Unsteady aerodynamic effects on the driving stability of passenger vehicles
Doktorsavhandling, 2023
Vehicles travelling on open roads are continuously exposed to changing crosswind conditions. Most road vehicles have the aerodynamic centre of pressure located at the front, making them sensitive to these unsteady crosswinds. Strong winds and sensitive vehicle designs degrade the driving stability perceived by drivers and passengers. Furthermore, as aerodynamic loads increase with flow velocity, the sensitivity becomes greater at high speeds. High speeds affect stability performance even without variations in crosswind. The balance of the time-averaged lift forces between the front and rear axles influences understeering and, consequently, vehicle handling. However, the averaged forces cannot always predict the stability performance, which increases the need to explore the unsteady aerodynamic effects on vehicle handling.
The assessment of driving stability for a vehicle in development is often done on test tracks in late design phases when prototype vehicles are available. However, the current demands of faster development times require robust virtual tools for earlier assessment. This thesis aims to develop virtual tools for assessing straight-line driving stability and to gain insights into the interdisciplinary physics between aerodynamics and vehicle dynamics.
By conducting on-track measurements, it was demonstrated that crosswinds deteriorate driving stability and that the vehicle motions of lateral acceleration and yaw velocity correlate with the drivers' subjective assessment. A driving simulator study confirmed these lateral motions, and the path curvature, as significant measures. To reduce the lateral vehicle response to crosswinds, the centre of gravity should move forward, while the aerodynamic yaw moment should be reduced (moving the centre of pressure rearward). For high speed stability, without varying crosswinds, it was demonstrated that the unsteady base wake also plays an important role. Stability issues on the test track correlated with bi-stable wake dynamics, primarily affecting the fluctuating rear lift force. Configurations that stabilised the wake led to subjective improvements on the test track, highlighting the importance of unsteady wake aerodynamics.
aerodynamics
wake dynamics
high speed
Vehicle dynamics
driving stability
crosswinds
Författare
Adam Brandt
Chalmers, Mekanik och maritima vetenskaper, Fordonsteknik och autonoma system
Quantitative High Speed Stability Assessment of a Sports Utility Vehicle and Classification of Wind Gust Profiles
SAE Technical Papers,;Vol. 2020-April(2020)
Artikel i vetenskaplig tidskrift
High speed driving stability of road vehicles under crosswinds: an aerodynamic and vehicle dynamic parametric sensitivity analysis
Vehicle System Dynamics,;Vol. 60(2022)p. 2334 -2357
Artikel i vetenskaplig tidskrift
Base wake dynamics and its influence on driving stability of passenger vehicles in crosswind
Journal of Wind Engineering and Industrial Aerodynamics,;Vol. 230(2022)
Artikel i vetenskaplig tidskrift
Brandt, A. Sebben, S. Jacobson, B. Wake dynamics of passenger vehicles and its influence on high speed stability
Brandt, A. Jacobson, B. Sebben, S. Drivers' perceived sensitivity to crosswinds and to low-frequency aerodynamic lift fluctuations
Idag kan bilens stabilitet endast utvärderas sent i utvecklingsfasen, då prototypbilar finns tillgängliga som testas i höga hastigheter. Om stabilitetproblem upptäcks så sent innebär det höga kostnader för att åtgärda problemet. Dessutom är merparten av bilens konstruktion redan bestämd, vilket ger litet utrymme för förbättringar.
Detta arbete avhandlar strategier för att flytta utvärderingen av bilens stabilitet från testbanorna till den virtuella miljön. Virtuella datorsimuleringar kan användas tidigt i utvecklingsfasen och möjliggör kostnadseffektiva förbättringar innan prototypbilarna byggs. Arbetet visar bland annat hur en bil kan designas mindre känslig för kastvindar, genom att flytta bilens tyngdpunkt framåt samt genom förbättrad aerodynamisk form. De metoder och resultat som presenteras i denna avhandling kan hjälpa ingenjörer att lösa stabilitetsproblem utan att öka luftmotståndet.
Aerodynamisk och fordonsdynamisk körstabilitet av personbilar vid hög fart
China-Euro Vehicle Technology (CEVT) AB, 2018-08-01 -- 2022-12-31.
Styrkeområden
Transport
Ämneskategorier
Farkostteknik
Strömningsmekanik och akustik
ISBN
978-91-7905-805-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5271
Utgivare
Chalmers
Chalmers campus Johanneberg , room HA4, Hörsalsvägen 4
Opponent: Prof. Dr.-Ing. Andreas Wagner, University of Stuttgart, Germany