Effect of sidewall spacing on the temperature field of a three-dimensional heated turbulent wall jet

Abstract

The effect of sidewalls on the temperature field of a three-dimensional heated turbulent wall jet is characterized by the temperature measurement inside the sidewall enclosure (SWE). The SWE is defined as the presence of sidewalls parallel to the vertical jet centerline plane on both the sides. The sidewalls are equally spaced from the vertical jet centerline plane, and the distance between the sidewall is termed as the width (W). Four different widths (W) 140 mm, 160 mm, 180 mm, and 200 mm SWE are considered at a Reynolds number of Re= 25,000. The temperature field decay rate is increased with an increase in the SWE width in the downstream locations after x/h= 35. The decay rate of the jet centerline temperature in 200 mm SWE is 4.6% higher than the 140 mm SWE. The lateral spread increases with a decrease in SWE width due to the accumulation of the thermal energy content in the lateral shear layers adjacent to the sidewalls. In the near field, thermal spread in the wall-normal direction increases with the increase in the SWE width, but in far-field locations (x/h= 30), the thermal spread increases with a decrease in the SWE width. The wall-normal thermal similarity is delayed with a decrease in the width of the SWE, and it is found at x/h= 25, 22, 19 and 15 for the 140 mm, 160 mm, 180 mm, and 200 mm SWEs, respectively. The temperature field shows the climbing effect over the sidewalls similar to the velocity field in the transverse plane (z−y). The spread of the temperature fields in the lateral direction increases with the increase in the width of the enclosure. The similarity of the temperature field gets distorted near the sidewall (λ=0.9, where λ=z/(W/2) and z= lateral location) due to thermal energy content in lateral shear layers. The one point temperature fluctuation shows the normal distribution of the probability density function along the jet centerline for all the cases of SWE. The probability density function is independent of the SWE width before the attachment (x/h≤ 10) of the flow stream at the sidewall, but after the attachment (x/h≥ 10) of the flow stream to the sidewalls, the probability density function deviated from the normal distribution curve. The skewness and flatness factors were also calculated based on the instantaneous temperature fluctuation inside the SWE.