Abstract
The aerodynamics of smooth and slightly rough prisms with square cross-sections and sharp edges is investigated through wind tunnel experiments. Mean and fluctuating forces, the mean pitch moment, Strouhal numbers, the mean surface pressures and the mean wake profiles in the mid-span cross-section of the prism are recorded simultaneously for Reynolds numbers between 1times10^{5}le Re_{D}le 1times10^{7}. For the smooth prism with k_s/D = 4times10^{-5}, tests were performed at three angles of incidence, i.e. alpha = 0^{circ }, −22.5^{circ } and −45^{circ }, whereas only both “symmetric” angles were studied for its slightly rough counterpart with k_s/D = 1times10^{-3}. First-time experimental proof is given that, within the accuracy of the data, no significant variation with Reynolds number occurs for all mean and fluctuating aerodynamic coefficients of smooth square prisms up to Reynolds numbers as high as mathcal {O}(10^{7}). This Reynolds-number independent behaviour applies to the Strouhal number and the wake profile as well. In contrast to what is known from square prisms with rounded edges and circular cylinders, an increase in surface roughness height by a factor 25 on the current sharp-edged square prism does not lead to any notable effects on the surface boundary layer and thus on the prism’s aerodynamics. For both prisms, distinct changes in the aerostatics between the various angles of incidence are seen to take place though.Graphic abstract
Highlights
The main motivation of the many experimental, numerical and analytical studies in the field of bluff body aerodynamics lies in the desire to being able to capture the highly complex relation between object shape, the flow behaviour around this type of bluff bodies and the resultant fluid–structure interactions into a robust theoretical model
The mean aerodynamic force and pitch moment coefficients as a function of the Reynolds number are shown in Fig. 2a–c for the three investigated angles of incidence
A clear indication for the occurrence of the latter phenomenon in the current study is the large value of the wake width of Zwake∕D = 6 still present at 5.75 diameters downstream of the model’s base surface C, as shown in Fig. 8a, d for the smooth and rough prism, respectively
Summary
The aerodynamic and aeroelastic behaviour of cylindrical structures with bluff cross-sections has received considerable attention in many different research fields like aerospace (Gatto and Graham 2017; Povoa et al 2018), civil (Demartino et al 2015; Chen et al 2017; Yu et al 2017; Helgedagsrud et al 2019) and mechanical engineering (Caliskan 2014; Mangrulkar et al 2019), as well as in marine sciences (Forrest et al 2016; Shukla et al 2019) and wind engineering (Bagbanci et al 2012; Hall et al 2014). The main motivation of the many experimental, numerical and analytical studies in the field of bluff body aerodynamics lies in the desire to being able to capture the highly complex relation between object shape, the flow behaviour around this type of bluff bodies and the resultant fluid–structure interactions into a robust theoretical model. In this context, the studied fluid flow around generic circular and prismatic structures has to be seen as an idealised representation of realistic applications. Whereas the flow structures around and the aerodynamic loading on 2D circular cylinders in cross-flow both possess
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