# Numerical and Experimental Characterization of a Coanda-Type Industrial Air Amplifier
## 5 Results
### Numerical Characterization  
#### 5.3.1 Flow Pattern Analysis  
A general perspective of the flow pattern through the air amplifier is shown in Figure 20, where streamline vectors are superimposed on velocity magnitude contours on the planes \(Z=0\) m (mid-plane of high-pressure line injection) and \(Y=0\) m (mid-cross-sectional plane). In section \(Y=0\) m, we found a symmetric flow pattern, dominated by the shear layers caused by the high velocity tangential flow. However, in section \(Z=0\) m, the flow becomes asymmetric with respect to the central axis, probably due to a non-homogeneous stagnation pressure distribution in the inner ring chamber of the air amplifier. This asymmetry was also observed in the wake profile analyses, as shown in Figure 19.  
Transverse slides of the flow solution through the air amplifier are gathered in Figure 21 for the planes \(X=1.2\cdot 10^{-4}\) m and \(X=1.7\cdot 10^{-3}\) m. The first depicts the flow pattern at the Coanda nozzle gap section, while the latter comprises the primary flow inlet section. A non-uniform velocity profile reflects how the flow progresses along the inner ring producing a non-symmetric flow.  
Figure 22 depicts a zoomed view around the injection gap, where the flow through the gap region appears choked near the outlet region. The following increase in the sectional area accelerates the flow to local Mach number values of \(M\approx 2\), with the tangential flow maintaining a supersonic velocity throughout the curved Coanda profile. The effect of this blockage phenomenon is detailed in Figure 23. The linear evolution of the primary volumetric mass flow rate \(Q_{c}\) is plotted against the primary flow pressure \(p_{c}\) from \(p_{c}=0.15\) MPa to 1 MPa for an injection gap of \(\delta=0.23\) mm in Figure 23(left), similar  
Figure 19: Comparison of numerical and refined experimental velocity profiles at downstream section \(X=3.5D\). Mean values of streamwise velocity are plotted from numerical () and experimental () tests. Red lines depict the standard deviation of the experimental data.  
to the trend found in the experimental results. However, the blockage effect is shown in Figure 23(right), where the non-dimensional mass flow (see Equation (5)) is plotted against \(p_{c}\). For small values of the primary flow pressure, there is a large growth in \(\dot{m}_{c}^{*}\), which finally saturates as a normal shock wave develops in the gap region. Except for the smallest pressure value evaluated, \(p_{c}=0.15\) MPa, a region of supersonic flow is observed in the gap region. A clear saturation trend is appreciated, with the non-dimensional mass flow varying approximately by \(5\%\) for the pressure range \(p_{c}\in[0.2,1]\) MPa. Note that the saturation achieved is not fully comprehensive due to the impact of viscous effects and the influence of the boundary layer in this confined area. This differs from the ideal flow theory seen in divergent-convergent nozzles, where the saturation is absolute. The development of the supersonic region along the Coanda surface as \(p_{c}\) increases is collected in Figure 24, where Mach number contours for several flow solutions depict the compressibility effects near the gap region.  
Figure 21: Line integral convolution colored by local Mach number values at sections \(X=1.2\times 10^{-4}\) m, (**left**) and \(X=1.7\times 10^{-3}\) m (**right**).  
Figure 20: Velocity magnitude streamlines at section \(Y=0\) m (**top**) and \(Z=0\) m (**bottom**).