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2025 Vol.58, Issue 6 Preview Page

Research Article

Analysis of flow rate variation by mixed flow in a drainage pipe using numerical simulation

수치모의를 이용한 배수관로의 혼합 흐름에 의한 유량 변동성 해석

Du Han Leea
,
Dong Sop Rheeb*
이 두한a
,
이 동섭b*
aSenior Research Fellow, Department of Hydro Science and Engineering Research, Korea Institute of Civll Engineering and Building Technology, Goyang, Korea
bResearch Fellow, Department of Hydro Science and Engineering Research, Korea Institute of Civll Engineering and Building Technology, Goyang, Korea
a한국건설기술연구원 수자원하천연구본부 선임연구위원
b한국건설기술연구원 수자원하천연구본부 연구위원
*Corresponding Author
30 June 2025. pp. 497-511
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Abstract

This study analyzes the characteristics of mixed flow occurring in a drainage pipe due to unsteady inflow using a numerical model. The numerical model utilizes the interIsoFoam solver in OpenFOAM to more accurately simulate the interface between air and water. To validate the model, it is applied to a slug flow experiment, demonstrating that the model effectively reproduces slug formation caused by water surface surges, as well as the movement and development of slugs. The characteristics of mixed flow in the pipe are simulated in a two-dimensional vertical plane under various air and water inflow conditions. To reproduce the unsteady nature of the water surface at the inlet boundary, a sinusoidal vertical velocity boundary condition is applied. Additionally, to analyze the flow rate variability induced by the mixed flow, the maximum outflow rate is calculated and compared against the inflow rate. Nine different mixed flow conditions are simulated. The results show that when both water and air velocities are sufficiently high, slugs formed and developed, leading to a maximum flow rate variability of 112.5%. In three-dimensional simulations, pressure flow is found to be more dominant, and the formation and development of the air layer differed from the two-dimensional results. In drainage pipes, the unsteady fluctuations in the inlet water level increase the likelihood of mixed flow formation. However, for mixed flow to persist along the pipeline and result in significant flow rate variability, sustained slug formation and development are necessary. This persistence depends on both the magnitudes of water and air velocities and their relative proportions.

Keywords
Drainage pipes
Mixed flow
Slug flow
Flow rate variability
Two phase flow

본 연구는 부정류 유입 흐름으로 배수관로에서 발생하는 혼합 흐름 특성을 수치모형을 이용하여 분석하였다. 수치모형은 OpenFoam의 interIsoFoam 솔버를 이용하여 공기와 물의 경계면을 보다 정확하게 모의하고자 하였다. 모형 검증을 위해 슬러그 흐름 실험에 적용하였으며, 수면 처오름에 의한 슬러그 형성과 슬러그의 이동 및 발달 과정을 잘 재현하는 것으로 나타났다. 다양한 공기와 물의 유입 조건에 따라 관로 내의 혼합 흐름 특성을 연직 2차원으로 모의하였다. 유입 경계에서 수면의 부정류 특성을 재현하기 위하여 사인함수 형태의 연직 유속 경계를 설정하였으며 혼합 흐름에 의한 유량 변동성을 해석하기 위하여 유입 유량에 대한 최대 유출 유량을 계산하여 비교하였다. 9개 조건의 혼합 흐름 모의를 수행하였으며 모의 결과에 의하면 물 유속과 공기 유속이 어느 정도 큰 경우 슬러그가 형성되어 발달하게 되며 이 경우에 유량 변동성이 최대 112.5%로 크게 나타났다. 3차원 모의에서는 압력 흐름이 보다 지배적이며 공기층의 형성과 발달이 상이함을 확인하였다. 배수관로는 유입 경계의 수위 요동으로 혼합 흐름이 형성될 가능성이 높으나 관로를 따라 혼합 흐름이 지속되고 유량 변동성이 커지기 위해서는 슬러그의 지속 또는 발달이 필요한데, 이는 물 유속과 공기 유속의 크기와 두 유속의 상대적 크기에 의존하는 것으로 판단된다.

키워드
배수관로
혼합 흐름
슬러그 흐름
유량 변동
OpenFoam
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Information
  • Publisher :KOREA WATER RESOURECES ASSOCIATION
  • Publisher(Ko) :한국수자원학회
  • Journal Title :Journal of Korea Water Resources Association
  • Journal Title(Ko) :한국수자원학회 논문집
  • Volume : 58
  • No :6
  • Pages :497-511
  • Received Date : 2025-03-31
  • Revised Date : 2025-05-09
  • Accepted Date : 2025-05-26
  • DOI :https://doi.org/10.3741/JKWRA.2025.58.6.497
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