A systematic procedure to consistently formulate a field theoretical, QCD b
ound state problem with a fixed number of constituents is outlined. The app
roach entails applying the Hamiltonian flow equations, which are a set of c
ontinuous unitary transformations, to a QCD motivated Hamiltonian with a co
nfining interaction. The method is developed in detail for gluodynamics in
the Coulomb gauge to obtain an effective block-diagonal Hamiltonian appropr
iate to a reduced Fock space with a fixed number of dynamical gluons. Stand
ard many body techniques are used to numerically diagonalize this Hamiltoni
an in a constituent two gluon Pock space. The calculated gluon condensates
and glueball masses are in good agreement with QCD sum rule and lattice res
ults.