Carl A. Trexler

Unsteady Pressure Behavior in a Ramjet/Scramjet Inlet

Mean and time-accurate pressures have been measured in the inlet of a dual-mode, ramjet/scramjet configuration. This configuration was designed for low hypersonic Mach number operation using a hydrocarbon-based fuel. The time-accurate measurements are presented for inlets operating at maximum permissible back-pressure during and after inlet unstart.

Mach 4 performance of hypersonic inlet with rectangular-to-elliptical shape transition

Wind-tunnel testing of a hypersonic inlet with rectangular-to-elliptical shape transition has been conducted at Mach 4.0. This fixed geometry inlet had a geometric contraction ratio of 4.8 and was designed using a quasi-streamline tracing technique to have a design point of Mach 5.7. These tests were performed to investigate the starting and backpressure limits of the inlet at conditions well below its design point. Results showed that the inlet required side spillage holes in order to self-start at Mach 4.0. Once started, the inlet generated a compression ratio of 12.6, captured almost 80% of available air and withstood a backpressure ratio of 30.3 relative to tunnel static pressure. The spillage penalty for self-starting was estimated to be 3.4% of available air. These experimental results, along with previous experimental results at Mach 6.2, indicate that fixed-geometry inlets with rectangular-to-elliptical shape transition are a viable configuration for airframe-integrated scramjets that operate over a significant Mach-number range.

Numerical Study of the Effects of Reverse Sweep on Scramjet Inlet Performance

A comparative numerical study of performance parameters of a similar and an opposite sweep sidewall compression inlet is made. The focus of the study is the investigation of the impact of alternate backward-forward sweep on the compression sidewalls as opposed to back-ward sweep on all the sidewalls. Two equivalent scramjet inlet configurations are designed for this purpose. These inlets have the same wetted areas of compression and expansion and same height and width; but in one inlet all the compression surface are swept back (similar sweep inlet) whereas in the other inlet, alternate surfaces are swept backward and forward (opposite sweep inlet). The cowl closure in both cases begins at the start of the throat region. A three-dimensional Navier-Stokes code is used to calculate the flow through these inlets. Results of these calculations are used to compare the two designs for their performance and flow quality. Effects of boundary- layer ingestion on the performance and overall flow features are also investigated.

Mach 4 Test Results of a Dual-Flowpath, Turbine Based Combined Cycle Inlet

An experimental study was conducted to evaluate the performance of a turbine based combined cycle (TBCC) inlet concept, consisting of a low speed turbojet inlet and high speed dual-mode scramjet inlet. The main objectives of the study were (1) to identify any interactions between the low and the high speed inlets during the mode transition phase in which both inlets are operating simultaneously and (2) to determine the effect of the low speed inlet operation on the performance of the high speed inlet. Tests were conducted at a nominal freestream Mach number of 4 using an 8 percent scale model representing a single module of a TBCC inlet. A flat plate was installed upstream of the model to produce a turbulent boundary layer which simulated the full-scale vehicle forebody boundary layer. A flowmeter/back pressure device, with remote actuation, was attached aft of the high speed inlet isolator to simulate the back pressure resulting from dual-mode scramjet combustion. Results indicate that the inlets did not interact with each other sufficiently to affect inlet operability. Flow spillage resulting from a high speed inlet unstart did not propagate far enough upstream to affect the low speed inlet. Also, a low speed inlet unstart did not cause the high speed inlet to unstart. The low speed inlet improved the performance of the high speed inlet at certain conditions by diverting a portion of the boundary layer generated on the forebody plate.

Mach 4 Performance of a Fixed-Geometry Hypersonic Inlet with Rectangular-to-Elliptical Shape Transition

Wind-tunnel testing of a hypersonic inlet with rectangular-to-elliptical shape transition has been conducted at Mach 4.0. These tests were performed to investigate the starting and back-pressure limits of this fixed-geometry inlet at conditions well below the Mach 5.7 design point. Results showed that the inlet required side spillage holes in order to self-start at Mach 4.0. Once started, the inlet generated a compression ratio of 12.6, captured almost 80% of available air and withstood a back-pressure ratio of 30.3 relative to tunnel static pressure. The spillage penalty for self-starting was estimated to be 4% of available air. These experimental results, along with previous experimental results at Mach 6.2 (Smart, M.K, “Experimental Testing of a Hypersonic Inlet with Rectangular-to-Elliptical Shape Transition”, Journal of Propulsion and Power, Vol. 17, No. 2, pp 276-283, 2001)indicate that fixed-geometry inlets with rectangular-toelliptical shape transition are a viable configuration for airframe-integrated scramjets that operate over a significant Mach number range.

Propulsion Airframe Integration Test Techniques for Hypersonic Airbreathing Configurations at NASA Langley Research Center (Invited)

ABSTRACT The scope and significance of propulsion airframe integration (PAI) for hypersonic airbreathing vehicles is presented through a discussion of the PAI test techniques utilized at NASA Langley Research Center. Four primary types of PAI model tests utilized at NASA Langley for hypersonic airbreathing vehicles are discussed. The four types of PAI test models examined are the forebody/inlet test model, the partial-width/truncated propulsion flowpath test model, the powered exhaust simulation test model, and the full-length/width propulsion flowpath test model. The test technique for each of these four types of PAI test models is described, and the relevant PAI issues addressed by each test technique are illustrated through the presentation of recent PAI test data. Nomenclature AF axial force ATE aftbody trailing edge C A axial force coefficient C D drag coefficient C L lift coefficient C M pitch moment coefficient C N normal force coefficient C P pressure coefficient NF normal force M Mach number P static pressure PM pitch moment q dynamic pressure SNPR static nozzle pressure ratio Xaft axial distance from CTE α, ΑΟΑ angle of attack γ ratio of specific heats

Three-Dimensional Simulation of a Translating Strut Inlet

A three-dimensional Navier-Stokes code is used to numerically simulate the flow through a variable-geometry, reverse-sweep side wall compression scramjet inlet. The strut of the inlet is allowed to translate back and forth, it is moved forward to help start the inlet by spilling some of the air at low speed, and is moved backward once the inlet has started to provide a high contraction ratio, and therefore, high compression at high speed. The focus of this study is on detailed examination of the flow characteristics in this complex three-dimensional geometry. Flowfield features such as the top wall separation and cowl pressure, as well as the effects of reverse sweep, compression, and flow distortion (nonuniformity) are investigated. The effects of vehicle undersurface boundary-layer ingestion on the flowfield are also investigated. Comparisons with experimental results are made to provide for the assessment of the present analysis.

A combined experimental/computational investigation of a rocket based combined cycle inlet

A rocket based combined cycle inlet geometry has undergone wind tunnel testing and computational analysis with Mach 4 flow at the inlet face. Performance parameters obtained from the wind tunnel tests were the mass capture, the maximum back-pressure, and the self-starting characteristics of the inlet. The CFD analysis supplied a confirmation of the mass capture, the inlet efficiency and the details of the flowfield structure. Physical parameters varied during the test program were cowl geometry, cowl position, body-side bleed magnitude and ingested boundary layer thickness. An optimum configuration was determined for the inlet as a result of this work.