Icing Wind Tunnel Measurements of Supercooled Large Droplets Using the 12 mm Total Water Content Cone of the Nevzorov Probe

Lucke, Johannes; Jurkat-Witschas, Tina; Heller, Romy; Hahn, Valerian; Hamman, Matthew; Breitfuss, Wolfgang; Bora, Venkateshwar Reddy; Moser, Manuel; Voigt, Christiane

doi:https://doi.org/10.5194/egusphere-2022-647

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https://doi.org/10.5194/egusphere-2022-647

Preprints

24 Aug 2022

| 24 Aug 2022

Icing Wind Tunnel Measurements of Supercooled Large Droplets Using the 12 mm Total Water Content Cone of the Nevzorov Probe

Johannes Lucke, Tina Jurkat-Witschas, Romy Heller, Valerian Hahn, Matthew Hamman, Wolfgang Breitfuss, Venkateshwar Reddy Bora, Manuel Moser, and Christiane Voigt

Abstract. Supercooled large droplet (SLD) icing can occur behind the protected surfaces of an aircraft and create severe aerodynamic disturbances, which represent a safety hazard for aviation. Liquid water content (LWC) measurements in icing conditions that contain SLD require instruments that are able to sample unimodal and bimodal droplet size distributions with droplet diameters from 2 to 2000 µm. No standardized detection method exists for this task. A candidate instrument, that is currently used in icing wind tunnel (IWT) research, is the Nevzorov probe. In addition to the standard 8 mm total water content (TWC) collector cone, a novel instrument version also features a 12 mm diameter cone, which might be advantageous for collecting the large droplets characteristic of SLD conditions. In the scope of the two EU projects SENS4ICE and ICE GENESIS we performed measurement campaigns in SLD icing conditions in IWTs in Germany, Austria and the USA. We obtained a comprehensive data set of measurements from the Hotwire, the 8 mm and 12 mm cone sensors of the Nevzorov probe and the tunnel reference instrumentation. In combination with measurements of the particle size distribution we experimentally derive the collision efficiency curve of the new 12 mm cone for median volume diameters (MVDs) between 12 and 58 µm and wind tunnel speeds from 40 to 85 µm. Knowledge of this curve allows us to correct the LWC measurements of the 12 mm cone (LWC₁₂) in particular for the inevitably high decrease in collision efficiency for small droplet diameters. In unimodal SLD conditions, with MVDs between 128 and 720 µm, LWC₁₂ generally agrees within 20 % with the tunnel LWC reference values from a WCM-2000 and an Isokinetic Probe. An increase in the difference between LWC₁₂ and the WCM-2000 measurements at larger MVDs indicates better droplet collision properties of the 12 mm cone. Similarly, the favorable detector dimensions of the 12 mm cone explain a 7 % enhanced detection efficiency compared to the 8 mm cone, however this difference falls within the instrumental uncertainties. Data collected in various bimodal SLD conditions with MVDs between 16 and 534 µm and LWCs between 0.22 and 0.72 g m^-3 also show an agreement within 20 % between LWC₁₂ and the tunnel LWC, which makes the Nevzorov sensor head with the 12 mm cone the preferred instrumentation for measurements of LWC in Appendix O icing conditions.

Received: 13 Jul 2022 – Discussion started: 24 Aug 2022

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Journal article(s) based on this preprint

22 Dec 2022

Icing wind tunnel measurements of supercooled large droplets using the 12 mm total water content cone of the Nevzorov probe

Johannes Lucke, Tina Jurkat-Witschas, Romy Heller, Valerian Hahn, Matthew Hamman, Wolfgang Breitfuss, Venkateshwar Reddy Bora, Manuel Moser, and Christiane Voigt

Atmos. Meas. Tech., 15, 7375–7394, https://doi.org/10.5194/amt-15-7375-2022,https://doi.org/10.5194/amt-15-7375-2022, 2022

Short summary

Johannes Lucke et al.

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-647', Anonymous Referee #1, 24 Aug 2022
Overview

The manuscript presents laboratory characterization of a new version of Nevzorov probe with respect to the measurements of liquid water content under the conditions including supercooled large droplets. Those conditions, challenging to measure with the existing instrumentation, are relevant for aviation safety which constitutes a solid motivation for the study. Experiments performed at three icing wind tunnels provided a valuable, comprehensive dataset. Accurate analysis of the collected data reached the objectives posed: to derive collision efficiency for a new sensor for small droplets, to verify the suitability of a new sensor for measuring LWC composed of large droplet size range. Some improvements in the presentation of the research and the results will be beneficial for the readers. Therefore, I recommend publication after minor revisions resulting from considering the comments below.

General comments

Please clarify whether the new Nevzorov probe featuring a 12 mm cone was developed within your study presented in the manuscript. If so, I consider that as an advantage of your work. Please provide details about the geometry and design of the probe then. If not, please provide information about the producer and whether there were any tests or experiments involving this probe preceding yours.

Section 2 introduces two research projects and three wind tunnel facilities. In my opinion, the information about the facilities is very important in this manuscript. Therefore, the section should focus primarily on the facilities participating in the current study rather than on the scope of broader projects. I suggest emphasizing the capabilities of the wind tunnels which justify their choice in the light of the objectives of this study and the differences between the wind tunnels which explain the advantage of using three facilities instead of one.

Please explain the choice of conditions for your test cases. As stated in section 4, many of them lie outside the range specified in Appendix C and Appendix 0 and some even feature above-zero temperatures. Is such a choice motivated by the limitations of the droplet generation systems, the limitations due to sampling statistics, the intention to explore the region outside Appendix 0 to allow for a possible extension of icing safety standards in the future?

MVD is not a particularly meaningful measure in the case of bimodal DSD, as you pointed out in section 7. Therefore, I suggest additionally including (e.g. in Table 3, at least for bimodal cases) the parameter you actually used to distinguish between FZDZ and FZRA, i.e. the diameter corresponding to the position of the maximum of the largest mode in LWC distribution. For unimodal cases, it is presumably close to MVD because the only mode is obviously the largest one. However, for bimodal cases it might give useful information concerning SLD in the DSD.

Figures 5, 6, 8. The range of the vertical axis is inappropriate for the presented results. Please refine the range accordingly so that the differences in position between the data points are visible.

Specific comments

Line 11. The sentence implies that the form of the curve was experimentally derived. I suggest mentioning that a specific function was assumed.

Line 113. Did you actually use Eq. (3) instead of Korolev’s value? Please specify.

Line 124. Which particular collection efficiencies from the literature did you use for the 8 mm cone in your analysis? Please specify and provide relevant references.

Section 4.1 and 4.2. At RTA, there were multiple reference instruments applied to measure LWC and DSD. How are those measurements combined to produce final estimates? With a similar procedure as you described for CDP and CIP? And what sampling statistics is considered sufficient while selecting the threshold size (line 180)? Did you follow any method described in the literature?

Section 4.3. As far as I understand, the estimated uncertainties of LWC measurements are valid only in the size range corresponding to Appendix C conditions, i.e. small droplets. Did you find any quantitative information about the uncertainties in SLD conditions?

Line 191. I assume here you give an estimate of the uncertainty of LWC measurements with a 8 mm collector cone. Please clarify.

Section 4.4. The number of test points documents extensive experimental work. Please consider whether it would be helpful for the reader to conceive the range of conditions explored if the test points and the regimes (SDS, FZDZ, FZRA) are illustrated in a figure, e.g. a scatter plot LWC vs. diameter of the largest mode (the parameter mentioned above in general comment #4 which you used to distinguish between FZDZ and FZRA). The overall LWC limits of Appendix C and Appendix 0 can then be marked for the respective regimes.

Lines 258-259 and Fig. 4. What collision efficiency correction did you use? Please provide a reference. Is such a selection of the sensor depending on MVD recommended in existing literature? If so, please cite a relevant source.

Table 5. Providing a 2 sigma interval is rather unusual. Typically, just 1 sigma is reported and it is understood in the context of estimated standard deviation of the distribution of the results. This remark regards reporting of uncertainties and does not interfere with the point you make in line 285 where even the 3 sigma test criterion can be applied.

Line 286. Please specify explicitly how you calculate LWC_12. Is it just measured LWC multiplied by a factor f(MVD) or does the computation involve DSD spectrum?

Line 304. How do you know that droplet coincidence was present? Is it simply implied by the high droplet concentration?

Section 7. I suggest modifying the section title to mark contrast to section 6, e.g. “Application of collision efficiencies in bimodal SLD conditions” or similarly.

Lines 350-354 and Figure 8. Please specify explicitly whether those results were obtained by applying the MVD approximation or by resolving the entire DSD.

Table 6. The values of epsilon_12 are not explained and commented on in the text. Do they result from the integration of DSDs multiplied by collision efficiency curve or represent a value f(MVD) of MVD approximation? If the latter, please explain why they do not agree with Fig. 4.

Minor issues

Please ensure the consistency and specificity among symbols.

K is used for thermal conductivity and the droplet inertia parameter.

T is used for temperature and test points.

Droplet diameter is denoted by d and D.

S is used for sensor surface and sum of squared residuals.

Line 9. Please rewrite the sentence so that it is clear whether Hotwire is a part of the Nevzorov probe or a separate instrument.

Line 33. “than” is missing.

Lines 34 and 36. I assume “they” refers to the last citation given in the text. Then another citation at the end of the sentence is confusing. Please be specific about which reference you mean.

Line 86. “PSD” was not defined. I suppose you mean “DSD” here.

Line 94. There should be a dot instead of a colon or a part of the sentence is missing.

Line 117 and Eq. (6). Please use either S_c or S for the collector sensor area.

Lines 173 and 176. I suppose “from” is not needed.

Table 3. The last FZDZ record for BIWT. Should the temperature be +5 deg or a star is erroneously given here?

Line 250. According to Table 4, Group 1 contains measurements from two wind tunnels. Please clarify.

Line 278. Just an integer index j is enough to denote the test points. The summation goes then from j=1 to n.
Citation: https://doi.org/10.5194/egusphere-2022-647-RC1
- AC1: 'Reply on RC1', Johannes Lucke, 27 Oct 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-647/egusphere-2022-647-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-647-AC1
RC2:
'Comment on egusphere-2022-647', Alexei Korolev, 15 Sep 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-647/egusphere-2022-647-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-647-RC2
- AC2: 'Reply on RC2', Johannes Lucke, 27 Oct 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-647/egusphere-2022-647-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-647-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2022-647', Anonymous Referee #1, 24 Aug 2022
Overview

The manuscript presents laboratory characterization of a new version of Nevzorov probe with respect to the measurements of liquid water content under the conditions including supercooled large droplets. Those conditions, challenging to measure with the existing instrumentation, are relevant for aviation safety which constitutes a solid motivation for the study. Experiments performed at three icing wind tunnels provided a valuable, comprehensive dataset. Accurate analysis of the collected data reached the objectives posed: to derive collision efficiency for a new sensor for small droplets, to verify the suitability of a new sensor for measuring LWC composed of large droplet size range. Some improvements in the presentation of the research and the results will be beneficial for the readers. Therefore, I recommend publication after minor revisions resulting from considering the comments below.

General comments

Please clarify whether the new Nevzorov probe featuring a 12 mm cone was developed within your study presented in the manuscript. If so, I consider that as an advantage of your work. Please provide details about the geometry and design of the probe then. If not, please provide information about the producer and whether there were any tests or experiments involving this probe preceding yours.

Section 2 introduces two research projects and three wind tunnel facilities. In my opinion, the information about the facilities is very important in this manuscript. Therefore, the section should focus primarily on the facilities participating in the current study rather than on the scope of broader projects. I suggest emphasizing the capabilities of the wind tunnels which justify their choice in the light of the objectives of this study and the differences between the wind tunnels which explain the advantage of using three facilities instead of one.

Please explain the choice of conditions for your test cases. As stated in section 4, many of them lie outside the range specified in Appendix C and Appendix 0 and some even feature above-zero temperatures. Is such a choice motivated by the limitations of the droplet generation systems, the limitations due to sampling statistics, the intention to explore the region outside Appendix 0 to allow for a possible extension of icing safety standards in the future?

MVD is not a particularly meaningful measure in the case of bimodal DSD, as you pointed out in section 7. Therefore, I suggest additionally including (e.g. in Table 3, at least for bimodal cases) the parameter you actually used to distinguish between FZDZ and FZRA, i.e. the diameter corresponding to the position of the maximum of the largest mode in LWC distribution. For unimodal cases, it is presumably close to MVD because the only mode is obviously the largest one. However, for bimodal cases it might give useful information concerning SLD in the DSD.

Figures 5, 6, 8. The range of the vertical axis is inappropriate for the presented results. Please refine the range accordingly so that the differences in position between the data points are visible.

Specific comments

Line 11. The sentence implies that the form of the curve was experimentally derived. I suggest mentioning that a specific function was assumed.

Line 113. Did you actually use Eq. (3) instead of Korolev’s value? Please specify.

Line 124. Which particular collection efficiencies from the literature did you use for the 8 mm cone in your analysis? Please specify and provide relevant references.

Section 4.1 and 4.2. At RTA, there were multiple reference instruments applied to measure LWC and DSD. How are those measurements combined to produce final estimates? With a similar procedure as you described for CDP and CIP? And what sampling statistics is considered sufficient while selecting the threshold size (line 180)? Did you follow any method described in the literature?

Section 4.3. As far as I understand, the estimated uncertainties of LWC measurements are valid only in the size range corresponding to Appendix C conditions, i.e. small droplets. Did you find any quantitative information about the uncertainties in SLD conditions?

Line 191. I assume here you give an estimate of the uncertainty of LWC measurements with a 8 mm collector cone. Please clarify.

Section 4.4. The number of test points documents extensive experimental work. Please consider whether it would be helpful for the reader to conceive the range of conditions explored if the test points and the regimes (SDS, FZDZ, FZRA) are illustrated in a figure, e.g. a scatter plot LWC vs. diameter of the largest mode (the parameter mentioned above in general comment #4 which you used to distinguish between FZDZ and FZRA). The overall LWC limits of Appendix C and Appendix 0 can then be marked for the respective regimes.

Lines 258-259 and Fig. 4. What collision efficiency correction did you use? Please provide a reference. Is such a selection of the sensor depending on MVD recommended in existing literature? If so, please cite a relevant source.

Table 5. Providing a 2 sigma interval is rather unusual. Typically, just 1 sigma is reported and it is understood in the context of estimated standard deviation of the distribution of the results. This remark regards reporting of uncertainties and does not interfere with the point you make in line 285 where even the 3 sigma test criterion can be applied.

Line 286. Please specify explicitly how you calculate LWC_12. Is it just measured LWC multiplied by a factor f(MVD) or does the computation involve DSD spectrum?

Line 304. How do you know that droplet coincidence was present? Is it simply implied by the high droplet concentration?

Section 7. I suggest modifying the section title to mark contrast to section 6, e.g. “Application of collision efficiencies in bimodal SLD conditions” or similarly.

Lines 350-354 and Figure 8. Please specify explicitly whether those results were obtained by applying the MVD approximation or by resolving the entire DSD.

Table 6. The values of epsilon_12 are not explained and commented on in the text. Do they result from the integration of DSDs multiplied by collision efficiency curve or represent a value f(MVD) of MVD approximation? If the latter, please explain why they do not agree with Fig. 4.

Minor issues

Please ensure the consistency and specificity among symbols.

K is used for thermal conductivity and the droplet inertia parameter.

T is used for temperature and test points.

Droplet diameter is denoted by d and D.

S is used for sensor surface and sum of squared residuals.

Line 9. Please rewrite the sentence so that it is clear whether Hotwire is a part of the Nevzorov probe or a separate instrument.

Line 33. “than” is missing.

Lines 34 and 36. I assume “they” refers to the last citation given in the text. Then another citation at the end of the sentence is confusing. Please be specific about which reference you mean.

Line 86. “PSD” was not defined. I suppose you mean “DSD” here.

Line 94. There should be a dot instead of a colon or a part of the sentence is missing.

Line 117 and Eq. (6). Please use either S_c or S for the collector sensor area.

Lines 173 and 176. I suppose “from” is not needed.

Table 3. The last FZDZ record for BIWT. Should the temperature be +5 deg or a star is erroneously given here?

Line 250. According to Table 4, Group 1 contains measurements from two wind tunnels. Please clarify.

Line 278. Just an integer index j is enough to denote the test points. The summation goes then from j=1 to n.
Citation: https://doi.org/10.5194/egusphere-2022-647-RC1
- AC1: 'Reply on RC1', Johannes Lucke, 27 Oct 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-647/egusphere-2022-647-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-647-AC1
RC2:
'Comment on egusphere-2022-647', Alexei Korolev, 15 Sep 2022

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-647/egusphere-2022-647-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2022-647-RC2
- AC2: 'Reply on RC2', Johannes Lucke, 27 Oct 2022
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-647/egusphere-2022-647-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2022-647-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Johannes Lucke on behalf of the Authors (08 Nov 2022) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (17 Nov 2022) by Wiebke Frey

RR by Anonymous Referee #1 (17 Nov 2022)

RR by Alexei Korolev (19 Nov 2022)

ED: Publish as is (22 Nov 2022) by Wiebke Frey

AR by Johannes Lucke on behalf of the Authors (29 Nov 2022)

Journal article(s) based on this preprint

22 Dec 2022

Icing wind tunnel measurements of supercooled large droplets using the 12 mm total water content cone of the Nevzorov probe

Johannes Lucke, Tina Jurkat-Witschas, Romy Heller, Valerian Hahn, Matthew Hamman, Wolfgang Breitfuss, Venkateshwar Reddy Bora, Manuel Moser, and Christiane Voigt

Atmos. Meas. Tech., 15, 7375–7394, https://doi.org/10.5194/amt-15-7375-2022,https://doi.org/10.5194/amt-15-7375-2022, 2022

Short summary

Johannes Lucke et al.

Data sets

Icing Wind Tunnel Measurements of Supercooled Large Droplets Using the 12 mm Total Water Content Cone of the Nevzorov Probe: Measurement Data Johannes Lucke, Tina Jurkat-Witschas, Romy Heller, Valerian Hahn, Matthew Hamman, Wolfgang Breitfuss, Venkateshwar Reddy Bora, Manuel Moser, Christiane Voigt https://doi.org/10.5281/zenodo.6817112

Johannes Lucke et al.

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Short summary

Flight testing in icing conditions requires instruments that are able to accurately measure the liquid water content of supercooled large droplets (SLD). This work finds, that the 12 mm cone of the Nevzorov hot-wire probe has excellent collection properties for SLD. We also derive a correction to compensate for the low collision efficiency of small droplets with the cone. The results provide a procedure to evaluate LWC measurements of the 12 mm cone during wind tunnel- and airborne experiments.


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