INCAS Bulletin (Jun 2019)
The unsteady turbulent flows structure study present status
Abstract
The processes of heat transfer and hydraulic plays a very important role in the design and prototyping of aerospace technology. In most cases this technique works under significant unsteady conditions. Steady approach for unsteady processes leads to high error in calculations. Models for unsteady processes calculation must be based on fundamental turbulent structure research. Experimental research data is very important to the matter as it has intrinsic reliability. This data can be used both independently for unsteady processes model creation and for theoretical model’s verification. Moscow Aviation Institute National Research University (MAI) accomplishes unsteady turbulent flow structure since year 1985. An experimental facility was designed to provide acceleration and deceleration gas flow in isothermal and non-isothermal conditions. The results of experimental turbulent flow research demonstrate fundamental unsteady processes influence on the flow structure. The principal results of acceleration and deceleration flow experimental research evidence three specific zones in turbulent flow structure exist: wall area, maximal turbulent structure transformation and flow core. The results show significant distinction in turbulent viscosity ca 3 times between steady and unsteady approach ca 3 times. The discrepancy of steady heat transfer and hydraulic resistance coefficients to actual unsteady data reaches up to 2 times. Clearly, such considerable difference in heat transfer and hydraulic resistance coefficients is inadmissible for processes calculation in aviation and space technology. Other research teams observed the same trend in their experiments. The present paper describes a method of experimental research, methodology of data processing and unsteady turbulent flow structure deformation results. Flow acceleration comes to velocity profile deformation and turbulence pulsations increase. Flow deceleration leads to opposite results - reverse velocity profile deformation and turbulence pulsations decrease. Experimental data also are a reliable basis for further unsteady turbulent flow theoretical parameters research.
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