Renewed interest in hypersonic propulsion systems has led to research
programs investigating combined cycle engines that are designed
to operate efficiently across the flight regime. The Rocket-Based
Combined Cycle Engine is a propulsion system under development
at the NASA Lewis Research Center. This engine integrates a high
specific impulse, low thrust-to-weight, airbreathing engine with
a low-impulse, high thrust-to-weight rocket. From takeoff to Mach
2.5, the engine operates as an air-augmented rocket. At Mach 2.5,
the engine becomes a dual-mode ramjet; and beyond Mach 8, the
rocket is turned back on. One Rocket-Based Combined Cycle Engine
variation known as the "Strut-Jet" concept is being
investigated jointly by NASA Lewis, the U.S. Air Force, Gencorp
Aerojet, General Applied Science Labs (GASL), and Lockheed Martin
Corporation. Work thus far has included wind tunnel experiments
and computational fluid dynamics (CFD) investigations with the
NPARC code.
The CFD method was initiated by modeling the geometry of the Strut-Jet
with the GRIDGEN structured grid generator. Grids representing
a subscale inlet model and the full-scale demonstrator geometry
were constructed. These grids modeled one-half of the symmetric
inlet flow path, including the precompression plate, diverter,
center duct, side duct, and combustor. After the grid generation,
full Navier-Stokes flow simulations were conducted with the NPARC
Navier-Stokes code. The Chien low-Reynolds-number k-e
turbulence model was employed to simulate the high-speed turbulent
flow. Finally, the CFD solutions were postprocessed with a Fortran
code. This code provided wall static pressure distributions, pitot
pressure distributions, mass flow rates, and internal drag. These
results were compared with experimental data from a subscale inlet
test for code validation; then they were used to help evaluate
the demonstrator engine net thrust.
The top contour plot shows contours of static pressure on the
inlet centerplane of the subscale inlet. These contours indicate
a series of strong oblique shocks initiated by the precompression
plate. Mach number contours in the bottom contour plot indicate
a large region of low-speed flow along the body side of the inlet
resulting from a shock-induced boundary layer separation.
The following graphs compare the static pressures obtained from
the NPARC code to experimental measurements made in NASA Lewis'
1- by 1-Foot Supersonic Wind Tunnel. Very good agreement is observed
for the pressures along the cowl and body centerline.
After good agreement was observed between the CFD solutions and
subscale wind tunnel experimental data, the NPARC code was applied
to the demonstrator engine to provide pretest predictions. Pressure
distributions and internal drag force calculations were obtained
to guide the demonstrator engine tests. The CFD method developed
here (including grid generation, flow computation, and postprocessing)
will allow for analyses of future combined-cycle engine concepts.
For more information, visit the NPARC Alliance.
DeBonis, J.R.; and Yungster, S.: Rocket-Based Combined Cycle Engine
Technology Development: Inlet CFD Validation and Application.
AIAA Paper 96-3145 (NASA TM-107274), 1996.
Previous articleLast updated May 6, 1997
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