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CHARACTERISTICS OF PRESSURE DISTRIBUTION AND SKIN FRICTION WITHIN THE LAMINAR SEPARATION BUBBLE AT DIFFERENT REYNOLDS NUMBERS

Donghwi Lee
Dept. of Aeronautics and Astronautics, University of Tokyo 3-1-1 Yoshinodai, Sagamihara, Kanagawa 252-5210, Japan; Department of Mechanical Engineering, Yonsei University, Seoul 03722, Korea

Soshi Kawai
Dept. of Space Flight System, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa, 252-5210, Japan; Department of Aerospace Engineering Tohoku University 6-6-01 Aramaki-Aza-Aoba, Aoba-ku, Sendai, Miyagi 980-8579, Japan

Taku Nonomura
Dept. of Space Flight System, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa, 252-5210, Japan

Akira Oyama
Dept. of Space Flight System, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency 3-1-1 Yoshinodai, Sagamihara, Kanagawa 252-5210, Japan

Kozo Fujii
Dept. of Space Flight System, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency 3-1-1 Yoshinodai, Sagamihara, Kanagawa 252-5210, Japan

Résumé

Mechanisms behind the pressure distribution within a laminar separation bubble (LSB) are investigated by largeeddy simulations around a 5% thickness blunt flat plate. The plate length based Reynolds numbers are set to be (Rec) 5.0×103, 6.1×103, 8.0×104, 1.1×104, and 2.0×104. From the results, two types of LSB are observed; steady laminar separation bubble (LSB S) at Rec = 5.0×103 and 6.1×103, and a steady-fluctuating laminar separation bubble (LSB SF) at Rec = 8.0×103, 1.1×104, and 2.0×104. As the Reynolds number increases, different shapes of pressure disribution appear such that a gradual pressure recovery in the LSB S and a plateau pressure distribution followed by a rapid pressure recovery in the LSB SF. The reasons of appearing the different shapes of pressure distributions depending on the Reynolds number are explained by deriving the Reynolds averaged pressure gradient equation. From the momentum budgets of the equation, it is confirmed that the viscous stress near the surface has an influence on determining the different shape of pressure distribution. The different viscous stress distributions near the surface are affected by grwoth of the separated laminar shear layer depending on the Reynolds number or generation of the Reynolds shear stress.