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STUDY ON HEAT TRANSFER OF STEADY AND PULSATING TURBULENTFLOWS IN STRAIGHT AND 90° CURVED PIPES（直管と 90°曲り管内の定常および脈動乱流場における熱伝達に関する研究）
カクカンメイ氏 名 郭 官明 (GUO, GUANMING)
The fluid flow and heat transfer in the intake/exhaust system, which is the subject of thisstudy, is also an important phenomenon that affects engine performance such as thermal
efficiency, fuel consumption, emissions, etc.... Straight and curved pipes are essential
components of the intake and exhaust manifold, and the flow and heat transfer characteristicsof the straight and curved pipes directly affect the performance of the downstream catalyst.
Therefore, both the fluid flow and heat transfer in the pipes is important for maintaining thehigh performance of the close-coupled catalytic converter (CCC) in automotive engines.
The heat transfer of the steady turbulent flow and the pulsating turbulent flow in straightand 90° curved square pipes were investigated in this study. An inner length of the pipes andtheir wall thickness are 32 mm and 4 mm, respectively. Both experimental temperature fieldmeasurements at the corresponding cross-sections of the pipes and conjugate heat transfer(CHT) simulation were performed. The steady turbulent flow was investigated and comparedto the pulsating flow under the same time-averaged Reynolds number.
The novelty and originalities of this research can be summarized as the following aspects:(1). The measurements of temperature fields inside pipes were investigated which haverarely been reported in other studies owing to the difficulty of measuring the internal
temperature of pipes in turbulent flow.
(2). The heat transfer of turbulent flow and pulsating flow in straight and curved pipes
based on the third type of wall thermal boundary condition (the heat transfer coefficient of thewall and ambient temperature are defined).
(3). Conjugate heat transfer (CHT) simulation was applied to obtain the instantaneous
information of both fluid domain and solid domain and reveal the heat transfer mechanism of
the pulsating flow.
The main points and results obtained in this study are summarized as the follows:
In the Chapter 2, both experimental and numerical investigations of turbulent forced
convection in the straight and the 90° curved square SUS pipes were performed. In both thestreamwise and circumferential directions, the experimental and numerical temperature field
results agreed well. Based on the analysis of the numerical time-averaged velocity fields, it
was discovered that the deviation and impingement of the high-velocity air core and theformation of secondary flow strengthened heat transfer. Conversely, the separation effectsuppressed heat transfer. The overall heat transfer performances of these two pipes wereinvestigated in the last section using the local averaged Nu number. It was demonstrated thatthe heat transfer performance of the 90° curved pipe was 20% higher than that of the straightpipe.
In the Chapter 3, both experimental and numerical investigations of turbulent forced
convection in the straight and the 90° curved square Aluminum pipes were reported. Thetemperature distribution in the straight and the curved aluminum pipes is similar to that of theSUS pipes, no matter it is in the direction of the streamwise or the circumferential direction ofthe cross section. Based on both fluid domain and solid domain of the comparison in thenumerical simulation, it was discovered that the material of the pipe has little effect on the flow
and heat transfer of the air in the pipe. However, in the solid domain, the temperature field isdirectly related to the pipe material.
In the Chapter 4, experiment of the pulsating flows was performed for straight and 90°
curved square aluminum pipes. The velocity measurement at the “Outlet” verified the existenceof reverse flow under a pulsating flow with a large velocity amplitude. In both the streamwise
and circumferential directions, the results of temperature fields in the experiment reported thedifference between the steady and pulsating flows in the straight and curved pipes. The local
heat flux of different cross-sections in the experiment provided quantitative results of the heattransfer. The local heat flux of the pulsating flow in a straight pipe exhibits a large variation indifferent cross-sections. The closer to the pulsation generator, the larger the temperatureoscillation and the higher the heat transfer performance are. It has an extremely large local heat
flux near the outlet of the curved part of the curved pipe. In the test section, for both the steadyand pulsating flows, the total heat flux of the curved pipe was higher than that of the straightpipe. For both straight and curved pipes, the total heat flux of the steady flow was higher thanthat of the pulsating flow.
In the Chapter 5, the fluid flow and heat transfer of pulsating flow in straight and 90°
curved pipes were studied by numerical simulation. Through the analysis of several typicalinstantaneous velocity and temperature fields of acceleration phase, maximum velocity,
deceleration phase, minimum velocity and inflection point at acceleration phase, themechanism of pulsating flow heat transfer was revealed, and the accuracy of the experimental
results was verified. In the straight pipe, the spatial-averaged temperature variation of thedifferent cross-sections shown that the closer to the pulsation generator, the greater theamplitude of the temperature oscillation and the better the heat transfer performance. The
instantaneous velocity and temperature fields of pulsating flow are more complicated in thecurved pipe. The behaviors, such as the obvious separation between the air and pipe wall, thelow-temperature core impingement, and the reverse flow suppressed the heat transfer.
As for the future prospect, changing the inlet boundary conditions such as the timeaveraged Reynolds number of the inlet, the frequency of the pulsation generator and the inlet
air temperature is necessary to further reveal the heat transfer mechanism of pulsating flow. Inaddition, it is necessary to study the pulsating flow and heat transfer of pipes with complex
geometries.