A continuous adjoint cut‐cell formulation for topology optimization of bi‐fluid heat exchangers

IF 4 3区 工程技术 Q1 MATHEMATICS, INTERDISCIPLINARY APPLICATIONS
Nikolaos Galanos, Evangelos Papoutsis-Kiachagias, Kyriakos Giannakoglou
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引用次数: 0

Abstract

Purpose

This paper aims to present a topology optimization (TopO) method for designing heat exchangers (HEx) with two working fluids to be kept apart. The introduction of cut–cells gives rise to the cut-cell TopO method, which computes the optimal distribution of an artificial impermeability field and successfully overcomes the weaknesses of the standard density-based TopO (denTopO) by computing the fluid–solid interface (FSI) at each cycle. This allows to accurately solve the flow and conjugate heat transfer (CHT) problem by imposing exact boundary conditions on the computed FSI and results to correct performances computed without the need to re-evaluate the optimized solutions on a body-fitted grid.

Design/methodology/approach

The elements of an artificial impermeability distribution field defined on a background grid act as the design variables and allow topological changes to take place. Post-processing them yields two fields indicating the location of the two flow streams inside the HEx. At each TopO cycle, the FSIs computed based on these two fields are used as the cutting surfaces of the cut-cell grid. On the so-computed grid, the incompressible Navier–Stokes equations, coupled with the Spalart–Allmaras turbulence model, and the temperature equation are solved. The derivatives of the objective and constraint functions with respect to the design variables of TopO are computed by the continuous adjoint method, using consistent discretization schemes devised thanks to the “Think Discrete – Do Continuous” (TDDC) adjoint methodology.

Findings

The effectiveness of the cut-cell–based TopO method for designing HEx is demonstrated in 2D parallel/counter flow and 3D counter flow HEx operating under both laminar and turbulent flow conditions. Compared to the standard denTopO, its ability to compute FSIs along which accurate boundary conditions are imposed, increases the accuracy of the flow solver, which usually leads to optimal, rather than sub-optimal, solutions that truly satisfy the imposed constraints.

Originality/value

This work proposes a new/complete methodology for the TopO of two-fluid systems including CHT that relies on the cut-cell method. This successfully combines aspects from both TopO and Shape Optimization (ShpO) in a single framework thus overcoming the well-known downsides of standard denTopO regarding its accuracy or the need for a follow-up ShpO after TopO. Instead of adding the well-known Brinkman penalization terms into the flow equations, it computes the FSIs at each optimization cycle allowing the solution of the CHT problem on a cut-cell grid.

一种用于双流体换热器拓扑优化的连续伴随切槽公式
目的提出一种拓扑优化(TopO)方法来设计两种工质分离的换热器(HEx)。切割单元的引入产生了切割单元TopO方法,该方法通过计算每个周期的流固界面(FSI),成功地克服了标准基于密度的TopO (denTopO)的缺点。这允许通过在计算的FSI上施加精确的边界条件来精确地解决流动和共轭传热(CHT)问题,并且结果可以纠正计算的性能,而无需在贴体网格上重新评估优化的解决方案。设计/方法论/方法在背景网格上定义的人工防渗分布场的元素充当设计变量,并允许发生拓扑变化。对它们进行后处理会产生两个字段,指示HEx中两个流的位置。在每个TopO循环中,基于这两个场计算的fsi用作切割细胞网格的切割面。在此网格上,求解了不可压缩的Navier-Stokes方程和温度方程,并结合了Spalart-Allmaras湍流模型。目标函数和约束函数对TopO设计变量的导数通过连续伴随方法计算,采用“Think Discrete - Do continuous”(TDDC)伴随方法设计的一致离散化方案。在层流和湍流条件下的二维平行/逆流和三维逆流HEx实验中,证明了基于切割单元的TopO方法设计HEx的有效性。与标准的denTopO相比,其计算精确边界条件下的fsi的能力提高了流动求解器的精度,这通常会导致真正满足所施加约束的最优解,而不是次优解。独创性/价值本工作提出了一种新的/完整的方法,用于包括CHT在内的两流体系统的TopO,该方法依赖于切割细胞方法。这成功地将TopO和形状优化(ShpO)的各个方面结合在一个框架中,从而克服了标准denTopO关于其精度或在TopO之后需要后续ShpO的众所周知的缺点。它没有将众所周知的Brinkman惩罚项添加到流动方程中,而是在每个优化周期计算fsi,从而允许在切细胞网格上求解CHT问题。
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来源期刊
CiteScore
9.50
自引率
11.90%
发文量
100
审稿时长
6-12 weeks
期刊介绍: The main objective of this international journal is to provide applied mathematicians, engineers and scientists engaged in computer-aided design and research in computational heat transfer and fluid dynamics, whether in academic institutions of industry, with timely and accessible information on the development, refinement and application of computer-based numerical techniques for solving problems in heat and fluid flow. - See more at: http://emeraldgrouppublishing.com/products/journals/journals.htm?id=hff#sthash.Kf80GRt8.dpuf
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