-- Research in pumps, fans and other rotating machinery is moving beyond conventional measurements of head, pressure rise and efficiency toward time-resolved analysis of three-dimensional, multiphase and highly unsteady internal flows.
That transition was reflected at the 9th International Conference on Pumps and Fans, or ICPF 2026, where research topics included pumps, compressors and fans; cavitation; mechanical dynamics; numerical simulation; digital technologies; and the behavior of key components such as impellers, guide vanes, diffusers, nozzles, bearings and seals.
For experimental fluid mechanics, the central challenge is increasingly clear: important flow structures inside rotating machinery can evolve too rapidly and in too complex a three-dimensional form to be adequately described by steady-state measurements or single-point velocity data.
Tip-leakage vortices, impeller wakes, cavitation clouds, flow separation and rotating stall may develop over millisecond or shorter time scales. High-speed cameras can resolve these transient events frame by frame, while particle image velocimetry, or PIV, converts tracer-particle motion into quantitative velocity fields and derived flow quantities such as vorticity, turbulent kinetic energy and Reynolds stresses.
Measuring fast, three-dimensional rotating flows
Experimental measurements inside pumps and fans face several constraints simultaneously.
As rotational speed increases, the characteristic time scales of vortex formation, shedding and cavitation decrease. Increasing camera frame rate alone does not ensure usable PIV data. Laser pulse duration, inter-pulse timing, tracer-particle displacement, image contrast and spatial resolution must also be coordinated.
The geometry presents another difficulty. Tip clearances, near-wall boundary layers and miniature impellers often require small fields of view and high optical magnification. These conditions make illumination, calibration and optical access more demanding.
Three-dimensionality is equally important. A single high-speed camera records a two-dimensional projection and cannot fully resolve out-of-plane velocity components. In swirling flows, jet-wake interactions and tip-leakage flows, those missing components can be critical to understanding transport and vortex dynamics.
For this reason, advanced rotating-machinery experiments increasingly combine high-speed imaging, multi-camera PIV, synchronized laser illumination and phase-resolved measurement.
Four high-speed cameras for 3D3C-PIV
A representative experiment conducted by a research team at the University of Science and Technology of China examined the air flow around miniature rotating machinery under low-Reynolds-number conditions using a multi-view 3D3C-PIV system built around Revealer high-speed cameras.
The test objects included a miniature propeller and a gyroscope-like helical rotating specimen. Researchers focused on tip vortices, root vortices, wake structures, local flow separation and the interaction between a central jet and the surrounding rotating flow.
Although the specimens were not conventional pump or fan impellers, the experiment reproduced several measurement difficulties common to compact high-speed turbomachinery: small physical scale, high rotational speed, strong three-dimensional flow and short-lived vortex structures.
The system used four Revealer NEO25M high-speed cameras in a multi-view 3D3C-PIV configuration. Each Revealer NEO25M camera has a resolution of 1,280 by 1,024 pixels and a full-resolution recording capability of 25,000 frames per second. The experiment was performed at 20,000 fps.
Illumination was provided by a 30-millijoule high-frequency dual-pulse laser. The optical system also included 100-millimeter F2.8 macro lenses, 532-nanometer narrow-band filters, a synchronization controller and atomized tracer particles suitable for low-speed air-flow measurements.
The effective measurement volume covered a field of approximately 30 by 30 millimeters.
The cameras, laser and rotating mechanism were synchronized to a common time base so that tracer-particle images from multiple viewing angles represented the same flow state.
Multi-camera calibration established the mapping between image coordinates and physical space. Researchers then performed image preprocessing, cross-correlation analysis, spurious-vector removal and three-dimensional velocity reconstruction.
Figure: 3D3C-PIV velocity-field reconstruction of miniature rotating machinery measured with Revealer high-speed cameras, showing three-dimensional swirl, jet flow and vortex structures.
The reconstructed velocity fields could subsequently be used to calculate vorticity, turbulent kinetic energy and Reynolds stresses, while vortex-identification criteria could be applied to determine vortex-core position, size and trajectory.
For periodic rotating systems, shaft-angle or key-phase signals can also support phase-locked acquisition and phase averaging, helping separate stochastic turbulence from deterministic unsteadiness associated with blade-passing frequency.
Reconstructing the three-dimensional vortex system
The reconstructed flow field showed that rotation of the gyroscope-like specimen produced a compound vortex system formed by the interaction between the central jet and the surrounding rotational flow.
Local flow separation developed near the sidewall of the rotating body, accompanied by small-scale shed vortices.
Compared with single-view flow visualization, the multi-view 3D3C-PIV measurement preserved out-of-plane velocity information and the spatial continuity of vortex structures. Researchers could therefore examine the coupling among jet flow, swirl and local separation using three-dimensional velocity vectors and reconstructed flow structures.
The result illustrates why volumetric or multi-view PIV has become increasingly important for rotating flows in which a two-dimensional measurement plane may omit a substantial part of the underlying transport mechanism.
Implications for pump and fan research
The same measurement framework can address several problems in pumps and fans.
Full-field PIV can identify recirculation, secondary flow, jet-wake structures, tip-leakage vortices and separation near impeller exits and blade-tip clearances. Unlike single-point velocimetry, PIV preserves the spatial relationship among these structures and allows researchers to follow vortex generation, transport and interaction.
Velocity fields can also be synchronized with pressure, flow rate, torque and other performance data. This makes it possible to connect regions of high shear, strong vortices, recirculation and mixing loss with changes in overall machine performance.
For cavitating pumps, high-speed cameras and PIV provide complementary information. High-speed imaging can record cavitation inception, cloud growth and shedding, bubble coalescence and collapse, while PIV measures simultaneous changes in the surrounding liquid-phase velocity and vortex field. When pressure and vibration measurements are added, researchers can investigate the timing between cavitation structures, pressure fluctuations and structural response.
The measurements can also provide validation data for computational fluid dynamics, or CFD. Turbulence models, cavitation models, interface treatments and boundary conditions can all affect numerical predictions. Phase-resolved PIV, time-resolved PIV and synchronized high-speed imaging provide experimental benchmarks for velocity distributions, vortex locations, dominant unsteady frequencies and cavitation morphology.
As pump and fan research becomes increasingly focused on unsteady and three-dimensional mechanisms, experimental systems must do more than produce visually striking flow images. Their scientific value depends on whether they can reproduce operating conditions, quantify uncertainty and establish measurable links between transient flow structures and machine dynamics.
High-speed cameras and advanced PIV systems are therefore becoming central tools in the transition from observing rotating-flow phenomena to quantitatively explaining their mechanisms. The experiment also demonstrates how Revealer high-speed camera technology can be integrated into multi-camera 3D3C-PIV systems for quantitative research on complex, unsteady rotating flows.
Contact Info:
Name: Harrison Shawn
Email: Send Email
Organization: HF Agile Device Co., Ltd.
Website: http://www.revealerhighspeed.com
Release ID: 89202321
Google
RSS