CAJ | 학술논문

恒定流与非恒定流是流动现象的最基本分类形式之一。非恒定流是实际存在的，是绝对的。恒定流是理想化的，是相对的。通常重视的是由于主动原因导致的流动整体非恒定性，运动要素整体上随时间变化在允许幅度内可以近似作为恒定流处理。往往被忽略的是由于被动原因导致的流动局部非恒定性，运动要素随时间明显变化的空间在允许范围内可以近似作为恒定流处理；否则则呈现为周期的或不规则的非恒定流。流动局部非恒定性是由流动实质所决定的，可由它所遵循的控制方程在相应局部边界条件下进行分析。现有一些流动的计算示例和工程实例就是该种类型非恒定流存在的佐证。
항정류여비항정류시류동현상적최기본분류형식지일。비항정류시실제존재적，시절대적。항정류시이상화적，시상대적。통상중시적시유우주동원인도치적류동정체비항정성，운동요소정체상수시간변화재윤허폭도내가이근사작위항정류처리。왕왕피홀략적시유우피동원인도치적류동국부비항정성，운동요소수시간명현변화적공간재윤허범위내가이근사작위항정류처리；부칙칙정현위주기적혹불규칙적비항정류。류동국부비항정성시유류동실질소결정적，가유타소준순적공제방정재상응국부변계조건하진행분석。현유일사류동적계산시례화공정실례취시해충류형비항정류존재적좌증。
The steady and unsteady flow is one of the most basic form in the classification of flow phenomena in hydrodynamics. Unsteady flow is real and absolute,while steady flow is idealized and relative. What is usually valued is that the unsteady of integrated flow is caused by active reasons. The motion elements change with time in an allowable range,so that the flow can be approximated as a steady flow. The unsteady of local flow caused by passive reasons is generally neglected,and if the motion elements of local unsteady flow change with time in an allowable range,the flow can be approximated as a steady flow,otherwise it appears as periodic or irregular unsteady flow. The unsteady of local flow is determined by the essence of the flow,which can be analyzed under the corresponding local boundary conditions by the control equation the flow follows. The existing flow calculation examples and engineering examples are the evidences for the existence of the unsteady flow.