PIV Measurement and Proper Orthogonal Decomposition Analysis of Annular Gap Flow of a Hydraulic Machine

Abstract

The fluid stress or flow-induced vibration of annular gap flow always has some influence on the stable working conditions of a hydraulic machine. A time-averaged analysis of flow may not have to explicitly acknowledge these factors. Accordingly, a finite-axial-length annular gap was measured via particle image velocimetry (PIV), with inner boundary motion and a stable outer boundary. As a statistic result regarding the fluid stress, the Reynolds stresses soared in the first region, were sustained in the middle region, but decreased at last. The flow had a higher convective transportation intensity in the radial direction than in other directions. Flow diagnostics were also performed by proper orthogonal decomposition (POD). As a result, the coherent structures were found. Then, the power spectrum density (PSD) functions were also calculated for finding the flow-induced vibration characteristics; the functions had high amplitude in the low-frequency domain and low amplitude in the high-frequency domain, with an order of magnitude between the two amplitudes of 10−1 to 10−2. In addition, the frequency was higher at a smaller gap width in the middle-frequency domain, but the condition was the opposite in the high-frequency domain. In conclusion, the fluid stresses were changeable and uneven along the flow direction, and flow-induced vibration obviously existed. Remarkably, the turbulence characteristics of the annular gap flow were not “laminar approximating,” while the diameter ratio of the gap was 0.6 to 0.8.

Transient Model for the Hydrodynamic Force in a Hydraulic Capsule Pipeline Transport System

“…Using the reduced-order method, the flow velocity field can be expressed by a few mode functions, and these mode functions can capture most of the flow turbulence characteristics and energy. The POD method process can be found in [21,28]. Here, we have only provided the velocity reduced-order model as:…”

“…The capsule moved through the measuring pipe, and the measuring devices measured the flow field around the motion capsule. The measuring device used particle image velocimetry (PIV), and the uncertainty analysis was conducted according to [21].…”

“…However, there is one problem with these time-averaged treatments of the pressure difference or friction stress. The pipe flow in an HCP system has a large Reynolds number, meaning that the flow around the capsule is fluctuating [21], and the wake vortex and the capsule motion speed show strongly transient characteristics. While the time-averaged treatment leads to steady results in terms of the fluid drag force and the capsule motion speed, there is a true necessity to model the fluid drag in terms of a transient view.…”

Research on Prediction Model of Interlayer Leakage in Separate Injection Wells in Offshore Oilfields

“…In fluid flow, slot flow is a kind of flow widely existing in machinery, such as annular clearance between plunger and cylinder, shaft and bearing [5,6]. Due to different geometric shapes, the flow laws of slot flow are usually not universal.…”

Wheeled Capsule Threshold of Motion at Different Locations in a Horizontal Bend Pipeline Based on Hydraulic Capsule Pipeline Transportation

“…Jia et al [17] and Zhang et al [18] studied the pressure drag of moving wheeled capsules. Zhao et al [19] used the proper orthogonal decomposition method to analyze the fluid stresses and flow-induced vibration characteristics of the flow field of a wheeled capsule, and they claimed that the forces on the capsule are decided by the flow characteristics. In fact, the threshold of motion of the capsule is initiated by the pipe flow making the drag a little larger than the maximum static friction of the capsule.…”