The T-38 talon currently serves as the primary United States Air Force trainer for fighter aircraft. This supersonic trainer was developed in the 1960s but continues to be used today as the result of various modernization programs throughout its service life. The latest propulsion modernization program focused on improved takeoff performance of the T-38’s inlets, improved reliability of the twin J85 afterburning turbojet engines, and reduced drag with an improved exhaust nozzle design. The T-38’s inlet includes bleed holes upstream of the engine face to provide cooling airflow from the inlet to the engine bay. However, at various flight conditions, the bay air is pressurized relative to the inlet, resulting in reverse flow of hot engine bay air into the inlet. This reverse flow causes total temperature distortion that may reduce the engine stability margin. Partial inlet instrumentation of the left engine was used to estimate the total temperature distortion associated with reverse flow, however, flight testing of highly transient maneuvers revealed levels of total temperature distortion greater than that predicted for reverse flow alone. This discovery led to the hypothesis that thermal energy storage of the aluminum inlet during transient flight maneuvers resulted in increased temperature distortion at the engine face. Flight data analysis demonstrated the need for a near-real-time thermal inlet distortion analysis capability. A two-dimensional (2D) transient axisymmetric heat and mass transfer model was developed through the use of a lumped-parameter boundary-layer model to simulate the inlet flow and determine the time-dependent inlet duct heat transfer. This model was validated with transient 2D computational fluid dynamics and two flight maneuvers. The analysis of flight maneuvers revealed that in the absence of engine bay air re-ingestion, the time lag associated with the heating and cooling of the inlet walls generates radial temperature distortion, which has the effect of reducing engine stability margin up to 5.44% for the maneuvers analyzed.

1.
Davis
,
M. W.
, Jr.
, and
Kidman
,
D. S.
, 2010, “
Prediction and Analysis of Inlet Pressure and Temperature Distortion on Engine Operability from a Recent T-38 Flight Test Program
,”
ASME
Paper No. GT2010-22047.
2.
Society of Automotive Engineers
, 1991, “
A Current Assessment of the Inlet/Engine Temperature Distortion Problem
,” Aerospace Resource Document, Paper No. ARD50015.
3.
Buning
,
P. G.
,
Jesperson
,
D. C.
,
Pulliam
,
T. H.
,
Chan
,
W. M.
,
Slotnick
,
J. P.
,
Krist
,
S. E.
, and
Renze
,
K. J.
, 1998, OVERFLOW User’s Manual-Version 1.8, NASA Langley Research Center.
4.
Adams
,
J. C.
, Jr.
, 1973, “
Numerical Calculation of the Subsonic and Transonic Turbulent Boundary Layer on an Infinite Yawed Airfoil
,” Paper No. AEDC-TR-73-112.
5.
Taslim
,
M. E.
, and
Ugarte
,
S.
, 2004, “
Discharge Coefficient Measurements for Flows Through Compound-Angle Conical Holes With Cross-Flows
,”
Int. J. Rotating Mach.
1023-621X,
10
, pp.
145
153
.
6.
White
,
F. M.
, 1979,
Fluid Mechanics
,
McGraw-Hill
,
New York
, pp.
408
409
.
7.
Kays
,
W. M.
, and
Crawford
,
M. E.
, 1980,
Convective Heat and Mass Transfer
,
2nd ed.
,
McGraw-Hill
,
New York
, pp.
206
207
.
8.
Calogeras
,
J. E.
,
Mehalic
,
C. M.
, and
Burstadt
,
P. L.
, 1971, “
Experimental Investigation of the Effect of Screen-Induced Total Pressure Distortion on Turbojet Stall Margin
,” NASA Paper No. TM X-2239.
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