Abstract:The effect of exit geometry of a rectangular nozzle on the instability modes and mixing characteristics of under-expanded supersonic jets is computationally investigated. The unsteady three-dimensional viscous simulation is based on the Proteus code developed at NASA Glenn Research Center. A shock adaptive grid generator was developed to enhance the shock simulation. The nozzle aspect ratio for both plane and notched rectangular nozzles in this study is 5.0 and the fully expanded jet Mach number is 1.526. For … Show more
“…Additional description for initial condition, boundary conditions and CFD parameters is detailed in Han et al. 18,19…”
Section: Rectangular Jet With Swirling Shear Layermentioning
confidence: 99%
“…(b) Details of the counterclockwise swirl vanes and their dimensions in the nozzle exit (from Han et al. 19 ).Figure 2.Corner flowfield modeled as a pair of co-rotating vortex filaments in high-aspect ratio rectangular nozzle.…”
Section: Rectangular Jet With Swirling Shear Layermentioning
confidence: 99%
“…(b) Details of the counterclockwise swirl vanes and their dimensions in the nozzle exit (from Han et al. 19 ).…”
Section: Rectangular Jet With Swirling Shear Layermentioning
confidence: 99%
“…To minimize the thrust penalty of large-scale (bulk) swirling jets, the case of embedded swirl in the nozzle exit boundary layer is investigated. 18,19 The solution offers the benefits of swirl in mixing enhancement without a major penalty of thrust loss. The external torque in our configuration, as an initial boundary condition, dominates the mechanism of jet rotation, whereas the switchover phenomenon in asymmetric jets is caused by ω θ -dynamics.…”
Section: Introductionmentioning
confidence: 99%
“…The temperature at the nozzle exit is 250 K and the fluid density is 1.414 kg/m 3 . Additional description for initial condition, boundary conditions and CFD parameters is detailed in Han et al 18,19 Schematic drawing of the rectangular nozzle with its exit flow condition is shown in Figure 1(a). Figure 1(b) shows the counterclockwise vane placement and its geometry in the nozzle exit.…”
A rectangular jet emerging from a nozzle with embedded swirl vanes in its exit boundary layer is studied. The swirling shear layer imposes an external torque on the jet boundary where it causes jet rotation in the direction of axis switching, skew deformation as well as enhanced mixing. In moderate aspect ratio rectangular nozzles, e.g. AR ¼ 5:1, a pair of co-rotating streamwise vortices is formed on the narrow boundary of the jet that dominates its dynamics in the near field. A vortex-induced model is developed that accounts for the rotation of the rectangular jet with embedded shear layer swirl. The model also shows that the jet rotation is diminished with increasing aspect ratio, as AR À2 . The higher entrainment rate in the rotating jet with skew deformation causes the jet mass flow rate with shear layer swirl to be 20-25% higher than the corresponding plain rectangular nozzle of the same aspect ratio (x/D e > 1). The proposed model is validated using computational simulation results of previous investigations that appeared in the literature.
“…Additional description for initial condition, boundary conditions and CFD parameters is detailed in Han et al. 18,19…”
Section: Rectangular Jet With Swirling Shear Layermentioning
confidence: 99%
“…(b) Details of the counterclockwise swirl vanes and their dimensions in the nozzle exit (from Han et al. 19 ).Figure 2.Corner flowfield modeled as a pair of co-rotating vortex filaments in high-aspect ratio rectangular nozzle.…”
Section: Rectangular Jet With Swirling Shear Layermentioning
confidence: 99%
“…(b) Details of the counterclockwise swirl vanes and their dimensions in the nozzle exit (from Han et al. 19 ).…”
Section: Rectangular Jet With Swirling Shear Layermentioning
confidence: 99%
“…To minimize the thrust penalty of large-scale (bulk) swirling jets, the case of embedded swirl in the nozzle exit boundary layer is investigated. 18,19 The solution offers the benefits of swirl in mixing enhancement without a major penalty of thrust loss. The external torque in our configuration, as an initial boundary condition, dominates the mechanism of jet rotation, whereas the switchover phenomenon in asymmetric jets is caused by ω θ -dynamics.…”
Section: Introductionmentioning
confidence: 99%
“…The temperature at the nozzle exit is 250 K and the fluid density is 1.414 kg/m 3 . Additional description for initial condition, boundary conditions and CFD parameters is detailed in Han et al 18,19 Schematic drawing of the rectangular nozzle with its exit flow condition is shown in Figure 1(a). Figure 1(b) shows the counterclockwise vane placement and its geometry in the nozzle exit.…”
A rectangular jet emerging from a nozzle with embedded swirl vanes in its exit boundary layer is studied. The swirling shear layer imposes an external torque on the jet boundary where it causes jet rotation in the direction of axis switching, skew deformation as well as enhanced mixing. In moderate aspect ratio rectangular nozzles, e.g. AR ¼ 5:1, a pair of co-rotating streamwise vortices is formed on the narrow boundary of the jet that dominates its dynamics in the near field. A vortex-induced model is developed that accounts for the rotation of the rectangular jet with embedded shear layer swirl. The model also shows that the jet rotation is diminished with increasing aspect ratio, as AR À2 . The higher entrainment rate in the rotating jet with skew deformation causes the jet mass flow rate with shear layer swirl to be 20-25% higher than the corresponding plain rectangular nozzle of the same aspect ratio (x/D e > 1). The proposed model is validated using computational simulation results of previous investigations that appeared in the literature.
An experimental investigation was undertaken to study the effect of placing a flat wall at the rectangular exit (Aspect Ratio =2) of a supersonic nozzle on the shock cell structure, and transverse deflection behavior of the jet issuing from the nozzle. The design exit Mach number (𝑀 𝑒 ) was 1.8. In the experiments, the length of the wall (𝐿 𝑤 ) and nozzle pressure ratio (NPR) were varied to explore their effect on the jet interaction with the wall.Schlieren images & wall pressure data obtained from the experiments were used to study shock cell structure and for calculation of two-dimensional normal force and moment coefficients. In over-expansion conditions, the interaction between the jet and the wall caused a downward deflection of the jet up to 𝐿 𝑤 = 𝐷 ℎ (hydraulic diameter). Underexpansion conditions of the jet made the jet deflect upward irrespective of the magnitude of 𝐿 𝑤 till 𝐿 𝑤 = 8𝐷 ℎ . The two-dimensional normal force and moment coefficients of the wall were more or less insensitive to the variation in 𝐿 𝑤 beyond 4𝐷 ℎ . However, for 𝐿 𝑤 < 4𝐷 ℎ , the jet expansion conditions determined the nature of variation with 𝐿 𝑤 .The effect of wall was such that reduction in wall-bound supersonic core length was maximum at 𝐿 𝑤 = 0.5𝐷 ℎ at over-expansion conditions and at 𝐿 𝑤 =𝐷 ℎ at under expansion conditions.
Purpose
This study aims to study the interaction effects between a rectangular supersonic jet with a flat wall computationally using wall length as a parameter. The purpose of this study is to investigate the effect of change in wall length on supersonic core length (SCL) reduction, jet deflection and jet decay behavior.
Design/methodology/approach
The design Mach number and aspect ratio at the rectangular exit were 1.8 and 2, respectively. To study the wall length effects on jet-wall interactions, wall length (Lw) was varied as 0.5Dh, 1Dh, 2Dh, 4Dh and 8Dh, where Dh was the hydraulic diameter of the nozzle exit. The flat wall with the matching width of the rectangular exit section of a supersonic nozzle was placed at the nozzle exit such that the supersonic jet grazed past the wall. The studies were carried out at over-expansion [nozzle pressure ratio (NPR) = 4], near optimum expansion (NPR = 6) and under-expansion (NPR = 8) levels.
Findings
Results indicated that significant reduction in wall-bounded SCL was noticed in the range of 0.5Dh
≤ Lw
≤ 1Dh for both over-expansion and under-expansion conditions. At Lw
≥ 4Dh, SCL got enhanced at NPR = 4 and 6 but had a negligible effect at NPR = 8.
Practical implications
Thrust vector control, noise reduction and easy take-off for high-speed aircraft.
Originality/value
The effect of change in flat wall length on interaction characteristics of a rectangular supersonic jet was not studied before in terms of SCL reduction and jet decay behavior.
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