Abstract
Flow and thermal fields of a pair of plane plumes in water are investigated by means of PIV and LIF experiments. The plumes are generated from thermal line sources, which are made out of electrically heated cylinders with a diameter of D = 1.21 mm. A cylinder-to-cylinder distance was 17.9 D . Either continuous or pulsating heating were used with the same heating input power. Because the cylinder-to-cylinder distance is moderately small, deflections of plumes from a vertical direction occur and the plumes are inclined together. This behavior is caused by a confined entrainment from a space between the both plumes. For a continuous heating, low frequency oscillations were identified and the natural frequency was evaluated as 0.5 Hz. Based on this finding, pulsating heating was used at the subharmonic frequency of 0.25 Hz. The maximum time-mean velocity magnitude at the continuous and pulsating heating were commensurable, approximately 0.007 m/s. On the other hand, pulsating heating achieves by 36 % higher velocity peaks. A very strong velocity oscillations were generated by pulsating heating at the distance approximately 8.3 D above the cylinders, where the velocity maxima oscillate along the time-mean value of 0.0057 m/s from −30% to +70 %. Temperature fields reasonably agree with this findings, despite a relatively fast equalization of the temperature field was concluded. The results demonstrate enhancement effects of pulsations in flow/thermal fields.
Highlights
A buoyant jet is a type of fluid motion and one of basic examples of free shear flows – see Schlichting [1], Blevins [2]
The following experiments were performed after well stabilized flow and temperature fields, i.e. at least 1 hour after filling the water tank with water of the laboratory temperature, and at least 5 minutes after heating was turned on
The measurements were performed for the investigated twin plumes, which are generated by either continuous or pulsating heating (CH or pulsating-supply heating (PH), respectively)
Summary
A buoyant jet is a type of fluid motion and one of basic examples of free shear flows – see Schlichting [1], Blevins [2]. It is generated by differences in fluid density. A buoyant jet whose initial momentum is approximately zero is called a plume. In the case of a thermal source, the plume is developed because a local temperature increase causes a decrease of density. For a line thermal source, a plane plume is developed. A twin of plane plumes has been investigated by means of PIV and LIF experiments in water
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