Numerical investigation of critical lip thickness of subsonic co-flowing jet

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Naren Shankar R. ◽  
Ganesan V.G. ◽  
Dilip Raja N. ◽  
Sathish Kumar K. ◽  
Vijayaraja K.
Keyword(s):  
Mach Number ◽  
Total Pressure ◽  
Static Pressure ◽  
Velocity Ratio ◽  
Critical Limit ◽  
Number Range ◽  
Content Type ◽  
Jet Mixing ◽  
Pressure Decay ◽  
Mach Numbers

Purpose The effect of increasing lip thickness (LT) and Mach number on subsonic co-flowing Jet (CFJ) decay at subsonic and correctly expanded sonic Mach numbers has been analysed experimentally and numerically in this study. This study aims to a critical LT below which mixing enhances and above which mixing inhibits. Design/methodology/approach LT is the distance, separating the primary nozzle and the secondary duct, present in the co-flowing nozzle. The CFJ with LT ranging from 2 mm to 150 mm at jet exit Mach numbers of 0.6, 0.8 and 1.0 were studied in detail. The CFJ with 2 mm LT is used for comparison. Centreline total pressure decay, centreline static pressure decay and near field flow behaviour were analysed. Findings The result shows that the mixing enhances until a critical limit and a further increase in the LT does not show any variation in the jet mixing. Beyond this critical limit, the secondary jet has a detrimental effect on the primary jet, which deteriorates the process of mixing. The CFJ within the critical limit experiences a significantly higher mixing. The effect of the increase in the Mach number has marginal variation in the total pressure and significant variation in static pressure along the jet axis. Practical implications In this study, the velocity ratio (VR) is maintained constant and the bypass ratio (BR) was varied from low value to very high values for subsonic and correctly expanded sonic. Presently, commercial aircraft engine operates under these Mach numbers and low to ultra-high BR. Hence, the present study becomes essential. Originality/value This is the first effort to find the critical value of LT for a constant VR for a Mach number range of 0.6 to 1.0, compressible CFJ. The CFJs with constant VR of unity and varying LT, in these Mach number range, have not been studied in the past.

Influence of bypass ratio on subsonic and correctly expanded sonic co-flowing jets with finite lip thickness

2018 ◽  
Vol 233 (7) ◽  
pp. 2536-2548 ◽  
Author(s):  
S Thanigaiarasu ◽  
R Naren Shankar ◽  
E Rathakrishnan
Keyword(s):  
Total Pressure ◽  
Strong Influence ◽  
Static Pressure ◽  
Pressure Variation ◽  
Jet Mixing ◽  
Free Jet ◽  
Pressure Decay ◽  
Sonic Jet ◽  
Mach Numbers ◽  
Bypass Ratio

The effects of bypass ratio on co-flowing subsonic and correctly expanded sonic jet decay have been studied experimentally. Co-flowing jets with lip thickness 1.0 Dp (where Dp is the diameter of primary nozzle and is equal to 10 mm) with bypass ratios of around 0.7, 1.4, and 6.4 at primary jet exit Mach numbers 0.6, 0.8, and 1.0 have been analyzed. A single free jet equivalent to primary nozzle of the co-flowing nozzle was considered for comparison. Primary jet centerline total pressure decay, spread, and static pressure variation were investigated. The results show that the mixing of the high bypass ratio co-flowing jet with lip thickness 1.0 Dp is superior to low bypass ratio co-flowing jet. Both lip thickness and bypass ratio have a strong influence on the co-flowing jet mixing. Bypass ratio 6.3 experiences a significantly higher mixing than bypass ratio 0.7 and 1.4. Selected jets were also investigated computationally. The computations capture the salient flow physics and reproduce well with the experiments.

Numerical analysis of supersonic co-flow jet with varying lip thickness

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Sathish Kumar K ◽  
Naren Shankar R ◽  
Anusindhiya K ◽  
Senthil Kumar B.R
Keyword(s):  
Mach Number ◽  
Total Pressure ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Supersonic Nozzle ◽  
Experimental Result ◽  
Content Type ◽  
Jet Mixing ◽  
Mixing Characteristics ◽  
Jet Axis

Purpose This study aims to present the numerical study on supersonic jet mixing characteristics of the co-flow jet by varying lip thickness (LT). The LT chosen for the study is 2 mm, 7.75 mm and 15 mm. Design/methodology/approach The primary nozzle is designed for delivering Mach 2.0 jet, whereas the secondary nozzle is designed for delivering Mach 1.6 jet. The Nozzle pressure ratio chosen for the study is 3 and 5. To study the mixing characteristics of the co-flow jet, total pressure and Mach number measurements were taken along and normal to the jet axis. To validate the numerical results, the numerical total pressure values were also compared with the experimental result and it is proven to have a good agreement. Findings The results exhibit that, the 2 mm lip is shear dominant. The 7.75 mm and 15 mm lip is wake dominant. The jet interaction along the jet axis was also studied using the contours of total pressure, Mach number, turbulent kinetic energy and density gradient. The radial Mach number contours at the various axial location of the jet was also studied. Practical implications The effect of varying LT in exhaust nozzle plays a vital role in supersonic turbofan aircraft. Originality/value Supersonic co-flowing jet mixing effectiveness by varying the LT between the primary supersonic nozzle and the secondary supersonic nozzle has not been analyzed in the past.

scholarly journals Novel Characteristics of Subsonic Coflowing Jets With Varying Lip Thickness

2020 ◽  
Author(s):  
Naren Shankar Radha Krishnan ◽  
Dilip Raja Narayana
Keyword(s):  
Mach Number ◽  
Atmospheric Pressure ◽  
Total Pressure ◽  
Radial Direction ◽  
Static Pressure ◽  
Axial Direction ◽  
Pressure Variation ◽  
Geometrical Constraints ◽  
The Mean ◽  
Mach Numbers

Effect of Mach number on coflowing jet at lip thickness of 0.2 Dp, 1.0 Dp and 1.5 Dp (where Dp is primary nozzle exit diameter, 10 mm) at Mach numbers 1.0, 0.8 and 0.6 were studied experimentally. It was found that an increase in Mach number does not have any profound effect on axial total and static pressure variation for 0.2 Dp. Decreasing the mean diameter is due to the geometrical constraints. In this study, the primary nozzle dimension and secondary duct is maintained constant for comparison. For the case of 0.2 Dp, static pressure is almost equal to atmospheric pressure for all Mach numbers. Whereas for other two lip thickness, increase in Mach number marginally influences axial total pressure and profoundly varies static pressure. It is noted that it varies considerably up to 11.1% in the axial direction and up to 17% in the radial direction for Mach number 1.0. For lower Mach numbers, such variation is not observed. Increase in Mach number increases static pressure variation in the coflowing jet flow field with lip thickness 1.0 Dp and 1.5 Dp.

Co-Flowing Jet Control Using Lip Thickness Variation

2018 ◽  
Vol 0 (0) ◽  
Author(s):  
R. Naren Shankar ◽  
S. Thanigaiarasu ◽  
S. Elangovan ◽  
E. Rathakrishnan
Keyword(s):  
Atmospheric Pressure ◽  
Total Pressure ◽  
Static Pressure ◽  
Pressure Variation ◽  
Thickness Variation ◽  
Nozzle Wall ◽  
Jet Mixing ◽  
Jet Control ◽  
Mach Numbers ◽  
Mixing Behaviour

Abstract The control of co-flowing jets by varying lip thickness has been studied experimentally. Lip thickness is defined as the thickness of primary nozzle wall separating primary jet and secondary jet at the co-flowing nozzle exit. Co-flowing jets from a primary nozzle of diameter 10 mm (1.0 Dp) and a secondary duct with lip thickness (LT) 0.2 Dp, 1.0 Dp and 1.5 Dp at Mach numbers 0.6, 0.8 and 1.0 have been studied. Jet centreline total pressure decay, static pressure variation and jet mixing behaviour were analysed. The results show that the mixing of the co-flowing jet with substantial values of lip thickness is superior to the co-flowing jets with comparatively lower values of lip thickness. Co-flowing jets with lip thickness 1.0 Dp and 1.5 Dp experience a significantly higher mixing than the lip thickness 0.2 Dp jet, for all Mach numbers analyzed in the present study. Moreover, in the case of correctly expanded jets, the local static pressure is assumed to be equal to atmospheric pressure. This assumption becomes invalid for co-flowing jets with substantial lip thickness. The centerline static pressure varies sinusoidally above and below atmospheric pressure by a maximum of 11 %, which is due to wake dominance.

Some Preliminary Results for Conical Diffusers with high Subsonic entry mach Numbers

1966 ◽  
Vol 8 (4) ◽  
pp. 384-391 ◽  
Author(s):  
J. L. Livesey ◽  
T. Hugh
Keyword(s):  
Mach Number ◽  
Pipe Flow ◽  
Pressure Loss ◽  
Total Pressure ◽  
Static Pressure ◽  
Loss Coefficient ◽  
Total Pressure Loss ◽  
Preliminary Results ◽  
Mach Numbers ◽  
High Mach

Some preliminary results are presented for the variation of total pressure loss coefficient with entry Mach number for conical diffusers. Included angles of 5, 8 and 12°, area ratios from 2 to 16 and entry lengths from 0 to 65 diameters are considered. In these initial tests the junction between the parallel entry pipe and the cone is sharp. The variation of Mach number and total pressure loss in the entry pipe is predicted simply using measured friction factors and typical velocity profiles. These calculations give the entry conditions to the diffusers in the absence of the diffusers. The effect of the junction of entry pipe and diffuser on the entry pipe flow is thus correctly attributed to the diffuser in the assessment of its total pressure loss. In addition a correctly specified mean entry Mach number is obtained. These considerations enable the losses in diffuser-pipe conjunctions of high Mach number to be logically analysed from separate pipe flow and diffuser data. The results obtained are unusual and indicate that previous assessments of diffuser performance at high Mach numbers have been confused by incorrect consideration of the effect of the diffuser entry pipe conjunction and incorrect specification of the effective mean entry Mach number. It is concluded that further experimental results are needed for developing compressible flows in constant area ducts in order that the present preliminary results may be made more precise. The momentum equation analysis in terms of suitable mean values is presented briefly. Previous diffuser results for low subsonic entry Mach numbers are considered briefly in comparison. Serious errors are shown to be present in these early results. Typically the errors originate in the definition of loss coefficient and static pressure efficiency and the use of the mass derived mean concept. In some cases the quoted static pressure efficiencies imply a decrease in entropy for the diffuser flow at low area ratios.

Measurement of the Profile Drag of Compressor and Turbine Cascades and the Effect of Wakes in Exciting Vibration

1953 ◽  
Vol 57 (515) ◽  
pp. 722-725 ◽  
Author(s):  
J. M. Stephenson
Keyword(s):  
Mach Number ◽  
Compressible Flow ◽  
Total Pressure ◽  
Static Pressure ◽  
Error Curve ◽  
Exciting Vibration ◽  
Turbine Cascades ◽  
Simplified Procedure

The Melvill Jones equation for the profile drag of a single aerofoil is adapted to the case of an aerofoil in cascade, where the static pressure may be permanently raised (compressor), or lowered (turbine). A simplified procedure for measuring the drag is then described, assuming that the total pressure wake has the form of an error curve. A table of multiplying factors is given, for compressible flow up to an outlet Mach number of 0·9. Many published measurements of cascade drag have ignored this factor, with a consequent error of up to 25 per cent.

Characteristics of a co-flowing jet with varying lip thickness and constant velocity ratio

2020 ◽  
Vol 92 (4) ◽  
pp. 633-644
Author(s):  
Naren Shankar R. ◽  
Kevin Bennett S. ◽  
Dilip Raja N. ◽  
Sathish Kumar K.
Keyword(s):  
Constant Velocity ◽  
Velocity Ratio ◽  
Critical Limit ◽  
Potential Core ◽  
Content Type ◽  
Free Jet ◽  
Current Scenario ◽  
Wake Zone ◽  
Bypass Ratio ◽  
Practical Implications

Purpose This study aims to analyze co-flowing jets (CFJs) with constant velocity ratio (VR) and varying primary nozzle lip thickness (LT) to find a critical LT in CFJs below which mixing enhances and beyond which mixing inhibits. Design/methodology/approach CFJs were characterized with a constant VR and varying LTs. A single free jet with a diameter equal to that of a primary nozzle of the CFJ was used for characteristic comparison. Numerical simulation is carried out and is validated with the experimental results. Findings The results show that within a critical limit, the mixing enhanced with an increase in LT. This was signified by a reduction in potential core length (PCL). Beyond this limit, mixing inhibited leading to the elongation of PCL. This limit was controlled by parameters such as LT and constant VR. A new region termed as influential wake zone is identified. Practical implications In this study, the VR is maintained constant and bypass ratio (BR) was varied from low value to very high values. Presently, subsonic commercial turbo fan operates under low to ultra-high BR. Hence the present study becomes vital to the current scenario. Originality/value To the best of the authors’ knowledge, this is the first effort to find the critical value of LT for a constant VR for compressible co-flow jets. The CFJs with constant VR and varying LT have not been studied in the past. The present study focuses on finding a critical LT below which mixing enhances and above which mixing inhibits.

Direct numerical simulation of hypersonic turbulent boundary layers. Part 3. Effect of Mach number

2011 ◽  
Vol 672 ◽  
pp. 245-267 ◽  
Author(s):  
L. DUAN ◽  
I. BEEKMAN ◽  
M. P. MARTÍN
Keyword(s):  
Mach Number ◽  
Boundary Layers ◽  
Large Scale ◽  
Free Stream ◽  
Turbulent Boundary Layers ◽  
Thermodynamic Quantities ◽  
Reynolds Analogy ◽  
Number Range ◽  
Free Stream Mach Number ◽  
Mach Numbers

In this paper, we perform direct numerical simulations (DNS) of turbulent boundary layers with nominal free-stream Mach number ranging from 0.3 to 12. The main objective is to assess the scalings with respect to the mean and turbulence behaviours as well as the possible breakdown of the weak compressibility hypothesis for turbulent boundary layers at high Mach numbers (M > 5). We find that many of the scaling relations, such as the van Driest transformation for mean velocity, Walz's relation, Morkovin's scaling and the strong Reynolds analogy, which are derived based on the weak compressibility hypothesis, remain valid for the range of free-stream Mach numbers considered. The explicit dilatation terms such as pressure dilatation and dilatational dissipation remain small for the present Mach number range, and the pressure–strain correlation and the anisotropy of the Reynolds stress tensor are insensitive to the free-stream Mach number. The possible effects of intrinsic compressibility are reflected by the increase in the fluctuations of thermodynamic quantities (p′rms/pw, ρ′rms/ρ, T′rms/T) and turbulence Mach numbers (Mt, M′rms), the existence of shocklets, the modification of turbulence structures (near-wall streaks and large-scale motions) and the variation in the onset of intermittency.

Aerodynamic Design and Testing of Three Low Solidity Steam Turbine Nozzle Cascades

2004 ◽  
Author(s):  
Bo Song ◽  
Wing F. Ng ◽  
Joseph A. Cotroneo ◽  
Douglas C. Hofer ◽  
Gunnar Siden
Keyword(s):  
Mach Number ◽  
Steam Turbine ◽  
Boundary Layer Transition ◽  
Experimental Results ◽  
Blade Surface ◽  
Layer Transition ◽  
Number Range ◽  
Baseline Design ◽  
Wide Range ◽  
Mach Numbers

Three sets of low solidity steam turbine nozzle cascades were designed and tested. The objective was to reduce cost through a reduction in parts count while maintaining or improving performance. The primary application is for steam turbine high pressure sections where Mach numbers are subsonic and high levels of unguided turning can be tolerated. The baseline Design A has a ratio of pitch to axial chord of 1.2. This is the pitch diameter section of a 50% reaction stage that has been verified by multistage testing on steam to have a high level of efficiency. Designs B and C have ratios of pitch to axial chord of 1.5 and 1.8 respectively. All three designs satisfy the same inlet and exit vector diagrams. Analytical surface Mach number distributions and boundary layer transition predictions are presented. Extensive cascade test measurements were carried out for a broad incidence range from −60 to +35 degrees. At each incidence, four outlet Mach numbers were tested, ranging from 0.2 to 0.8, with the corresponding Reynolds number variation from 1.8×105 to 9.0×105. Experimental results of loss coefficient and blade surface Mach number are presented and compared for the three cascades. The experimental results have demonstrated low losses over the tested Mach number range for a wide range of incidence from −45 to 15 degrees. Designs B and C have lower profile losses than Design A. The associated flow physics is interpreted using the results of wake profile, blade surface Mach number distribution and blade surface oil flow visualization, with the emphasis placed on the loss mechanisms for different flow conditions and the loss reduction mechanism with lower solidity. The effect of the higher profile loading of the lower solidity designs on increased end wall losses induced by increased secondary flow, especially on low aspect ratio designs, is the subject of ongoing studies.

Direct simulation of turbulent supersonic boundary layers by an extended temporal approach

2001 ◽  
Vol 429 ◽  
pp. 187-216 ◽  
Author(s):  
THIERRY MAEDER ◽  
NIKOLAUS A. ADAMS ◽  
LEONHARD KLEISER
Keyword(s):  
Numerical Simulation ◽  
Mach Number ◽  
Direct Numerical Simulation ◽  
Boundary Layers ◽  
Stokes Equations ◽  
Navier Stokes ◽  
Mean Flow ◽  
Navier Stokes Equations ◽  
Number Range ◽  
Mach Numbers

The present paper addresses the direct numerical simulation of turbulent zero-pressure-gradient boundary layers on a flat plate at Mach numbers 3, 4.5 and 6 with momentum-thickness Reynolds numbers of about 3000. Simulations are performed with an extended temporal direct numerical simulation (ETDNS) method. Assuming that the slow streamwise variation of the mean boundary layer is governed by parabolized Navier–Stokes equations, the equations solved locally in time with a temporal DNS are modified by a distributed forcing term so that the parabolized Navier–Stokes equations are recovered for the spatial average. The correct mean flow is obtained without a priori knowledge, the streamwise mean-flow evolution being approximated from its upstream history. ETDNS reduces the computational effort by up to two orders of magnitude compared to a fully spatial simulation.We present results for a constant wall temperature Tw chosen to be equal to its laminar adiabatic value, which is about 2.5 T∞, 4.4 T∞ and 7 T∞, respectively, where T∞ is the free-stream temperature for the three Mach numbers considered. The simulations are initialized with transition-simulation data or with re-scaled turbulent data at different parameters. We find that the ETDNS results closely match experimental mean-flow data. The van Driest transformed velocity profiles follow the incompressible law of the wall with small logarithmic regions.Of particular interest is the significance of compressibility effects in a Mach number range around the limit of M∞ ≃ 5, up to which Morkovin's hypothesis is believed to be valid. The results show that pressure dilatation and dilatational dissipation correlations are small throughout the considered Mach number range. On the other hand, correlations derived from Morkovin's hypothesis are not necessarily valid, as is shown for the strong Reynolds analogy.

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