Background Image
Previous Page  6 / 15 Next Page
Information
Show Menu
Previous Page 6 / 15 Next Page
Page Background

the flow pattern changing as well (Fig. 4

b

). Experimental angle of the

shockwave front deflection from the wedge (

α

= 13

,

β

= 5

for the

lower 10

wedge) was used to calculate the Mach number for the ram air

according to the formula [5]

M

= sin

2

α

γ

1

2

sin

α

sin

β

cos(

α

β

)

1

/

2

.

Mach number for the lower 10

wedge was 7.09 (Fig. 4

a

). The flow

parameter values for a semi wedge can be estimated with lesser accuracy

(a greater angle of shockwave deflection from its upper surface can be

observed), which is caused by the model being at a distance from the

nozzle symmetry axis.

Under similar initial conditions flow tests were conducted on models

simulating air intake of a pespective HA. These models were represented

by two blunt-nose 10

wedges with 1.5 mm bluntness radius and 10 mm

thickness. In order to investigate shockwave interaction in a complex

configuration duct simulating flame holders in the gas dynamic passage,

the models were provided with special cavities, 3 mm deep. The models

were positioned symmetrically to the nozzle axis at 2 cm distance from

each other. This was done to ensure homogeneous field flow parameters

between the models. Fig. 5 presents shadow images of the test.

The process presented in Fig. 5,

a

is caused by the first stage of the

driven gas expansion through the nozzle on to the model, which is optimally

suited for the high-speed test, since at this period the flow parameters from

the nozzle unit are approximately constant, with M

= 7

. At the shadow

video it is experimentally observed for 15 ms.

After the rarefaction waves fan and the contact surface of the driver gas

hit the LPC right end wall, the pressure at the nozzle entrance decreases

and the flow parameters start to fluctuate significantly. This perturbation

is shown in Fig. 5

b

, it lasts for about 5. . . 7 ms. After that the shockwave

interaction process in the shock tube is determined by multiple passes and

rarefactions of shock waves between LPC and HPC sidewalls. However,

it is possible to identify time intervals in which gas parameters at the

nozzle entrance change insignificantly. Such type periods can be directly

connected and numerically characterized with the data presented in the

oscillograph pattern (Fig. 3

c

). In particular, fragment

C

in the oscillograph

pattern corresponds to the second, lower velocity quazi steady flow mode

presented in 5 c. The duration of this period is

t

c

30

ms, M

= 4

.

5

.

In the course of the experiments the third quazi steady flow stage

( M

= 3

) was identified which corresponded to fragment

D

of the

oscillograph pattern in Fig. 3.

ISSN 0236-3941. HERALD of the BMSTU. Series “Mechanical Engineering”. 2015. No. 1 9