  The nonlinear evolution of two fluid interfacial structures like bubbles and
spikes arising due to the combined action of Rayleigh-Taylor and
Kelvin-Helmholtz instability or due to that of Richtmyer-Meshkov and
Kelvin-Helmholtz instability resulting from oblique shock is investigated.
Using Layzer's model analytic expressions for the asymptotic value of the
combined growth rate are obtained in both cases for spikes and bubbles.
However, if the overlying fluid is of lower density the interface perturbation
behaves in different ways. Depending on the magnitude of the velocity shear
associated with Kelvin-Helmholtz instability both the bubble and spike
amplitude may simultaneously grow monotonically (instability) or oscillate with
time or it may so happen that while this spike steepens the bubble tends to
undulate. In case of an oblique shock which causes combined action of
Richtmyer-Meshkov instability arising due to the normal component of the shock
and Kelvin Helmholtz instability through creation of velocity shear at the two
fluid interface due to its parallel component, the instability growth
rate-instead of behaving as $1/t$ as $t \rightarrow \infty$ for normal shock,
tends asymptotically to a spike peak height growth velocity $\sim
\sqrt{\frac{5(1+A_{T})}{16(1-A_{T})}(\Delta v)^2}$ where $\Delta v $ is the
velocity shear and $A_T$ is the Atwood number. Implication of such result in
connection with generation of spiky fluid jets in astrophysical context is
discussed.
