## 4 Results and Analysis
### The Bernoulli Effect in the Valve Gap  
The Bernoulli effect (Bernoulli's principle) reflects the relationship between the pressure and the flow rate. When the flow velocity increases, the pressure on the interface between the object and the fluid decreases, whereas the pressure increases. It was stated in [10] that the Bernoulli effect in the valve gap was one of the reasons for delayed opening of the valve, because low pressure on the reed surface was caused by the Bernoulli effect. The low pressure prevents the valve from opening until the pressure in the cylinder increases enough to overcome the low pressure. Due to the complex structure of the compressor, it is impossible to observe the flow field in the valve gap through the experiment. In this paper, the Bernoulli effect in the valve gap is studied by using the validated FSI method. The movement of the valve was controlled by the pressure difference between the upper and lower sides of the reed. Figure 11 shows the pressure distribution on the upper and lower surface of the reed when the suction valve was opened. Because the flow velocity on the lower surface of the reed was low, it had little influence on the pressure distribution. Consequently, the pressure distribution on the lower surface of the reed was more uniform. Since the flow velocity in the narrow valve gap was high, the Bernoulli effect led to a distinct low-pressure zone on the upper surface of the reed. Therefore, the pressure distribution on the upper surface of the reed was investigated in this paper. Figure 10: (**a**) The p-\(\theta\) diagram in the experiment and FSI simulation. (**b**) The Movement of the suction valve in the experiment and FSI simulation. In order to quantitatively express the pressure distribution in the flow field, as shown in Figure 11, horizontal and vertical coordinate systems were established. The Y direction represents the width direction of the reed valve, and the X direction represents the length direction of the suction reed valve. To observe the Bernoulli effect of the valve gap more clearly, the slice pressure contour along the Y direction was established, as shown in Figure 12. Due to the Bernoulli effect caused by high-speed flow through the valve gap, there is an obvious low-pressure zone in the gap between the top of the cylinder and the reed. In order to study the variation of the pressure distribution of the upper surface of the reed with time, three characteristic crank angles were selected to study the pressure distribution, as shown in Figure 13, such as the crank angle (41.4\({}^{\circ}\)) when the valve started to open, the crank angle (55.8\({}^{\circ}\)) when the valve lift reached its maximum for the first time, and the crank angle (90.0\({}^{\circ}\)) when the valve was fully opened. The pressure distribution on the reed at three characteristic crank angles along the X direction is shown in Figure 14a. The pressure on the reed was the highest at the O point, while the pressure decreased on both sides of the O point. In the Figure 14, with the increase of the characteristic crank angle, the pressure distribution on surface of the reed tended to be more even. The reason for this phenomenon is that with the increase of lift, the velocity in the narrow region between the upper surface of the reed and the valve plate decreases, and the Bernoulli effect weakens. Figure 11: The pressure distribution on the lower and upper surface of the reed when the suction valve was opened. Figure 12: The pressure distribution along the Y direction. The pressure distribution along the Y direction is also shown in Figure 14b,  
and the upper surface of the reed, the pressure at the edge of the suction hole dropped sharply, forming a low-pressure zone. However, after passing through the low-pressure zone, the pressure increased due to the decrease of the flow velocity and weakening of the Bernoulli effect. With the increase of the reed valve lift, the pressure distribution along the Y direction of the suction reed valve also tended to be flat.