The objective of this study is to investigate the forced convection from and the flow around a heated cylinder. Experimental and computational results are presented for laminar flow around a heated circular cylinder with a diameter of 10 mm. The experiments were carried out using Particle Image Velocimetry (PIV) in a wind tunnel, and numerical simulations using an in-house code and a commercial software package, FLUENT. This paper presents comparisons for vorticity and temperature contours in the wake of the cylinder. Experimental and computational results are compared with those available in the literature for heated and unheated cylinders. An equation is suggested for a temperature-dependent coefficient defining a reference temperature to be used in place of the constant used in other studies. An attempt is also made to correct differences between average cylinder surface temperature and measured interior temperature of the cylinder.
This article describes a novel approach to generate increased turbulence levels in an incoming flow. It relies on a cost-effective and robust semi-active jet grid, equipped with flexible tubes as moving elements attached onto tube connections placed at the intersections of a fixed, regular grid. For the present study, these flexible tubes are oriented in counter-flow direction in a wind tunnel. Tube motion is governed by multiple interactions between the main flow and the jets exiting the tubes, resulting in chaotic velocity fluctuations and high turbulence intensities in the test section. After describing the structure of the turbulence generator, the turbulent properties of the airflow downstream of the grid in both passive and active modes are measured by hot-wire anemometry and compared with one another. When activating the turbulence generator, turbulence intensity, turbulent kinetic energy, and the Taylor Reynolds number are noticeably increased in comparison with the passive mode (corresponding to simple grid turbulence). Furthermore, the inertial subrange of the turbulent energy spectrum becomes wider and closely follows Kolmogorov's -5/3 law. These results show that the semi-active grid, in contrast to passive systems, is capable of producing high turbulence levels, even at low incoming flow velocity. Compared to alternatives based on actuators driven by servo-motors, the production and operation costs of the semi-active grid are very moderate and its robustness is much higher.
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