However, a more useful and more standard way is to plot cl vs cd, with α simply a dummy parameter along the curve. This plot is called a drag polar, and is shown in the figure on the right. One reason for using the drag polar format is that when evaluating the aerodynamic per-formance of an airfoil, the α values are not really relevant.

2003年8月28日 · We went to a lot of trouble picking out the CL's and Cd's of the airfoils used by reading off the graphs in the "Theory of Wing Sections", but now I can't find any way of relating those CL's, Cd's to 3D values.

It is useful to illustrate the complexity of the flow around an object, the changes with Reynolds number and the consequent changes in the drag by way of an example.

The 2D approach has a number of shortcomings. The approach assumes that geometry variation and flow gradients are negligible in the third dimension (i.e., spanwise). Thus, wings of infinite span (yawed or unyawed) and axisymmetric bodies are perfectly suited for 2D analysis. However, real wings are finite and may be tapered.

2016年7月5日 · While simulating fluids using CFD tools on 2D / planar mesh and 3D / volume mesh the flow will differ according to the cross-section obviously.

2017年10月1日 · For such cases, the current work compares flow-profiles and forces computed by a 3D, 2.5D and 2D CFD models along the different sections of the NREL 5 MW turbine. The 2D CFD results are compared with experimentally measured drag and lift coefficient values as reported in DOWEC report [2].

2012年1月9日 · The 2D representation (i.e. side view) of this would be a simple square and the 2D CFD run would be axisymmetric. Or, do you mean your CFD runs are 2D and you are comparing it to a 3D wind tunnel test?

Advantages 3D CD has clearly more advantages towards the limitations of 2D CD (as shown in Table 1), as the 3D geometric information is free of illumination variations and perspective...

2019年5月12日 · When I run a 2D simulation using the Spalart-Allmaras turbulence model I get values that correspond to the Xfoil Polars at http://airfoiltools.com/airfoil/deta...il=naca0008-il (Cd of 0.025 and Cl of 0.6)

2008年10月29日 · I'm modeling a flying wing in XFLR5 and in the Xfoil 2D analysis I get beautiful Cl/Cd of 50-60 or so. However, once I model the wing I only get a Cl/Cd of 15-20 although the lift distribution is almost (within 2%) perfectly elliptical and there are no other things on the wing (like fuselage or winglets).