A New Method of Modeling Underexpanded Exhaust Plumes for Wind Tunnel Aerodynamic Testing

1989 ◽  
Vol 111 (4) ◽  
pp. 748-754
Author(s):  
V. Salemann ◽  
J. M. Williams
Keyword(s):  
Wind Tunnel ◽  
Free Stream ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Area Ratio ◽  
Full Scale ◽  
New Method ◽  
Thrust Coefficient ◽  
Model Scale ◽  
Exhaust Plumes

A new method for modeling hot underexpanded exhaust plumes with cold model scale plumes in aerodynamic wind tunnel testing has been developed. The method is applicable to aeropropulsion testing where significant interaction between the exhaust and the free stream and aftbody may be present. The technique scales the model and nozzle external geometry, including the nozzle exit area, matches the model jet to free-stream dynamic pressure ratio to full-scale jet to free-stream dynamic pressure ratio, and matches the model thrust coefficient to full-scale thrust coefficient. The technique does not require scaling of the internal nozzle geometry. A generalized method of characteristic computer code was used to predict the plume shapes of a hot (γ = 1.2) half-scale nozzle of area ratio 3.2 and of a cold (γ = 1.4) model scale nozzle of area ratio 1.3, whose pressure ratio and area ratio were selected to satisfy the above criteria and other testing requirements. The plume shapes showed good agreement. Code validity was checked by comparing code results for cold air exhausting into a quiescent atmosphere to pilot surveys and shadowgraphs of model nozzle plumes taken in a static facility.

Model-Scale and Full-Scale CFD Calculations for Current Loads on Semi-Submersible

2011 ◽  
Author(s):  
Arjen Koop ◽  
Alexei Bereznitski
Keyword(s):  
Wind Tunnel ◽  
Scale Effects ◽  
Full Scale ◽  
Grid Resolution ◽  
Wind Tunnel Experiments ◽  
Force Coefficients ◽  
Model Scale ◽  
Coarse Grids

In this paper results of CFD calculations with the MARIN in-house code ReFRESCO are presented for the JBF-14000 Semi-Submersible designed by Huisman Equipment BV. The objective of the CFD calculations is to investigate the applicability, the costs and the accuracy of CFD to obtain the current coefficients of a semi-submersible for all headings. Furthermore, full scale CFD calculations are carried out to investigate possible scale effects on the current coefficients. An extensive verification study has been carried for the model-scale current loads on a semi-submersible using 10 different grids of different grid type for 3 different headings, i.e. 180, 150 and 90 degrees. These headings represent the main different flow regions around the semi-submersible. The CFD results are compared with the results from wind tunnel experiments and tests in the Offshore Basin for a range of current headings. The results for the force coefficients are not very dependent on grid resolution and grid type. The largest differences found are less than 10% and these are obtained for CX results for 180 degrees. For the results obtained on the same grid type the results change less than 4% when the grid is refined. These verification results give good confidence in the CFD results. For the angles with larger forces, i.e. the range [180:130] for CX and the range [150:90] for CY the CFD results are within 12% or better from the experiments. Full-scale force coefficients are calculated using 5 subsequently refined grids for three different headings, i.e. 180, 150 and 90 degrees. Scale effects should only be determined when the effect of grid refining is investigated. The trend of the force coefficients when refining the grid, can be different for model-scale and full-scale. The use of coarse grids can lead to misleading conclusions. On average the full-scale values are approximately 15–20% lower than for model-scale. However, larger differences for a number of angles do exist.

Turbulent jet in crossflow analysis with LES approach

2016 ◽  
Vol 88 (6) ◽  
pp. 717-728 ◽  
Author(s):  
Mojtaba Tahani ◽  
Mohammad Hojaji ◽  
Seyed Vahid Mahmoodi Jezeh
Keyword(s):  
Mach Number ◽  
Free Stream ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Content Type ◽  
Order Polynomial ◽  
Pressure Area ◽  
Barrel Shock ◽  
Free Stream Mach Number ◽  
Shock Zone

Purpose This study aims to investigate effects of sonic jet injection into supersonic cross-flow (JISC) numerically in different dynamic pressure ratio values and free stream Mach numbers. Design/methodology/approach Large Eddy simulation (LES) with dynamic Smagorinsky model is used as the turbulence approach. The numerical results are compared with the experimental data, and the comparison shows acceptable validation. Findings According to the results, the dynamic pressure ratio has critical effects on the zone related to barrel shock. Despite free stream Mach number, increasing dynamic pressure ratio leads to expansion of barrel shock zone. Consequently, expanded barrel shock zone would bring about more obstruction effect. In addition, the height of counter-rotating vortex pair increases, and the high-pressure area before jet and low-pressure area after jet will rise. The results show that the position of barrel shock is deviated by increasing free stream Mach number, and the Bow shock zone becomes stronger and close to barrel shock. Moreover, high pressure zone, which is located before the jet, decreases by high free stream Mach number. Practical implications In this study, LES with a dynamic Smagorinsky model is used as the turbulence approach. Effects of sonic JISC are investigated numerically in different dynamic pressure ratio values and free stream Mach numbers. Originality/value As summary, the following are the contribution of this paper in the field of JISC subjects: several case studies of jet condition have been performed. In all the cases, the flow at the nozzle exit is sonic, and the free stream static pressure is constant. To generate proper grid, a cut cell method is used for domain modelling. Boundary condition effect on the wall pressure distribution around the jet and velocity profiles, especially S shape profiles, is investigated. The results show that the relation between representing the location of Mach disk centre and at transonic regime is a function of second-order polynomial, whereas at supersonic regime, the relationship is modelled as a first-order polynomial. In addition, the numerical results are compared with the experimental data demonstrating acceptable validation.

Analysis of Propulsion and Lift Power Requirements for the Artic Surface Effect Vehicle

1972 ◽  
Author(s):  
J. H. Garrett ◽  
R. K. Muench
Keyword(s):  
Free Stream ◽  
Surface Effect ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Total Power ◽  
Specific Power ◽  
Vehicle Speed ◽  
System Parameters ◽  
Fuel Fraction

The power requirements of large surface effect vehicles are parametrically examined. The results are first derived in terms of total specific power as a function of the cushion to free stream dynamic pressure ratio and other propulsion and lift system parameters. The propulsion, lift and total power requirements are then examined as a function of vehicle speed, vehicle gross weight and daylight clearance. The fuel fraction-range and payload-range relationship for a given cushion pressure is also examined.

A New Method for Scaling Submarine Resistance Model Data

2017 ◽  
Author(s):  
Young T. Shen ◽  
Michael J. Hughes
Keyword(s):  
Frictional Resistance ◽  
Resistance Coefficient ◽  
Full Scale ◽  
The Body ◽  
New Method ◽  
Momentum Thickness ◽  
Residual Resistance ◽  
New Approach ◽  
Model Scale ◽  
Scale Resistance

A new method is presented for obtaining full-scale resistance predictions from model-scale submarine resistance tests. Traditionally, model-scale submarine resistance data is scaled using Froude’s Hypothesis, where the resistance is decomposed into frictional resistance and residual resistance. The frictional resistance is computed from a flat plate friction line formula at both model- and full-scale. The residual resistance coefficient is measured model-scale and is assumed to be independent of Reynolds number. Since the flow is assumed to be turbulent at fullscale, turbulence stimulators are placed at about 5% x/L to trip the flow in the model tests. The parasitic drag from the turbulence stimulators must be measured and subtracted from the model-scale resistance. In the new approach a momentum thickness simulator is used in place of a traditional turbulence stimulator. The purpose of the momentum thickness simulator is to achieve similarity for model-scale and full-scale normalized momentum thickness of the boundary layer at the stern of the vessel as momentum thickness is directly related to ship resistance. The size and location of the momentum thickness simulator is computed to assure the flow is turbulent downstream of the simulator and to produce similar momentum thickness on the body downstream of the simulator. With this approach the total resistance is scaled from model-scale to full-scale without decomposing the resistance into frictional resistance and residual resistance. The parasitic drag is not measured and subtracted, as the additional drag from the momentum simulator is computed to produce the correctly scaled momentum thickness. In the new approach the physics associated with resistance is more clearly expressed and improved accuracy of resistance predictions is expected.

Wind Tunnel Investigation of a Double Stacked Wagon in Free-Stream

2015 ◽  
Author(s):  
Chao Li ◽  
Michael Kost ◽  
David Burton ◽  
John Sheridan ◽  
Mark C. Thompson
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Pressure Distribution ◽  
Free Stream ◽  
Dynamic Pressure ◽  
Pressure Profile ◽  
Surface Flow ◽  
Measuring Systems ◽  
Side Pressure ◽  
Shedding Frequency

The surface flow structure and pressure distribution of a model representative of a 48ft, double-stacked container wagon of an intermodal freight train is characterized. The model used is 1: 14.6 in scale, and all experiments are conducted in Monash University’s 450kW closed loop wind tunnel. The model employs 474 pressure taps in total, and data is logged with two dynamic pressure-measuring systems. Flow visualizations are carried out on the top and side surfaces using fluorescent Kaolin china clay with kerosene as a carrier. Testing is performed under three different floor boundary-layer profiles in order to assess the sensitivity of the surface flow variation in the floor boundary-layer. It is shown that in a time-averaged sense, the shear-layer separating off the leading edges of the wagon roll up to form three recirculating bubbles on the top and side surfaces. The consequent surface pressure profile matches closely to that of a surface-mounted cube where top and side pressure recovery occurs. For the three boundary-layer profile tested, pressure distribution displays very minor changes. A Karman like left-right wake shedding is observed in the wake with a shedding frequency of St = 0.195.

Wind Tunnel to Full Scale Mapping of Winds and Loads for Launch-Vehicle Ground Wind Loads

2021 ◽  
Author(s):  
Thomas G. Ivanco ◽  
Donald F. Keller ◽  
Jennifer L. Pinkerton
Keyword(s):  
Wind Tunnel ◽  
Launch Vehicle ◽  
Full Scale ◽  
Wind Loads

Experimental research on the performance of the forward variable area bypass injector for variable cycle engines

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Binglong Zhang ◽  
He Liu ◽  
Jianhua Zhou ◽  
Hui Liu
Keyword(s):  
Pressure Ratio ◽  
Effective Means ◽  
Experimental System ◽  
Area Ratio ◽  
Back Pressure ◽  
Mode Transition ◽  
Bypass Valve ◽  
Injection Coefficient ◽  
Bypass Ratio ◽  
Specific Working

AbstractThe forward variable area bypass injector (FVABI) is a key component of double bypass variable cycle engine (VCE) to achieve mode transition and bypass ratio adjustment. In this paper, an experimental system for FVABI was constructed based on the analysis of relevant experimental theories, and then the experiments on FVABI were carried out for a specific working state in double bypass mode of VCE and for the comparison working states with different area ratios and different back pressure ratios. The results showed that the FVABI designed in this paper meets the requirements of VCE at this working state. The analysis of the influence of area ratio and back pressure ratio on the injection coefficient showed that the first bypass valve and back pressure were effective means to control the mass flow of FVABI.

Characterization of wind-induced pressure on membrane roofs based on full-scale wind tunnel testing

2021 ◽  
Vol 235 ◽  
pp. 112101
Author(s):  
Johnny Estephan ◽  
Changda Feng ◽  
Arindam Gan Chowdhury ◽  
Mauricio Chavez ◽  
Appupillai Baskaran ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Full Scale ◽  
Wind Tunnel Testing ◽  
Tunnel Testing

Roles of vanes in diffuser on stability of centrifugal compressor

2019 ◽  
Vol 233 (14) ◽  
pp. 5380-5392
Author(s):  
Wangzhi Zou ◽  
Xiao He ◽  
Wenchao Zhang ◽  
Zitian Niu ◽  
Xinqian Zheng
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Centrifugal Compressors ◽  
Compression System ◽  
The Stability ◽  
Rotating Instability

The stability considerations of centrifugal compressors become increasingly severe with the high pressure ratios, especially in aero-engines. Diffuser is the major subcomponent of centrifugal compressor, and its performance greatly influences the stability of compressor. This paper experimentally investigates the roles of vanes in diffuser on component instability and compression system instability. High pressure ratio centrifugal compressors with and without vanes in diffuser are tested and analyzed. Rig tests are carried out to obtain the compressor performance map. Dynamic pressure measurements and relevant Fourier analysis are performed to identify complex instability phenomena in the time domain and frequency domain, including rotating instability, stall, and surge. For component instability, vanes in diffuser are capable of suppressing the emergence of rotating stall in the diffuser at full speeds, but barely affect the characteristics of rotating instability in the impeller at low and middle speeds. For compression system instability, it is shown that the use of vanes in diffuser can effectively postpone the occurrence of compression system surge at full speeds. According to the experimental results and the one-dimensional flow theory, vanes in diffuser turn the diffuser pressure rise slope more negative and thus improve the stability of compressor stage, which means lower surge mass flow rate.

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