Acikmese and Berning, 2016). As a vehicle moves with velocity of V it creates a tube behind that is made of the swirling air. The cross section area of this tube is similar to the cross sectional area of frontal part of the vehicle. The swirling speed of air is about same to the V.
mairv2 / 2 = (pAvt* v2 ) / 2
The cross sectional area of the Tube is A which is relatively smaller than the actual cross sectional area of car. In this equation the ratio of effective area of tube to the crosss section area of car is known as drag coefficient CD.
A = Effective area of Car, CDAcar.
Mass of tube is Represented as mair
mair = pAvt
In this equation the density of the air is considered as P and the speed of swirling v.
(mairv2 / 2) / t = (pAvt * v3 ) / 2
the over all rate of energy produced by the car ca be represented as -
Power going into the breaks + Power going in the Swirling air
= 1 / 2 (mcv3) / d + pAv3
mc > pAd
There is one one more equation that can be used to calculate the aerodynamic drag. The force that resists the vehicle in moving. The force which is required to reduce this resistance is known as aerodynamic drag. As per the approximate model this resistance can be considered as-
R = (1/2)pCAv2
In this case R is the aerodynamic drag force that is in newtons. p is the considerd as the density of air which is in terms of kg/m3.. .C is condition is considered as aerodynamic drag coefficient, A is cross sectional area of the vehicle and v is the vehicle of the vehicle. For different vehicle the value of aerodynamic drag coefficient and cross sectional area is different. By making some assumptions for MATLAB program aerodynamic drag can be calculated for different vehicles. The energy that is consumed in the over come the aeriodynamic drag can be reflected as-
E = Rd
Here R is aerodynamic drag and d is the distance that is travelled by vehicle in meters. In this case distance that is covered by vehicle is 100 Kilometres. Velocity can be assumed to calculate the over all resistance that isrequired to calculate the energy required to overcome aerodynamic drag.
MATLAB Program
|
Clear all close all clc % Inputs % c_d = [0:25]; %Range of Drag coefficients % v = [0:25]; % Range of Velocities % V = 80; % Constant Velocity % A = 2; %Frontal Area% rho = 1.2; %Density of Air% % Drag force function % Drag_Force1 = 0.5*rho*A*c_d. *v.^2; Drag_Force2 = 0.5*rho*A*c_d. *v.^2; %Plot% figure Subplot(2,1,1,=) %Subplot function to accomodate% Plot(Drag_force1, v) %Both graph in one Figure% xlabel('Velocity') %Label% Ylabel('Drag Force') title('Drag Force vs Velocity') %Title% grid on subplot(2,1,2) plot(drag_force2, c_d) xlabel('Drag Coefficient') ylabel('Drag Force') title('Drag Force vs Drag Coefficient') grid on |
Aerodynamic Drag of Cars
There are three different cars are selected for the evaluation of aerodynamic drag at different speed for distance of 100 Km. By this process fuel efficiency of the vehicle can be compared.
Porsche 718 Cyman GTS 4.0
This model is high power sports car. It is a 2 seater car that comes with 294 KW six cylinder boxer engine and drag coefficient of this car is 0.31 with frontal area of 1.99 m2 and CdA is .62. the length of car is 4405 mm width is 1801 mm and hight of car is 1276. the weight of car is 1405 kg.
Porsche 718 Boxster GTS 4.0
This car is 2+2 seater convertible car which is consists of two doors. The drag coefficient of Porsche 718 Boxster GTS 4.0 I is 0.32 with 1.98 m2 frontal area. CdA of car is .63. length of car is 4391, hight is 1262 and width is 1801. the weight of car is 1405 Kg.
Toyota Avalon Touring
Toyota Avalon Touring ins a four - Five seater car. Length of car is 4976 mm, width of car is 1849 mm and hight of Toyota Avalon Touring is 1435 with weight of 1680 Kg
|
Car Model |
Drag Coefficient |
Cross Sectional Area |
Energy Consumption (/100 Km) |
|
Porsche 718 Cyman GTS 4.0 |
.31 |
1.99 m2 |
15.3 -Urban 29.0 – Extra Urban 21.8 - Combined |
|
Porsche 718 Boxster GTS 4.0 |
0.32 |
1.98 m2 |
15.4- Urban 8.1- Extra Urban 10.8- Combined |
|
Toyota Avalon Touring |
0.27 |
72.8 m2 |
10.7 - Urban 7.6 - Extra Urban 9.4 - Combined |
Ways to reduce Drag
As per the above derivation it is found that there are various techniques can be used to reduce the fuel consumption. Some of the most common method that is used by the car manufacturer is by reducing the mass of vehicle. Regenerative breaking can be really helpful in saving energy. By reducing the speed of the vehicle drag force can be reduced. This are major changes that can be used to in various factors apart from these process there are some other process are their that can help to improve the fuel efficiency of the vehicle. These changes are possible in alignment and structure of the vehicle to reduce the fuel consumption. These methods are – By reducing the cross sectional area of vehicle pressure and area of contact cab be reduced. Lower nose of the vehicle can lowered to make better aerodynamic structure (Terra, Sciacchitano and Scarano, 2017). By reduce the area of surface friction due to air can be reduced. Smooth and frictionless paints can be used to reduce the level of friction. By using spoiler in the vehicles can help to reduce the drag by reducing the tube that consists of swirling air to focus on the pressure areas of the vehicle.
CONCLUSION
This report is concluding the importance of the study of aerodynamic drag of various vehicles that can affect the fuel efficiency. The structural factors that can increase the drag for the vehicle also has been studied in the report. As per the understanding developed of factors that can cause aerodynamic drag to vehicle, different changes has been suggested in order to improve the fuel efficiency of vehicle. A derivation has been explained in report that can help to understand their relationship with the drag and fuel efficiency and cross sectional area.
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