scholarly journals The Influence of Different Unsteady Incident Flow Environments on Drag Measurements in an Open Jet Wind Tunnel

Fluids ◽  
2020 ◽  
Vol 5 (4) ◽  
pp. 178
Author(s):  
Xiao Fei ◽  
Christoph Jessing ◽  
Timo Kuthada ◽  
Jochen Wiedemann ◽  
Andreas Wagner
Keyword(s):  
Wind Tunnel ◽  
Unsteady Flow ◽  
Pressure Gradient ◽  
Test Section ◽  
Static Pressure ◽  
Signal Amplitude ◽  
Correction Method ◽  
Scale Model ◽  
Signal Frequency ◽  
On The Road

Aerodynamic development for road vehicles is usually carried out in a uniform steady-state flow environment, either in the wind tunnel or in Computational Fluid Dynamics (CFD) simulations. However, out on the road, the vehicle experiences unsteady flow with fluctuating angles of incidence β, caused by natural wind, roadside obstacles, or traffic. In order to simulate such flow fields, the Forschungsinstitut für Kraftfahrwesen und Fahrzeugmotoren Stuttgart (FKFS) swing® system installed in the quarter scale model wind tunnel can create a variety of time-resolved signals with variable β. The static pressure gradient in the empty test section, as well as cD values of the Society of Automotive Engineers (SAE) body and the DrivAer model, have been measured under these transient conditions. The cD measurements have been corrected using the Two-Measurement Correction method in order to decouple the influence of the unsteady flow from that of the static pressure gradient. The investigation has determined that the static pressure gradient in the empty test section varies greatly with different excitation signals. Thus, it is imperative to apply a cD correction for unsteady wind tunnel measurements. The corrected cD values show that a higher signal amplitude, as in, signals with large β, lead to higher drag forces. The influence of the signal frequency on drag values varies depending on the vehicle geometry and needs to be investigated further in the future.

The Effect of Pulsed Injection on Supersonic Shear Layer Mixing in a Scramjet Combustor

2018 ◽  
Vol 35 (3) ◽  
pp. 203-215
Author(s):  
Leslie Smith ◽  
Saeed Farokhi
Keyword(s):  
Wind Tunnel ◽  
Shear Layer ◽  
Test Section ◽  
Pulse Width ◽  
Static Pressure ◽  
Experimental Studies ◽  
Lower Wall ◽  
Supersonic Wind Tunnel ◽  
Scramjet Combustor ◽  
Secondary Injection

Abstract A novel injector has been designed and cold flow injection tests were performed in a modified supersonic wind tunnel. To complement these experimental studies three dimensional STAR-CCM+CFD simulations were developed. The pulse width may be varied, with options of injecting gas for 33 %, 50 % and 66 % of the injection period. The scramjet combustor environment is simulated in a supersonic wind tunnel through a backward facing step for secondary injection purposes and a 157.5 cm (62-inch) long test section. The gas in secondary injection is carbon dioxide and the primary flow is air. The simulations show a coupled interaction between the forcing from injection and the shear layer. Steady state static pressure measurements on the lower wall of the wind tunnel test section agree well with the simulated static pressure along the lower wall. The pulse width strongly impacts shear layer reattachment on the lower wall and varies between 2.4 and 4.3 step heights. Reduction in duty cycle from 66 % to 33 % at 1 kHz caused ~30 % reduction in the shear layer reattachments distance, which points to large scale mixing enhancement.

Experimental investigation of the effect of nozzle shape and test section perforation on the stationary and non-stationary characteristics of flow field in the large transonic TsAGI T-128 Wind tunnel

2005 ◽  
Vol 109 (1092) ◽  
pp. 75-82 ◽  
Author(s):  
V. I. Biryukov ◽  
S. A. Glazkov ◽  
A. R. Gorbushin ◽  
A. I. Ivanov ◽  
A. V. Semenov
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Test Section ◽  
Static Pressure ◽  
Pressure Fluctuations ◽  
Flow Characteristics ◽  
Experimental Investigations ◽  
Drive Power ◽  
Static Pressure Distribution ◽  
Nozzle Shape

Abstract The results are presented for a cycle of experimental investigations of flow field characteristics (static pressure distribution, static pressure fluctuations, upwash, boundary-layer parameters) in the perforated test section of the transonic TsAGI T-128 Wind Tunnel. The investigations concern the effect of nozzle shape, wall open-area ratio, Mach and Reynolds numbers on the above-outlined flow characteristics. During the tests, the main Wind-tunnel drive power is measured. Optimal parameters of the nozzle shape and test section perforation are obtained to minimise acoustic perturbations in the test section and their non-uniformity in frequency, static pressure field non-uniformity, nozzle and test section drag and, accordingly, required main Wind-tunnel drive power.

scholarly journals Reynolds number and wind tunnel wall effects on the flow field around a generic UHBR engine high-lift configuration

2020 ◽  
Vol 11 (4) ◽  
pp. 1009-1023 ◽  
Author(s):  
Junaid Ullah ◽  
Aleš Prachař ◽  
Miroslav Šmíd ◽  
Avraham Seifert ◽  
Vitaly Soudakov ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Flow Field ◽  
Test Section ◽  
Large Scale ◽  
Scale Model ◽  
Small Scale ◽  
Wall Effects ◽  
Tunnel Wall ◽  
High Lift

Abstract RANS simulations of a generic ultra-high bypass ratio engine high-lift configuration were conducted in three different environments. The purpose of this study is to assess small scale tests in an atmospheric closed test section wind tunnel regarding transferability to large scale tests in an open-jet wind tunnel. Special emphasis was placed on the flow field in the separation prone region downstream from the extended slat cut-out. Validation with wind tunnel test data shows an adequate agreement with CFD results. The cross-comparison of the three sets of simulations allowed to identify the effects of the Reynolds number and the wind tunnel walls on the flow field separately. The simulations reveal significant blockage effects and corner flow separation induced by the test section walls. By comparison, the Reynolds number effects are negligible. A decrease of the incidence angle for the small scale model allows to successfully reproduce the flow field of the large scale model despite severe wind tunnel wall effects.

Uncertainty Analysis in a Scale Model Wind Turbine Array Boundary Layer

2017 ◽  
Author(s):  
John J. Turner ◽  
Martin Wosnik
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Turbulent Boundary Layer ◽  
Uncertainty Analysis ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Test Section ◽  
Scale Model ◽  
Acquisition Time ◽  
Flow Physics

Uncertainty estimates from an experimental investigation of a scale model wind turbine array, conducted with (on the order of) 100 0.25 meter diameter model wind turbines in a high Reynolds number turbulent boundary layer facility, are reported. An expanded uncertainty analysis using the Taylor series method is executed to predict uncertainty for the system of interest in the mean flow. A workable comprise has been found for data acquisition time mitigating changing initial conditions due to exposure to atmospheric conditions and temperature drift. The study was conducted in the University of New Hampshire (UNH) Flow Physics Facility (FPF) which is the worlds largest flow physics quality turbulent boundary layer wind tunnel, with test section dimensions of 6 m wide, 2.7 m tall and 72 m long. Naturally grown turbulent boundary layers with scale ratios of energy-containing to dissipative scales (Karman number) of up to 20,000 can be generated, and are on the order of 1 m thick near the downstream end of the test section. The long fetch of the facility offers unique opportunities to study the downstream evolution of the wake of single wind turbines, and the flow through model wind turbine arrays over long distances. Far downstream within a wind farm it is proposed that the farm reaches a fully developed state where the flow field becomes similar from one row to the next. The goal of this work is to accurately determine the uncertainty associated with open to atmosphere wind tunnel data for use in validation of numerical models regarding the fully developed wind turbine array boundary layer.

scholarly journals The forces on a body placed in a curved or converging stream of fluid

1928 ◽  
Vol 120 (785) ◽  
pp. 260-283 ◽  
Keyword(s):  
Wind Tunnel ◽  
Pressure Gradient ◽  
Static Pressure ◽  
Practical Interest ◽  
Point Of View ◽  
The Body ◽  
Primary Object ◽  
Body Experiences ◽  
Measured Resistance ◽  
Hydrodynamical Theory

The force which a body experiences when placed in a converging stream of fluid has a certain practical interest in aeronautics because the flow in the centre of a parallel-walled wind tunnel is of this type. The convergence is due to the retardation of a layer of air close to the walls. This retarded layer increases in thickness as the air passes down the channel, thus causing a corresponding increase in the velocity in the central part of the channel. This increase in velocity is associated with a decrease in pressure in accordance with Bernouilli’s equation, the pressure in a Pitot tube being very nearly constant down the channel at all points outside the retarded layer. In measuring the resistance of models of airships it has been customary to correct the observed readings by subtracting what is called the “horizontal buoyancy,” i. e. , the force which would act on the body if the air were a stationary fluid in which the existing pressure gradient down the channel was maintained by some external force like gravity. Expressed mathematically, if dp / dx is the pressure gradient, i. e. , the gradient of static pressure in the channel, and V the volume of the body, the “horizontal buoyancy” is — V dp / dx . This correction to the measured resistance of an airship model is believed to be approximately correct from the point of view of wind tunnel practice, and the primary object of the present work was to find out how far it is justified from the point of view of hydrodynamical theory.

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