It really depends on what you are trying to model. If you'd like to model a simple array of veins, this should not be too difficult. Open-source CFD packages such as OpenFOAM can be used to do this. I would suggest looking at the following paper by Pinto et al. Once you have a grid established of your vein or artery structure, you can apply boundary conditions of pressure which will drive the flow of your liquid, blood in this case.
You should better detail what is your goal...Some years ago I worked on the subjet of flow in the diastole phase, the pressure measurements being one of the keys. You can read the references below. But you will also find much more recent papers from several authors, published on journals. For example, you shoud read the works of Peskin.
Dear Bhaskar, some other useful sources can be papers by Prof. Alfio Quarteroni (e.g. articles in Researchgate) where numerical methods are explained on the matter of CFD blood flowing. Gianluca