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Figure 4.—Measurements of thrust augmentation on the 2.2 inch diameter, 7.6 inch long, 0.75 inch inlet radius ejector, as a function of detonation tube exit to ejector entrance distance. Frequency = 20Hz, o= 1.2.

Figure 4 —Measurements of thrust augmentation on the 2.2 inch diameter, 7.6 inch long, 0.75 inch inlet radius ejector, as a function of detonation tube exit to ejector entrance distance. Frequency = 20Hz, o= 1.2.

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Figure 1—Schematic diagram of the detonation tube, ejector, thrust plate, and thrust spring system.
Figure 1—Schematic diagram of the detonation tube, ejector, thrust plate, and thrust spring system.
Figure 2(a).—Photograph of the original pulsed detonation tube, with the exit end pointing to the lower right. The short 3 inch diameter ejector is mounted downstream of the tube exit, and (b) the modified tube permitting the ejector entrance to be upstream of the tube exit, and mounted on air bearings for the spring extension technique of thrust measurements. The ballistic thrust plate can be seen at the right.
Figure 2(a).—Photograph of the original pulsed detonation tube, with the exit end pointing to the lower right. The short 3 inch diameter ejector is mounted downstream of the tube exit, and (b) the modified tube permitting the ejector entrance to be upstream of the tube exit, and mounted on air bearings for the spring extension technique of thrust measurements. The ballistic thrust plate can be seen at the right.
Figure 3(a).—Schematic diagram of the set of ejectors used in the statistical experiment and (b) the tapered ejector.
Figure 3(a).—Schematic diagram of the set of ejectors used in the statistical experiment and (b) the tapered ejector.
TABLE 1.—SET OF RUNS COMPRISING THE BOX-BEHNKEN EXPERIMENTAL DESIGN, WITH RESULTS IV. Experimental Results A. The statistical experiment te nner en The maximum thrust augmentation measured for a given combination of D, L, and R is given in table 1, together with the distance between detonation tube exit and ejector entrance at which that maximum was achieved. This distance is positive when the ejector entrance is downstream of the tube exit. As can be seen in figure 4, for the 2.2 inch diameter ejector, a maximum in thrust augmentation occurred with the ejector entrance downstream of the tube exit. This was true of all the ejectors tested in the statistical experiment. There is no obvious correlation between the distances for maximum thrust augmentation and the parameters L, D, and R, although they do seem to increase as D increases. The thrust augmentation can be fitted with a response surface of the form:
TABLE 1.—SET OF RUNS COMPRISING THE BOX-BEHNKEN EXPERIMENTAL DESIGN, WITH RESULTS IV. Experimental Results A. The statistical experiment te nner en The maximum thrust augmentation measured for a given combination of D, L, and R is given in table 1, together with the distance between detonation tube exit and ejector entrance at which that maximum was achieved. This distance is positive when the ejector entrance is downstream of the tube exit. As can be seen in figure 4, for the 2.2 inch diameter ejector, a maximum in thrust augmentation occurred with the ejector entrance downstream of the tube exit. This was true of all the ejectors tested in the statistical experiment. There is no obvious correlation between the distances for maximum thrust augmentation and the parameters L, D, and R, although they do seem to increase as D increases. The thrust augmentation can be fitted with a response surface of the form:
Figure 5.—Maximum thrust augmentation for each ejector plotted against ejector length. The lines are response surface contours for R = 0.5, and D = 2.2 (—), D = 3 (—) and D =4 (—». Frequency = 20 Hz, 6 = 1.2.
Figure 5.—Maximum thrust augmentation for each ejector plotted against ejector length. The lines are response surface contours for R = 0.5, and D = 2.2 (—), D = 3 (—) and D =4 (—». Frequency = 20 Hz, 6 = 1.2.
Figure 6—The effect of varying the ejector length for the 3 inch diameter, 0.75 inch inlet radius ejector. The frequency was 20 Hz., equivalence ratio = 1.2.
Figure 6—The effect of varying the ejector length for the 3 inch diameter, 0.75 inch inlet radius ejector. The frequency was 20 Hz., equivalence ratio = 1.2.
Figure 7.—Thrust amplification as a function of distance between the detonation tube exit and the ejector entrance. Positive values indicate ejector entrances downstream of the detonation tube exit. The results are for two different frequencies. The equivalence ratio = 1. The ejector length was 17 inches, the diameter was 3 inches, and inlet radius 0.75 inches.
Figure 7.—Thrust amplification as a function of distance between the detonation tube exit and the ejector entrance. Positive values indicate ejector entrances downstream of the detonation tube exit. The results are for two different frequencies. The equivalence ratio = 1. The ejector length was 17 inches, the diameter was 3 inches, and inlet radius 0.75 inches.
*D/Dye = 3 might have given a higher value of o at a larger value of L/D than was tested The air is flowing continuously in both the experiments of Rasheed et al., and the present work. Consequently the thrust augmentation of the air flow (and the air/fuel mixture also) will be the steady state value. A graph of steady state thrust augmentation against the ratio of ejector area ratio to jet area given by Porter and Squyers (ref. 9), indicates that for Rasheed et al., a value of o,, = 1.1 is not unreasonable, and a value of a,, = 1.2 is appropriate for
*D/Dye = 3 might have given a higher value of o at a larger value of L/D than was tested The air is flowing continuously in both the experiments of Rasheed et al., and the present work. Consequently the thrust augmentation of the air flow (and the air/fuel mixture also) will be the steady state value. A graph of steady state thrust augmentation against the ratio of ejector area ratio to jet area given by Porter and Squyers (ref. 9), indicates that for Rasheed et al., a value of o,, = 1.1 is not unreasonable, and a value of a,, = 1.2 is appropriate for
Figure 8.—Thrust amplification plotted against ejector length for the tapered ejector. The frequency is 20 Hz, and = 1. Open symbols and dashed lines represent results using the damped spring-displacement technique, and solid lines with filled symbols represent results with the thrust plate system.
Figure 8.—Thrust amplification plotted against ejector length for the tapered ejector. The frequency is 20 Hz, and = 1. Open symbols and dashed lines represent results using the damped spring-displacement technique, and solid lines with filled symbols represent results with the thrust plate system.
Figure 9—DPIV measurement of vorticity in the vortex ring emerging from the pulsed detonation tube.
Figure 9—DPIV measurement of vorticity in the vortex ring emerging from the pulsed detonation tube.
A parametric investigation has been made of thrust augmentation of a 1-inch diameter pulsed detonation tube by ejectors. A set of ejectors was used which permitted variation of the ejector length, diameter, and nose radius, according to a statistical design of experiment scheme. The maximum augmentations for each ejector were fitted using a polynomial response surface, from which the optimum ejector diameters, and nose radius, were found. Thrust augmentations above a factor of 2 were measured. In these tests, the pulsed detonation device was run on approximately stoichiometric air-hydrogen mixtures, at a frequency of 20 Hz. Later measurements at a frequency of 40 Hz gave lower values of thrust augmentation. Measurements of thrust augmentation as a function of ejector entrance to detonation tube exit distance showed two maxima, one with the ejector entrance upstream, and one downstream, of the detonation tube exit. A thrust augmentation of 2.5 was observed using a tapered ejector.
A parametric investigation has been made of thrust augmentation of a 1-inch diameter pulsed detonation tube by ejectors. A set of ejectors was used which permitted variation of the ejector length, diameter, and nose radius, according to a statistical design of experiment scheme. The maximum augmentations for each ejector were fitted using a polynomial response surface, from which the optimum ejector diameters, and nose radius, were found. Thrust augmentations above a factor of 2 were measured. In these tests, the pulsed detonation device was run on approximately stoichiometric air-hydrogen mixtures, at a frequency of 20 Hz. Later measurements at a frequency of 40 Hz gave lower values of thrust augmentation. Measurements of thrust augmentation as a function of ejector entrance to detonation tube exit distance showed two maxima, one with the ejector entrance upstream, and one downstream, of the detonation tube exit. A thrust augmentation of 2.5 was observed using a tapered ejector.
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Mechanical EngineeringAerospace EngineeringDesign of experiment
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