Laser-Doppler Studies of the Wake-Effected Flow Field in a Turbine Cascade

1987 ◽  
Vol 109 (2) ◽  
pp. 170-176 ◽  
Author(s):  
S. Wittig ◽  
K. Dullenkopf ◽  
A. Schulz ◽  
R. Hestermann
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Laser Doppler ◽  
Wake Flow ◽  
Axial Distance ◽  
Turbulence Structures ◽  
Measuring Techniques ◽  
Turbine Cascades

The interaction between consecutive blade rows can be expected to have important effects on the heat transfer in cooled gas turbine cascades. In determining the local heat transfer under the influence of wake flow, nonintrusive optical measuring techniques were used to obtain the flow velocities and turbulence structures in the cascade inlet flow as well as along the test blade’s surface. The main purpose of the measurements is to provide accurate experimental data for the development of predictive codes. The applicability primarily of the laser-Doppler technique is discussed and problems arising from the use of laser-dual-focus anemometry are reported. In simulating the effects of wake flow, a plane airfoil was traversed in front of the cascade. Both the axial distance between the airfoil and the cascade and the position in circumferential direction were changed in discrete steps. Turbulence intensities between 1.4 and 15 percent were recorded in cold gas flow. The effects on the blade heat transfer are illustrated.

Flow Boiling Heat Transfer on Micro Pin Fins Entrenched in a Microchannel

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Axial Distance ◽  
Mass Fluxes ◽  
Pin Fins

Flow boiling of 1-methoxyheptafluoropropane (HFE 7000) in 222 μm hydraulic diameter channels containing a single row of 24 inline 100 μm pin fins was studied for mass fluxes from 350 kg/m2 s to 827 kg/m2 s and wall heat fluxes from 10 W/cm2 to 110 W/cm2. Flow visualization revealed the existence of isolated bubbles, bubbles interacting, multiple flow, and annular flow. The observed flow patterns were mapped as a function of the boiling number and the normalized axial distance. The local heat transfer coefficient during subcooled boiling was measured and found to be considerably higher than the corresponding single-phase flow. Furthermore, a thermal performance evaluation comparison with a plain microchannel revealed that the presence of pin fins considerably enhanced the heat transfer coefficient.

scholarly journals Nonstationary gas-dynamics and local heat transfer in the output channel of the turbocharger compressor

2019 ◽  
Vol 196 ◽  
pp. 00007 ◽  
Author(s):  
Leonid Plotnikov ◽  
Nikita Grigor'ev ◽  
Nikolaj Kochev
Keyword(s):  
Heat Transfer ◽  
Gas Dynamics ◽  
Gas Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measuring System ◽  
Rotor Speed ◽  
Outlet Channel ◽  
Thermomechanical Characteristics ◽  
Channel Configuration

Thermomechanical characteristics of the gas flow at the turbocharger compressor outlet largely determine the quality of the intake process in piston engines with boost. The article presents the results of an experimental study of gas-dynamics and heat transfer of gas flows after compression in a turbocharger centrifugal compressor. A brief description of the experimental setup, the configuration of pipes under investigation, the measuring system and the experimental features are given. The studies were carried out on a free compressor, i.e. without considering the piston part. Different conditions in the compressor outlet channel were created by installing special nozzles with different hydraulic resistances. It has been established that the local heat transfer increases from 23 to 46 % with an increase in the turbocharger rotor speed, depending on the outlet channel configuration. It should be noted that an increase in rotor speed is also accompanied by an increase in air flow through the channel. The increase in flow rate was from 10 to 42 %.

Annular Liquid Film Flow Under Local Heating in Microchannel

2005 ◽  
Author(s):  
Elizaveta Ya. Gatapova ◽  
Vladimir V. Kuznetsov ◽  
Oleg A. Kabov ◽  
Jean-Claude Legros
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Biot Number ◽  
Gas Flow ◽  
Film Flow ◽  
Local Heating ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Local Heat ◽  
Liquid Film Flow

In our previous investigations the formation of liquid bump of locally heated laminar liquid film with co-current gas flow was obtained [1,2]. The evaporation of liquid was left out of account. Heat transfer to the gas phase was approximately specified by a constant Biot number [2,3]. The aim of this work is an investigation of the evaporation effect, the hydrodynamics and the heat transfer of liquid film flow in a channel 0.2–1 mm height. The 2-D model of locally heated liquid film moving under gravity and the action of co-current gas flow with low viscosity in a channel are considered. The channel can be inclined at an angle with respect to horizon. It is supposed that the height of the channel is much less than its width. Surface tension is assumed to depend on temperature. The velocity profiles for gas and liquid regions are found from problem of joint motion of isothermal non-deformable liquid film and gas flow. Using the findings the joint solution of heat transfer and diffusion problem with corresponding boundary condition is calculated. Having the temperature field in the whole of liquid and gas flow region we find a local heat transfer coefficient on the gas-liquid interface and Biot number as a function of flow parameters and spatial variables.

Convective Heat Transfer of Alumina Nanofluids in a Microchannel

2010 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Axial Distance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

This work reports an experimental study of convective heat transfer of aqueous alumina nanofluids in a horizontal microchannel under laminar flow condition. The variation of local heat transfer coefficients, in both entrance and developed flow regime, is obtained as a function of axial distance. The heat transfer coefficient of nanofluids is found to be dependent upon not only nanoparticle concentration but also mass flow rate. Different to the behavior in conventional-sized channels, the major heat transfer coefficient enhancement is observed in fully developed region in microchannels. Discussions of the results suggest that the heterogeneous nature of nanoparticle flow should be considered.

Heat Transfer, Pressure Loss and Flow Field Measurements Downstream of Staggered Two-Row Circular and Elliptical Pin Fin Arrays

2005 ◽  
Vol 127 (5) ◽  
pp. 458-471 ◽  
Author(s):  
Oguz Uzol ◽  
Cengiz Camci
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Pressure Loss ◽  
Total Pressure ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Wake Flow ◽  
Pin Fin ◽  
Pin Fin Arrays

This paper presents the results of heat transfer, total pressure loss, and wake flow field measurements downstream of two-row staggered elliptical and circular pin fin arrays. Two different types of elliptical fins are tested, i.e., a Standard Elliptical Fin (SEF) and a fin that is based on NACA four digit symmetrical airfoil shapes (N fin). The results are compared to those of a corresponding circular pin fin array. The minor axis lengths for both types of elliptical fins are kept equal to the diameter of the circular fins. Experiments are performed using Liquid Crystal Thermography and total pressure probe wake surveys in a Reynolds number range of 18 000 and 86 000 as well as Particle Image Velocimetry (PIV) measurements at ReD=18 000. The pin fins had a height-to-diameter ratio of 1.5. The streamwise and the transverse spacings were equal to one circular fin diameter, i.e., S/D=X/D=2. For the circular fin array, average Nusselt numbers on the endwall within the wake are about 27% higher than those of SEF and N fin arrays. Different local heat transfer enhancement patterns are observed for elliptical and circular fins. In terms of total pressure loss, there is a substantial reduction in case of SEF and N fins. The loss levels for the circular fin are 46.5% and 59.5% higher on average than those of the SEF and N fins, respectively. An examination of the Reynolds analogy performance parameter show that the performance indices of the SEF and the N fins are 1.49 and 2.0 times higher on average than that of circular fins, respectively. The thermal performance indices show a collapse of the data, and the differences are much less evident. Nevertheless, N fins still show slightly higher thermal performance values. The wake flow field measurements show that the circular fin array creates a relatively large low momentum wake zone compared to the SEF and N fin arrays. The wake trajectories of the first row of fins in circular, SEF and N fin arrays are also different from each other. The turbulent kinetic energy levels within the wake of the circular fin array are higher than those for the SEF and the N fin arrays. The transverse variations in turbulence levels correlate well with the corresponding local heat transfer enhancement variations.

The Transition From Turbulent to Laminar Gas Flow in a Heated Pipe

1970 ◽  
Vol 92 (4) ◽  
pp. 569-579 ◽  
Author(s):  
C. A. Bankston
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Heat Fluxes ◽  
External Boundary ◽  
Transfer Coefficients ◽  
Adiabatic Flow ◽  
Heat Transfer Coefficients

Experimental results are reported on the heat transfer and fluid friction of heated hydrogen and helium gas flows undergoing transition from turbulent to laminar flow in a circular tube. The entering Reynolds numbers range from 2350 to 12,500 and the nondimensional heat-flux parameter ranges from 0.0021 to 0.0061. Local heat-transfer coefficients and friction factors are obtained, and the flow transition, which is evident in these results, is verified at small heat fluxes by measuring directly the turbulence intensity at the center line with a hot-wire anemometer. At large heat fluxes, laminarization is found to occur at local bulk Reynolds numbers well in excess of the minimum number for fully turbulent adiabatic flow, and the resulting heat-transfer coefficients are much lower than those associated with fully turbulent flow at the same Reynolds number. The relation between laminarization in heated tubes and in severely accelerated external boundary layers is investigated and some similarities are noted. The acceleration and pressure-gradient parameters used to predict boundary-layer laminarization are modified for tube flow and used to correlate the initiation and completion of laminarization in the heated tube.

Experimental research into the methods for controlling the thermal-mechanical characteristics of pulsating gas flows in the intake system of a turbocharged engine model

2021 ◽  
pp. 146808742098736
Author(s):  
Leonid V Plotnikov
Keyword(s):  
Heat Transfer ◽  
Gas Dynamics ◽  
Gas Flow ◽  
Mechanical Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Gas Flows ◽  
Intake System ◽  
Instantaneous Values ◽  
Technical Solutions

It is a relevant objective in thermal physics and piston engine construction to develop technical solutions for controlling the gas dynamics and heat exchange of gas flows in the intake system of turbocharged engines in order to improve performance. The article presents other authors’ data on the improvement of processes in the gas exchange systems of piston engines. It also provides a description of experimental set-ups, instruments, measurement tools and research methods for establishing the thermal-mechanical characteristics of pulsating flows in the intake system of a turbocharged engine. The instantaneous values of the gas flow rate and the local heat transfer coefficient were determined using the measured results by applying a constant temperature hot-wire anemometer (H-WA). The article describes technical solutions for influencing the gas dynamics and heat exchange of gas flows by stabilising and turbulising the flow. The regularities of changes in the instantaneous values of the flow velocity, pressure and the local heat transfer coefficient in time for a pulsating gas flow with different intake system configurations are obtained. It is shown that the installation of a levelling grid in the compressor outlet channel leads to the stabilisation of the flow and the suppression of heat transfer in the engine intake system by an average of 15% compared to the base system. It was found that the presence of a channel with grooves in the intake system leads to flow turbulisation and the intensification of heat transfer in the intake system by an average of 25%.

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