Science Pictures

Airflow around the Hypersonic Vehicle JAPHAR

copyright © ONERA 1996-2006 - All rights reserved
Numerical simulation of the airflow around hypersonic vehicle JAPHAR
(DCPS)

Many hypersonic vehicles have flown: when not powered, they are atmospheric reentry bodies. Powered, they are the scramjet-powered launch vehicles used since the begining of space conquest. The problem with the scramjet is that you have to carry large quantities of both fuel and oxidizer.

An airbreathing engine* burns oxidizer scooped up from the atmosphere rather than carried on board. As a result, the payload is increased and the launch costs are lower. Ramjets**, relatively simple engines with no moving parts, are airbreathing engines. The principle was devised by the French engineer Lorin in 1913. Currently, ramjets are used operationally only to power cruise missiles, like ASMP cruise missiles, around Mach 3.

Airbreathing Propulsion

The flight is supersonic at speeds approaching Mach 4 or 5, hypersonic above. The transition from supersonic to hypersonic flight is not brutal, but continuous.

For an airbreathing propulsion system, the transition from supersonic to hypersonic flight has important consequences. When a ramjet flies at supersonic speed, the internal airflow remains subsonic because it has to be slowed down to reach the high temperatures and pressures required. At higher speeds (Mach 6/7), the slowdown of the internal airflow causes a dramatic increase of the losses: the air is too hot and the engine no longer works efficiently. The best solution is to slow down the airflow, but not under supersonic speeds (Mach 2 to 3): you have a ramjet with a supersonic combustion process or scramjet***.

With a subsonic internal flow, the air does not stay long enough in the combustion chamber for the combustion to be complete. If the internal flow is supersonic, the air is not as much slowed down: it is colder and the fuel stays very little time (1 millisecond) in the combustion chamber. In this period of time, the fuel has to be mixed with the air and the reactions have to be completed before the coming out of the engine.

LEA Program in the Onera

The objective is to have the scramjet fly even faster, i.e. up to Mach 10 or 12, in order to replace the launchers' scramjets in the atmospheric phase, accelerate missiles or drones.

That is why Onera and MBDA France launched the LEA program in 2003: they will develop a simplified experimental hypersonic vehicle equipped with a dual-mode ramjet****. The later will undergo flight-tests in the Mach number range from 4 to 8, in order to check if the aeropropulsive balance (or generalized thrust-minus-drag balance) corresponds to what was forecast using the methodology. Development of operational, civilian or military applications of the hypersonic airbreathing propulsion largely depends on the capability to predict with reasonable accuracy the aeropropulsive balance.

Onera's Hypersonic Programs

PREPHA (1992-1998), with Aerospatiale, Dassault Aviation, Sep and Snecma
national program for a space-oriented scramjet (reusable launcher)
JAPHAR (1997-2002), with DLR
vehicle concept with a fixed dual-mode ramjet using gaseous hydrogen
PROMETHEE (1999-2002), with MBDA France
development of a variable-geometry dual-mode ramjet for long-range air-to-ground missiles
LEA (2003-2012), with MBDA France
development of an experimental hypersonic vehicle equipped with a dual-mode ramjet to fly at Mach 4 to 8

Glossary

* Airbreathing Engine
Engine using atmospheric oxygen as an oxidizer.

** Ramjet
Engine with no moving parts (neither turbine nor air blower), made up of an air intake, a diffusor, a combustion chamber and a nozzle. The pressurization is created only by dynamic air pressurization due to the high speed of the engine. The thruster works only at a speed above Mach 1.5 or 2, which means that a booster engine is needed for initial acceleration. The flow in the combustion chamber is subsonic.

*** Scramjet
The principle is the same as for the ramjet, but with supersonic intern flow. The scramjet becomes more efficient than the ramjet above Mach 6.

**** Dual-Mode Ramjet
Ramjet concept working in subsonic combustion at the beginning of the flight, in supersonic combustion later, in order to be able to fly at speeds from 2 to 8 Mach.


		Last Update: September 1^st, 2004 - © ONERA 2009 - Terms of use

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Airflow around the Hypersonic Vehicle JAPHAR