1. C 2 - 1 t2-ij C 2 - 1 where the remainders denoted by (.) in Eqs. (10) and (11) contain parameters such a s the boundary-layer edge quantities upon which the vector-valued function Q is dependent.
2. Calculated results correspond to the AGARD CT cases 6,7,gnd 8 of Ref. 1151. A Reynolds number of 12.510 and a Mach number of 0.796 at zero mean incidence were used for a l l cases. The pitch axis was located at 25% of the chord. In case 6. the reduced frequency is 0.202 and the amplitude of oscillation is 1 degree. The time history of the surface pressure distributions obtained from the unsteady inviscid and true unsteady interaction solutions are compared with the experimental data a t selected instantaneous angles of attack in Fig. 8. The viscous effects are evident from the repositioning of the shock waves as in the steady case. An earlier computation for the same case using the flux-vector split Euler scheme of Ref. [101 reveals that the true unsteady and quasi-unsteady interactions produce similar solutions. A minimum time-step of about 0.045 is calculated in the inviscid part of the code for this case, whereas the boundarylayer part yields a minimum time-step of about 0.014. For the true-unsteady interaction, which uses the minimum time-step of 0.014 in both parts of computations, it takes 5582 cycles to complete 4 periods of oscillation. When the quasi-unsteady method is applied, the number of cycles for 4 periods reduces to 1736, i.e., a reduction of 69%. Since each cycle of the quasi-unsteady method contains several iterations of the boundary-layer solution, the overall reduction in computational time is about 50%for this case.