Investigations of unsteady aerodynamic effects generated by heave and pitch motion in different vehicle body shapes with model excitation tests

Abstract

In this study, unsteady aerodynamic forces induced by forced pitch and heave motions are measured and formulated to the unsteady aerodynamic coefficients by utilizing the 1/4-scale nearly actual vehicle model with wheels and wheel-houses and a system without unnecessary stings exposed to the flow. The unsteady aerodynamic lift forces are measured as input forces at front and rear axles in vehicle suspensions for each, and are expressed as the aerodynamic inerter, aerodynamic damping and aerodynamic spring coefficients which are equivalent in vehicle suspension property. These studies are conducted with less than 1.4 × 10 6 of Reynolds number and with less than 0.2 of non-dimensional frequency. From the results, it is observed the effect of front aerodynamic forces in proportion to motion acceleration which works as an inerter can be ignored in both of pitch and heave motion, but the effect of rear aerodynamic forces as an inerter must be considered in both motion, and the first-order lag must be considered additionally about the rear only in heave motion. Furthermore, the large difference of unsteady aerodynamic characteristics is obtained while comparing in different vehicle body shapes which are without and with a protrusion on the roof. Especially, the difference of unsteady aerodynamic forces of rear in pitch motion is much large. In the case without the protrusion, the aerodynamic inerter which restrains pitch motion is occurred. On the other hand, in the case with the protrusion, the effect of aerodynamic inerter decreases and other aerodynamic forces promotes pitch motion in opposite. The phenomenon of this difference is closely related to the behavior of flow velocities at near surface around the model. From the above, it is confirmed that the large difference of unsteady aerodynamic forces induced by motions occurs in the detail difference of body shapes at a nearly actual vehicle model, and can be expressed quantitatively as the difference of aerodynamic response.

Coupling analysis of unsteady aerodynamics and vehicle behavior with road input: Modeling and verification in road tests

“…(1). Their aerodynamic formulations have been studied in a previous report (Maeda et al, 2020), and they are defined by summing the aerodynamic forces caused by the pitch motion ( , ) and heave motion ( , ) for the front and rear axles, as shown in Fig. 1.…”

“…To further improve vehicle performance, motion analyses that evaluate the difference in vehicle behaviors with respect to vehicle shape in road input are necessary in actual running conditions. Maeda et al (2020) in their wind tunnel experiments quantitatively measured the differences in unsteady aerodynamic forces according to vehicle shape as aerodynamic response functions. These aerodynamic forces were measured using excitation tests on the scale model, which comprised wheels and a wheelhouse similar to a real vehicle.…”

“…Accordingly, the necessity of considering the influence of unsteady aerodynamic forces on vehicle motions and the coupling analysis of aerodynamics with vehicle motions were demonstrated. : suspension force at the front axle, and at the rear axle z : first-order delay occurring for aerodynamic forces according to the heave motion with no dimension (only at the rear axle, and these values are quoted from Maeda et al 2020) : wind velocity : body displacement at the wheel-base center ( = ( + ) 2 ⁄ ) ,…”