End-Wall Heat Transfer in a Rarefraction Wave Tube

1965 ◽  
Vol 87 (3) ◽  
pp. 349-352 ◽  
Author(s):  
B. T. Chao
Keyword(s):  
Heat Transfer ◽  
Thermal Boundary Layer ◽  
Free Stream ◽  
Published Data ◽  
Temperature Profiles ◽  
Wall Heat Transfer ◽  
A Posteriori ◽  
Wave Tube ◽  
Title Problem ◽  
End Wall

An analysis is presented for the title problem based on the governing conservation equations and the measured free-stream temperature variation with time as reported by Levy and Potter. The results compare very favorably with the published data. Several temperature profiles are illustrated which confirm a posteriori the validity of the thin thermal boundary-layer assumption used.

The Effect of Hot-Streaks on HP Vane Surface and Endwall Heat Transfer: An Experimental and Numerical Study

2005 ◽  
Author(s):  
T. Povey ◽  
K. S. Chana ◽  
T. V. Jones ◽  
J. Hurrion
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Cooling System ◽  
Numerical Study ◽  
Inlet Temperature ◽  
Temperature Profiles ◽  
Wall Heat Transfer ◽  
Hot Streak ◽  
End Wall

Pronounced non-uniformities in combustor exit flow temperature (hot-streaks), which arise because of discrete injection of fuel and dilution air jets within the combustor and because of end-wall cooling flows, affect both component life and aerodynamics. Because it is very difficult to quantitatively predict the affects of these temperature non-uniformities on the heat transfer rates, designers are forced to budget for hot-streaks in the cooling system design process. Consequently, components are designed for higher working temperatures than the mass-mean gas temperature, and this imposes a significant overall performance penalty. An inadequate cooling budget can lead to reduced component life. An improved understanding of hot-streak migration physics, or robust correlations based on reliable experimental data, would help designers minimise the overhead on cooling flow that is currently a necessity. A number of recent research projects sponsored by a range of industrial gas turbine and aero-engine manufacturers attest to the growing interest in hot-streak physics. This paper presents measurements of surface and end-wall heat transfer rate for an HP nozzle guide vane (NGV) operating as part of a full HP turbine stage in an annular transonic rotating turbine facility. Measurements were conducted with both uniform stage inlet temperature and with two non-uniform temperature profiles. The temperature profiles were non-dimensionally similar to profiles measured in an engine. A difference of one half of an NGV pitch in the circumferential (clocking) position of the hot-streak with respect to the NGV was used to investigate the affect of clocking on the vane surface and end-wall heat transfer rate. The vane surface pressure distributions, and the results of a flow-visualisation study, which are also given, are used to aid interpretation of the results. The results are compared to two-dimensional predictions conducted using two different boundary layer methods. Experiments were conducted in the Isentropic Light Piston Facility (ILPF) at QinetiQ Farnborough, a short duration engine-size turbine facility. Mach number, Reynolds number and gas-to-wall temperature ratios were correctly modelled. It is believed that the heat transfer measurements presented in this paper are the first of their kind.

Some Transient Measurements in a Rarefaction Wave Tube

1964 ◽  
Vol 86 (4) ◽  
pp. 365-370 ◽  
Author(s):  
M. J. Levy ◽  
J. H. Potter
Keyword(s):  
Heat Transfer ◽  
Rarefaction Wave ◽  
Variable Density ◽  
Gas Temperature ◽  
Wave Tube ◽  
Transfer Rates ◽  
Integral Procedure ◽  
End Wall ◽  
The Heat Balance ◽  
Transient Measurements

This paper reports upon an experimental investigation in which a heat-transfer instrument was designed, built, and applied in a rarefaction wave tube. An analysis of the heat-transfer instrument was made to evaluate the significant parameters which influence the instrument performance in the measurement of transient heat flux between the gas and wall. A mathematical analysis based upon the heat balance integral procedure, considering variable density and time-dependent free stream gas temperature, was performed to interpret the gas-to-end-wall heat transfer in a rarefaction wave tube. The heat-transfer rates predicted by the analysis com pared favorably with values measured by the calorimeter type thermistor heat-transfer instrument.

scholarly journals Cooling Intensification of a Continuously Moving Stretching Surface Using Different Types of Nanofluids

2012 ◽  
Vol 2012 ◽  
pp. 1-11
Author(s):  
M. B. Akgül ◽  
M. Pakdemirli
Keyword(s):  
Heat Transfer ◽  
Power Law ◽  
Free Stream ◽  
System Of Equations ◽  
Temperature Profiles ◽  
Governing Equations ◽  
Stretching Surface ◽  
Flow Parameters ◽  
Different Types ◽  
Physical Quantities

The effect of different types of nanoparticles on the heat transfer from a continuously moving stretching surface in a concurrent, parallel free stream has been studied. The stretching surface is assumed to have power-law velocity and temperature. The governing equations are converted into a dimensionless system of equations using nonsimilarity variables. Resulting equations are solved numerically for various values of flow parameters. The effect of physical quantities on the temperature profiles is discussed in detail.

On the sensitivity of heat transfer in the stagnation-point boundary layer to free-stream vorticity

1963 ◽  
Vol 16 (4) ◽  
pp. 497-520 ◽  
Author(s):  
S. P. Sutera ◽  
P. F. Maeder ◽  
J. Kestin
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Prandtl Number ◽  
Stagnation Point ◽  
Thermal Boundary Layer ◽  
Free Stream ◽  
Stokes Equations ◽  
Point Boundary ◽  
Oncoming Flow ◽  
Flat Plates

Experiments have given evidence of strong sensitivity of the stagnation-point heat transfer on cylinders to small changes in the intensity of free-stream turbulence. A similar effect on local heat-transfer rates to flat plates has been measured, but only when a favourable pressure gradient is present. In this work it is theorized that vorticity amplification by stretching is a possible, and perhaps the dominant, underlying mechanism responsible for this sensitivity. A mathematical model is presented for a steady, basically plane stagnation flow into which is steadily transported disturbed unidirectional vorticity having the only orientation susceptible to stretching. The resulting velocity and temperature fields in the stagnation-point boundary layer are analysed assuming the fluid to be incompressible and to have constant properties. By means of iterative procedures and electronic analogue computation an approximate solution to the full Navier-Stokes equations is achieved which indicates that amplification by stretching of vorticity of sufficiently large scale can occur. Such vorticity, present in the oncoming flow with a small intensity, can appear near the boundary layer with an amplified intensity and induce substantial three-dimensional effects therein. It is found that the thermal boundary layer is much more sensitive to the induced effects than the velocity boundary layer. Computations indicate that a certain amount of distributed vorticity in the oncoming flow causes the shear stress at the wall to increase by 5%, while the heat transfer there is augmented by 26% in a fluid with a Prandtl number of 0.74. Preliminary computations reveal that the sensitivity of the thermal boundary layer increases with Prandtl number.

Experimental Investigation of Turbine Leakage Flows on the 3D Flow Field and End Wall Heat Transfer

2006 ◽  
Author(s):  
Hans-Ju¨rgen Rehder ◽  
Axel Dannhauer
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Secondary Flow ◽  
Mass Flow ◽  
Flow Behavior ◽  
Leakage Flow ◽  
Wall Heat Transfer ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
End Wall

Within a European research project the tip end wall region of LP turbine guide vanes with leakage ejection was investigated at DLR in Go¨ttingen. For this purpose a new cascade wind tunnel with three large profiles in the test section and a contoured end wall was designed and built up, representing 50% height of a real low pressure turbine (LPT) stator and simulating the casing flow field of shrouded vanes. The effect of tip leakage flow was simulated by blowing air through a small leakage gap in the end wall just upstream of the vane leading edges. Engine relevant turbulence intensities were adjusted by an active turbulence generator mounted in the test section inlet plane. The experiments were performed with tangential and perpendicular leakage ejection and varying leakage mass flow rates up to 2%. Aerodynamic and thermodynamic measurement techniques were employed. Pressure distribution measurements provided information about the end wall and vane surface pressure field and its variation with leakage flow. Additionally streamline pattern (local shear stress directions) on the walls were detected by oil flow visualization. Downstream traverses with 5-hole pyramid type probes allow a survey of the secondary flow behavior in the cascade exit plane. The flow field in the near end wall area downstream of the leakage gap and around the vane leading edges was investigated using a 2D Particle Image Velocimetry (PIV) system. In order to determine end wall heat transfer distributions, the wall temperatures were measured by an infra-red camera system, while heat fluxes at the surfaces were generated with electric operating heating foils. It turned out from the experiments that distinct changes in the secondary flow behavior and end wall heat transfer mainly occur when the leakage mass flow rate is increased from 1% to 2%. Leakage ejection perpendicular to the main flow direction amplifies the secondary flow, in particular the horse-shoe vortex, whereas tangential leakage ejection causes a significant reduction of this vortex system. For high leakage mass flow rates the boundary layer flow at the end wall is strongly affected and seems to be highly turbulent, resulting in entirely different heat transfer distributions.

Evaluation of Wall Heat Transfer in Blade Trailing-Edge Cooling Passage

2013 ◽  
Vol 284-287 ◽  
pp. 738-742 ◽  
Author(s):  
Yu Feng Yao ◽  
Marwan Effendy ◽  
Jun Yao
Keyword(s):  
Heat Transfer ◽  
Transfer Model ◽  
Internal Cooling ◽  
Wall Heat Transfer ◽  
Trailing Edge ◽  
Pin Fin ◽  
Pin Fins ◽  
Cooling Passage ◽  
End Wall ◽  
Good Agreement

Model configurations of turbine blade trailing-edge internal cooling passage with staggered elliptic pin-fins in streamwise and spanwise are adopted for numerical investigation using computational fluid dynamics (CFD). Grid refinement study is performed at first to identify a baseline mesh, followed by validation study of passage total pressure loss, which gives 2% and 4% discrepancies respectively for two chosen configurations in comparison with experimental measurements. Further investigations are focused on evaluation of wall heat transfer coefficient (HTC) of both pin-fin and end walls, and it is found that CFD predicted pin-fin wall HTC are generally in good agreement with test data for the streamwise staggered elliptic pin-fins, but not the spanwise staggered elliptic pin-fins in which some discrepancies occur. CFD predicted end wall HTC have shown reasonable good agreement for the first three rows, but discrepancies seen in downstream rows are around a factor of 2-3. A ratio of averaged pin-fin and end walls HTC is estimated 1.3-1.5, close to that from a circular pin-fin configuration that has 1.8-2.1. Further study should focus on improving end wall HTC predictions, probably through a conjugate heat transfer model.

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