The study of flow physical specifics in a 2D supersonic air intake unit

Aeronautical and Space-Rocket Engineering


DOI: 10.34759/vst-2023-2-35-45

Аuthors

Rakhmanin D. A.*, Karpov E. V.**, Rakhmanina V. E.

Central Aerohydrodynamic Institute named after N.E. Zhukovsky (TsAGI), 1, Zhukovsky str., Zhukovsky, Moscow Region, 140180, Russia

*e-mail: d.rakhmanin@gmail.com
**e-mail: e-karpov@list.ru

Abstract

In modern supersonic aircraft, air intake units (AIU) exert a key effect on the entire power plant operation. The AIU main purpose is the gas flow supplying to the engine with minimal total pressure loss. The AIU development is a complex scientific and engineering task, which solution is being put into effect with computational and experimental methods.

The presented article considers methodological issues related to validation of the ANSYS Fluent software package (TsAGI license No. 501024), and provides a detailed description of the physical processes occurring in the AIN channel while throttling.

The authors performed numerical simulation of the flow in a flat supersonic AIU employing various turbulence models. The AIU geometry was borrowed from [1]. The oncoming flow parameters were as follows: Mach number М∞= 2.41, angle of attack α = 10°, Reynolds number Reх∞=5.07 × 107 [1/m], total pressure P0 = 540 кPa, total temperature T0 = 305 К. Data obtained by computing the static pressure distribution on the AIU channel walls were being compared with the experimental results from [1]. The authors revealed that the best match of computed and experimental data on static pressure distribution of the AIU upper and lower walls are ensured by the two turbulence models, namely k-ωSST-CC (CC stands for compressibility correction) and Reynolds Stress Model.

The turbulence model k-ω SST—СС, considered in more detail in this article, allows reproducing a qualitative flow pattern with stationary separation zones, shock waves (including those from separation zones), rarefaction waves, and vorticity regions.

The two-dimensional calculation comparison with the three-dimensional one revealed that the Mach number fields were practically the same for both 3D- and 2D-flow in the AIU symmetry plane. An angular vortex is being formed near the AIU side wall, which drastically changes in the sections close to the wall the flow field and static pressure distribution on the AIU channel lower wall in the transverse direction compared to the flow in the AIU plane of symmetry.

To study the effect of backpressure being set at the channel outlet boundary on the flow field properties of the supersonic air intake, throttling of the model channel was being executed. The backpressure coefficient d was equal to d = Pback/Р∞, where Pback is the static pressure set at the outlet boundary of the channel, and Р∞ is the static pressure of the incident flow.

The studies revealed that with the opened throttle (d = 0) the flow in the AIU channel was supersonic. The local zone of the boundary layer separation originates herewith behind the break in its contour and a fan of rarefaction waves in the area of interaction of falling compression shock from the cowl with the AIU lower wall boundary layer.

With the backpressure coefficient of d = 5.5, an extensive separation region appears in the expanding (diffuser) part of the channel and a transition from supersonic to subsonic flow occurs.

At backpressure coefficient d = 8.5, a flow similar to a Mach disk is being formed at the AIU inlet: a direct shock wave is located in the central part of the inlet, and on top (near the shell) and below (near the compression wedge) two λ-shaped shocks are formed.

With the backpressure further increase (d ≥ 9.25), the direct shock wave is shiftiing forward and locating prior to the shell, while the upper λ-shaped of shock waves disappears, and the lower one moves forward, increasing in size.

Keywords:

turbulence model, flat air intake, intake throttling, three-dimensional separation, λ-shaped shock wave, supersonic flow

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