Two-pass Square Research Articles

Enhancement of the Thermohydraulic Performance in a Double Passage Square Duct with the Use of Inclined Ribs of 45°: A Comparative Computational Study

The modern gas turbines need to run at very high inlet temperature to promote their power output. Thus, improvements in cooling technologies play a significant role for enhancing the gas turbine blade life. In this paper, thermohydraulic performance (THP) of a two-pass square channel with inclined ribs at 45° was scrutinized employing the k–ε realizable model with enhanced wall treatment in ANSYS Fluent. The calculations were performed for the rib pitch to height ratio (p/e) of 5-10, rib height to hydraulic diameter ratio (e/Dh) of 0.1-0.2, and Reynolds number (Re) of 20,000-40,000. Detailed analysis of the flow structure in a double passage square duct was carried out to understand the interaction of the rib and bend-induced secondary flows and its contribution to heat transfer enhancement for the rib configurations with distinct p/e and e/Dh, which was not available in any other existing numerical or experimental investigations. The results revealed that the ribs with higher e/Dh generated the stronger stream-wise secondary flows which led to the augmentation of the cooling performance with the disadvantage of pressure loss increment. The maximum THP of 26.55% was achieved with the ribbed configuration having p/e=5 and e/Dh=0.1 at Re=20,000. The new correlations were developed from the computational data to predict the normalized Nusselt number and friction factor (Nu/Nu0 and f/f0, where 0 is the correlation), taking the e/Dh and flow Re into consideration.

Experimental study of heat-transfer and pressure-drop performances of a rotating two-pass channel with composite stepped skew ribs and internal effusion

The full-field endwall Nusselt number (Nu) distribution, Fanning friction factor (f), and aerothermal performance index (API) of a rotating two-pass square channel with the stepped composite skew ribs and internal effusion are measured at rotation (Ro), Reynolds (Re) and buoyancy (Bu) numbers in the respective ranges of 0.05-0.4, 5000-15,000, and 0.003-0.325. The novel composite ribs in the static channel raise the area-average Nusselt numbers to 5.97-4.9 times Dittus-Boelter (D-B) correlation levels with Fanning friction factors between 13-9.6 times Blasius equation (B-E) values to give rise to the high aerothermal performance index (API∞) of 2.65-2.39. With rotation, the averaged Nusselt numbers on leading and trailing ribbed endwalls are, respectively modified to 1.1-1.62 and 0.94-1.42 times of the non-rotating values with the channel averaged Fanning friction factors increased to 1.01-1.31 times of the static-channel references. The minimum Nusselt number on each rotating endwall is identified and compared with its area-average Nusselt number to highlight the safety margin of surplus coolant flow rate for hot spot prevention when a cooling network in a gas turbine blade is designed with reference to the area-averaged heat transfer data. Empirical heat-transfer and pressure-drop correlations for the present rotating channel are generated to assist the relevant applications.

Effects of Attack Angle and Relative Thickness of Novel Wing-Shaped Turbulators on Turbulent Hydrothermal Performance in a Two-Pass Square Channel

Abstract This work aims to combine the effects of the near-wall and core flow disturbance by proposing novel wing-shaped turbulators. The new turbulators are fabricated with the fused deposition modeling (3D printing) technology. To explore their effects on detailed flow fields, local temperature distributions, and pressure drops in a two-pass square channel, particle image velocimetry (PIV), infrared thermography (IR camera), and pressure transducer measurements are performed. The turbulator pitch, clearance, and truncation gap ratio based on the channel hydraulic diameter of 45.5 mm are, respectively, fixed at 0.7, 0.25, and 0.06. Varied parameters include turbulator attack angle (α = 10 deg, 15 deg, 20 deg, and 30 deg), maximum thickness to chord line ratio (t/C = 0.08, 0.13, 0.16, 0.20, and 0.23), and bulk Reynolds number (Re = 5000–20,000). From the experimental results and flow parameters analyzed, the dimensionless spanwise-averaged mean transverse velocity and cross-sectionally averaged vorticity magnitude are identified to be the most relevant ones to spanwise-averaged local Nusselt number ratio in the first and second pass. Among all examined cases and previous data with Fanning friction factor ratio (f¯/fo) less than 50, the case with α = 20 deg and t/C = 0.20 attains the highest thermal performance factor (TPF) and overall Nusselt number ratio Nu¯/Nuo up to 1.68 and 5.36, respectively. Furthermore, empirical correlations of Nu¯/Nuoandf¯/fo versus α, t/C, and Re are proposed.

Influence of slat attack angle and pitch ratio on turbulent hydrothermal characteristics in a louvered two-pass square channel

This study reports an innovative design of 3-D louver-type turbulator based on previous ribs, baffles, and 2-D louver-type turbulators. Its effects on turbulent flow field, detailed temperature distribution, and pressure loss in a two-pass channel with square cross-section are investigated by Particle Image Velocimetry (PIV), Infrared Thermography (IRT), and pressure transducer. Four pitch ratios (Pi/DH), namely 1, 2, 3, and ∞, are explored, and the slat attack angle (α) of the louver-type turbulator ranges from −40° to 30°. The Reynolds number (Re) for PIV and IRT measurement is fixed at 10,000 and in the range of 5000–20,000, respectively. It is found that the present turbulators with Pi/DH = ∞ not only disturb the core flow and degenerate wake zone behind the turbulator but also induce four pairs of Dean-like counter-rotating vortices which result in strong impingement on the bottom and top walls. The main contributions of this study are twofold: (1) the present design fills the blank at moderate friction factor ratio (f‾/f∞ ≤100) compared with previous ribs and baffles; (2) it attains much higher Nusselt number ratio (Nu‾/Nu∞ up to 4.4) at that f‾/f∞ region or for the same value of Nu‾/Nu∞ the value of f‾/f∞ is 44.1% lower.

Heat Transfer in Internal Cooling Channels of Gas Turbine Blades: Buoyancy and Density Ratio Effects

The present work investigates the effects of buoyancy and wall heating condition on the thermal performance of a rotating two-pass square channel with smooth walls. The U-bend channel has a square cross section with a hydraulic diameter of 5.08 cm (2 in.). The lengths of the first and second passes are 514 mm and 460 mm, respectively. The turbulent flow entered the channel with Reynolds numbers of up to 34,000. The rotational speed varied from 0 to 600 rpm with rotational numbers up to 0.75. For this study, two approaches were considered for tracking the buoyancy effect on heat transfer. In the first case, the density ratio was set constant, and the rotational speed was varied. In the second case, the density ratio was changed in the stationary case, and the effect of density ratio was discussed. The range of buoyancy number along the channel is 0–6. The objective was to investigate the impact of buoyancy forces on a broader range of rotation number (0–0.75) and buoyancy number scales (0–6), and their combined effects on heat transfer coefficient for a channel with an aspect ratio of 1 : 1. Results showed that increasing the density ratio increased the heat transfer ratio in both stationary and rotational cases. Furthermore, in rotational cases, buoyancy force effects were very significant. Increasing the rotation number induced more buoyancy forces, which led to an enhancement in heat transfer. The buoyancy effect was more visible in the turning region than any other region.

Numerical Simulation of the Effect of Channel Orientation on Fluid Flow and Heat Transfer at High Buoyancy Number in a Rotating Two-Pass Channel With Angled Ribs

Convective heat transfer in a rotating two-pass square channel with 45 deg ribs is numerically investigated to simulate turbine blade cooling operation under extreme design cooling conditions (high rotation number, high density ratio, and high buoyancy number). Two channel orientations are examined β = 0 deg and β = 45 deg in order to determine the effects of passage orientation on flow and heat transfer. For a reference pressure of 10-atm and a Reynolds number of 25,000, the results show that at low buoyancy number and for both channel orientations, the combined effect of Coriolis and centrifugal buoyancy forces generates an important thermal gradient between low- and high-pressure surfaces of the first passage, while the second passage remains almost unchanged compared to the stationary cases. At high buoyancy number, and unlike low buoyancy number, the interaction of Coriolis-driven cells, rib-induced vortices, and buoyancy-driven cells are destructive, which degrade the heat transfer rate on trailing and leading surfaces in the first passage for β = 0 deg. In contrast, for β = 45 deg, this interaction is constructive, which enhances the heat transfer rate on co-trailing and co-leading surfaces. In the second passage, the interaction of rib-induced vortices and buoyancy-driven cells deteriorates significantly the heat transfer rate in case of β = 0 deg than in case of β = 45 deg compared to low buoyancy number. The computations are performed using the second-moment closure turbulence model and the numerical results are in fair agreement with available experimental data.

Experimental Investigation of Heat Transfer Enhancement in a Two-Pass Square Duct by Permeable Ribs

ABSTRACTThis investigation presents the heat transfer enhancement results of flow past repeated permeable ribs mounted on the bottom surface of a two-pass square channel. Spatially periodic flow interruption generated by rib arrays mounted on the walls is extensively used for augmentation of heat transfer in turbine blade cooling passages. To remove the local heat transfer deterioration in the vicinity region of the solid ribs, permeable ribs have been proposed in the literature for single pass coolant passages. This study intends to investigate the performance of permeable ribs array placed on the lower wall of a two-pass channel compared to that of the solid rib array. The heat transfer and friction characteristics are investigated for smooth, solid-ribbed, slit-ribbed, and split-slit-ribbed square channels for the Reynolds numbers of 5,500, 12,800, and 16,400. An array of ribs (consisting of fifteen ribs) has been mounted over the total test section, with seven each in the first and second passes, and one in the bend. The performance analysis has been carried out using thermal performance on the basis of constant pumping power and entropy generation principle.

Thermal-hydraulic performance of longitudinal wavy rib along wavy two-pass channel

An experimental study investigates the thermal-hydraulic characteristics of the novel longitudinal wavy ribs along a wavy two-pass square channel. The detailed Nusselt number (Nu) distributions over the ribbed wavy endwall are measured using the steady-state infrared thermography method together with the Fanning friction factors (f) evaluated from the pressure drop measurements. Relative heat transfer enhancements (HTE) and pressure drop augmentations for present HTE element are disclosed by comparing the Nu and f data measured from the wavy channels with and without wavy ribs, as well as the straight two-pass channels with V- or W-ribs. Acting by the additional HTE mechanisms induced by the wavy ribs, the regionally averaged Nu over inlet leg, sharp bend and outlet leg of present ribbed two-pass wavy channel are respectively raised to 5.8–5.5, 6.04–5.52, 5.81–4.94 and 5.7–5.12 times of Dittus-Boelter levels at 5000 < Re < 30,000. Accompanying with the channel averaged f factors in the range of 43.67–21.43 times of Balssius correlation values, the thermal performance factors (TPF) of 1.51–1.62 are achieved for present ribbed two-pass wavy channel. To assist relevant engineering applications, two set of empirical correlations permitting the evaluations of regionally averaged Nu and the channel averaged f are devised.

Thermal performance of radially rotating two-pass S-shaped zig-zag channel

The detailed Nusselt number distributions, Fanning friction coefficients and thermal performance factors of a radially rotating two-pass square S-shaped zig-zag channel are measured. The fanning friction coefficients are measured from the inner and outer sidewalls, as well as from the leading and trailing endwalls of the rotating channel. At the criterion of constant pumping power consumptions, the thermal performance factors (TPF) are evaluated. The test conditions specified by Reynolds number (Re), rotation number (Ro), density ratio (Δρ/ρ) and buoyancy number (Bu) are 5000≤Re≤15,000, 0≤Ro≤0.5, 0.03≤Δρ/ρ≤0.12 and 0.0049≤Bu≤0.15. The individual and combined impacts of Reynolds number, rotation number and buoyancy number on the endwall heat transfer properties for present rotating channel are illustrated using a selective set of heat transfer data. Acting by the Coriolis and rotating buoyancy forces to modify the flow structures, the area averaged Nusselt number ratios between the rotating and static channels for the leading and trailing endwalls fall in the respective ranges of 0.93–2.34 and 0.91–2.25. The heat transfer correlations which permit the evaluations of individual and interdependent effects of rotation number and buoyancy number on the regionally averaged Nusselt numbers over the rotating inlet leg, outlet leg and bend region are devised. Correlations evaluating the Fanning friction coefficients of the inner, outer, leading and trailing channel walls are also developed for present rotating channel. Due to the combined Re, Ro and Bu effects on the heat transfer properties and pressure drop performances of present S-shaped two-pass channel, the area averaged Nusselt numbers on leading and trailing endwalls are respectively raised to 3.17–6.83 and 3.22–6.92 times of the Dittus-Boelter Nusselt number (Nu∞) references. With the accompanying thermal performance factors in the range of 1.25–2.04 at all the static and rotating test conditions, present S-shaped two-pass channel appears as an efficient heat transfer enhancement method with cooling applications to gas turbine blades.

Numerical simulations on flow and heat transfer in ribbed two-pass square channels under rotational effects

The main objective of this research is to study the flow and heat transfer characteristics in a rotating two-pass square channel with ribbed walls. In this study, the channel length-to-hydraulic diameter ratio of the rotating two-pass square channel (L/Dh), the rib height-to-hydraulic diameter ratio (e/Dh), rib angle of attack (α) and the rib pitch-to-height (p/e) ratio are fixed at 11.33, 0.13, 60° and 10, respectively. The test fluid is air having the flow rate in terms of constant Reynolds number (Re) of 10,000. The rotation numbers (Ro) are varied from 0.1 to 0.4. The details of the local heat transfer distribution and the flow field of the rotating two-pass square channel are numerically studied by using commercial software ANSYS Fluent (ver.15.0). The results show that the ribbed walls enhance the heat transfer rate significantly. Under rotation, the average Nu in the first pass with radial outward flow is increased while that in the second pass is decreased, and also found that maximum heat transfer rate is observed for rotation number of 0.4 which is higher about 10-20% when compared with the other rotation number cases.

Numerical flow and experimental heat transfer of S-shaped two-pass square channel with cooling applications to gas turbine blade

This study experimentally detected the endwall Nusselt numbers (Nu) distributions, Fanning friction factors (f) and thermal performance factors (TPF) for a stationary S-shaped two-pass square channel with the associated turbulent flow fields analyzed by ANSYS Fluent code to disclose the flow mechanisms responsive to the measured thermal performances. The full-field Nu distributions over the endwalls of present S-shaped inlet/outlet legs and 180° sharp bend at Reynolds numbers (Re) of 5000, 7500, 10,000, 12,500, 15,000, 20,000 and 30,000 were measured using the steady-state infrared thermography method; while the validated RNG k-ε turbulence model was adopted to reveal the fields of time-mean fluid velocity, turbulent kinetic energy and cross-plane secondary flow. Acting by sectional vortices induced along the inlet/outlet S-pathways and 180° sharp bend, the core-to-wall momentum/heat exchanges are boosted to elevate both Nu and f values. Accompanying with the f augmentations from 10.19–8.27 times of Balssius f∞ levels, the area-averaged Nusselt numbers (Nu‾A) over the entire S-shaped endwall were elevated to 3.21–3.09 times of Dittus-Boelter Nusselt number (Nu∞) values at 5000⩽Re⩽30,000, resulting in the TPF between 1.4 and 1.44. To assist relevant engineering applications, two sets of empirical correlations evaluating the regionally averaged endwall Nusselt numbers and f factors are devised.

Effect of Coriolis and centrifugal forces on flow and heat transfer at high rotation number and high density ratio in non orthogonally internal cooling channel

Numerical predictions of three-dimensional flow and heat transfer are performed for a two-pass square channel with 45° staggered ribs in non-orthogonally mode-rotation using the second moment closure model. At Reynolds number of 25,000, the rotation numbers studied were 0, 0.24, 0.35 and 1.00. The density ratios were 0.13, 0.23 and 0.50. The results show that at high buoyancy parameter and high rotation number with a low density ratio, the flow in the first passage is governed by the secondary flow induced by the rotation whereas the secondary flow induced by the skewed ribs was almost distorted. As a result the heat transfer rate is enhanced on both co-trailing and co-leading sides compared to low and medium rotation number. In contrast, for the second passage, the rotation slightly reduces the heat transfer rate on co-leading side at high rotation number with a low density ratio and degrades it significantly on both co-trailing and co-leading sides at high buoyancy parameter compared to the stationary, low and medium rotation numbers. The numerical results are in fair agreement with available experimental data in the bend region and the second passage, while in the first passage were overestimated at low and medium rotation numbers.

Characterization of heat transfer enhancement and frictional losses in a two-pass square duct featuring unique combinations of rib turbulators and cylindrical dimples

Transient heat transfer experiments using liquid crystal thermography have been carried out on a two-pass square channel for testing several unique combinations of ribs and cylindrical dimples. Four different rib shapes, viz. 45° angled, V, W and M have been studied. In compound channels, the rib pitch accommodates cylindrical dimples arranged in the shape of the rib, hence following the direction of rib induced secondary flows. For each rib shape, three different configurations – rib alone, dimple alone and rib–dimpled compound cases were studied. The rib-height-to-channel hydraulic diameter ratio was 0.125 and rib-pitch-to-rib-height ratio was 16. The dimple-depth-to-print diameter ratio was 0.3. The experiments were carried out for a wide range of Reynolds number (19,500–69,000), covering a spectrum typically found in both land-based and air-breathing engines. A total of 52 experiments were carried out to measure detailed heat transfer coefficient on the bottom wall of the two-pass channel. A transient liquid crystal thermography technique was used for heat transfer measurement. Static pressure measurements were carried out to measure the overall pressure drop in the two pass channel. From globally averaged Nusselt number and overall pressure drop, thermal-hydraulic performance of the 13 configurations were determined, compared and analyzed. It has been observed that 45° angled and V compound configurations resulted in higher heat transfer augmentation as well as higher thermal hydraulic performance when compared with their corresponding ribs alone and dimples alone configurations.

Thermal performance of rotating two-pass ribbed square channel with wavy sidewalls

Detailed Nusselt number (Nu) distributions over Leading Endwall (Le-E) and Trailing Endwall (Tr-E), Fanning friction coefficients (f) and thermal performance factors (TPF) of a radially rotating two-pass square channel enhanced by in-line 45° endwall ribs and wavy sidewalls were measured at the test conditions of 5000⩽Re⩽20,000, 0⩽Ro⩽0.3 and 0⩽Bu⩽0.053. No previous study has examined the thermal performances of a rotating ribbed two-pass channel with wavy sidewalls. A selection of heat transfer data illustrates the individual and interdependent effects of Re, Ro and Bu on local and region-averaged Le-E and Tr-E Nu. A set of Le-E and Tr-E heat transfer correlations that determines the rib-wise and regionally averaged Nu over the inlet and outlet ribbed endwalls, as well as over the smooth bend endwall is generated. Along with the f data detected from the ribbed endwalls and wavy sidewalls at isothermal conditions, the TPF values at various rotating conditions are evaluated. The heat transfer, pressure drop and TPF performances for the two-pass channel with present combined passive Heat Transfer Enhancement (HTE) device at rotating conditions are subsequently compared with those generated by the typical HTE devices deployed in the internal coolant channels of a gas turbine rotor blade. Acting by the combined Re, Ro and Bu effects, present region-averaged Nusselt numbers over the rotating Le-E (Tr-E) of the inlet-leg, sharp bend and outlet-leg are respectively raised to 3.20–5.80 (4.10–8.59), 4.26–10.48 (5.03–15.47) and 1.48–12.47 (4.64–8.24) times of the Dittus–Boelter reference levels. With the f coefficients increased to 9.61–25.7 times of the Blasius equation levels by present HTE measure and the 180° sharp bend, present TPF values obtained at the rotating test conditions fall in the range of 2.87–0.71, suggesting the favorable heat transfer effectiveness with cooling applications to gas turbine rotator blades.

Effect of rib spacing on heat transfer and friction in a rotating two-pass square channel with asymmetrical 90-deg rib turbulators

Effect of rib spacing on heat transfer and friction in a rotating two-pass square channel is experimentally investigated. The Reynolds numbers and rotation numbers vary from 20000 to 50000 and 0 to 0.8, respectively. The 90-deg ribs are arranged on leading and trailing surfaces asymmetrically with height-to-hydraulic diameter (e/Dh) ratio of 0.1. The rib pitch-to-height (p/e) ratio on the pressure side varies from 3.8 to 14.4 at positive rotational direction, while keeps the constant value of 10 on the suction side. The results indicate that the rib spacing effect is more pronounced in the first radially outward flow passage than the second passage. Rotation reduces rib spacing effect and p/e=10 has the best surface average heat transfer enhancement except for the trailing wall of the first passage. As more ribs are added, the channel friction increases until p/e down to 5. But rotation cause lower pressure drop at low rotation number for most cases. The very close rib spacing of p/e=3.8 has the best thermal performance for positive rotational direction. For negative direction, p/e=10 turns to be the best rib spacing ratio.

CFD Visualizations of Flow Features in Two-Pass Square and Parallelogram Channels with a 180-Deg Sharp Turn

CFD Visualizations of Flow Features in Two-Pass Square and Parallelogram Channels with a 180-Deg Sharp Turn

Heat transfer in two-pass smooth square channel under large rotation numbers

The rotation number range was expanded significantly through increasing the absolute pressure of the channel to about 5 atm. Experiments were carried out to investigate heat transfers in a smooth square two-pass channel under large rotation numbers. In current study,Reynolds and rotation number range from 10 000 to 70 000 and zero to 2. 08 respectively,which covered the real engine parameters. It is found that when the rotation number is large enough,the effect of rotation dominates the heat transfer at the inlet and the turn portion,instead of the entrance effect and the turn effect. As the channel rotated,the Nusselt number of the first pass was found to increase monotonically on the trailing wall,however to increase on the middle and downstream of leading wall exceeding certain critical rotation numbers. And a new phenomena is found in the downstream of the second pass,which is that the heat transfer on trailing surface exceeds the leading surface at high rotation numbers.

Numerical Calculations on Flow and Heat Transfer in Smooth and Ribbed Two-Pass Square Channels under Rotational Effects

U-shaped channel, which is also called two-pass channel, commonly exists in gas turbine internal coolant passages. Ribbed walls are frequently adopted in internal passage to enhance the heat transfer. Considering the rotational condition of gas turbine blade on operation, the effect of rotation is also investigated for the coolant channel which is close to real operation condition. Thus, the objective of this study is to discuss the effect of rotation on fluid flow and heat transfer performance of U-shaped channel with ribbed walls under high rotational numbers. Investigated Reynolds number is Re=12500and the rotation numbers areRob=0.4and 0.6. In the results, the spatially heat transfer coefficient distributions are exhibited to discuss the effect of rotation and roughened walls. It is found that ribbed walls enhance the heat transfer rate significantly. Under the rotational condition, theNuin the first pass with outward flow is increased while that in the second pass is decreased. Finally, averageNuratio, friction ratio, and thermal performance are all presented to discuss the thermal characteristics.

Numerical simulations of heat transfer distribution of a two-pass square channel with V-rib turbulator and bleed holes

The blade tip region in gas turbine encounters high thermal loads due to temperature difference and hence efforts for high durability and safe operations are essential. Improved and robust methods of cooling are required to downgrade heat transfer rate to turbine blades. The blade tip regions, which are exposed to high gas flow, suffers high local thermal load which are due to external tip leakage. Jet impingement, pin cooling etc. are techniques used for cooling blades. A more usual way is to use serpentine passage with 180-degree turn. In this study, numerical simulation of heat transfer distribution of a two-pass square channel with rib turbulators and bleed holes were done. Periodical rib turbulators and bleed holes were used in the channel. The ribs arrangement were 60 degree V rib, 60 degree inverted V ribs, combination of 60 degree V rib at inlet and 60 inverted V rib at outlet section and combination of Inverted V at inlet and V rib at the outlet. The results were numerically computed using Fluent with Reynolds number of 12,500 and 28,500. Turbulence models used for computations were k-ω-SST and RSM. Temperature based and shear stress based techniques were used for heat transfer distribution prediction. The results for 60 degree V rib, 60 degree inverted V ribs were compared with the experimental results for validation of the results obtained. Detailed distribution shows distinctive peaks in heat transfer around bleed holes and rib turbulator. Comparisons of the overall performance of the models with different orientation of rib turbulator are presented. It is found that due to the combination of 60 degree inverted V rib in inlet and 60 V rib in outlet with bleed holes provides better heat treatment. It is suggested that the use of rib turbulator with bleed holes provides suitable for augmenting blade cooling to achieve an optimal balance between thermal and mechanical design requirements.

An experimental investigation on fluid flow characteristics in a real coolant channel of LP turbine blade with PIV technique

Using a planar particle image velocimetry (PIV) system, the fluid flow characteristics including mean velocity and pressure fields in a real coolant channel of a low pressure (LP) turbine blade have been investigated. To understand the flow characteristics within the real LP turbine blade in detail, the studied channel has a real blade-similar cross section, and the entire channel consists of two dividing walls, three passes, a 180° bend, 2 tip exits and 25 trailing edge exits. At first, the flow structures in the channel are captured by the PIV system at an inlet Reynolds number of 44,000, when all the exits are open. The experimental results exhibit different secondary flow features from the previous investigations, which were conducted mostly in simplified two-pass square or rectangular channels. Secondly, through a statistical post-processing of measured instantaneous velocity fields, the Reynolds-averaged Navier–Stokes (RANS) equations are solved to obtain the mean pressure distributions at several typical cross sections. At last, the effects of the inlet Reynolds numbers and coolant ejection from the tip exit above the 1st pass on the flow characteristics are discussed. From the comparisons of the flow characteristics obtained at different flow conditions, it can be concluded that the flow characteristics are sensible to the inlet Reynolds number and coolant ejection from tip exit.