Influences of Design Parameters on a Double Serpentine Convergent Nozzle

Abstract

Serpentine nozzles are supplied in stealth bombers and unmanned aerial vehicles (UAVs) to evidently suppress the infrared radiation signatures (IRSs) emitted by engine exhausts. It is commonly known that excessive geometric parameters are included in the double serpentine nozzle design and, as a result, the aim of this paper is to study the influences of the design parameters on the performance of double serpentine nozzle. To this end, the design method of the serpentine nozzle was concisely introduced, and the qualifications to completely shield turbine were given. Simulations using six different turbulence models were conducted and compared to the experimental data in order to determine the suitable turbulence model for serpentine duct simulations. Then, the effects of geometric design parameters at the first serpentine paragraph exit (the dimensionless width of W1/D, area of A1/Ain, and offset distance of ΔY1/L1) on the flowfield, and the performance of double serpentine nozzle was investigated numerically. The validation study shows that the simulations with shear-stress transport (SST) κ–ω turbulence model adopted can accurately predict the flux rate, the axial thrust, and the static pressure of the experimental nozzle, and therefore, SST κ–ω turbulence model is the most suitable turbulence model in the selected six turbulence models to be used for the simulation of the double serpentine nozzles. The numerical results show that friction loss increases with the increment of W1/D due to the increased wetted perimeter, but small value of W1/D would lead to large secondary flow loss; even the shock loss appears because of the steep curvature of the second turning. Small area of the first serpentine duct A1/Ain induces high flow velocity in the first duct, which corresponds to large friction loss. Steep offset distance of the first serpentine duct ΔY1/L1 induces high local losses. As the geometric design parameters of the double serpentine nozzle interact mutually with the qualifications to completely shield the turbine, the range of design parameters should be synthetically chosen during the design progress. Thus, the width of the first serpentine duct W1/D is recommended to be from 1.0 to 1.3. The area of the first serpentine duct A1/Ain should be as large as possible, and the offset distance of the first serpentine ΔY1/L1 should be small in the permission range of the design parameters.

Internal flow and external jet characteristics of double serpentine nozzle with different aspect ratio

“…SST κ–ω with compressible effect validated by the experimental data in Sun et al. 21 was chosen as the turbulent model. The predictions of wall pressure, flux rate, and axial thrust were used to validate the turbulent model, as seen in Figure 4.…”

“…This variation tread of Ma distribution around the second inflection is different from that in the previous work. 20,21 In the previous work, just the curvature radius around the second inflection is changed with the variety of geometry parameters, and thus the variation tread of Ma distribution is monotonous. However, both the curvature and the duct height are changed with the variety of AR in this paper.…”

“…Results denoted that the width–height ratio had little effect on the edge diffraction field of the serpentine nozzles under horizontal and vertical polarization ways, and the difference of the RCS was less than 4 dB among these serpentine nozzles, while the outlet width–height ratio had great influence on the total scattering field. 19 The effects of the geometric design parameters on the flow characteristics and aerodynamic performance of the double serpentine nozzle were also investigated computationally and experimentally in the author’s previous work, 20,21 including the centerline distributions, the length ratio of first serpentine passage to second serpentine passage, and the geometric design parameters at first serpentine passage exit (the dimensionless width, area, and offset distance). Results recommended that the value of the length ratio of first serpentine passage to second serpentine passage was chosen from 2:5 to 2:3, curves with a gentle turning at each serpentine passage exit should be selected.…”

Compressible flow characteristics in bent duct with constant flow section

“…The flow direction vortex, heat mixing efficiency and wall temperature distribution of S-nozzle with asymmetric lobe mixer were studied by Liu and Du. 10 – 13 Local acceleration and transvers flow features were also shown by Sun, 14 – 16 in which the influence of geometric parameters on the flow characteristics of convergent S-nozzle was investigated. And the results showed that even if the nozzle pressure ratio was lower than the critical pressure ratio, local supersonic region and shock wave was still induced in the convergent S-nozzles due to large curvature.…”

Parametric Design Method and Performance Analysis of Double S-Shaped Nozzles

“…It showed that two-equation standard k − ε turbulence is accurate to reveal the aerodynamic performances. A further study of Sun et al [14] presented a range of values of some important parameters for achieving better aerodynamic performances. Cheng et al [15] investigated the influences of the shield ratio on the infrared signature for the serpentine nozzle.…”