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Memorial Tributes
NATIONAL ACADEMY OF ENGINEERING
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JAKOB ACKERET
1898-1981
BY ALEXANDER FLAX
PREPARED WITH THE ASSISTANCE OF
NICHOLAS ROTT
JAKOB ACKERET, whose fundamental, comprehensive, and path
breaking contributions to fluid mechanics and the under-
standing of high-speed and supersonic flows led to significant
improvements in the science of flight, died April I, 1981, in
Kusnacht, Switzerland, at age eighty-three after a long illness.
Professor Ackeret was born March 17, 189S, in Switzerland.
He received his diploma in mechanical engineering in 1920
and his Ph.D. in engineering science in 1930, both from the
Federal Institute of Technology (ETH), Zurich. He served in
1920 and 1921 as a research assistant of Professor Stodola at
ETH. From 1921 to 1927 he was a research associate of Profes-
sor Ludwig Prandt! at the University of Gottingen, Germany.
He took part in the planning and preparations for the estab-
lishment there of the Kaiser Wilhelm Institute for Fluid
Mechanics Research (today the Max Planck Institute for Fluid
Mechanics Research) becoming its first director when it went
into full operation in 1925. In 1928 he became chief engineer
at Escher Wyss Ltd., Zurich, where he served until 1932, when
he became a professor at ETH. There he founded and be-
came director of the Institute for Aerodynamics, which
became fully operational in 1934. He made that institute fa-
mous as a center for research on high-speed gas dynamics and
thermodynamics and served as its director until his retirement
from ETH in 1967. However, he maintained continuing, life
3
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MEMORIAL TRIBUTES
long connections with Escher Wyss and contributed to the
solution of many design problems and to inventions such as
gas turbines and variable-pitch propellers.
Professor Ackeret was one of the pioneers in the theoreti-
cal and experimental investigation of supersonic flows about
airfoils and in channels. He published in 1925 a definitive
paper describing the small perturbation theory of supersonic
flow of a perfect gas over a thin airfoil. The methods and
results he obtained are to this day often identified as "the
Ackeret theory," "the Ackeret pressure," and "the Ackeret lift."
He was personally responsible for innumerable important
contributions to theoretical and applied aerodynamics and
fluid dynamics. He clesigned, built, and operated several high-
quality subsonic and supersonic wind tunnels at both the
University of Gottingen and at the ETH. His closed-circuit
supersonic wind tunnel at ETH driven by a multistage com-
pressor permitted independent variation of Mach number
en cl Reynolds number and served for many pioneering exper-
imental investigations. (The term "Mach number" was
introduced by Ackeret in his inaugural lecture at ETH in
1929.) Professor Ackeret was one of the first to give clear,
theoretically based, and experimentally valiclated explanations
of the effects of compressibility in flow over aircraft compo-
nents and thereby contributed uniquely to the successful
design of high-speed flying machines.
Professor Ackeret's aerodynamic research inclu~led the
problems of gas flow at very high speeds through cascades
en c! grids, and the basic problems of boundary layers en c!
heat transfer at high subsonic and supersonic speeds. He was
one of the early workers in the study of the effects of
roughness on airfoil form drag and the bounclar,v layer, and
with his students he pioneered in fundamental investigation
of shock-boundary layer interactions in supersonic flows. He
did early significant work on the application of boundary layer
suction on airfoils, which work was later carried on by his
students, especially in investigations of the complex problems
of practical applications.
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JAKOB ACKERET
5
His work in the 1930s ant! 1940s established much of the
fluid mechanics en c! basic technology of the present-day gas
turbine, as evidenced by his many technical papers at that
time. He worked with Escher Wyss in the application of the
gas turbine with a closed-circuit and a multistage axial com-
pressor (the Ackeret-Keller turbine) as a stationary power
source. He also investigated hydraulic turbine problems, espe-
cially cavitation. On Professor Ackeret's sixtieth birthday,
Professor Theodore von Karman complimented him as the
outstanding mechanical engineer among the pioneers of aero-
dynamics. Professor Ackeret's leadership in aeronautical
engineering and fluid mechanics at ETH produced a great
center of learning en c! many students who influenced practi-
cal aeronautics and aeronautical education around the world.
He was a respected student of the history of science, ap-
plied mechanics, and aerodynamic and hydraulic technology.
His most significant contribution in this field was the editing
of a volume of Euler's works on hydrodynamics.
Elected a foreign associate of the National Academy of Engi-
neering in 1976, he was an honorary fellow of the American
Institute of Aeronautics and Astronautics, the Royal Aeronauti-
cal Society of London, and the Institute of Aeronautical Sciences
of New York. Ele was an honorary member of the American Soci-
ety of Mechanical Engineers, a member of the Max Planck
Institute for Aerodynamic Research in Gottingen, and a recipi-
ent of the Guggenheim Medal and the Prandtl Ring. He gave
the second Daniel and Florence Guggenheim Memorial Lecture
to the International Astronautical Federation in 1960.
Professor Ackeret's original publications numbered more
than one hundred. In addition he contributed to twenty-four
papers for the Institute of Aerodynamics and to forty-eight
other publications with various collaborators. A bibliography
of his work (and most of the work that was completed under
his direction) was published in the journal of Applied Mechanics
and Physics (CAMP), Vol. IXB, 1958.
Representative terms from entire chapter:
escher wyss
