Complex Three-dimensional Flow Field Research Articles

Coupling of Eddy-Viscosity-Scale Reynolds-Stress Model with an Algebraic Transition Model

Attempts to extend a Reynolds-stress model (RSM) for transition flow simulations have begun to cause concern in recent years based on the fact that the RSM has more potential than an eddy viscosity model when applied to complex three-dimensional flowfields. In terms of the RSM, however, coupling more transport equations will further increase its complexity (may worsen robustness and convergence rate). In this paper, a γ-based algebraic transition model originating from the SA-BC model is coupled with an νt-scale RSM (EV-RSM) to form a new transition/turbulence model, called tEV-RSM. Some numerical tests are conducted with a fifth-order scheme, WCNS, including the well-known T3 flat plate series, a two-dimensional airfoil (S809), a two-dimensional three-element airfoil (30P-30N), a three-dimensional prolate-spheroid, and a three-dimensional circular cylinder. The proposed model is compared with the SA-BC and γ-Reθt SST models, which indicates that it can predict the flows primarily governed by Tollmien–Schlichting transition or bypass transition well and has an advantage in predicting the flows with detached separation. Meanwhile, the iteration convergence rate of the tEV-RSM is fast enough considering it as a seven-equation model.

Tomographic Reconstruction of Hypersonic Aircraft Flowfields in Large-Scale Wind Tunnel Experiments

Three-dimensional flowfield features around a hypersonic aircraft model were reconstructed using a computed tomography background-oriented schlieren technique. Datasets of projection images were acquired in hypersonic wind tunnel experiments conducted at the Japan Aerospace Exploration Agency’s 0.5m hypersonic wind tunnel facility, by rotating the test model with an increment of 2° azimuth. A telecentric optical configuration was applied to the background-oriented schlieren measurement at the large-scale hypersonic wind tunnel facility. A basic tomographic reconstruction method, such as filtered backprojection, was used to reconstruct the projection datasets with some combination of denoising calculations. Results showed that the reconstructed flowfield was first noisy without denoising. With the denoising considerations proposed in this study, the flow physics, such as oblique shock waves emanating from the vehicle nose tip and engine lip, were clearly visualized. Therefore, the telecentric optical setup and denoising processes proposed in this study can successfully reconstruct a complex three-dimensional flowfield obtained at a large-scale wind tunnel facility. This setup and denoising process can also apply to other applications in large-scale wind tunnel experiments.

Development of a Performance-Based Design Technique for an Axial-Flow Fan Unit Using Airfoil Cascades Based on the Blade Strip Theory

Axial-flow fans are widely used as cooling fans in the outdoor units of split-type air conditioners. The design of an axial-flow fan blade involves stacking several airfoils that can be differently designed for each spanwise section. However, the complex flow field around the fan blade, including circumferential and axial flows, presents challenges when applying the single airfoil theory. This study proposed a systematic performance-based design method for axial-flow fans using a cascade of airfoils based on the blade strip theory. The theory characterized the complex three-dimensional flow field driven by an axial-flow fan in terms of a two-dimensional cascade of airfoil flows. Computational fluid dynamics based on finite volume methods were used to predict the flow field and aerodynamic sound sources of an existing low-pressure axial-flow fan partially covered by a fan shroud, and the results were validated against experimental measurements. Three radial locations in the spanwise region from the hub to the blade tip that have a significant impact on aerodynamic performance were selected, and the two-dimensional flow field on a cylindrical surface with a constant radius was extracted from the three-dimensional flow field to characterize the performance of an axial fan. Then, the airfoils at the targeted span locations were optimized for a higher flow rate and greater efficiency via two-dimensional simulations using the cascades of the airfoil, and the selected optimized airfoils were applied to existing fan blades. The effectiveness of the proposed performance-based design method for low-pressure axial-flow fans was validated by the results, which showed that the redesigned fan blades with cascades of airfoils performed as predicted, increasing the intended higher flow rate by about 1%, improving power consumption by 8%, and lowering the overall sound pressure level by 1.5 dBA.

Understanding of tip clearance flow structure in high speed mixed flow compressor

This paper addresses the necessity to make a physical interpretation of a highly complex three-dimensional tip clearance flow field study for high-speed mixed-flow compressor having stage exit static pressure to inlet total pressure ratio of 3.8 with 39,836 rpm rotor speed. The four different tip configurations namely the constant (λ = 0.016 and 0.019) and variable (λ = 0.011 (inlet)-0.019 (exit) and 0.019 (inlet)-0.022 (exit)) tip clearances were numerically analysed using available experimental data-set. The numerical investigation reveals that in contrast to the classic jet-wake pattern, two anomalous velocity profiles formed at the impeller exit which results in pressure losses in the vaneless diffuser. Near the impeller inlet, the tip leakage flow rolls up to discrete tip leakage vortex structure for each tip clearance configuration. This results in the formation of a region of momentum deficit, recirculation zone, which gets weakened as it moves downstream. The tip clearance configuration is observed to profoundly influence the extent and vorticity of the tip leakage vortex. In the splitter blade passage, the tip leakage flow and Coriolis flow interact with passage flow, resulting in the formation of two secondary passage vortices that move downstream along the pressure and suction surface of the splitter blade. The tip clearance configuration directly influences the impeller exit jet-wake pattern by modulating the secondary passage vortices trajectory and vorticity. Moreover, off-design analysis for tip clearances λ = 0.016 and λ = 0.019, depict distinctive tip leakage vortex characteristics. When operating near the stall conditions (80% of design mass flow rate), λ = 0.019 exhibits bubble shape tip leakage vortex breakdown occurring near the impeller inlet. This result in a substantial change in the tip leakage vortex nature; expansion of the recirculation zone and early weakening of the vorticity in the tip leakage vortex. It is observed that vortex breakdown plays a vital role in characteristics of the passage flow field structure and compressor performance near the stall conditions.

Investigation of the three-dimensional flow field for proton exchange membrane fuel cell with additive manufactured stainless steel bipolar plates: Numerical simulation and experiments

A bipolar plate with a complex three-dimensional (3D) flow field structure could bring better performance of proton exchange membrane fuel cell (PEMFC). In this paper, three types of 3D flow field bipolar plates with different porosity (M1, M2 and M3) and a conventional two-dimensional (2D) serpentine flow field bipolar plate (SP), were fabricated using selective laser melting (SLM). The forming quality of the bipolar plate was determined. The distribution characteristics of current density, oxygen, water content and temperature in different flow field structures and their effects on the performance of PEMFC were analyzed by numerical simulation. By using T3-100 cell test system and MTS exceeded E44 electronic universal test system, the polarization test and contact resistance test were conducted on the conventional SP bipolar plate and the M3 bipolar plate. Results show that the different bipolar plates prepared by the SLM process exhibit high forming quality, and the forming error for the 3D flow field bipolar plates is less than 4%. The M3 flow field exhibits the best capabilities for heat and mass transfer and water management. The M3 flow field produces a maximum power density of 0.547 W/cm2, which is 8.96% higher than that of the SP flow field. This is attributed to the more uniform distribution of gas and liquid in the M3 flow field as well as the lower contact resistance.

The Control of Corner Separation with Parametric Suction Side Corner Profiling on a High-Load Compressor Cascade

Nowadays, with the increase of the thrust-to-weight ratio of the aero engines, the high aerodynamic load has made corner separation an issue for axial compressors. The complex three-dimensional flow field makes it challenging to suppress the corner separation, especially considering the performance at multi-working conditions. To suppress the corner separation and reduce loss, the investigation in this paper proposed a new parametric suction side corner profiling method, which includes few variables but enables the flexible variation of the shape. A bi-objective auto-optimization design process for the corner profiling was carried out on a high-load linear compressor cascade, with the companion of end wall and blade profiling. The aim was to investigate the effective flow control rules for the corner separation and practical design guidelines for its geometry under multiple working conditions. The numerical results identified that the suction side corner profiling brings a much more dominant effect to corner separation than end wall profiling and blade profiling. The most critical flow control rule is to accelerate the climbing second flow on the bottom of the suction surface to suppress the reverse trend of the boundary layer and further relieve the corner separation. In addition, the design point and near-stall point have different well-fitting thicknesses and axial positions. A medium value between the design and near-stall well-fitting parameters will make the suction side corner profiling a best-matching case for a medium inflow condition and adequate performance at a range of conditions.

Experimental study on smoke movement characteristics in tunnel fires with different canyon cross wind yaw angles

High-speed canyon cross wind with random directions is common in mountain areas and induces complex three-dimensional flow fields inside the tunnel while flowing across the tunnel portal, which changes smoke temperature distribution and movement characteristics in tunnel fires. The effect of canyon cross wind yaw angle on maximum ceiling gas temperature, position of maximum ceiling gas temperature, smoke back-layering length and downstream smoke spread length of tunnel fires was investigated by experiments. Results showed that the maximum ceiling gas temperature increased with the increasing wind yaw angle in the range of 45°-90°, but remained steady when the angle was in 90°-135°. The maximum ceiling gas temperature was higher than other fire locations when the fire was close to the upstream portal because of the airflow barrier. Additionally, a normalized maximum ceiling gas temperature linear correlation was established based on dimensional analysis. The position of maximum ceiling gas temperature was different in both horizontal and longitudinal directions due to the canyon wind. The transverse smoke distribution in the tunnel was uneven, which resulted in a double peak value phenomenon of ceiling gas temperature. Besides, when the wind yaw angle was in 45°-90°, the smoke back-layering was resisted and the downstream smoke spread was promoted by the canyon wind. However, the smoke back-layering was promoted and the downstream smoke spread was resisted due to the negative pressure induction when the angle was in 90°-135°.

Introductory measurements of in-cylinder flow past intake valve ports with a film split-fiber probe

A new steady flow test bench test facility has been designed and fabricated for exploration of complex three-dimensional flowfields inside a cylinder of an internal combustion engine. An engine cylinder head of a currently produced car engine with four head valves is utilized as an inlet section of the newly built test bench test. No piston is located in the cylinder and the intake valves are not periodically operated. They remain open during the test periods. An extensive set of initial experimental data has been acquired for both open intake valves and for the location of the probes at two different axial stations in the engine cylinder. The experimental technique of thermo-anemometer split-fiber probes is employed in this research work, which is a novelty never applied before to this class of flows. The probe properties are explained in the paper with emphasis on the probe directional characteristics. The verification tests proved the operational readiness of the new test bench to acquire reliable experimental data at a range of flow conditions simulating real engine settings. The acquired data set base will be used for validations of improved CFD engine design codes. An analysis of the initial set of experimental data clearly indicates that two vortices, or more likely down-flowing spiral flow structures. are present side by side in the cylinder. Mutual interaction of these two flow structures and the ability to generate faithful numerical simulation of this flow pattern for additional planes of measurement and various valve openings will be reported separately.

Compressed sensing MRI to characterize sodium alginate deposits during cross-flow filtration in membranes with a helical ridge

Cross-flow membrane ultrafiltration of the polysaccharide sodium alginate in aqueous solution was investigated in polymeric Helix membranes by in-situ magnetic resonance imaging (MRI) non-invasively and non-destructively. MRI allows velocity and NMR intensity measurements during filtration. In the present case and under the conditions used in the experiments, signal intensity is mainly generated by 1H of water. Lower intensities can therefore be understood as a measure for material accumulation. Compressed sensing allows faster data acquisition, enabling a reliable, time resolved measurement of the ultrafiltration progress. Even under cross-flow filtration conditions, the membrane filtration is impaired by the increasing filtration resistance due to gel layer formation during the filtration of aqueous sodium alginate with CaCl2. The Helix membrane has an additional helical ridge along the membrane wall to provide fouling inhibition, resulting in a complex three-dimensional flow field that was measured via compressed sensing MRI. Furthermore, the behavior of the deposit was classified more precisely by backwashing in the Helix membrane. Summarizing, the flow field, the deposit formation during cross-flow filtration in a Helix membrane and its backwashing was monitored and investigated by fast MRI methods.

Error Estimates of Double-Averaged Flow Statistics due to Sub-Sampling in an Irregular Canopy Model

Exploration of the flow inside the roughness sublayer often suffers from sub-sampling of its complex three-dimensional and non-homogeneous flow fields. Based on detailed particle image velocimetry within a randomly-ordered canopy model, we analyze the potential differences between single-location flow statistics and their spatially-averaged values. Overall, higher variability exists inside the canopy than above it, and is two to four times higher than found inside similar, however ordered, canopy arrangements. The local mean absolute percentage error (MAPE), vertically averaged within three different regions (below, above, and at canopy height), provides a measure for quantifying and characterizing the spatial distribution of errors for various flow properties (mean velocity and stresses). We calculated the value of MAPE at predefined farthest-locations based only on geometric considerations (i.e., farther away from surrounding roughness elements), as commonly done in the field. Interestingly, most of the vertical profiles at the farthest locations lie within the interquartile range of the measured spatial variability for all studied flow and turbulent properties. Additionally, our results show that, for at least 23% of the total canopy plan area, the double-averaged streamwise velocity component and its variance inside the canopy can be reproduced from a single measured profile for which the value of MAPE does not exceed 25%. These regions also constitute most of the farthest locations. The property that exhibits the highest MAPE value inside the canopy is the Reynolds stress (up to $$130\%$$ ); however, these errors are dramatically reduced in the upper half of the canopy. Furthermore, at the canopy interface and above it, the errors rarely exceed $$20\%$$ . The variability is also manifested in the computed integral length scales. The single-point velocity autocorrelation always underestimates the length scales obtained from the two-point statistics. These findings have implications for canopy flow and transport modelling inside the roughness sublayer and can help explain and evaluate the source of discrepancies between measurements and transport models.

Recent advancements towards large-scale flow diagnostics by robotic PIV

The present work reviews the recent developments in the domain of particle image velocimetry (PIV) with attention to its use for large-scale problems of interest for industrial aerodynamics. The article introduces the fundamental principles of flow seeding for large-scale experiments based on the helium-filled soap bubble (HFSB) technique. The measurement of flow tracers in a three-dimensional domain is presented, which is based on Lagrangian tracking methods. Furthermore, the concept of co-axial volumetric velocimetry is introduced and its combination with robotic arm manipulation is shown. The work presents two main examples of applications to aerodynamic problems: the first is the flow field around a propeller aircraft at wind tunnel free-stream velocity up to 50 m s−1, which to date is considered the boundary of large-scale PIV application with HFSB. The second example is the complex three-dimensional flow field around a cyclist at full scale. The work summarizes developments obtained in the last 3 years of research, demonstrating that the domain of PIV techniques is still undergoing vivid developments.

Numerical Simulation of Instabilities in the Boundary-Layer Transition Experiment Flowfield

The development of disturbances in the boundary-layer transition (BoLT) flight experiment flowfield is investigated using a recently developed “quiet direct numerical simulation (DNS)” approach. By using a combination of low-dissipation numerics and a novel shock capturing method, numerical noise is significantly reduced, enabling the simulation and analysis of early stages of the transition process that are governed by the linear growth of small-amplitude disturbances. The freestream conditions of the present simulations correspond to experiments conducted in the Purdue Boeing/U.S. Air Force Office of Scientific Research Mach 6 quiet tunnel under quiet flow at a unit Reynolds number of . First, the steady-state flowfield is computed and then compared to infrared images, demonstrating excellent agreement with experimentally measured steady streamwise wall heat flux streaks. Next, an unsteady numerical simulation is performed with continuous stochastic forcing to excite boundary-layer instabilities. Two-dimensional time-series snapshots of the disturbance flowfield are saved at several streamwise locations. Sparsity-promoting dynamic mode decomposition (SPDMD) is used to extract dominant modes from the snapshot sequences. The frequencies of dominant modes are compared to power spectral densities obtained from wall pressure fluctuations measured in the experiments. Based on numerical and experimental data, three distinct instabilities in the BoLT flowfield are identified. The quiet DNS approach used in conjunction with controlled disturbances to excite instabilities, as well as SPDMD to analyze them, represents a new high-fidelity method of investigating stability and transition in complex three-dimensional flowfields.

Dynamic mode decomposition analysis of the flow characteristics in a centrifugal compressor with vaned diffuser

To understand the flow dynamic characteristics of a centrifugal compressor, the dynamic mode decomposition (DMD) method is introduced to decompose the complex three-dimensional flow field. Three operating conditions, peak efficiency (OP1), peak pressure ratio (OP2), and small mass flow rate (near stall, OP3) conditions, are analyzed. First, the physical interpretations of main dynamic modes at OP1 are identified. As a result, the dynamic structures captured by DMD method are closely associated with the flow characteristics. In detail, the BPF/2BPF (blade passing frequency) corresponds to the impeller–diffuser interaction, the rotor frequency (RF) represents the tip leakage flow (TLF) from leading edge, and the 4RF is related to the interaction among the downstream TLF, the secondary flow, and the wake vortex. Then, the evolution of the dynamic structures is discussed when the compressor mass flow rate consistently declines. In the impeller, the tip leakage vortex near leading edge gradually breaks down due to the high backpressure, resulting in multi-frequency vortices. The broken vortices further propagate downstream along streamwise direction and then interact with the flow structures of 4RF. As a result, the 8RF mode can be observed in the whole impeller, this mode is transformed from upstream RF and 4RF modes, respectively. On the other hand, the broken vortices show broadband peak spectrum, which is correlated to the stall inception. Therefore, the sudden boost of energy ratio of 14RF mode could be regarded as a type of earlier signal for compressor instability. In the diffuser, the flow structures are affected by the perturbation from the impeller. However, the flow in diffuser is more stable than that in impeller at OP1–OP3, since the leading modes are stable patterns of BPF/2BPF.

A Novel Vortex Identification Technique Applied to the 3D Flow Field of a High-Pressure Turbine

Abstract The efficiency of modern axial turbomachinery is strongly driven by the secondary flows within the vane or blade passages. The secondary flows are characterized by a complex pattern of vortical structures that origin, interact, and dissipate along the turbine gas path. The endwall flows are responsible for the generation of a significant part of the overall turbine loss because of the dissipation of secondary kinetic energy and mixing out of nonuniform momentum flows. The understanding and analysis of secondary flows requires a reliable vortex identification technique to predict and analyze the impact of specific turbine designs on the turbine performance. However, the literature shows a remarkable lack of general methods to detect vortices and to determine the location of their cores and to quantify their strength. This paper presents a novel technique for the identification of vortical structures in a general 3D flow field. The method operates on the local flow field, and it is based on a triple decomposition of motion proposed by Kolář. In contrast to a decomposition of velocity gradient into the strain and vorticity tensors, this method considers a third, pure shear component. The subtraction of the pure shear tensor from the velocity gradient remedies the inherent flaw of vorticity-based techniques, which cannot distinguish between rigid rotation and shear. The triple decomposition of motion serves to obtain a 3D field of residual vorticity whose magnitude is used to define vortex regions. The present method allows to locate automatically the core of each vortex, to quantify its strength, and to determine the vortex bounding surface. The output may be used to visualize the turbine vortical structures for the purpose of interpreting the complex three-dimensional viscous flow field and to highlight any case-to-case variations by quantifying the vortex strength and location. The vortex identification method is applied to a high-pressure turbine with three optimized blade tip geometries. The 3D flow field is obtained by computational fluid dynamics (CFD) computations performed with Numeca FINE/Open. The computational model uses steady-state Reynolds-averaged Navier–Stokes (RANS) equations closed by the Spalart-Allmaras turbulence model. Although developed for turbomachinery applications, the vortex identification method proposed in this work is of general applicability to any three-dimensional flow field.

Active attenuation of a trailing vortex inspired by a parabolized stability analysis

Designing effective control for complex three-dimensional flow fields proves to be non-trivial. Often, intuitive control strategies lead to suboptimal control. To navigate the control space, we use a linear parabolized stability analysis to guide the design of a control scheme for a trailing vortex flow field aft of a NACA0012 half-wing at an angle of attack $\unicode[STIX]{x1D6FC}=5^{\circ }$ and a chord-based Reynolds number $Re=1000$ . The stability results show that the unstable mode with the smallest growth rate (fifth wake mode) provides a pathway to excite a vortex instability, whereas the principal unstable mode does not. Inspired by this finding, we perform direct numerical simulations that excite each mode with body forces matching the shape function from the stability analysis. Relative to the uncontrolled case, the controlled flows show increased attenuation of circulation and peak streamwise vorticity, with the fifth-mode-based control set-up outperforming the principal-mode-based set-up. From these results, we conclude that a rudimentary linear stability analysis can provide key insights into the underlying physics and help engineers design effective physics-based flow control strategies.

Vortex Valve – Principle, Design and Application

The paper contains the overview of so-called vortex valve, used as outlet device on retention reservoirs for retention of rainstorms and later slow outflow into drainage etc. Simple one-dimensional equations are well known, but for complex three-dimensional flow fields inside the valve the method of flow numerical simulation is used. Particular paragraphs contain the theory of flow fields inside, explanation of branched flow characteristic, separated by transitional area, basics of designing and influence of both inlet/outlet opening sizes on the form of characteristic, valve adaptation for high flows at low water levels etc. Results are used for designing of new model series of valves for various water flows and levels.

Application of Entropy Generation to Improve Heat Transfer of Heat Sinks in Electric Machines

To intensify heat transfer within the complex three-dimensional flow field found in technical devices, all relevant transport phenomena have to be taken into account. In this work, a generic procedure based on a detailed analysis of entropy generation is developed to improve heat sinks found in electric machines. It enables a simultaneous consideration of temperature and velocity distributions, lumped into a single, scalar value, which can be used to directly identify regions with a high potential for heat transfer improvement. By analyzing the resulting entropy fields, it is demonstrated that the improved design obtained by this procedure is noticeably better, compared to those obtained with a classical analysis considering separately temperature and velocity distributions. This opens the door for an efficient, computer-based optimization of heat transfer in real applications.

Combined particle-image velocimetry and force analysis of the three-dimensional fluid–structure interaction of a natural owl wing

Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which therefore can serve as role models of how to overcome the well-known problems of low Reynolds number flight. The flight of the barn owl is characterized by a very low flight velocity in conjunction with a low noise emission and a high level of maneuverability at stable flight conditions. To investigate the complex three-dimensional flow field and the corresponding local structural deformation in combination with their influence on the resulting aerodynamic forces, time-resolved stereoscopic particle-image velocimetry and force and moment measurements are performed on a prepared natural barn owl wing. Several spanwise positions are measured via PIV in a range of angles of attack 6° and Reynolds numbers 40 000 120 000 based on the chord length. Additionally, the resulting forces and moments are recorded for −10° ≤ α ≤ 15° at the same Reynolds numbers. Depending on the spanwise position, the angle of attack, and the Reynolds number, the flow field on the wing’s pressure side is characterized by either a region of flow separation, causing large-scale vortical structures which lead to a time-dependent deflection of the flexible wing structure or wing regions showing no instantaneous deflection but a reduction of the time-averaged mean wing curvature. Based on the force measurements the three-dimensional fluid–structure interaction is assumed to considerably impact the aerodynamic forces acting on the wing leading to a strong mechanical loading of the interface between the wing and body. These time-depending loads which result from the flexibility of the wing should be taken into consideration for the design of future small flying air vehicles using flexible wing structures.

Numerical simulation of dynamic flow characteristics in a centrifugal water pump with three-vaned diffuser

The complex three-dimensional turbulent flow field in a centrifugal water pump with three asymmetrical diffusers was numerically simulated. The characteristics of pressure and force fluctuations inside the model pump were investigated. Fast Fourier transformation was performed to obtain the spectra of pressure and force fluctuations. It indicates that the dominant frequency of pressure fluctuations is the blade passing frequency in all the sub-domains inside the pump and the first blade passing frequency energy (first order of blade passing frequency) is the most significant. The dominant frequency of pressure fluctuations at the location of diffuser outlet is featured by low frequency (less than 1 Hz), which may be due to the locally generated eddy structures. Besides, the dominant frequency force fluctuations on the impeller blades are also the blade passing frequency. The existence of the three asymmetrical diffusers has damping effect on the pressure fluctuation amplitude and energy amplitude of pressure fluctuations in the diffuser domain dramatically, which indicates that the diffusers can effectively control the hydraulically excited vibration in the pump. Besides, the prediction of the dominant frequency of pressure fluctuations inside the pump can help to utilize the pump effectively and to extend the pump life. The main findings of this work can provide prediction of the pump performance and information for further optimal design of centrifugal pumps as well.

Three-dimensional investigation of liquid slug Taylor flow inside a micro-capillary using holographic velocimetry

Digital holography is an optical technique which is capable of providing instantaneous three-components of fluid flow velocity in three-dimensions (3D-3C) using a single camera. Digital holographic microscopy has been implemented in the present study to analyze liquid slug Taylor flow in a micro-channel of cross-sectional dimensions of 1,000 × 1,000 µm2. The working fluids are water (liquid) and air (gas), with superficial velocities of liquid, U L = 0.6 mm/s and gas, U G = 1.2 mm/s, respectively. The corresponding Capillary number, Ca = 0.035 × 10−3 and Bond number, Bo = 0.144. The holographic velocimetry technique has been implemented and appropriately validated by comparing the velocity profile from present experiment with that from analytical velocity profile for single-phase flow. Complete flow field results, i.e., u-, v- and w-components of velocity inside the liquid slug volume, i.e., in both streamwise (x–y) and cross-stream (y–z) planes are presented. The present experiments on liquid slug Taylor flow show strong cross-stream velocity near the advancing and receding meniscus due to higher capillary pressure. The stream traces show converging and diverging radial flow in the cross-stream plane near the receding and advancing meniscus, respectively. Two three-dimensional recirculation bubbles are observed inside the liquid slug. Overall, this paper reports the complex three-dimensional flow field inside a liquid slug Taylor flow from the 3D-3C flow field measurements.