Curved baffle introduction impact on flat jet nozzle characteristics analysis

Аuthors

Siluyanova M. V.^*, Shpagin V. P.^**, Yurlova N. Y.^***

Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia

*e-mail: dc2mati@yandex.ru
**e-mail: vshpag@gmail.com
***e-mail: yurlovanadia@mail.ru

Abstract

At present the air force faces the challenge of visibility of a flying vehicle in infrared band, caused by hot parts of an engine, turbine blades, afterburner components, nozzle, as well as jet exhaust stream. In principle, the visibility problem can be eliminated by flat nozzle implementation. It becomes possible due to angle of visibility reduction of hot engine parts. However, implementation of flat nozzle only, as a rule, is not enough. To achieve full shielding of hot engine parts bending of nozzle channel is needed. As a rule, bending range is strictly limited, and, thus, one must apply more complicated methods. One of such methods is integration of buffles of special form into nozzle channel. It allows concealing the problematic engine parts behind the smaller curve of a nozzle. The presented study considers the similar case.

We designed the subsonic nozzle blocking entirely the visibility of engine hot parts. We achieved this effect by bending the flow duct of the channel and integrating into it specially curved buffles. We considered linear law of variation on the length of a rectilinear tapering channel cross-sectional area as an initial model. We worked hereafter at the nozzle of the initial version, but with already described engine shielding method. The effect was reached by bending the initial channel and integrating specially bended buffles into it.

In this work, we carried out the analysis of introduction of deflectors into the channel impact on gas-dynamic losses. The calculations were performed with software ANSYS CFX. Three-dimensional viscous turbulent flow of compressible gas modeled using the Reynolds, averaged Navier-—Stokes based equations, closed with the SST Menter turbulence model.

Computational domain of the calculation was a nozzle channel without considering external flow around it. The unstructured mesh consisting of tetrahedrals with a layer of prisms on all surfaces, with the condition of the wall, was used. The calculations were conducted with the following equals for both cases of boundary conditions:

∙— input — the pressure and the temperature;

—∙output — the average static pressure.

The boundary conditions correspond to the turbofan with a bypass ratio degree of m ≈ 4 (engine — analog of the turbofan engine PS-90A).

The calculation reveal that base flat nozzle does not have separation areas, and losses inside the channel are related only to tтhe of the stream wall friction. The value of the velocity coefficient for this option is φ = 0.994.

The curved channel with deflectors does not also have found separation areas, but due to the increased contact area the friction losses increased too. A numerical calculation showed, that in case of the channel with integrated deflectors, the nozzle coefficient of velocity, compared with the original version, decreased by 4.4% and φ = 0.952.

This work results in conclusion about the possibility of profiling non-separable flat unobtrusive nozzle using the proposed method of deflectors integrated into the channel. In this case, the velocity coefficient of the nozzle, selected as a criterion for estimating losses in the output device, in this case fell within 5%, and the pressure field and the output speed remain uniform. The obtained results allow speaking about the possibility of using presented method for designing nozzles with limited sizes.

Keywords:

flat nozzle, curved baffle, airflow

References

1. Siluyanova M.V. Formirovanie i otsenka variantov konstruktivno-tekhnologicheskikh reshenii sovremennykh gazoturbinnykh dvigatelei. Sbornik nauchnykh trudov po materialam Mezhdunarodnoi nauchno-prakticheskoi konferentsii «Razvitie nauki i obrazovaniya v sovremennom mire». Moscow, OOO «AR-Consult», 2014, pp. 25-26.

2. Siluyanova M.V., Shpagin V.P., Yurlova N.Y. // Nauchnye trudy (Vestnik MATI)., 2014. no. 23 (95). pp 77-81.

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