A study on unpredictable changes in fluid-force characteristics due to wake bistability of 3D bluff body

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K04286
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 19010:Fluid engineering-related
• Research Institution: Hiroshima University
• Principal Investigator: NAKASHIMA Takuji 広島大学, 先進理工系科学研究科(工), 准教授 (40444707)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 流体工学 / 応用空気力学 / ３次元ブラフボディ / 自動車空力 / 双安定性 / 非定常空気力 / 流体構造連成 / 後流

Outline of Final Research Achievements

In this study, we investigated the unpredictable changes in fluid-force characteristics of a practical 3-D bluff body traveling in ground effect, mainly assuming an automobile. This phenomenon occurs when the flow around the bluff body becomes "bi-stable," which means that the flow can take two different states under the same conditions, and the flow transitions from one state to the other.
We conducted both experimental and numerical studies of bluff bodies, around which the flow show bi-stability under certain disturbance conditions. Specifically, the unsteady flow measurements in wind-tunnel and circulating water-tank facilities and the numerical simulations of unsteady turbulent flow fields around the bodies were conducted. Through these studies, we clarified the characteristics of the sudden changes in fluid-force characteristics, and also discussed techniques to suppress the bi-stability causing the changes.

Free Research Field

流体工学

Academic Significance and Societal Importance of the Research Achievements

本研究では，地面効果中を進行する実用的３次元ブラフボディに発現する，双安定な空力現象の特性を明らかにした．同一の周囲流れ条件下において，ボディ局所の流れ特性が切替ることで，ブラフボディ周りの流れ構造全体が大きく異なる2状態を生じる，空力双安定状態の理解が促進したことは，流体工学的に有意義な成果である．
また，現在の自動車空力設計では，極限まで空気抵抗を低減する形状の追及や新技術普及に伴うデザイン自由度拡大に伴って，空力双安定状態を避ける設計マージンが縮小しつつある．このため，本研究による双安定状態の特性解明と，双安定状態の発現の効果的な抑制手法の提案は，自動車工学的にも有意義な成果である．