Experimental investigation of debris damming loads under transient supercritical flow conditions

Debris loads during flood events have been well-documented by forensic engineering field surveys of affected communities. Research has primarily focused on debris impact loading and less emphasis has been placed into quantifying the loads and effects associated with debris damming, which occurs when solid objects accumulate at the front of structures. The formation of the debris dam has been shown to results in increased drag forces, backwater rise, and flow accelerations which can influence the stability of the structure. This study examined the formation of a debris dam in steady-state conditions of debris common to flood-prone communities. The study determined that the hydraulic conditions, in particular flow velocity, influenced the formation of the debris dam. Additionally, the study examined the influence of the blockage ratio on the backwater rise as well as the drag coefficient.

https://www.mdpi.com/2076-3263/7/3/74/pdf

Experimental investigation of debris-induced loading in tsunami-like flood events

Aerodynamic investigation of tucked positions in alpine skiing.

In this paper, we have reviewed the state-of-the-art of research on flow past a circular cylinder symmetrically placed between two parallel plates separated by a finite distance. Such flow, referred to as a confined flow or flow past a confined cylinder in this study, is characterized by the blockage ratio—the ratio of the cylinder diameter to the distance between the plates. Confined flows are common in engineering systems, but the interest in studying flows over confined cylinders was motivated by the need to correct unavoidable blockage effects in physical experiments for unconfined cylinders. A very early work on this topic was published in 1944. Since then, interest has gradually expanded to understanding the wake dynamics and hydrodynamic properties of confined cylinders at different blockage ratios. The emergence and further developments of the Computational Fluid Dynamics and Particle Image Velocimetry techniques have enabled researchers to unveil important and complex features of confined flows, such as the two-dimensional to three-dimensional flow transition, the analogy of the separated shear layers to mixing layers, different vortex shedding modes, and the asymmetry of confined flows at high blockage ratios. To date, there has been no systematic review dedicated to confined flows. The present review fills the gap and is aimed to provide a comprehensive account of relevant studies including a historical perspective of the studies, significant research findings, and most recent advancement of the knowledge. Further, we have also identified a number of research gaps for further investigations.

A state-of-the-art review of flows past confined circular cylinders

Placing a test model in the wind tunnel test section creates an interaction between the flow and the model and walls of the test section. This interaction affects the accuracy of data reading of the wind tunnel. One of the significant factors is the blockage which affects the drag and lift coefficients, causing inaccurate readings. This paper considered streamlined and blunted shapes of different sizes to investigate and assess the effect of the shape and size of the test model on the reading accuracy. Wind tunnel tests were conducted with the three different sizes for each shape to determine the aerodynamic coefficients of the models. Different correction methods were applied to find the correction coefficient. CFD simulations were performed using ANSYS Fluent software. A comparison of numerical and experimental results was carried out to determine the most suitable blockage correction method for the chosen models. It is found that a blockage ratio of less than 16% has the least blockage effect. The blockage correction of drag reduction for these models is very minimal, less than 1%. Correction coefficients for both shapes were derived to correct the blockage effect created by models with a blockage ratio of 16% or higher.

Investigation of the Blockage Correction to Improve the Accuracy of Taylor’s Low-Speed Wind Tunnel

This paper explains how to correctly measure the drag coefficient of a circular cylinder in wind tunnels with large blockage ratios and for the sub-critical to the super-critical flow regimes. When dealing with large blockage ratios, the drag has to be corrected for wall constraints. Different formulations for correcting blockage effect are compared for each flow regime based on drag measurements of smooth circular cylinders performed in a wind tunnel for three different blockage ratios. None of the correction model known in the literature is valid for all the flow regimes. To optimize the correction and reduce the scatter of the results, different correction models should be combined depending on the flow regime. In the sub-critical regime, the best results are obtained using Allen and Vincenti\'s formula or Maskell\'s theory with ?=0.96. In the super-critical regime, one should prefer using Glauert\'s formula with G=0.6 or the model of Modi and El-Sherbiny. The change in the formulations appears at the flow transition with a variation of the wake pattern when passing from sub-critical to super-critical flow regimes. This parameter being not considered in the known blockage corrections, these theories are not valid for all the
flow regimes.

Wind-tunnel blockage effect on drag coefficient of circular cylinders

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Wind-tunnel blockage effect on drag coefficient of circular cylinders