DRAG REDUCTION AND SHAPE OPTIMIZATION OF AIRSHIP BODIES, Th. Lutz and S. Wagner, Institute for Aerodynamics and Gas Dynamics, University of Stuttgart, Germany, 1997, American Institute of Aeronautics and Astronautics, Inc. (You can find it on the web).
In this paper bodies with minimal drag are presented for five design regimes that are defined with the volumetric Reynolds Number. Volumetric Reynolds Number and drag coefficient are defined as:
U_inf undisturbed free stream velocity
V body volume
v kinematic viscosity
rho air density
The figures below are from the paper. For my velomobile Re_v would be 10*1^(1/3)/15e-6 = 7e5. At Re_v = 1e6 the body of figure 7 has a Cd_v of ~0.075. In my CFD of the Quattro I have found a total drag of ~3 N at 10 m/s. When I assume the volume of the Quattro to be 0.7 m3 the Cdv is: 3/(1.2/2*10^2*0.7^(2/3)) = 0.06. I will try to evaluate the body of figure 7 with OpenFOAM.