Flow-Induced Vibration in a Single Row of Cylinders With p/D = 1.26

Crossflow over a row of cylinders with a close space ratio presents an asymmetric configuration with large and narrow wakes behind the cylinders. The wake interaction can impact the vibration response of the cylinders. In tube banks, the impact results in damages to the equipment. The present experimental study aims to analyze the influence of close space observed in a single row of cylinders on the flow-induced vibration. The study compares a single row with fixed cylinders and a single row with one cylinder free to vibrate. The cylinder free to vibrate is tested in four configurations. The study was conducted with an aerodynamic channel with a cross-section of 0.193 × 0.146 m and smooth cylinders with a diameter of 25.1 mm, space ratio is 1.26. The measurements are executed with hot-wire anemometry and accelerometers, for the cases with one cylinder free to vibrate and with hot-wire anemometry and microphones for the case with all fixed cylinders. The Reynolds number ranges between 1.0 × 104 and 4.5 × 104, obtained with the reference flow velocity, measured with a Pitot tube, and the cylinder diameter. The comparison between the wake response for single row fixed and single row and free to vibrate are executed using Fourier transform and Wavelet Transform. The comparison of the results with the models presented in the literature to predict the elastic instability of the fluid in a single row of cylinders is performed.

Accurate Boundary Layer Measurements using Hot-Wire Anemometry - Improvements and Error Analysis

In this paper two approaches are presented dealing with common challenges of 2D boundary layer measurements with hot-wire anemometry under challenging test conditions. Novel procedures for accurate determination of the sensor position and correction of the wall heat effect were developed and tested at high free stream velocities of about M1 = 0.3 and thin boundary layers (δ99 = 0.7 - 3.5 mm) of different transitional state in a low density environment. First of all, a novel procedure for automatized determination of the accurate hot-wire sensor position relative to the wall is presented. The quantification and correction of possible sub-miniature sensor misalignments is achieved by taking advantage of the linear nature of the laminar sub-layer of each boundary layer. The statistical approaches for identification and verification of the linear sub-layer demonstrate satisfying results of minimized position uncertainties of about 24 μm. Secondly, a highly adaptable method for correction of the well-known wall heat effect is presented. In contrary to a series of static correction approaches, the biased velocity information is corrected by optimizing the parameters of an exponential approach, where the correction term is optimized for each boundary layer individually. This novel approach resolves the problem of limited applicability of static correction methods, caused by system inherent measurement uncertainties.

Simplified Calibration Method for Constant-Temperature Hot-Wire Anemometry

This study proposes a unique approach to convert a voltage signal obtained from a hot-wire anemometry to flow velocity data by making a slight modification to existing temperature-correction methods. The approach was a simplified calibration method for the constant-temperature mode of hot-wire anemometry without knowing exact wire temperature. The necessary data are the freestream temperature and a set of known velocity data which gives reference velocities in addition to the hot-wire signal. The proposed method was applied to various boundary layer velocity profiles with large temperature variations while the wire temperature was unknown. The target flow velocity was ranged between 20 and 80 m/s. By using a best-fit approach between the velocities in the boundary layer obtained by hot-wire anemometry and by the pitot-tube measurement, which provides reference data, the unknown wire temperature was sought. Results showed that the proposed simplified calibration approach was applicable to a velocity range between 20 and 80 m/s and with temperature variations up to 15 °C with an uncertainty level of 2.6% at most for the current datasets.

Experimental investigation of the airflow generated by the human foot tapping using the hot-wire anemometry

Human-walking-induced particle resuspension in indoor environments is believed to be an important source of particulate matter. Aerodynamic disturbance generated by the human foot during a gait cycle are the main driver for particle detachment and dispersion in the room. In this work, the hot-wire anemometry technique was employed to investigate the airflow generated by one phase of the human gait cycle: the foot tapping. This phase was simulated by a mechanical simulator that consists of a wooden rectangular 25 × 8 × 1.2 cm plate, and a servomotor that allows downward and upward rotations of the plate with a constant velocity. A correction procedure based on the hot-wire velocity measurements and the analytical solution of Falkner–Skan has been derived to correct the hot-wire readings in the near-wall region. Results show a sharp increase of airflow velocity in front of the simulator after the simulator rotation. Transverse hot-wire measurements downstream of the simulator show that the profile of the maximal velocities reaches a peak at a distance y = 8 × 10−3 m from the wall. The expulsed air from the volume under the simulator propagates downstream from the foot to reach near zero velocity values at 0.15 m away from the top of the simulator.