Optimum design of wind tunnel contractions

Mikhail, M. N.; Rainbird, W. J.

doi:10.2514/6.1978-819

Cited by 11 publications

(7 citation statements)

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“…The swirling jet ends in a smooth converging nozzle attached to the outer cylinder and mounted on top of a large transparent tank of square cross-section 120×40×40 cm 3 (figure 2). The contraction zone is designed according to the optimum method (Mikhail 1979) in order to avoid flow separation. The exit diameter of the contraction zone is D 1 = 40 mm.…”

Section: Theoretical Considerations: a Simple Vortex Breakdown Criterionmentioning

confidence: 99%

Experimental study of vortex breakdown in swirling jets

1998

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The goal of this study is to characterize the various breakdown states taking place in a swirling water jet as the swirl ratio S and Reynolds number Re are varied. A pressure-driven water jet discharges into a large tank, swirl being imparted by means of a motor which sets into rotation a honeycomb within a settling chamber. The experiments are conducted for two distinct jet diameters by varying the swirl ratio S while maintaining the Reynolds number Re fixed in the range 300<Re<1200. Breakdown is observed to occur when S reaches a well defined threshold Sc≈1.3–1.4 which is independent of Re and nozzle diameter used. This critical value is found to be in good agreement with a simple criterion derived in the same spirit as the first stage of Escudier & Keller's (1983) theory. Four distinct forms of vortex breakdown are identified: the well documented bubble state, a new cone configuration in which the vortex takes the form of an open conical sheet, and two associated asymmetric bubble and asymmetric cone states, which are only observed at large Reynolds numbers. The two latter configurations differ from the former by the precession of the stagnation point around the jet axis in a co-rotating direction with respect to the upstream vortex flow. The two flow configurations, bubble or cone, are observed to coexist above the threshold Sc at the same values of the Reynolds number Re and swirl parameter S. The selection of breakdown state is extremely sensitive to small temperature inhomogeneities present in the apparatus. When S reaches Sc, breakdown gradually sets in, a stagnation point appearing in the downstream turbulent region of the flow and slowly moving upstream until it reaches an equilibrium location. In an intermediate range of Reynolds numbers, the breakdown threshold displays hysteresis lying in the ability of the breakdown state to remain stable for S<Sc once it has taken place. Below the onset of breakdown, i.e. when 0<S<Sc, the swirling jet is highly asymmetric and takes the shape of a steady helix. By contrast above breakdown onset, cross-section visualizations indicate that the cone and the bubble are axisymmetric. The cone is observed to undergo slow oscillations induced by secondary recirculating motions that are independent of confinement effects.

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Section: Theoretical Considerations: a Simple Vortex Breakdown Criterionmentioning

confidence: 99%

Experimental study of vortex breakdown in swirling jets

1998

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“…The contraction section (C) is designed to aid flow coalescence and has a smooth internal contour that ends at zero (straight) gradient. Section C is based on a cubic polynomial contour (defined below), which minimises boundary layer separation and improves flow uniformity after the contraction [34,[36][37][38]:…”

Section: Introductionmentioning

confidence: 99%

Impingement pressure characteristics of swirling and non-swirling turbulent jets

Ahmed

Al-Abdeli

Guzzomi

2015

Experimental Thermal and Fluid Science

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“…Curve 1 represents a flow in which significant separation occurs and as will be seen from Figure 11 this has an unfavourable effect on the loss generation. Evidently the flow near separation at R = 2.8 gives a much lower loss at exit as compared with the incipient separation of curve (2). This is coupled with a better pressure recovery, as will be seen from the velocity curves of Figure 12 Figure 10 gives the lowest loss in Figure 11, it will be seen from Figure 7 that the pressure recovery at exit is inferior to the H = 2.8 case, which gives the best pressure recovery of all.…”

Section: Sample Results and Concluding Remarksmentioning

confidence: 90%

An inverse method for the design of axisymmetric optimal diffusers

Ahmed

Myring

1986

Numerical Meth Engineering

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SUMMARYAn inverse inviscid-boundary-layer interaction scheme is presented for the optimal design of axisymmetric ducts for subsonic, rotational flows. Distribution of the shape factor R on the duct wall, giving minimum total pressure loss and maximum static pressure rise, is used as boundary condition for the inverse integral boundary-layer solution, to obtain the velocity and displacement thickness distributions on the wall. Vector addition of the inviscid core radius, derived from the solution of the inverse inviscid flow equations, and the displacement thickness produces the desired duct shape.

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Optimum design of wind tunnel contractions

Cited by 11 publications

References 0 publications

Experimental study of vortex breakdown in swirling jets

Experimental study of vortex breakdown in swirling jets

Impingement pressure characteristics of swirling and non-swirling turbulent jets

An inverse method for the design of axisymmetric optimal diffusers

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