为了在微流控管道中实现诸如混合强化、反应控制和材料合成等应用，经常需要编辑其中的流束轮廓。传统的流束轮廓编辑方法通过激发惯性二次流，使管道中流体重新分布，然而在惯性流可以忽略的微流控环境中，难以借助这类方法形成流束轮廓。传统方法使用的对称式管道内结构也限制了可以创造的流束轮廓的多样性。此外，这类方法生成的每个流束轮廓均对应一个严格定义的特定流动环境，因而在有变化的流动环境中，难以再现这些轮廓。为了解决上述问题，我们提出一种基于非惯性二次流的工程方法来编辑流束轮廓：在微管道内部署一系列级联的具有不同几何形状的阶梯来操控处于斯托克斯流范围内的流体；通过调整这些微阶梯的形状可以定制输出任意的流束轮廓；设计数值式流束轮廓预测程序，可快速预测以任意次序排列的预定义的微阶梯所输出的流束轮廓。该方法可用于生成包括非对称流束轮廓在内的各种稳定的流束轮廓，并且广泛适用于多种微流控流动环境，促进对复杂微流场的预测和设计。

Flow profiles are frequently engineered in microfluidic channels for enhanced mixing, reaction control, and material synthesis. Conventionally, flow profiles are engineered by inducing inertial secondary flow to redistribute the streams, which can hardly be reproduced in microfluidic environments with negligible inertial flow. The employed symmetric channel structures also limit the variety of achievable flow profiles. Moreover, each of the flow profiles specifically corresponds to a strictly defined flow condition and cannot be generalized to other flow environments. To address these issues, we present a systematic method to engineer the flow profile using inertialess secondary flow. The flow is manipulated in the Stokes regime by deploying a cascaded series of microsteps with various morphologies inside a microchannel to shape the flow profile. By tuning the shapes of the microsteps, arbitrary outflow profiles can be customized. A numerical profile-transformation program is developed for rapid prediction of the output profiles of arbitrary sequences of predefined microsteps. The proposed method allows the engineering of stable flow profiles, including asymmetric ones, over a wide range of flow conditions for complex microfluidic environmental prediction and design.