The Effects of Air Resistance on Vehicle Speed Calculations: A Quantitative Analysis
0
Citation
0
Reference
20
Related Paper
Abstract:
This article explores the mathematics involved in calculating air resistance as it is utilized in vehicle speed calculations. The author focuses on the various forces that affect a vehicle skidding on a surface and how the drag force, caused by a vehicle's travel through the air, is defined. The article first presents a basic example of a speed calculation that ignores drag. The article goes on to consider vehicle speed estimates with drag, finding an equation for velocity, and a comparison of speed calculations (no drag versus drag). The author concludes that, based on the mathematics present, drag is negligible. Since friction is dependent upon the weight of the vehicle and the fact that vehicles are relatively heavy compared to the force of drag, thus drag can be ignored under typical conditions. There is a brief mention of the need to continue to consider the role of drag for vehicle design.Keywords:
Zero-lift drag coefficient
Cite
SUMMARY Vehicles which travel on uneven roadways or rough surfaces require power beyond that associated with air drag, rolling resistance or other sources of friction even though kinetic and potential energy may be conserved on the average. This is true because damped relative motions within the vehicle dissipate energy, and, even for nearly rigid vehicles, energy is lost at impact with the ground whenever the vehicle loses contact with the ground surface due to the finite downward acceleration of gravity. Using elementary vehicle models, the nature and magnitude of the component of propulsive force associated with these energy loss mechanisms is estimated. In certain speed ranges, this force is found to vary dramatically with speed for several types of periodic roadway profiles studied. While the force due to unevennesss may be small compared to other forces for high-speed vehicles operating on smooth surfaces, it can be the major source of required power for off-road vehicles operating on very rough terrain.
Traverse
Rolling resistance
Mechanical energy
Road surface
Railgun
Cite
Citations (26)
This paper presents the solution for the motion of an air-cushion vehicle (ACV) starting from rest under the action of a propulsor of given thrust-speed characteristics. The wave resistance is based on linearized potential theory, while the aerodynamic drag components are assumed to be strictly quasi-steady. The problem is treated in two different ways: calculating the wave resistance in a truly unsteady manner, and on the simplified quasi-steady basis. The results show that the shape of the propeller characteristics has only a minor effect on the velocity pattern. However, the effect of overloading the ACV is shown to have crucial effects on its ability to surpass the critical depth hump. In this respect, the simpler quasi-steady calculations lead to unnecessarily pessimistic estimates of the acceleration margin. Under certain circumstances in relatively shallow water, the quasi-steady analysis would suggest that the ACV could not overcome the critical hump, while the more elaborate unsteady calculations show that it has indeed adequate power to reach its final cruising speed.
Propulsor
Cite
Citations (5)
Under a global impulse for less man-made emissions, the automotive manufacturers search for innovative methods to reduce the fuel consumption and hence the CO2-emissions. Aerodynamics has great potential to aid the emission reduction since aerodynamic drag is an important parameter in the overall driving resistance force. As vehicles are considered bluff bodies, the main drag source is pressure drag, caused by the difference between front and rear pressure. Therefore increasing the base pressure is a key parameter to reduce the aerodynamic drag. From previous research on small-scale and full-scale vehicles, rear-end extensions are known to have a positive effect on the base pressure, enhancing pressure recovery and reducing the wake area. This paper investigates the effect of several parameters of these extensions on the forces, on the surface pressures of an SUV in the Volvo Cars Aerodynamic Wind Tunnel and compares them with numerical results. To decrease the dependency of other effects within the engine bay and underbody, the SUV has been investigated in a closed-cooling configuration with upper and lower grille closed and with a smoothened underbody. These results might change if the study would be conducted with a less smooth underbody and in an open-cooling configuration. Extensions with different shapes and dimensions have been placed around the perimeter of the base exterior. The chosen design philosophy of the extensions allowed for different combinations with variable inclination angles depending on their position along the base perimeter, multiple extension lengths and shapes to be investigated. The results show that the extension shape is an important factor in reducing the aerodynamic drag. Significant drag reductions could be obtained while maintaining the vehicle's rear lift within acceptable levels for stability with a kicker attached to the extension. The investigation shows the reduction with a kicker holds for up to 7.5° yaw angles. With a beneficial shape, the extension length can be significantly reduced. The reduced drag is visible in the wake by a more concentric wake.
Aerodynamic force
Cite
Citations (12)
Recent trends in the automobile industry focus towards enhancing the operating efficiency of the road vehicle. One can achieve this by a combination of increasing the powertrain efficiency, reducing the weight and increasing the aerodynamic performance. The scope of this study is on the latter, i. e. enhancing the aerodynamic performance. Most cars are optimized for minimum drag in idealized conditions, driving engineers to design for the test rather than for to optimize for actual flow encountered in real world conditions. These realistic conditions include (un)steady cross-wind flows encountered by the vehicle, rather than a perfectly aligned flow as is the case in an idealized situation. Different researchers studied the effect of these real world conditions on the performance of a vehicle. Many of these studies focussed upon the vehicle stability rather than the potential to reduce aerodynamic drag. This is because typical drag reducing means (such as radiused edges) tend to have a detrimental effect on the cross-wind stability and comfort of the vehicle. The introduction of the fully electric Tesla Model S created new opportunities within this conception. This 2500 {kg vehicle has an 800 {kg battery underneath the car, which results in a different - relatively flexible - position of the center of gravity, total mass and corresponding mass moments of inertia. As a result it is questioned if this difference in vehicle specifications allow for drag reducing shape modifications on a vehicle which is then still stable during cross-wind flows. After a careful trade-off it was chosen to use the recently launched open-source CFD software suite SU2 in order to find an answer to the following research objective: What design modifications reduce the drag coefficient of a simplified vehicle model which experiences a cross-wind flow, and how does this affect the lateral dynamic performance? An interesting follow-up question on this would be to identify which design variables are (most) sensitive to drag increments in realistic crosswind flows. This document describes the process of solving the research objective within the framework of a Master of Science thesis. A thorough vehicle dynamics study was performed in order to assess the most influential parameters which affect the lateral deviation of a vehicle. Within this study it was found that the cross-wind induced lateral deviation with a longitudinal velocity of 30m/s and a cross-wind flow of 3.15m/s or 6 degrees is roughly similar to the situation where the steering wheel angle is set to 1 degree. This implies that the lateral deviation during cross-wind flows is not much of an issue during steady cross-wind flows of up to 6 degrees. Experiments were designed for three different cross-wind flows; 0 degrees, 3 degrees and 6 degrees cross-wind flow for both conventional and electric vehicles. Here the effects of the following shape modifications have been studied: arrowing the front of the vehicle, tapering the aft of the vehicle, applying a side-window tumblehome angle, varying the front and rear window angle, and varying the A - and C - pillars. The resulting drag coefficients for each configuration has been averaged over the three cross-wind angles. Here it was found that the most important shape modifications for the drag coefficient occur aft of the vehicle. The optimal angles are listed below, where the original angle is shown in parentheses. The resulting cross-wind flow averaged drag coefficient is shown per shape modification. Arrowing angle (0) - 15 degrees: 5% Tapering angle (0) - 15 degrees: 27% Tumblehome angle (0) - 15 degrees: 10% Front window angle (30) - 25 degrees: 2% Rear window angle: (25) - 15 degrees: 16% A-pillar radius: (0.10) - 0.15m: 4% C-pillar radius: (0.15) - 0.15m: 0% When these design modifications are simultaneously applied it was found that the drag coefficient is reduced by 17% for symmetric flow conditions, 30% during 3 degrees cross-wind flow and as much as 43% during 6 degrees during cross-wind flow conditions. This combines into a cross-wind averaged drag reduction of 30%.
Crosswind
Cite
Citations (0)
For the aerodynamic development of an aircraft the induced drag is an important quantity and it has a significant impact on the design of the wing. The induced drag corresponds to the power requirement of the wing to generate the necessary lift. In many cases this is the dominant source of drag for aircraft. In ground vehicle aerodynamics the concept of induced drag up to now has attracted much less attention. This is partly due to the fact, that vehicle aerodynamicists usually optimize the vehicles to generate little or no lift. The second reason is that it is much more difficult for a ground vehicle to separate the total drag into the different contributions. During wind tunnel tests of vehicles with and without ground simulation some astonishing results were found, especially when comparing results for different rear end shapes. Notchback vehicles typically displayed lower drag results when measured with ground simulation, whereas wagon backs showed higher drag figures compared with the case without ground simulation. To explain these surprising results, the contribution of induced drag to the total drag was analyzed in detail. The proportion of induced drag was determined from measured polar diagrams. Different lift levels of the vehicles were created using an adjustable rear spoiler, whereas the trim level of the vehicle was kept constant. Notchbacks typically generate rear lift and wagon backs rear downforce. The two rear end types therefore are b-cated on different branches of the parabola describing the induced drag. By improvement of the ground simulation typically the lift is reduced and thus the induced drag is modified. Due to the difference in the basic lift level the drag is reduced for the notchback and increased for the wagon back. Induced drag can of course describe only a part of the complex influence of improved ground simulation. Notchback vehicles do not generally show lower drag results when using ground simulation. Nevertheless induced drag can explain some significant influences found in recent test results.
Ground Effect
Cite
Citations (22)
In 'Teclhnical Soaring', Vol. V, No. 4, June 1980, pages 39-45, Frank Irving has analyzed the energy loss of sailplanes in pitching maneuvers. A pull-up flight maneuver temporarily increases the load factor and hence increases the drag. As far as drag is concerned, the influence of load factor deviations from unity has satisfactorily been treated in the above-mentioned paper. 8ut load variation also significantly affects energy transfer when the glider traverses moving air masses. In this author's opinion this effect is most important and deserves full consideration. In the following I shall focus on the energy extraction from the movements of the atmosphere and on the influence of the load factor on it, rather than on drag effects.
Load factor
Cite
Citations (0)
Class 8 tractor-trailers consume 11-12% of the total US petroleum use. At highway speeds, 65% of the energy expenditure for a Class 8 truck is in overcoming aerodynamic drag. The project objective is to improve fuel economy of Class 8 tractor-trailers by providing guidance on methods of reducing drag by at least 25%. A 25% reduction in drag would present a 12% improvement in fuel economy at highway speeds, equivalent to about 130 midsize tanker ships per year. Specific goals include: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; (2) Develop innovative drag reducing concepts that are operationally and economically sound; and (3) Establish a database of experimental, computational, and conceptual design information, and demonstrate the potential of new drag-reduction devices. The studies described herein provide a demonstration of the applicability of the experience developed in the analysis of the standard configuration of the Generic Conventional Model. The modeling practices and procedures developed in prior efforts have been applied directly to the assessment of new configurations including a variety of geometric modifications and add-on devices. Application to the low-drag 'GTS' configuration of the GCM has confirmed that the error in predicted drag coefficients increases as the relative contribution of the base drag resulting from the vehicle wake to the total drag increases and it is recommended that more advanced turbulence modeling strategies be applied under those circumstances. Application to a commercially-developed boat tail device has confirmed that this restriction does not apply to geometries where the relative contribution of the base drag to the total drag is reduced by modifying the geometry in that region. Application to a modified GCM geometry with an open grille and radiator has confirmed that the underbody flow, while important for underhood cooling, has little impact on the drag coefficient of the vehicle. Furthermore, the evaluation of the impact of small changes in radiator or grille dimensions has revealed that the total drag is not particularly sensitive to those changes. This observation leads to two significant conclusions. First, a small increase in radiator size to accommodate heat rejection needs related to new emissions restrictions may be tolerated without significant increases in drag losses. Second, efforts to reduce drag on the tractor requires that the design of the entire tractor be treated in an integrated fashion. Simply reducing the size of the grille will not provide the desired result, but the additional contouring of the vehicle as a whole which may be enabled by the smaller radiator could have a more significant effect.
Zero-lift drag coefficient
Tractor
Cite
Citations (7)
Relative Motion
Aerodynamic force
Longitudinal static stability
Relative velocity
Cite
Citations (29)
Uncertainty in concept-design zero-lift-drag estimation has significant downstream design consequences. Typically, key decisions regarding the overall vehicle weight, vehicle dimensions, aerodynamic configuration, wing loading and thrust loading are frozen during concept design. If imprecise drag estimates are made up front, the actual performance of the production aircraft may diverge widely from its intended performance. Plots of steady-state aircraft cruise performance metrics in “Energy-Maneuverability” format (as a function of Mach number and flight altitude) facilitate this discussion. This paper explains how multidisciplinary effects magnify the impact the zero-lift-drag uncertainty substantially beyond what one would expect using a simplified, Breguet analysis. Moreover, the detrimental effects of excess drag disproportionately impacts smaller airframes. However, increased thrust-loading mitigates the unintended effects of excess drag.
Lift (data mining)
Zero-lift drag coefficient
Cite
Citations (0)
The advantage of tripping boundary layer turbulence around bluff bodies in order to reduce the aerodynamic drag and stabilize the flow has been known for many decades and applied in a number of engineering fields. However, its use in the sport technology area is quite recent. The first practical application of modeled surfaces used to reduce drag has been in golf balls, with the introduction of a dimpled surface. This solution allowed the ball to experience a drag value that is nearly half of the drag value of the same ball with a smooth surface. More recently, with the introduction of the NIKE swift suit in 2002 the focus of sports companies and athletes moved to the so called "low drag suits". Recent published research proved that low drag suits with panels with different types of roughness clearly improve the athletes' performances. Currently, most of the research carried out on textiles aerodynamics relies on static measurements on cylindrical models and limited research considers a possible hysteresis in the drag crisis phenomenon for low drag suits applications. The hysteresis phenomenon in the drag crisis is however a well-known phenomena and previous authors have been addressing it. In the present work, the instant drag on a cylinder model mounted in the wind tunnel and covered with different fabrics has been measured and compared with static measurements made on the same model. The experiments were carried out with a sampling frequency of 200 Hz using an AMTI BP-600400 HF with a natural frequency of 470 Hz and thus capable of measuring dynamic forces. Results show that a hysteresis process exists and that dynamic measurements could be a good alternative to static measurements requiring less testing time and giving more accurate results.
Zero-lift drag coefficient
Cite
Citations (5)