In an article on flow dynamics yesterday, the name of a key developer of the new computer model was omitted. He is Yves Pomeau, of the Ecole Normale Superieure in France.
Scientists at the Los Alamos National Laboratory and in France have developed a new computerized method to predict the flow of air and fluids that may improve the aerodynamics of cars and planes, track weather systems more reliably and expedite development of "Star Wars" weapons.
The new method of predicting flow dynamics, still in the early testing stage, could allow relatively unsophisticated computers to make calculations that can now be done only by new-generation supercomputers over days or weeks.
According to the method's developers, this has led researchers and defense specialists to question whether the discovery may not be of great value to the Soviet Union, which lags behind the United States in computer sophistication and capacity.
Brosl Hasslacher of the Los Alamos laboratory, who created the new computer model in collaboration with Uriel Frisch of the Observatoire d'Nice in France, said Defense Department officials at the lab questioned whether his technical paper, expected to be published in the next few weeks in Physical Review Letters, should be classified to keep it out of Soviet hands.
But, he said, everyone quickly decided that the basic mathematics are in an area of research well-known to mathematicians and physicists in many countries and could not be kept secret.
The determination of flow and turbulence is vital because many physical phenomena involve questions of flow: the movement of objects through fluids, such as bullets, rockets, autos and airplanes, or the movement of fluids themselves such as air movement in weather patterns, chemicals being mixed or streams of particles striking the atmosphere in particle-beam weapons.
Calculations of these flows are necessary, for example, to develop wings with more efficient lift, or make weather predictions that come closer to reality.
Air flowing over a wing includes a thin layer of air -- like a coating on top of the wing -- that is stable and moves slowly while the air inches above it passes by at hundreds of miles an hour. This layer, with its lower pressure, is what gives the wing its lift.
When the plane's speed slows, this "boundary layer" of air can become turbulent and break away from the wing. This occurs just as the wing loses its lift, and the plane stalls. Designers watch for the turbulence in the boundary layer to alert them at what speed the wing will stall.
Even particle beam weapons involve a flow of atomic particles that strike air and either bounce off it or flow into it like a fast stream into a lake.
It is also possible that wind tunnels could be replaced with more precise computer simulations. Wind tunnels do not show fine detail of turbulence along a surface and are inaccurate in other details because vehicles remain still while the air moves. In real life, the vehicles move through air.
The Hasslacher-Frisch model essentially involves a computerized calculation of the movement of extremely small patches of air or fluid. The movement of each of these millions of tiny units is then combined to give a minutely accurate picture of flow.
The work of Hasslacher and Frisch has been called "stunning" and "drastic" by specialists in the field. Early tests have been successful, but researchers say it may be some time before tests are complete and a determination is made whether it has a wide practical use.
But early results suggest that the model can calculate flow 1,000 to 1 million times faster than previous methods, say researchers familiar with the work, making it at least theoretically possible to push forward the field of flow calculations in one sudden jump.
The current methods of doing these calculations now are based on equations more than a century old and are cumbersome. The current equations also take thousands of lines of computer instructions; the new method has only 100 lines.
"This is an exciting idea, intellectually very nice and . . . the potential benefits of this are enormous," said Robert Kraichnan, a researcher in flow and turbulence.
"The work is at an early stage, but it has aroused a great deal of interest because the guts of the calculation is intellectually very simple compared to other calculations. There is a hope of tremendous computational advantages with this method. They may or may not materialize."
The fundamental idea behind calculation of flow and turbulence is that, in theory, each atom's motion could be tracked as a separate unit, then all added together to make a detailed picture of flowing material and all its eddies, curves and swirls. But since making a calculation for each atom would reach far beyond anyone's power to compute, researchers have used equations that assume millions of atoms acting together produce smoothly varying curves, speeds and direction changes.
To make such calculations with any kind of useful detail, many complex differential equations must be solved.
Hasslacher and Frisch chose model atom-like units pushing and colliding against one another. They use hexagonal cells in a huge honeycomb array. The flow is pictured as jumping from one cell to another.
Depending on the angle of the flow as it heads into a cell, it will come out at one of several different angles on the other side of a hexagon. The action is displayed on a computer screen as a moving flow of many shifting lines. It resembles the movement of a stream flowing around a rock.
Stuart Patterson, former head of two supercomputing facilities and now running his own company, Technical Computation Systems of Boulder, says that it may take a year of running tests -- mimicking known flow patterns -- to see the accuracy of the method. "Something as adventuresome as this -- it is hard to tell how good it will be in the end. But it is well worth pursuing," he said.
With current powerful computers and the older methods of modeling, he said, researchers are just beginning to gain the ability to model systems better than a wind tunnel.
The new method, if it holds up, will make such calculations with relative ease.