  A systematic procedure to consistently formulate a field theoretical, QCD
bound state problem with a fixed number of constituents is outlined. The
approach entails applying the Hamiltonian flow equations, which are a set of
continuous unitary transformations, to a QCD motivated Hamiltonian with a
confining interaction. The method is developed in detail for gluodynamics in
the Coulomb gauge to obtain an effective block-diagonal Hamiltonian appropriate
to a reduced Fock space with fixed number of dynamical gluons. Standard
many-body techniques are used to numerically diagonalize this Hamiltonian in a
constituent two gluon Fock space. The calculated gluon condensates and glueball
masses are in good agreement with QCD sum rule and lattice results.
