Injection of working fluid into a centrifugal compressor in the reverse tangent direction has been invented as a way of preventing flow instabilities (stall and surge) or restoring stability when stall or surge has already commenced. The invention applies, in particular, to a centrifugal compressor, the diffuser of which contains vanes that divide the flow into channels oriented partly radially and partly tangentially. In reverse-tangent injection, a stream or jet of the working fluid (the fluid that is compressed) is injected into the vaneless annular region between the blades of the impeller and the vanes of the diffuser. As used here, "reverse" signifies that the injected flow opposes (and thereby reduces) the tangential component of the velocity of the impeller discharge. At the same time, the injected jet acts to increase the radial component of the velocity of the impeller discharge

Skoch, Gary J.

NASA Technical Reports Server

NASA Tech Briefs, September 2007 27
Injection of working fluid into a cen-
trifugal compressor in the reverse tan-
gent direction has been invented as a
way of preventing flow instabilities (stall
and surge) or restoring stability when
stall or surge has already commenced. If
not suppressed, such instabilities inter-
rupt the smooth flow of the working
fluid and, in severe cases of surge, give
rise to pressure and flow oscillations that
can be strong enough to damage the
compressor and adjacent equipment. 
The invention applies, in particular, to
a centrifugal compressor, the diffuser of
which contains vanes that divide the flow
into channels oriented partly radially and
partly tangentially. In reverse-tangent in-
jection, a stream or jet of the working
fluid (the fluid that is compressed) is in-
jected into the vaneless annular region
between the blades of the impeller and
the vanes of the diffuser (see figure). As
used here, “reverse” signifies that the in-
jected flow opposes (and thereby re-
duces) the tangential component of the
velocity of the impeller discharge. At the
same time, the injected jet acts to in-
crease the radial component of the veloc-
ity of the impeller discharge. The net ef-
fect is to turn the impeller discharge flow
toward a more radial direction; in other
words, to reduce the flow angle of fluid
entering the vaned diffuser passage,
thereby reducing diffusion ahead of the
passage throat, reducing the pressure
load and the incidence of flow on the
leading edges of the vanes. The reduc-
tion of the flow angle also changes the dy-
namic coupling between the impeller
and diffuser in such a way as to prevent
the development of certain instability
modes in the diffuser. 
The number and distribution of re-
verse-tangent injectors can be tailored to
match the expected stall/surge charac-
teristics of the compressor and the space
available for installation. Reverse-tan-
gent injection can be implemented in
any of three operating modes: 
1. Continuous operation, in which the
working fluid is injected continuously; 
2. Open-loop operation, in which injec-
tion is initiated by on-off valves upon
detection of compressor instability or
conditions known to precede com-
pressor instability and the injection is
Reverse-Tangent Injection in a Centrifugal Compressor 
The compressor flow can be stabilized against stall and surge. 
John H. Glenn Research Center, Cleveland, Ohio 
Impeller
Rotation
Reverse-Tangent
Injector
Hub Hub
Working
Fluid In
Working
Fluid In
Impeller
Blade
Impeller
Blade
Reverse-
Tangent
Injector
Reverse-
Tangent
Injector
Injected Flow
(Out of Page)
Injected Flow
(Out of Page)
Working Fluid Out Working Fluid Out
Diffuser
Vane
Diffuser
Vane
MERIDIONAL CROSS SECTION SHOWING REVERSE-TANGENT
INJECTION FROM SHROUD SIDE
MERIDIONAL CROSS SECTION SHOWING REVERSE-TANGENT
INJECTION FROM HUB SIDE
AXIAL VIEW SHOWING REVERSE-TANGENT INJECTION
ferred to subsequent projects by use of
simple cut-and-paste routines. 
BAT includes a library of tempera-
ture-dependent cryogenic bearing-ma-
terial properties for use in the mathe-
matical models. BAT implements
algorithms that (1) enable the user to
select combinations of design and/or
operating-condition parameters, and
then (2) automatically optimize the de-
sign by performing trade studies over
all of the parameter combinations. This
feature enables optimization over a
large trade space in a fraction of the
time taken when using prior bearing-
model software.
This program was written by James D.
Moore, Jr., and Ed Troy of SRS Technologies for
Marshall Space Flight Center. Further 
information is contained in a TSP (see page 1).   
MFS-31864-1.
Working Fluid Is Injected in the direction opposing the tangential component of impeller discharge
velocity at multiple points (eight in this example) in the vaneless region between the impeller blades
and the diffuser vanes. 
https://ntrs.nasa.gov/search.jsp?R=20100010919 2019-08-30T09:01:52+00:00Z
28 NASA Tech Briefs, September 2007
terminated when stable compressor
operation returns; or 
3. Closed-loop or feedback-controlled
operation, in which compressor stabil-
ity is monitored and the number of ac-
tive injectors and the injection rate are
continually adjusted, using a dynamic
control model and controlled valves. 
In each of these operating modes, the
injected working fluid can be supplied
from an external source or from a down-
stream compressor stage where the total
pressure is sufficient to produce the in-
jected stream(s). 
This work was done by Gary J. Skoch of the
U.S. Army Research Laboratory for Glenn Re-
search Center. Further information is con-
tained in a TSP (see page 1).
Inquiries concerning rights for the commer-
cial use of this invention should be addressed
to NASA Glenn Research Center, Commercial
Technology Office, Attn: Steve Fedor, Mail
Stop 4–8, 21000 Brookpark Road, Cleveland,
Ohio 44135. Refer to LEW-17560-1. 
Analysis of Complex Valve and Feed Systems
Stennis Space Center, Mississippi
A numerical framework for analysis of
complex valve systems supports testing of
propulsive systems by simulating key valve
and control system components in the
test loop. In particular, it is designed to
enhance the analysis capability in terms
of identifying system transients and quan-
tifying the valve response to these tran-
sients. This system has analysis capability
for simulating valve motion in complex
systems operating in diverse flow regimes
ranging from compressible gases to cryo-
genic liquids. A key feature is the hybrid,
unstructured framework with sub-models
for grid movement and phase change in-
cluding cryogenic cavitations. 
The multi-element unstructured frame-
work offers improved predictions of valve
performance characteristics under steady
conditions for structurally complex valves
such as pressure regulator valve. Unsteady
simulations of valve motion using this
computational approach have been car-
ried out for various valves in operation at
Stennis Space Center such as the split-
body valve and the 10-in. (≈25.4-cm) LOX
(liquid oxygen) valve and the 4-in. (≈10
cm) Y-pattern valve (liquid nitrogen). Such
simulations make use of variable grid topolo-
gies, thereby permitting solution accuracy
and resolving important flow physics in the
seat region of the moving valve. 
An advantage to this software includes
possible reduction in testing costs in-
curred due to disruptions relating to un-
expected flow transients or functioning of
valve/flow control systems. Prediction of
the flow anomalies leading to system vi-
brations, flow resonance, and valve stall
can help in valve scheduling and signifi-
cantly reduce the need for activation tests.
This framework has been evaluated for its
ability to predict performance metrics like
flow coefficient for cavitating venturis and
valve coefficient curves, and could be a
valuable tool in predicting and under-
standing anomalous behavior of system
components at rocket propulsion testing
and design sites. 
This program was written by Vineet Ahuja,
Ashvin Hosangadi, Jeremy Shipman, Peter
Cavallo, and Sanford Dash of Combustion
Research and Flow Technology (CRAFT),
Inc. for Stennis Space Center. 
In accordance with Public Law 96-517,
the contractor has elected to retain title to this
invention. Inquiries concerning rights for its
commercial use should be addressed to:
Dr. Vineet Ahuja
Combustion Research and Flow Technology
(CRAFT Tech), Inc.
6210 Keller’s Church Road
Pipersville, PA 18947-1020
Phone No.: (215) 766-1520
Fax: (215) 766-1524
E-mail: vineet@craft-tech.com
Refer to SSC-00245, volume and number
of this NASA Tech Briefs issue, and the
page number.
Inertial Measurements for Aero-assisted Navigation (IMAN)
NASA’s Jet Propulsion Laboratory, Pasadena, California
IMAN is a Python tool that provides in-
ertial sensor-based estimates of spacecraft
trajectories within an atmospheric influ-
ence. It provides Kalman filter-derived
spacecraft state estimates based upon
data collected onboard, and is shown to
perform at a level comparable to the con-
ventional methods of spacecraft naviga-
tion in terms of accuracy and at a higher
level with regard to the availability of re-
sults immediately after completion of an
atmospheric drag pass. A benefit of this
architecture is that this technology is con-
ducive to onboard data processing and
estimation and thus can compute near
real-time spacecraft state estimates mak-
ing it suitable for autonomous operations
and/or closed-loop guidance, navigation,
and control strategies.
This tool can be used to reliably predict
subsequent periapsis times and locations
over all aerobraking regimes. It also yields
accurate peak dynamic pressure and heat-
ing rates, which are critical for a successful
corridor control strategy. These data are
comparable to radiometric-based naviga-
tion team reconstructed values. IMAN also
provides the first instance of the use of the
Unscented Kalman Filter (UKF) for the
purpose of estimating an actual spacecraft
trajectory arc about another planet. A sig-
nificant advantage to the implementation
of this type of filter is that the UKF is a
non-linear filter and thus accurate to at
least second order. It provides more mean-
ingful and realistic covariances and has
been shown to be robust in the presence
of sparse data sets.
Currently, IMAN is being used in an
experiment to demonstrate Inertial
Measurement Unit (IMU)-based aero-
braking navigation for the Mars Recon-
naissance Orbiter (MRO). It also can be
used in other operational missions such
as those using the atmosphere for entry-
descent-landing or solar sail missions
that experience significant solar radia-
tion pressure for propulsion.
This program was written by Moriba Jah,
Michael Lisano, and George Hockney of Cal-
tech for NASA’s Jet Propulsion Laboratory.
Further information is contained in a TSP
(see page 1). 
This software is available for commercial
licensing. Please contact Karina Edmonds of
the California Institute of Technology at
(626) 395-2322. Refer to NPO-43677.


Reverse-Tangent Injection in a Centrifugal Compressor

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