Journal of Korea Water Resources Association (한국수자원학회논문집)

Korea Water Resources Association (한국수자원학회)
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Experimental investigation of turbulent effects on settling velocities of inertial particles in open-channel flow

개수로 흐름에서 난류가 관성입자의 침강속도에 미치는 영향에 대한 실험연구

  • Baek, Seungjun (Department of Civil and Environmental Engineering, Seoul National University) ;
  • Park, Yong Sung (Department of Civil and Environmental Engineering, Seoul National University) ;
  • Jung, Sung Hyun (Department of Civil and Environmental Engineering, Yonsei University) ;
  • Seo, Il Won (Department of Civil and Environmental Engineering, Seoul National University) ;
  • Jeong, Won (Department of Civil and Environmental Engineering, Seoul National University)
  • 백승준 (서울대학교 건설환경공학부) ;
  • 박용성 (서울대학교 건설환경공학부) ;
  • 정성현 (연세대학교 건설환경공학부) ;
  • 서일원 (서울대학교 건설환경공학부) ;
  • 정원 (서울대학교 건설환경공학부)
  • Received : 2022.08.04
  • Accepted : 2022.10.21
  • Published : 2022.11.30
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Abstract

Existing particle tracking models predict vertical displacement of particles based on the terminal settling velocity in the stagnant water. However, experimental results of the present study confirmed that the settling velocity of particles is influenced by the turbulence effects in turbulent flow, consistent with the previous studies. The settling velocity of particles and turbulent characteristics were measured by using PTV and PIV methods, respectively, in order to establish relationship between the particle settling velocity and the ambient turbulence. It was observed that the settling velocity increase rate starts to grow when the particle diameter is of the same order as Kolmogorov length scale. Compared with the previous studies, the present study shows that the graphs of the settling velocity increase rate according to the Stokes number have concave shapes for each particle density. In conclusion, since the settling velocity in the natural flow is faster than in the stagnant water, the existing particle tracking model may estimate a relatively long time for particles to reach the river bed. Therefore, the results of the present study can help improve the performance of particle tracking models.

기존의 입자추적모델에서 입자의 연직방향 변위 예측은 정지 수체에서의 최종침강속도를 바탕으로 계산되었다. 그러나 난류 수체에서의 침강속도에 관한 선행 연구들은 난류가 입자의 침강속도에 영향을 미치는 것으로 보고하고 있다. 본 연구에서는 난류에 따른 침강속도의 변화 특성을 규명하고자 개수로 흐름에서 입자의 침강 실험을 수행하였다. 입자의 침강속도와 난류 특성은 각각 PTV, PIV 기법을 통해 측정하였고, 측정된 침강속도 증가율과 입자 및 난류 특성에 따른 난류 수체에서의 침강속도의 변화 특성을 분석하였다. 그 결과, 입자 직경이 Kolmogorov 길이 스케일의 1~2배가 될 때, 침강속도 증가율이 커지기 시작하였다. 본 실험 결과를 선행 연구들과 비교하였을 때, Stokes 수와 침강속도 증가율의 그래프가 입자의 밀도에 따라 각각 최댓값을 보이는 곡선 형태를 가지는 것으로 나타났다. 결론적으로, 입자의 침강속도는 개수로 흐름에서 정지 수체에서보다 빠르기 때문에, 기존의 정지 수체에서의 침강속도를 이용한 입자추적모델은 연직방향으로 바닥에 도달하는 시간을 과대산정하게 될 수 있다. 이러한 측면에서 본 연구의 결과는 입자추적모델의 성능 개선에 도움을 줄 것으로 기대된다.

Keywords

Acknowledgement

이 연구는 서울대학교 신임교수 연구 정착금, 환경부 미세플라스틱 측정 및 위해성평가 기술개발사업(2021003110003)과 국토교통부의 스마트시티혁신인재육성사업으로 지원되는 연구비에 의하여 수행되었으며 이에 감사드립니다. 또한, 서울대학교 공학연구원 및 건설환경종합연구소의 지원에도 감사드립니다.

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