Spiral shocks in accretion discs

We perform two-dimensional numerical calculations of the tidal interaction between the companion star and the disc around the primary in a cataclysmic variable system with parameters appropriate for the eclipsing dwarf nova binary IP Peg. We show that a spiral shock pattern is indeed obtained. We find, however, that it is impossible to reproduce the two-armed spiral that has been recently observed in IP Peg for realistic discs.