Influence of Air Humidity on Transonic Flows with Weak Shock Waves
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https://doi.org/10.1007/s11630-019-1182-9
Article ID: 1003-2169(2019)00-0000-00
Influence of Air Humidity on Transonic Flows with Weak Shock Waves DYKAS Sławomir*, MAJKUT Mirosław, SMOŁKA Krystian Institute of Power Engineering and Turbomachinery, Silesian University of Technology, Konarskiego 18, Gliwice 44-100, Poland © The Author(s) 2019
Abstract: The paper presents CFD results for the transonic flow of dry and moist air through a diffuser and a compressor rotor. In both test geometries, i.e. the Sajben transonic diffuser and the NASA Rotor 37, the air humidity impact on the structure of flows with weak shock waves was examined. The CFD simulations were performed by means of an in-house CFD code, which was the RANS-based modelling approach to compressible flow solutions. It is shown that at high values of relative humidity, above 70%, the modelling of the transonic flow field with weak shock waves by means of the dry air model may produce wrong results.
Keywords: dry air, moist air, transonic flow, weak shock wave, steam condensation
1. Introduction Atmospheric air always contains a certain amount of water or steam. The water content in atmospheric air is usually represented using relative humidity, which is the ratio between the amount of water actually contained in the air and the amount the air can hold. It is expressed in percentages and the relative humidity value for saturated air is 100%. Atmospheric air relative humidity depends on geographical location and current weather. The most humid places on Earth are generally located closer to the equator, near coastal regions. There are a lot of places in the world where average relative humidity is higher than 70%. For instance, in many big cities with a huge transport of air, relative humidity of the day may reach up to 90% (e.g., Houston in Texas). Therefore, it is natural to check how air humidity can affect the aerodynamics of aircraft elements, especially in the region of transonic air velocities. In moist air transonic flows above the sonic line, there are suitable conditions for the homogeneous condensation process to arise. In the presence of air impurities, Received: Feb 26, 2019
AE: GOVARDHAN M.
additional phenomena may occur, like heterogeneous condensation, which is investigated in our previous works (e.g. [1]). In the field of experimental and numerical studies on moist air transonic flows, the most popular ones are the works of Schnerr and his research team [2, 3]. Schnerr proposed a physical model for steam condensing flow modelling, which has been successfully used by many researchers until today. Elevated relative humidity values affect the characteristic of the wing under the transonic flow conditions [2–5]. They may also have a significant influence on the flow in the turbine engine elements [6]. The moist air transonic flow in the turbine engine can take place in the compressor (or fan) inlet channels or in the compressor (or fan) rotor blade-to-blade channels. In both cases, the transition from subsonic to supersonic conditions (and v
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