Temperature Measurements in High-Velocity Air Streams

1945 ◽  
Vol 12 (1) ◽  
pp. A25-A32
Author(s):  
H. C. Hottel ◽  
A. Kalitinsky
Keyword(s):  
Axial Flow ◽  
Extensive Study ◽  
Recovery Factor ◽  
Scale Model ◽  
Kinetic Temperature ◽  
Flat Plates ◽  
Air Velocity ◽  
Theoretical Predictions ◽  
Air Streams ◽  
Thermocouple Junction

Abstract When a stream of air is partially stopped by an inserted temperature probe, the temperature increase due to the conversion of kinetic energy affects the reading of the probe. The fraction of the total kinetic temperature rise which is registered by the probe, i.e., the so-called “recovery factor” of the probe, is a function of a number of variables. Tests dealing with the effect of probe shape and air velocity on this recovery factor, and with the influence of radiation on the accuracy of the measurements, are reported in this paper. Bare-wire probes gave recovery factors of approximately 0.65 in transverse flow and, in axial flow, approached 0.87 as the air velocity increased (in good agreement with theoretical predictions for flow over flat plates). With a spherical enlargement at the thermocouple junction, recovery approached 0.75. Recovery of twisted-wire couples varied from 0.72 to 0.83. A reduced-scale model of the Franz probe was found unsatisfactory after extensive study. Two simpler probes were developed, having high recovery (above 0.98 as velocity approaches sonic) and satisfactory insensitivity to yaw and radiation errors.

Validating Numerical CFD Simulations With Experimental Data for Turbulence Phenomena in Axial Flow Gas Turbine Diffusers

2009 ◽  
Author(s):  
Farrokh Zarifi-Rad ◽  
Hamid Vajihollahi ◽  
James O’Brien
Keyword(s):  
Experimental Data ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Axial Flow ◽  
Experimental Results ◽  
Scale Model ◽  
Data Set ◽  
Pressure Profiles ◽  
Scale Models ◽  
Inlet Conditions

Scale models give engineers an excellent understanding of the aerodynamic behavior behind their design; nevertheless, scale models are time consuming and expensive. Therefore computer simulations such as Computational Fluid Dynamics (CFD) are an excellent alternative to scale models. One must ask the question, how close are the CFD results to the actual fluid behavior of the scale model? In order to answer this question the engineering team investigated the performance of a large industrial Gas Turbine (GT) exhaust diffuser scale model with performance predicted by commercially available CFD software. The experimental results were obtained from a 1:12 scale model of a GT exhaust diffuser with a fixed row of blades to simulate the swirl generated by the last row of turbine blades five blade configurations. This work is to validate the effect of the turbulent inlet conditions on an axial diffuser, both on the experimental front and on the numerical analysis approach. The object of this work is to bring forward a better understanding of velocity and static pressure profiles along the gas turbine diffusers and to provide an accurate experimental data set to validate the CFD prediction. For the CFD aspect, ANSYS CFX software was chosen as the solver. Two different types of mesh (hexagonal and tetrahedral) will be compared to the experimental results. It is understood that hexagonal (HEX) meshes are more time consuming and more computationally demanding, they are less prone to mesh sensitivity and have the tendancy to converge at a faster rate than the tetrahedral (TET) mesh. It was found that the HEX mesh was able to generate more consistent results and had less error than TET mesh.

The Effect of Air Velocity on Thermal Comfort

1983 ◽  
Vol 27 (8) ◽  
pp. 733-737 ◽  
Author(s):  
Stephan Konz ◽  
Sudad Al-Wahab ◽  
Helen Gough
Keyword(s):  
Environmental Temperature ◽  
Axial Flow ◽  
Air Velocity ◽  
Mean Velocity ◽  
Air Stream ◽  
The Face ◽  
The Individual ◽  
The Right ◽  
C 78 ◽  
Straight Ahead

Experiment 1 investigated oscillating vs fixed fans. Eight males were exposed to seven conditions in each of three temperatures (25.6, 27.8, and 30 C (78, 82, 86 F); all at 50% rh). The seven conditions were: still air, velocity of 0.4, 0.8 and 1.2 m/s from a fixed fan, and mean velocity of 0.3, 0.5, and 0.7 m/s from an oscillating fan. For equal comfort, for every increase of mean air velocity of 0.1 m/s (between 0.4 and 1.2 m/s), environmental temperature can be increased by .27 C for the oscillating fan and by 0.40 C for the fixed fan. At the same mean velocity, oscillating fans are voted more comfortable than fixed fans. Experiment 2 investigated the effect of a small directional axial-flow desk fan on comfort at 26.1 C (79 F). The 16 females tested fan off vs a 1.5 m/s flow on all six combinations of: torso vs face impact of air stream, and impact from straight ahead, 30° to the right, and 60° to the right. Angle was not significant. The use of the fan was equivalent to a decrease of air temperature of 0.63 C (i.e., 0.1 m/s = 0.042 C). Thus the personal desk fan can be used as a “fine tuner” in an acceptable environment. Those wearing glasses preferred air on the face, those wearing contacts preferred the torso; those wearing neither were divided. Thus fan placement should be left to the individual.

Large-Reynolds-number asymptotic analysis of viscous centre modes in vortices

2007 ◽  
Vol 585 ◽  
pp. 153-180 ◽  
Author(s):  
STÉPHANE LE DIZÈS ◽  
DAVID FABRE
Keyword(s):  
Reynolds Number ◽  
Spatial Structure ◽  
Asymptotic Analysis ◽  
Layer Structure ◽  
Axial Flow ◽  
Multiple Scale ◽  
Large Reynolds Number ◽  
Leading Order ◽  
Vortex Model ◽  
Theoretical Predictions

This paper presents a large-Reynolds-number asymptotic analysis of viscous centre modes on an arbitrary axisymmetrical vortex with an axial jet. For any azimuthal wavenumber m and axial wavenumber k, the frequency of these modes is given at leading order by ω0 = mΩ0 + kW0 where Ω0 and W0 are the angular and axial velocities of the vortex at its centre. These modes possess a multi-layer structure localized in an O(Re−1/6) neighbourhood of the vortex. By a multiple-scale matching analysis, we demonstrate the existence of three different families of viscous centre modes whose frequency expands as ω(n) ∼ ω0 + Re−1/3ω1 + Re−1/2ω(n)2. One of these families is shown to have unstable eigenmodes when H0 = 2Ω0k(2kΩ0 − mW2) < 0 where W2 is the second radial derivative of the axial flow in the centre. The growth rate of these modes is given at leading order by σ ∼ (3/2)(H0/4)1/3Re−1/3. Our results prove that any vortex with a jet (or jet with swirl) such that Ω0W2 ≠ 0 is unstable if the Reynolds number is sufficiently large. The spatial structure of the viscous centre modes is obtained and simple approximations which capture the main feature of the eigenmodes are also provided.The theoretical predictions are compared with numerical results for the q-vortex model (or Batchelor vortex) for Re ≥ 105. For all modes, a good agreement is demonstrated for both the frequency and the spatial structure.

Experiments on Dispersive Pulse Propagation in Laminated Composites and Comparison With Theory

1969 ◽  
Vol 36 (3) ◽  
pp. 485-490 ◽  
Author(s):  
J. S. Whittier ◽  
J. C. Peck
Keyword(s):  
Pulse Propagation ◽  
Laminated Composites ◽  
Rear Surface ◽  
Step Function ◽  
Surface Velocity ◽  
Flat Plates ◽  
Theoretical Predictions ◽  
Long Time ◽  
Capacitance Gauge ◽  
High Degree

Transient stress-wave experiments on laminated composites are described, and the results are compared with theoretical predictions. The composites are laminated from alternating layers of high and low-modulus material, which cause a high degree of geometric dispersion of waves propagating in the composite. Experiments were conducted in which waves propagated parallel to the laminations. Flat plates were subjected on one face to a uniform pressure with step-function time dependence induced by a gas-dynamic shock wave. Under this loading, the central portion of the specimen initially responds as if it were laterally unbounded. The average velocity over a 3/8-in-dia area of the backface of the plate was measured with a capacitance gauge. The results are in good agreement with theoretical predictions made with a long-time asymptotic approximation called the head-of-the-pulse approximation. The theory isolates the dominant character of the response and predicts timing and amplitude of oscillations in normalized rear surface velocity within a few percent.

Design, Evaluation and Performance Analysis of Staged Low Emission Combustors

2012 ◽  
Author(s):  
Gajanana B. Hegde ◽  
Bhupendra Khandelwal ◽  
Vishal Sethi ◽  
Riti Singh
Keyword(s):  
Combustion Chamber ◽  
Gas Turbine ◽  
Design Methodology ◽  
Reverse Flow ◽  
Axial Flow ◽  
Design Procedure ◽  
Extensive Study ◽  
Theoretical Design ◽  
Low Emission ◽  
And Performance

The most uncertain and challenging part in the design of a gas turbine has long been the combustion chamber. There has been large number of experimentations in industries and universities alike to better understand the dynamic and complex processes that occur inside a combustion chamber. This study concentrates on gas turbine combustors as a whole, and formulates a theoretical design procedure for staged combustors in particular. Not much of literatures available currently in public domain provide intensive study on designing staged combustors. The work covers an extensive study of design methods applied in conventional combustor designs, which includes the reverse flow combustor and the axial flow annular combustors. The knowledge acquired from this study is then applied to develop a theoretical design methodology for double staged (radial and axial) low emission annular combustors. Additionally a model combustor is designed for each type; radial and axial staging using the developed methodology. A prediction of the performance for the model combustors is executed. The main conclusion is that the dimensions of model combustors obtained from the developed design methodology are within the feasibility limits. The comparison between the radially staged and the axially staged combustor has yielded the predicted results such as lower NOx prediction for the latter and shorter combustor length for the former. The NOx emission result of the new combustor models are found to be in the range of 50–60ppm. However the predicted NOx results are only very crude and need further detailed study.

Long-to-Short Length Scale Transition: A Stall Inception Phenomenon in an Axial Compressor With Inlet Distortion

2005 ◽  
Author(s):  
Feng Lin ◽  
Meilin Li ◽  
Jingyi Chen
Keyword(s):  
Axial Compressor ◽  
Axial Flow ◽  
Short Length ◽  
Scale Model ◽  
Future Research ◽  
Length Scale ◽  
Stall Inception ◽  
Inlet Distortion ◽  
Scale Transition ◽  
Asymmetric Flows

A theoretical and experimental study of stall inception processes in a three-stage low-speed axial flow compressor with inlet distortion is presented in this paper. Since inlet distortion provides asymmetric flows imposing onto the compressor, the main goal of this research is to unveil the mechanism of how such flows initiate long and/or short length-scale disturbances and how the compression system reacts to those disturbances. It is found that the initial disturbances are always triggered by the distorted flows, yet the growth of such disturbances depends on system dynamics. While in many cases the stall precursors were the short length scale spikes, there were some cases where the compressor instability was triggered after the disturbances going through a long-to-short length scale transition. A Moore-Greitzer based (system scale) model was proposed to qualitatively explain this phenomenon. It was found that when the compressor operated in a region where the nonlinearity of the characteristics dominated, long length-scale disturbances induced by the inlet distortion would evolve into short length-scale disturbances before they disappeared or triggered stall. However, the model was not able to predict the fact that many disturbances that were triggered by the distorted sector(s) were completely damped out in the undistorted sector(s). It is thus suggested that in future research of compressor instability, one should consider the flows in blade passage scale, the dynamics in system scale and their interaction simultaneously.

scholarly journals The Core of a Quiescent Cloud, L183

1980 ◽  
Vol 87 ◽  
pp. 91-92
Author(s):  
C. M. Walmsley ◽  
H. Ungerechts ◽  
G. Winnewisser
Keyword(s):  
Spatial Resolution ◽  
Velocity Structure ◽  
Dust Cloud ◽  
Extensive Study ◽  
Core Region ◽  
Kinetic Temperature ◽  
Measured Velocity ◽  
Interstellar Clouds ◽  
The Core ◽  
The North

Simultaneous observation of the J,K=1,1 and 2,2 inversion transitions of ammonia (NH3) with high spatial resolution (≲1 arc min) offers a powerful method of probing the core region of interstellar clouds for evidence of molecular clumping and of prevailing physical conditions which could lead to star formation. We have therefore used the Effelsberg 100-m radiotelescope to make an extensive study of the central region of the nearby dark dust cloud L183 (also known as L134N) in the NH3 (1,1) transition; the spatial resolution was 40 arcsec. The core region as mapped in the NH3 (1,1) transition with a velocity resolution of 0.08 km s-1 consists of two elongated condensations separated by about 2 arcmin in north-south direction (see Fig. 1). The central part of the NH3 cloud has an approximate dimension of 6′ (N-S) by 2′ (E-W) corresponding to a linear extent of 0.17 × 0.06 pc at an assumed distance of 100 pc. The measured velocity structure of the NH3 cloud seems to reflect the double peaked nature of the cloud in that it increases from 2.30 km s-1 in the south to about 2.5 km s-1 at the northern end of the southern NH3 peak, and then decreases again to 2.3 km s-1 towards the north. The intrinsic linewidths of NH3 (corrected for hyperfine blending) do not vary significantly with position and are between 0.2 and 0.3 km s-1. The two ammonia peaks are part of a central molecular ridge from which we have observed NH3 (2,2) emission at 9 positions (see Fig. 1). The rotation temperature T21 as determined from the optical depths of the (1,1) and (2,2) transitions is ∼9K for all positions, and hence the kinetic temperature Tkin seems close to this value as well, i.e. ∼10K throughout the central part of L183. A more detailed account is being publsihed elsewhere (Ungerechts, Walmsley and Winnewisser).

Application of Computional Fluid Dynamics for Study of the Occurrence of Aerodynamic Effect for its Application in the Construction of Electric Race Car

2015 ◽  
Vol 809-810 ◽  
pp. 956-961
Author(s):  
Łukasz Grabowski ◽  
Andrzej Baier ◽  
Andrzej Buchacz ◽  
Michał Majzner ◽  
Michał Sobek
Keyword(s):  
Fluid Dynamics ◽  
Aerodynamic Drag ◽  
The Body ◽  
Air Velocity ◽  
Race Car ◽  
Drag Forces ◽  
Graphic Analysis ◽  
Aerodynamic Effect ◽  
Air Streams ◽  
The Ideal

In this article the issues related to Computional Fluid Dynamics of the occurrence of innovative aerodynamic effect were presented. Analysis were performed to determine the occurrence of Kammback aerodynamic effect and its application in a shape of a body of the real racing car in order to minimize drag forces of the vehicle. For the analysis, ideal aerodynamic shapes were modeled, subsequently they were subjected to modifications which were used to determine the occurrence of effect. The basic modeled shape was the raindrop shape solid, which is generally regarded as the ideal shape in terms of aerodynamics. The result of analysis was compared with the drag values known from the literature. Afterwards changes in the shape of the base solid were made to verify and determine the optimum Kammback shape, selected from a set of possible solutions, in which the geometrical changes has the lowest difference of values of drag force and drag coefficientCx(Cd)in comparison to the basic raindrop shape. Results of the study were subjected to graphic analysis, especially the distribution of air pressure on the surface of a solid and in a virtual wind tunnel, distribution of the air velocity and the course of air streams around the shape. The results were used to design the body of electric race car. The main objective was to minimize the aerodynamic drag of the vehicle.

Towards Energy Efficient Air-Conditioned Space: Fluid Flow and Thermal Behavior

2013 ◽  
Author(s):  
Essam E. Khalil ◽  
Ahmed A. Medhat
Keyword(s):  
Numerical Modeling ◽  
Full Scale ◽  
Measuring Instruments ◽  
Air Velocity ◽  
Air Supply ◽  
Seminar Room ◽  
Computer Based ◽  
Prandtl Numbers ◽  
Forced Air ◽  
Air Streams

This paper focuses on both experimental investigation and numerical modeling of full-scale modelled air-conditioned multipurpose hall fully operable. Two methodologies were used, firstly full scale experimental setup was incorporated to map the hall making use of a well-developed fully automated wireless mobile test rig remotely controlled by pre-programmed computer and using high precision state-of-the-art measuring instruments. While the Second methodology was a numerical modeling using a well developed [CFD] 3DHVAC and FLUENT computer simulation programs. Physical and Numerical investigations enable the analyses of the influence of Reynolds, Archimedes and Prandtl numbers for the air as well as the effects of shape, location, inlet air velocity of supply outlet on the flowing air parameters. These parameters include throw, drop, air induction, room local velocities, humidity ratio and temperatures distributions. The forced air supply of cooled air streams out of high wall mounted, downward inclined jets is investigated with mechanically extracted air from the top of the split air-conditioning units. On the other hand an experimental traversing mechanism, computer-based and operated by PLC was developed and used to map the velocity and temperature contours. The room was typically used as the chairman office, meeting room and seminar room. One of the main conclusions is that good agreement between both of full-scale physical modeling and numerical modeling were reported. While the reported comparisons concluded that qualitative agreements were shown, some discrepancies were also observed in the thermal parameters for comfort conditions required by different occupants.

scholarly journals Optimization Scheme for Construction Ventilation in Large-Scale Underground Oil Storage Caverns

2018 ◽  
Vol 8 (10) ◽  
pp. 1952 ◽  
Author(s):  
Heng Zhang ◽  
Jianchun Sun ◽  
Fang Lin ◽  
Shougen Chen ◽  
Jiasong Yang
Keyword(s):  
Turbulence Model ◽  
Large Scale ◽  
Axial Flow ◽  
Navier Stokes ◽  
Ventilation Mode ◽  
Air Velocity ◽  
Gas Dispersion ◽  
Air Inlet ◽  
Oil Storage ◽  
Heavy Trucks

The ventilation effect has a direct influence on the efficiency and security of the construction of an underground cavern group. Traditional forced ventilation schemes may be ineffective and result in resource wastage. Based on the construction ventilation of the Jinzhou underground oil storage project, an axial flow gallery ventilation mode using shafts as the fresh air inlet was proposed. A 3D steady RANS (Reynolds Averaged Navier-Stokes) approach with the RNG (Renormalization-group) k-ε turbulence model was used to study airflow behavior and hazardous gas dispersion when different ventilation schemes were employed. Field test values of the air velocity and CO concentration in the main cavern and construction roadway were also adopted to validate the RNG k-ε turbulence model. The results showed that the axial flow gallery ventilation mode can ensure that the direction of air flow is the same as that of heavy trucks, fresh air is always near the excavation face, and the disturbance of the construction process is greatly reduced. The scheme is suitable for large-scale caverns with a ventilation distance less than 2 km, and an intermediate construction shaft is not needed. When the ventilation distance exceeds 2 km, it is possible to use jet fans to assist the axial flow gallery ventilation mode or to completely adopt jet-flow gallery ventilation.

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