Effect of Varying Inflow Reynolds Number on Pressure Recovery and Flow Uniformity of 3-D Turning Diffuser

Abstract

Various diffuser types characterized by the geometry are introduced in the flow line to recover the energy. A 3-D turning diffuser is a type of diffuser that its cross-section diffuses in all 3 directions of axes, i.e. x, y and z. In terms of applicability, a 3-D turning diffuser offers compactness and more outlet-inlet configurations over a 2-D turning diffuser. However, the flow within a 3-D turning diffuser is expected to be more complex which susceptible to excessive losses. As yet there is no established guideline that can be referred to choose a 3-D turning diffuser with an optimum performance. This paper aims to investigate the effects of varying inflow Reynolds number (Rein) on the performance of 3-D turning diffuser with 90o angle of turn. The outlet pressure recovery (Cp) and flow uniformity (σu) of 3-D turning diffuser with an area ratio (AR = 2.16) and outlet-inlet configurations (W2/W1 = 1.44, X2/X1 = 1.5), operated at inflow Reynolds number of Rein = 5.786E+04 - 1.775E+05 have been experimentally tested. The experimental rig was developed by incorporating several features of low subsonic wind tunnel. This was mainly to produce a perfect fully developed and uniform flow entering diffuser. Particle image velocimetry (PIV) was used to examine the flow quality, and a digital manometer was used to measure the average static pressure of the inlet and outlet of turning diffuser. There is a promising improvement in terms of flow uniformity when a 3-D turning diffuser is used instead of a 2-D turning diffuser with the same AR. An unexpected trend found with a drop of pressure recovery at maximum operating condition of Rein = 1.775E+05 shall require further investigations. The results obtained from this study will be in future used to validate the numerical codes. Upon successful validation, several other configurations will be numerically tested in order to establish the guidelines in the form of mathematical models.

Effect of Angle of Turn on Loss Characteristics and Flow Rectification of Curve Diffuser

“…Curve diffusers with turning angles from 30° to 180° were modelled as shown in Table 1 in which each to configure area ratio of 1.6 to 4.0. As shown in Figure 2, hybrid mesh to consist of hexahedral and tetrahedral elements was generated to provide acceptable quality of skewness 0.3 [5][6][7][8][9]12]. Enhanced wall treatment of y + = 1.2 -1.7 was applied to allow an optimum number of nodes obtained particularly close to the inner wall region to capture presences of flow separation.…”

“…Three k- turbulence models (ske, rngke, rke) were considered to simulate the case with the best model opted from validation. Pressure recovery coefficient (Cp) and flow uniformity index (out) are the parameters used to assess the performance [5][6][7][8][9][10][11][12][13][14][15][16][17]:…”

“…An applicable Rein should be therefore decided to provide less flow disruption. Rein was proven by Nordin et al, [5][6][7][8][9] to affect the performance of 90 o curve diffuser, with 3D expansion yielded higher pressure recovery than 2D expansion, when was operated at low Rein = 5.786x10 4 -6.382x10 4 . Xian et al, [8] has developed performance correlations of curve diffuser to integrate effects of turning angle, however less discussion was given on turning angle effects configured with other important parameters in turns.…”

“…Curve diffusers with an angle of turn (30 o , 90 o , 120 o , 150 o , 180 o ), area ratio (1.60, 2.16, 4.00) and inflow Reynolds number (5.934x10 4 , 8.163x10 4 , 1.783x10 5 ) are considered. These ranges of variables are opted to serve common operating settings of curve diffuser for subsonic applications such as wind tunnel and HVAC systems [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”