M.Sc Student | Mittelman Amir |
---|---|

Subject | Aft-Sting Mount Effects on Missile Longitudinal Stability and Base Flow Characteristics |

Department | Department of Aerospace Engineering |

Supervisors | Professor Jacob Cohen |

Dr. Eran Arad |

The longitudinal
stability margin was measured in both subsonic flow conditions (*U*=70,90
m/s) and transonic Mach numbers (*M*=0.7,0.9), using an aft-mounted six
component balance. When testing the missile configuration with small
stabilizers, the longitudinal stability margin was found to be insensitive to
the diameter ratio of the BFS in case of shear layer flow (from *d*^{*}=0.3
and up to *d*^{*}=0.8). Whilst the elimination of the flow
separation downstream of the base plane of the model, in case of boundary layer
flow (*d*^{*}=1) was found to have an unstabilizing effect on the
longitudinal stability of the missile. Additionally, this effect grows with
Mach number, in the transonic flow regime. The effect of changes in the base
flow on the longitudinal stability margin decreases as result of increasing the
stabilizer's span.

In addition,
hot-wire measurements were conducted for evaluating the mean and instantaneous
velocity field downstream of the base plane of the model. These measurements
were carried out at a free stream velocity of *U*=10 m/s and Reynolds
number of *Re*_{d}=49,000 (based on the body diameter). The mean
velocity profiles measured show expected behavior for both the wake flow (*d*^{*}=0)
and the shear layer flow (*d*^{*}=0.4) in terms of the mean
velocity field, the recirculation zone geometry and flow velocities and the
reattachment point location. A distinct peak in the velocity fluctuations at
Strouhal number of *St*_{d}=0.21 (based on body diameter) was
observed in case of wake flow (*d*^{*}=0). The presence of an
aft-sting, while altering the flow to a shear layer topology (*d*^{*}=0.4),
was shown to have a damping effect on the velocity fluctuations. Linear
spectral stability analysis for inviscid small disturbances was carried out
using Chebyshev collocation technique. The stability analysis shows similar
trends to those measured. In the *d*^{*}=0 case (wake flow), the
most unstable wave number calculated corresponds to the Strouhal number of *St*_{d}=0.25,
but the instability is not restricted solely to this frequency. In the *d*^{*}=0.4
case, a weaker instability at a broadband low frequency was calculated.