3D NAVIER-STOKES SIMULATION OF HSTDV LAUNCH VEHICLECRUISE VEHICLE SEPARATION
T.K.Ganesh Anavaradham $, B Rajinikanth$ , R K Sharma$$
$
Scientist, DRDL, Hyderabad – 500 058, India, Email– aganesh@drdl.drdo.in
$$
Project Director, HSTDV, DRDL, Hyderabad – 500 058, India
1. INTRODUCTION
The aim of HSTDV project is to demonstrate airframe integrated scramjet engine for a duration of 20 seconds. The
cruise vehicle (CV) is placed on top of a booster and covered by suitable aerodynamic fairings. The launch vehicle
(LV) will boost the CV covered with panels to an altitude around 31 km and Mach no. around 6.1. The panel
separation and the non-axi-symmetric CV-Booster stage separation sequence happen at high dynamic pressure
conditions. Although these operations constitute a very minor part of the whole flight sequence, these are by far the
most complex aerodynamic phenomenon encountered and are crucial for successful testing of scramjet engine. In
order to understand the stage separation of non-axi-symmetric CV from Booster, creation of an aerodynamic
database (force and moment coefficients with respect to separation distance and CV, Booster attitudes) is required.
Presently, around 100+ CFD simulations are compiled and post processed. This data will be used towards
performing trajectory analysis to ensure risk free stage separation.
2. CONFIGURATION
The cruise vehicle and its components are shown in Fig. 1. The wing is kept horizontal and the tail surfaces are kept
at 34 degs orientation with respect to horizontal. The scramjet engine has an intake and combustor; the single
expansion ramp nozzle is a part of the airframe. The adaptor-booster configuration considered for the current study
is shown in the Fig. 2. A gap of 70 mm is provided between ramp and Cruise vehicle to ensure clean separation
without any re-contact between launch vehicle and cruise vehicle during the separation event.
3. METHODOLOGY
A 3D Navier-Stokes Steady flow analysis was carried out to understand the stage separation event. Simulating the
unsteady separation event at these speeds is a time consuming effort. Hence a steady flow analysis was carried out.
Initially the Booster and CV are attached and flow field is initialized with free-stream velocity and simulation
carried out till convergence. The separation distance is measured between the CV base and the booster adaptor
interface. It is shown in Fig.3. Thereafter, a grid with Booster and CV at a separation distance of 50 mm was
prepared and flow field of Booster and CV attached case was used as the initial solution and simulation carried out
till convergence. This procedure of increasing the gap and initializing the flow field with previous separation
distance flow field was done until a Booster CV separation gap value of 1000mm was achieved. A Second order
accurate density based explicit solver with two equation turbulence closure (K-Omega-SST) was used in the
simulations. Free stream condition of Mach no. 6.13, temperature and pressure corresponding to an altitude of 31.2
km is used for all the cases. The fluid was considered as air with thermally perfect gas assumptions. Variation of Cp
with temperature was modeled using a polynomial function and viscosity with Sutherland’s law. The Grid size for
all the stage separation case was around 12 Million.
4. RESULTS
(i) LV-CV Attached (With intake closed and intake open case):
Before the initiation of the stage separation process the intake is in closed position. Simulations were carried out for
this configuration at different angle of attacks to predict the aerodynamic forces and moments on the LV-CV
attached configuration. In the next phase, the intake cowl is opened and the internal flow is established within the
scramjet engine. Simulations were carried out for this configuration at different angle of attacks to predict the
aerodynamic forces and moments on the LV-CV attached configuration. Figure 5 shows the symmetry plane Mach
no. contours for the intake open and intake closed case. The stage separation event occurs after the internal flow has
been established within the scramjet engine. When the booster is close to CV, a separation bubble is produced on the
top side due to flow being brought to rest near the adaptor section. The effect of bubble is felt on the CV C6 section.
The intake remains in started condition at all separation distances. Plots of pressure distribution on the top side of
the CV at different separation distances shows that the pressure rise happening on the top surface is due to the
separation bubble formation. So the location of separation and the onset of interference free CV flight can be
inferred from these plots. The separation bubble size decreases with the separation distance and reaches the
interference free condition between 600mm to 700mm separation distance. The separation bubble on the top side
disappears (meaning CV aero data will be interference free) at a separation distance of 700 mm. Figure 6 shows the
plots of Normal force coefficient (Cz), Axial force coefficient (Cx), Pitching moment coefficient (Cmy) variation with
respect to separation distance for CV and separated booster at 0 degs. Angle of attack. The normal force and
pitching moment becomes equal to the CV free flight values after a separation distance of 700 mm. Similarly, the
effect of angle of attack on the aerodynamic coefficients has been evaluated.
5 CONCLUSION
The aerodynamic data on the cruise vehicle and booster has been generated as a function of separation distance and
angle of attack. The normal force and pitching moment becomes equal to the CV free flight values after a separation
distance of 700 mm . The data has been used for trajectory analysis during LV and CV separation.
Fig.1 Cruise vehicle – Components
Fig.2 Cruise vehicle – Booster configuration
Fig.3 Depiction of separation distance
Fig.4 Grid – symmetry plane
Fig. 5 Mach No contours on Symmetry Plane at Angle of Attack 0o
Normal Force
Coefficient
0.6
0.5
0.4
0.3
0.2
0.1
0.0
2Ramp Adaptor Configuration
CV Alone
0
200
400
600
800
Seperation Distance (mm)
1000
Axial Force Coefficient
Fig. 6 (a) Normal force coefficient on CV in the presence/absence of booster configuration
0.45
0.35
0.25
0.15
0.05
-0.05 0
2Ramp Adaptor
Configuration
200
400
600
800
Seperation Distance (mm)
1000
Fig. 6 (b) Axial force coefficient on CV in the presence/absence of booster configuration