VELA is an ambitious project to create appropriate innovative transport aircraft concepts and associated development tools for Very Efficient Large Aircraft.  The fire and evacuation modelling aspects of this collaborative EU project is lead by FSEG of the Centre for Numerical Modelling and Process Analysis, University of Greenwich. The project runs from 2002 - 2005.

The partners for the project are: Airbus, FSEG University of Greenwich, ONERA, INTA, DLR, NLR, CIRA, VZLU, TU, Bristol University, PEDECE, IBK, SENER

Modern jet-aircraft are accepted as a part of the transport system throughout the world. They have a high level of commercial success and operate under state-of-the-art safety standards and environmental regulations, but it will be impossible for this type of aircraft to meet the requirements for ecologically-acceptable air transport in the next 30 to 50 years. Only new unconventional civil transport aircraft configurations promise a considerable progress in productivity as well as meeting future economic demands and challenging ecological constraints. Studies carried out on wing/body lifting configurations during the last decades have shown a huge potential for these unconventional configurations. Advantages of these types of aircraft include reduced fuel consumption, increased passenger numbers, aerodynamic and structural weight efficiency. Project VELA explored Blended Wing Body (BWB) configurations for their suitablility as mass passenger transportation systems.

The VELA (critical technology project – CTP) configurations are among the most promising to cope with future demand on air-traffic in the new millennium under strong economic and even more challenging ecological constraints. The VELA will not result in a final configuration for a future aircraft. It will provide a first step in a long-term work plan and it will be followed by further research work.

FSEG Project Objectives

When considering a BWB passenger aircraft design there are many challenging questions that need to be addressed concerning the aerodynamics, structures and flight mechanics of such an aircraft.  However, in all of these areas industry has the luxury of past experience through military aircraft design to initiate and guide design efforts.  Two vital areas in which the industry has no prior experience concerns passenger egress safety and the associated possible fire development resulting from a post crash fire.

BWB designs being considered by project VELA are capable of carrying in excess of 700 passengers involving a single deck but with more than two longitudinal aisles. Questions concerning seating arrangement, nature and design of recreational space, the number, location and type of exits, nature of longitudinal cabin partitions, nature of cross aisles linking each cabin section, the number of cabin crew required and the nature of the cabin crew emergency procedures are just some of the issues that need to be addressed.  These issues have been addressed by FSEG in Work Package 5.

Ultimately, the practical limits on passenger capacity and aircraft design are not based on technological constraints concerned with aircraft aerodynamics but on the ability to evacuate the entire complement of passengers within agreed safety limits.  These proposed safety limits must be seen to provide an equivalent level of safety to today’s standards for conventional aircraft.  These issues have been addressed in VELA work package 5 through subtasks T5.1 (Adapting an aircraft evacuation model to accommodate BWB configurations), T5.2 (Assessing BWB cabin concepts for safe egress and short turn around times) and T5.4 (Development of flying wing evacuation certification requirements). 

The key factor driving aircraft evacuation is fire spread and the resulting development of non-survivable conditions within the cabin.  The traditional prescriptive approach to aircraft fire safety regulation is based on engineering judgement derived from operating experience and a limited amount of full-scale and laboratory scale test fire testing. Full-scale fire testing is important for obtaining extensive information relative to the characteristics of aircraft fires, especially with respect to occupant survival. However, realistic full-scale fire tests are time consuming and financially costly.  The evacuation requirement for conventional aircraft stipulates that you must be able to evacuate the complete aircraft in 90 seconds through half the normally available exits.  The 90 second requirement provides an estimate of the Available Safe Egress Time (ASET), which is derived from full-scale fire tests.  A basic question that needs to be asked is whether 90 seconds is an appropriate ASET for BWB designs?  If not, what is an acceptable ASET for flying wing designs? 

To address these challenging key issues FSEG will:

• Modify their airEXODUS aircraft evacuation model to accommodate the unique features of BWB aircraft

• Undertake a series of evacuation analyses of the proposed VELA BWB designs and suggest alternative cabin layouts

• Undertake CFD based fire analysis of the BWB cabin layout to estimate fire spread and smoke filling times for a representative fire scenario and provide a first estimate of the flashover time based on a simple flashover criterion

Blended Wing Body configuration


VELA 1, 1 Class configuration


VELA2, 3 Class configuration

Mesh used to model the fire propagation

VELA 1, 1 Class, Status 1, Visibility at 1.68m height at 120sec


BWB model airplane for testing aerodynamics and flight characteristics

Evacuation Scenarios

Two BWB configurations were proposed by the VELA partnership.  These were identified as consisted of VELA 1 and VELA 2.  These two aircraft consisted of fundamentally different aircraft configurations and hence internal cabins.  For each of these aircraft configurations two cabin layouts were considered, a single class layout and a three class layout.  Each aircraft consisted of 25 Type-A exits.  In the evacuation scenarios, half the exits on one side of the aircraft were made available.

airEXODUS Model Development

SMARTFIRE Model Development

The fire simulations were undertaken using the FSEG SMARTFIRE software.  A number of modifications to the code were required to accommodate the requirements of this project.  These included modifications to:

• The flame propagation model

• The toxic gas model

• (optimisation of) the radiation model

In addition, a burn through model was developed to represent the failure of the cabin partitions. 

Fire Scenarios

The scenarios investigated were based around the VELA 1 configuration which was exposed to an external kerosene fuelled post-crash fire.  The fire gained access to the cabin via a single rupture immediately opposite the external fuel fire.  The size of the rupture was the equivalent of a Type-A exit.  Scenarios involving half the available exits being open and all available exits closed were examined.  Cabin material properties were provided by Airbus.

VELA 1 and VELA 2 Configurations

The VELA configurations:

VELA 1, 1 Class configuration. Click image for VR animation


VELA 2, 3 Class configuration.

Evacuation Analysis and Results

More than 12 different models were run and analysed for VELA 1 and VELA 2. All aircraft have 25 crew members, one at each exit and five within the middle area of the aircraft. Only the left hand side exits are functioning and each PAX initially attempts to evacuate via the nearest exit. Within the model, the simulated crew members attempt to redirect the PAX from their current exit to an alternative exit in an attempt to minimise the overall evacuation time of the aircraft.

It should be noted that the quoted evacuation times are out of aircraft times and not on-ground times.

Fire Analysis and Results

The computational mesh used in these simulations consisted of over 900,000 cells. The mesh was an unstructured mesh in order to capture the shape of the aircraft nose. The computational mesh also captured the passenger seats and overhead locker configurations.

View of mesh used for fire simulations

Three dimensional layout of VELA cabin fire geometry constructed within SMARTFIRE

.A key finding of this work is that for the fire scenarios considered, flashover did not occur within 480 seconds (after ignition of the external fire). Thus, unlike conventional aircraft, flashover is not the factor driving the available safe egress time (ASET) as this is predicted to occur after 480 seconds – long after passengers would have evacuated the cabin. However, the ASET will be affected by the development of the heat, toxic environment and smoke produced by the fire. The atmospheric conditions within the cabin may have a significant detrimental impact on the evacuation capabilities of the passengers. Furthermore, in the immediate area of the rapture, conditions become quite severe after only 60 seconds thus it is essential that an evacuation strategy be developed to rapidly evacuate passengers in the vicinity of any rupture associated with an external fire.
 

VELA 1, 1 Class, Status 1, Visibility distance at 1.68m for Scenario 1 at 120sec

 
VELA 1,1 Class, Predicted temperature contours at the cross aisle connecting the exit 5R at 120 seconds

VELA 1, 1 Class, predicted spread of fire, red dots depict solid surface which is on fire. Click image to view the animation.

VELA 1, 1 Class, predicted temperature evolution at 1.64 m above the floor. Click image to view the animation.

Follow up project

FSEG is carrying out further examination of the fire and evacuation performance of BWB configurations which is continuing in the EU Framework 6 project NACRE.

Project Partners

Further Information

Prof. Ed Galea
Fire Safety Engineering Group
University of Greenwich
Greenwich Maritime Campus
Old Royal Naval College
Queen Mary Building
Greenwich SE10 9LS
UK

Tel: +44 (020) 8331 8730
Fax: +44(020) 8331 8925
e-mail: E.R.Galea@gre.ac.uk

The VELA project is funded by the European Commission's 5th Framework Programme