The Busemann Air Intake for Hypersonic Speeds DOI: http://dx.doi.org/10.5772/intechopen.82736

back-pressure is lowered to be replaced by a weak shock structure. This now opens a possibility. We calculate a Busemann intake module, with a strong shock, such that it starts spontaneously, at a high overall contraction ratio, and then reduce the back-pressure to remove the strong shock and obtain a supersonic exit flow, with a weak shock. This yields an exit flow which is suitable for scramjet operation. In doing this, we note that the flow, from the freestream to the location of the strong shock has not changed as we switch to the weak shock, so that the intake remains on the strong-shock design flow up to the corner while being started. Also, the amount of internal contraction remains the same and we could really start the intake with the weak shock structure in the first place. The strong Busemann shape is really a design tool which leads to a modified Busemann flow but with a started intake of high compression and efficiency having a supersonic exit Mach number-an intake with a high overall contraction but with a low internal, startable contraction. The supersonic exit flow is no longer conical although its axial symmetry is preserved.

In comparison to the weak shock case (Figure 24) there is a considerable enhancement of startability in the enlarged yellow domain so that starting can be expected near the S = 0.1 curve, which is acceptable for scramjet applications.

The reason for this improvement in startability stems from the fact that, for the strong shock option, the angular distance between the strong shock (at the corner) and the inflection cone is small so that A<sup>f</sup> and A<sup>3</sup> areas are close in size, i.e., there is not much internal contraction. This makes it easy for the conical normal shock, at the inflection location, to be swallowed. The strong shock design's aim is to produce a wavecatcher Busemann intake with a high overall contraction ratio and a low internal contraction that starts spontaneously. The calculated shape is compatible with a normal conical shock positioned at the inflection location (angle) and we select the intakes, with internal contractions, that permit the shock to be swallowed. Flow downstream of the inflection shock is subsonic. The strong shock is present only fleetingly during flow starting. After swallowing a weak shock system appears in the exit with supersonic flow downstream. This flow is suitable for a scramjet combustor. Within the calculated strong shock contour the supersonic weak shock flow is no longer conically symmetric and has to be examined via CFD and experiment. The end result is a wavecatcher Busemann intake with a high overall contraction (S 0.1) but with a low internal, self-starting contraction and hence a startable intake and supersonic exit flow.

Figure 26 is a schlieren picture of four quarter-circle Busemann intake modules each with flows started by the unsteady gun tunnel starting flow [4]. Arrow points

#### Figure 26. Impulsively started 4-module Busemann intake in the gun tunnel at Mach 8.33 (model is similar to Figure 19).

desirable to operate intakes near the curve S = 0.1 in Figure 24. Startable weak shock Busemann designs do not produce this amount of contraction—the prospect of obtaining startable full or wavecatcher intakes, with sufficient compression,

Busemann intake startability based on weak shock design: green—full Busemann start; green and yellow—

Startability calculations for the full and wavecatcher Busemann intakes were done also by starting the integration of Eqs. (5) and (6) from strong shock waves,

The outcomes are plotted in Figure 25. Each result is shown as a dot that is coloured green if the totally internal flow Busemann intake duct starts, green or yellow if the wavecatcher Busemann intake module starts (as determined in d)

The strong shock version has high overall contraction but low internal contrac-

tion so that it will self-start at overall contractions useful to the scramjet as a wavecatcher, but the strong shock and subsonic exit flow are not useful to the scramjet engine. In a wavecatcher module the about-to-start strong shock will be held in place by the appropriate back-pressure. It will move downstream if the

Busemann intake startability regimes based on strong shock design. green—full Busemann start; green and

from weak shock Busemann flows is disappointing.

Hypersonic Vehicles - Past, Present and Future Developments

8.2 Startability of the strong shock Busemann

wavecatcher start with spillage; and red—no start.

following the (a–e) steps above.

Figure 24.

Figure 25.

106

above) and red if there is no start.

yellow—module start with spillage; and red—no start.

to weak shock emanating from the v-notch in the cowl of one of the modules. Exit Mach number is 5.23.
