1093 Measurement of Fluctuating Temperature and Analysis of Eigenmodes by Kl Expansion in a Heated Plane Jet

Abstract

In this study, simultaneous measurement of the temperature at two points with cold-wire sensors is performed at three different downstream locations of a heated plane jet. The measurement apparatus consists of a wind tunnel, a skimmer, a side-wall, and a heater set at the blower intake of the wind tunnel. The temperature of the jet is controlled to become 5 K higher than the ambient fluid. A thin tungsten wire whose diameter is 3.0 m is used as a sensor and is connected to the self-made constant current circuit. The output of the cold-wire sensor is compensated theoretically to increase the temporal resolution of the measurement. By applying the Karhunen-Loève (KL) expansion in space and time, the structural development of the heated plane jet is investigated from the viewpoint of both space and frequency. Results obtained in the selfpreserving region show that the energy contribution of the 1st mode of the temperature is approximately 20%. It was also found that the dominant mode of the fluctuating temperature field in a plane jet expresses and relates to a flapping motion, which is the coherent structure observed in the plane jet.